Download DC power supply Operating for Rotor Winding Resistance

Instruction for the setting and adjusting procedure for
excitation equipment of HFx5, HFx6, HSR7 series
Hyundai Generators
1. The field to apply this guide for Excitation Equipments(ExEq)
1.1. This guide describes about the method of the adjustment of ExEq which has the voltage regulator
with parallel operation(droop compensation) equipment in 3 phases brushless alternator being
produced in HHI.
1.2. Here we describe about ExEq for low voltage alternators(HF-5,HF_6 series) only.
For the medium voltage alternators(3.0/3.3kV, 6.0/6,6 kV HSR series), all description is same as that
of low voltage alternator except additional ‘step down transformer(T6)’.
1.3. This guide for adjustment can be important reference for the trouble-shooting during operating on
the field.
2. Abstract of Excitation Equipments(ExEq)
3 phases brushless alternator, equipped with ExEq which has the voltage regulator with parallel
operation(droop compensation) equipment, consists of several parts but can be described as 3 main
parts as below.
The main roles for each part will be described.
Fig (1) Control circuit
load
reference value
voltage measuring (sensing)
AVR.
droop compensator
current transformer
rectifier transformer
bypass resistor
static rectifier
thyristor
main stator
reactor
capacitor
exciter field
stator part
rotor part
main rotor
main
rotating rectifier
exciter
exciter rotor
residual magnetic flux
2.1. Main stator:
(1) Main armature or main stator of main machine
Main winding(static part) which generators the electric power proportional to the main rotor current or
main field current and supplies power to the load.
2.2. Rotor:
(1) Main field(rotating field of main machine)
(2) Rotating rectifier
(3) Armature(Exciter rotor) of exciter machine
The three-phase current(A.C.) generated in the rotor winding of the exciter is rectified to direct
current(D.C.) by rotating silicon diodes(three-phase bridge circuit) and applied to the rotating pole
winding of the main generator which produces the magnetic flux required to generate the
voltage(electric power) at Main winding.
2.3. Static exciter:
(1) Automatic voltage regulator(controller, AVR.)
(2) Exciter field(exciter stator))
(3) Excitation Equipment(ExEq) besides A.V.R
Static exciter contains exciter field and ExEq with AVR, but generally it means ExEq(AVR, Transformers,
Static rectifier and etc.) except exciter field. Brief operating sequence is as below.
2.3.1. Exciting current(current required to produce about 110% of no-load rated output voltage)
proportional to the no-load voltage of Main stator is transferred to the Rectifier Transformer(T6) via
Reactor(L1) - 분권 특성
2.3.2. Exciting current(current required to produce about 105% of full load rated output voltage by
compensating armature reaction and armature reactance) proportional to the load voltage of Main
stator is transferred to the Rectifier Transformer(T6) via Current transformers(T1.T2.T3). - 직권 특성
2.3.3. The exciter currents transferred to the rectifier transformer via Reactor and current
transformer are magnetically combined and transferred to the static rectifier(V1, V29).
2.3.4. The static rectifier transforms A.C power transferred via rectifier transformer to D.C power and
this D.C power is supplied to the exciter field.
2.3.5. AVR. compares the terminal voltage(sensing voltage) compensated by droop compensator and
the reference voltage set by reference value setter and transforms the difference between sensing
voltage and reference voltage to the pulse. That pulse turns on the gate of thyristor.
2.3.6. By turning on Thyristor gate, the excess current(transferred from rectifier transformer over the
current required to keep proper output
voltage bypasses through the bypass resister(R1,R48). By
controlling the bypass current the output terminal voltage of main stator can be kept required proper
voltage value.
Fig. (2) load current vs terminal voltage
voltage
bypass component
100[%]
voltage line without A.V.R.
voltage with A.V.R.
Load current
100[%]
3. Cabling, preliminary setting and pre-magnetizing
3.1. Cabling
3.1.1. main power cable, exciter field cable, voltage control cables, measuring equipment cables(CTs,
PTs, winding sensors), sensing cable for over voltage or over current protection and
Control cable for switchboard equipped AVR shall be properly connected with proper specification.
If differential current transformers(D-CTs) were equipped on the generator, secondary winding of them
shall be shorted together to protect from burning at secondary winding by excess temperature(infinite
resistance).
3.2. Preliminary setting
3.2.1. If the same type of generator with that of the generator to be tested(test object:T/O) has been
tested before, pre-set the components of test object to the same setting points of components tested
before.
If the test object(T/O) is completely new type pre-set all the components to the points that the
exciting current would be lower than designed value.
Ex.) design value (L1) = 4.0[mm],
(T1 ∼ T3) = 2.1- 2.4,
(T6) = 1U1/6.6.6-4.4.4
setting value (L1) = 3.0[mm],
(T1 ∼ T3) = 2.1- 2.5,
(T6) = 1U1/5.5.5-5.5.5
3.2.2. HFx5 series generators :
Disconnect the cables for voltage sensing(cable Nos. = 17,18,19) and for by-pass(cable Nos. = 1,5)
from Automatic Voltage Regulator(AVR, A1), and then set the potentiometers Usoll = 6.0, Vr = 3.0, Tn
= 6.0.
Switch on ‘reference value setter ON/OFF’ switch and select ‘1.5[kΩ] reference setter’ and then
preset it to about 650[Ω] marked already.
3.2.3. HFx5 series generators HFx6 :
Disconnect the multi-connect for voltage sensing(X1) and for by-pass(X3) from Automatic Voltage
Regulator(AVR, A1), and then set the potentiometers S = 50, U = 60, K = 30, T = 50, R47 = 20.
Switch off ‘reference value setter ON/OFF’ switch and select ‘4.7[kΩ] reference setter’ and then
preset it to about 2.3[kΩ] marked already.
3.3. Pre-exciting(initial charging)
During first operating after manufactured newly, the brushless constant voltage alternator has to be
pre-excited to produce residual magnetism on exciter field core. After once building up the rated
voltage the alternator can be operated without additional pre-exciting because residual magnetism
acts to build the voltage.
According to actual situation with test equipment one of the following 2
methods could be used for pre-exciting.
3.3.1. Pre-exciting by operating as motor:
Check
operating
condition
and
polarity
of
main
ammeter(Ja),
main
voltmeter,(Ua)
exciter
ammeter(Jef) and exciter voltmeter(Uef) after starting the test object as motor.
If the exciter ammeter is not operated(no moving) check whether the line between static diode(V1)
and exciter field would be ‘open’, ‘incorrect connection’ or ‘bad contact at the connector’.
And increase the speed of test object slowly till the voltage is built-up then decrease the speed until it
stops. If the voltage is not built-up or the built-up voltage is too high above rated value, examine the
cause of such abnormal status after stopping the test object.
3.3.2. Pre-exciting by external power :
Connect the line for external D.C power source to the terminals F1, F2 of exciter field, and increase the
D.C voltage power slowly from minimum value to the value that makes the current of maximum 70%
of rated exciter field current and keep 3 seconds at that point and then decrease D.C power to the
minimum value. Repeat three times the process ‘increase, keep, decrease’.
Confirm that there is not any abnormal operating condition such as over voltage during no load
operation.
4. Tap setting for No-Load voltage
(1) The meaning of ‘No-Load’ is that any load is not connected to three phases output terminals when
T/O(test object) is running as generator, or that almost zero or minimum current is flowing(cosΦ = 1)
on the power line when T/O is running as motor(More than 5% of rated effective power(KW) of T/O
should not loaded on the shaft).
(2) Keep attention that there could be any clearance with the measured no-load voltage or any
insulation defect on the transformer if the voltage of T/O would be bigger than 110% of rated voltage
of transformer used for balancing of the impedances between T/O and power supply generator.
(3) Attention is required
because the terminal voltages when the exciting current to be
increased(adjusting from over exciting to cosΦ = 1) and decreased(adjusting from under exciting to
cosΦ = 0) could be different during operating as motor.
(4) During tap adjusting for T6(rectifier transformer):
There is not any big problem to adjust the T6 taps during operating the low capacity of T/O. But there
would be insulation break by high voltage induced by reactance during opening or shortening the lines
or by high voltage produced by unbalance between phases for high capacity generator. .
So, During tap adjusting
T/O should be stopped or remove the exciting power by the S/W for
shortening the exciter field power if T/O is driven by loading machine(driving machine).
4.1. Tap setting for no-load maximum voltage
4.1.1. During driven by loading machine:
4.1.1.1 Increase slowly the speed of T/O by loading machine checking the built-up of output voltage
and keep rated speed(Ns).
4.1.1.2 T6 taps(no-load tap) at the secondary winding of T6 wired to the static rectifier shall be
adjusted that the generator output voltage is 110%~115% of rated voltage.
If the output voltage of new type of generator has big difference from 110~115% of rated voltage,
Stop the generator.
Adjust the air gap of Reactor(L1) and primary tap of T6 to proper points.
Operate the generator in rated speed. Adjust T6 secondary tap to keep the output voltage at
110~115% of rated voltage.
If the output voltage of experienced type of generator has big difference from 110~115% of rated
voltage, try to find the reason of that by checking whether there would be any incorrect wiring or
defect on the concerned components.
4.1.2. During driven as motor:
Basically the setting procedure is same as that of 4.1.1 except that the speed is controlled by changing
the speed of power supply generator. And the loaded current(Ja) should be kept at the minimum
value(cosΦ = 1) during voltage measuring or no-load tap setting. At any case attention should be
given not to flow excessive load current during no-load tap setting by proper adjusting the exciting
current of power supply generator.
4.1.3. After finishing 4.1.1 and 4.1.2 successfully, record Ua, Ja, Uef, Jef on the ‘AVR setting sheet’.
4.1.4. The higher setting value between 110% ~ 115% would be recommended during no-load tap
setting for the high speed generators such as 4poles or 6poles because generally the no-load exciting
current and voltage variation ratio for the high speed generators are smaller than those of low speed
generator because of smaller short circuit ratio. And additional consideration is necessary because the
higher voltage than set value could be generated for the high speed generator because of the higher
residual magnetism.
4.2. Tap setting for no-load rated voltage :
4.2.1. For HFx5 type of generator:
Reconnect the opened circuits such as cable nos. 17,18,19 for sensing and 1,5 for by-pass To A1.
Adjust the potentiometer ‘Usoll’ on the AVR(A1) to keep the output voltage of the generator at the
rated value
4.2.2. For HFx6 series generator:
Reconnect the opened circuits such as multi connectors X1 for sensing and X3 for by-pass to A1.
Adjust the potentiometer ‘U’ on the AVR(A1) to keep the output voltage of the generator at the rated
value.
4.2.3 After finishing 4.2.1 and 4.2.2 successfully, record Ua, Ja, Uef, Jef on the ‘AVR setting sheet’.
4.3. Tap setting for no-load minimum voltage:
Even though there is not any problem that the minimum voltage value is lower than 95% of rated
value, around 90% of rated value is recommended. Except special case do not decrease the minimum
voltage below 80% of rated value because the hunting could be seen if the minimum voltage value is
too low.
4.3.1. For HFx5 series generator:
Confirm the minimum voltage value by turning the ‘reference value setter’ fully to the anticlockwise
side,. If the minimum voltage value is higher than 92% of rated value, reset the voltage below 92%
of rated value by decreasing the resistance of ‘bypass resister(R1)’
4.3.2. For HFx6 series generator:
After changing over the ‘reference value setter’ switch from ‘OFF’ to ‘ON’ and make the micro-switch
S1-3 ‘OFF’, confirm the minimum voltage value by turning the ‘reference value setter’ fully to the
anticlockwise side.
If the minimum voltage value is higher than 92% of rated value, reset the
voltage below 92% of rated value by decreasing the resistance of ‘bypass resister(R47)’ on the AVR
board.
4.3.3. After finishing 4.3.1 and 4.3.2 successfully, record Ua, Ja, Uef, Jef on the ‘AVR setting sheet’.
4.4. Check voltage hunting and setting of ‘rated voltage’ by adjusting the ‘reference value
setter’
4.4.1. For HFx5 series generator:
Confirm that the output voltage could be smoothly adjusted by turning the reference value setter from
anticlockwise to clockwise and then adjust the reference value setter to set the output voltage to the
rated value. If the hunting on the output voltage or exciting current would be seen, remove it by
adjusting the potentiometers(Vr, Tn) on AVR(A1).
shop test are Vr = 3.0 and
The standard position of potentiometers during
Tn = 6.0.
4.4.2. For HFx6 series generator:
Confirm that the output voltage could be smoothly adjusted by turning the reference value setter from
anticlockwise to clockwise and then adjust the reference value setter to set the output voltage to the
rated value. If the hunting on the output voltage or exciting current would be seen, remove it by
adjusting the potentiometers(K, T, R47) on AVR(A1).
shop test are K = 3.0, T = 50 and R47 = 20.
The standard positions of potentiometers during
4.5. Completion of no-load setting and preparation of load setting
Stop the test object slowly and disconnect the sensing cables or multi-connector and by-pass cables or
multi-connector from A1. It is not necessary to stop the T/O when it is being operated as motor
5. Tap setting for on-load
The ‘on-load’ mentioned on this instruction means ‘the current flowing on the armature(stator
winding)’ with over-excited status by decreasing the exciting current of power supply generator while
the T/O is being operating as motor.
5.1. Tap setting for on-load maximum voltage:
5.1.1. Keep the rated speed after stating the T/O as motor. Decrease the exciting current of power
supply generator until the load current of T/O reaches to the rated current. Adjust the taps on T6
side of the cables from secondary winding of current transformers(T1,T2, T3) to the secondary
windings of rectifier transformer(T6) to reach the output voltage to 107% ~ 110% of rated value.
If the output voltage is largely different from 107% ~ 110% of rated value adjust the secondary
winding taps of T1,T2,T3 to get the output voltage near to required value after stopping the T/O and
then try again to adjust T6 load taps as above. If the output voltage of experienced type of generator
has big difference from 107% ~110% of rated voltage, try to find the reason of that by checking
whether there would be any incorrect wiring or defect on the concerned components.
5.1.2. After finishing 5.1.1. successfully, record Ua, Ja, Uef, Jef on the ‘AVR setting sheet’.
5.1.3. The lower setting value between 107% ~ 110% would be recommended during load tap setting
for the low speed generators such as 8poles or 10poles because generally the no-load exciting current
and voltage variation ratio for the low speed generators are bigger than those of high speed generator
because of larger short circuit ratio. And additional consideration is necessary because the higher
voltage than set value could be generated for high speed generator because of the higher residual
magnetism.
5.1.4. There is not any big problem to adjust the T6 taps after reducing the load current to the
minimum value by adjusting the exciting current of power supply generator during operating the low
capacity of T/O. But for high capacity generator there would be insulation break by high voltage
induced by reactance during opening or shortening the lines or by high voltage produced by
unbalance between phases.
So, it is recommended to stop the T/O during load tap adjusting for high capacity T/O.
5.2. Droop setting for parallel operation during on load operation
5.2.1. HFx5 series generator:
Adjust the load current to about 30% of rated value and reconnect the opened circuits such as cable
nos. 17, 18, 19 for sensing and 1, 5 for by-pass to A1. Adjust the load current to the rated value, and
then adjust the output voltage to 94%(6% voltage droop) of rated value by increasing the tandem
potentiometer(R2) for reactive current compensation.
5.2.2. HFx6 series generator:
Adjust the load current to about 30% of rated value and reconnect the opened circuits such as
connectors X1 for sensing and X3 for by-pass to A1. Adjust the load current to the rated value, and
then adjust the output voltage to 94%(6% voltage droop) of rated value by increasing the tandem
potentiometer(S) on A1 for reactive current compensation.
5.2.3. If the rated load current cannot be loaded due to the low supply power, the droop should be set
to the lower value proportional to the possible load comparing to rated load.( 6[%] droop at 100[%]
rated current)
(ex.) rated current = 2000 [A], rated voltage = 450 [V], possible load current = 1600 [A]
Droop setting value [%] = 6[%] * (1600 / 2000) = 4.8[%], output voltage = (1 - 0.048) *
450 = 428.4 [V]
5.2.4. The load current decreases when the voltage decreases due to voltage droop by adjusting the
tandem potentiometer(R2 for HF5 series, S for HF6 series) for reactive current compensation, so the
load current should be kept at the rated value by controlling the exciting current of power supply
generator during droop setting. But the set value of reference value setter during no-load operation
should be kept unchanged.
5.2.5. After finishing droop setting successfully, record Ua, Ja, Uef, Jef on the ‘AVR setting sheet’.
5.3. Record all the parameters under rated load after finishing all the adjustment:
Record all the parameters such as Ua, Ja, Uef, Jef on ‘AVR setting sheet’ under rated load after
finishing all the adjustment under no-load and rated load.
And then stop the T/O.
5.4. Completion of AVR setting sheet and final works
Record all the set-points and adjusted taps on the AVR setting sheet and confirm that all the handled
connecting pins should be retightened to avoid abnormal state by incomplete connection.
Sheet (1) parameters at each setting item
Setting items
Pre-set
Initial charging
No-load max. voltage
No-load rated voltage
No-load min. voltage
No-load voltage adjust
range
No-load rated voltage
Load max. voltage
Droop(voltage) under
Setting component
HFx5
HFx6
All Component
All Component
N/A
N/A
L1, T6(pri), T6(sec)
L1, T6(pri), T6(sec)
A1(Usoll)
A1(U)
R1
R47
with
AVR
N/A
N/A
X
O
O
Voltage
[%] of Un
N/A
N/A
110∼115
100
80∼95
Current
[%] of Jn
N/A
N/A
0
0
0
Operating
mode
S
S, M, G
M, G
M, G
M, G
RVS., A1(Vr), A1(Tn)
RVS., A1(K), A1(Tn)
O
80 ∼115
0
M, G
RVS.
CT, T6(sec)
R2
RVS.
CT, T6(sec)
A1(S)
O
X
O
100
107∼110(105∼108)
94
0
0
100
M, G
M
M
rated load
Rated voltage w/rated
load
RVS.
Notes RVS.: reference value setter
RVS.
S: standstill condition
O
100
M: motor operation
100
M
G: generator operation
6. Adjustment procedure if the rated voltage of T/O is not matched with the system voltage
of test facility(with different impedances)
6.1. Following procedure would be applied when the rated voltage of T/O is 600 ~ 2000[V] because
the normal setting procedure cannot be applied due to different voltage value(different impedance)
with the system voltages(220 ~ 600[V] and 3000 ~ 14000[V]) of test facility. In this case the set
values, especially for the ‘max. voltage setting under rated load’ and voltage droop setting, could not
be accurately correct.
6.2. The maximum voltage difference should be smaller than 20% of rated voltage of T/O and the T/O
should be coupled with loading machine before performing the test.
6.3. Any load except PT should not be connected and main switch(ACB, DS) should be OFF during noload adjustment. And the adjustment should be carried out during the T/O is being operated as
generator(driven by loading machine mechanically coupled with T/O.
6.4. Perform initial charging according to the procedure ‘3.3..’.
6.5. Perform no-load setting(maximum voltage, rated voltage, minimum voltage) according to the
procedure ‘4…’.
6.6. Adjust(reduce?) the size of Reactor(L1) air gap after stopping the generator. Operate the
generator without load and adjust the output voltage near to the maximum system voltage but below
that voltage. This adjustment should be performed only by changing the size of Reactor(L1) air gap
not by changing the taps of Rectifier Transformer(T6).
6.7. Set the output voltage to 95 ~96% of no-load maximum voltage by adjusting the reference value
setter(RVS.) under AVR connected and record the result. Then do not touch the reference value
setter(RVS) until the droop setting will be finished.
6.8. Set the output voltage near to no-load maximum voltage by adjusting the load tap of rectifier
transformer(T6) or CT taps under AVR disconnected and record the result.
6.9. According to the procedure 5.2. ., set the output voltage to 94%(6% droop) of the rated
voltage(not test voltage) by adjusting the tandem potentiometer(R2 for HF5, S for HF6 series) at rated
load under connected AVR and record the result.
(ex.) rated voltage = 710 [V], maximum system voltage = 700 [V], if the voltage value is 670V set at procedure
6.7. ., the voltage droop [V] = 0.06 * 710 = 42.6, Output voltage[V] = 700 – 42.6 = 657,4[V]
6.10. Set the output voltage to the same value as that adjusted at the procedure 6.7. by adjusting the
reference value setter(RVS.) and set the load current to the rated value under AVR connected and
record the result.
6.13. Adjust the Reactor(L1) air gap to the same size set at the procedure 6.5. during standstill and
than Set the output voltage to the rated value by adjusting the reference value setter(RVS.) after
operating the generator without load(no-load) under AVR connected.
6.14. Stop and finish the adjustment.
7. Function of the components of excitation equipment
7.1. Reactor(L1):
Reactor(L1) transforms the main terminal voltage to the current which is supplied to the exciter field
as exciting current(Ifo:no-load exciting current) through rectifier transformer(T6).
The current can be
adjusted by changing the size of L1 air gap located upper side of it. Ifo is almost proportional to the
size of L1 air gap. It means that the bigger air gap supplies bigger Ifo and the smaller air gap supplies
smaller Ifo.
Fig.(3) Vector diagram for exciting current
Ua: terminal voltage(phase)
Ja: armature current
ep: internal voltage
Ja.Ra: voltage drop by resistance
Ja.Xp: voltage drop by Potier reactance
Φ: power factor angle
Ja.Xp
ep
Ja.Ra
Jf(Reactor): supply current from reactor
Jf(current): supply current from current transformer
* Jf = exciter field current before static rectifier bridge
Ua
Jf(total)∼
Ja
Φ
Φ
Jf(current)∼
Jf(Reactor)∼
7.2. Capacitor(C1, C2, C3):
By resonance with the reactance of reactor(L1) during increasing the rotating speed of the generator,
the capacitors(C1,C2,C3) acts to reduce the voltage built-up time.
7.3. Current transformer(T1, T2, T3):
CTs supply to the exciter field the exciting current proportional to load current via the rectifier
transformer. The CTs compensate the voltage drop coming from armature reaction and armature
reactance by supplying the load proportional current to the exciter field.
The load compensating
current which is adjusted by changing the turn ratio of CTs keeps the output voltage at the constant
value under same condition by supplying additional exciting current required to compensate the
voltage drop due to armature reaction and armature reactance.
7.4. Rectifier transformer(T6):
It acts as power transformer. The current supplied by Reactor(L1) from main bus and current
transformers(T1,T2,T3) is transformed and compounded magnetically by this rectifier transformer(T6)
and supplied to the exciter field. The current supplied by Reactor from main bus is amplified by the
turn ratio of the primary winding and secondary winding(the winding at static rectifier side), and the
current supplied by current transformer(T1,T2,T3) from main bus is amplified by the turn ratio of the
input winding(from current transformer) and output winding(the winding at static rectifier side) of the
rectifier transformer. These two currents were compounded magnetically and supplied to the exciter
field. The exciting current is changed according to following regulation.
(1) Reduction of primary winding turn number(1U1  1U3) :
The exciting current proportional to the output voltage of generator decreases during no-load
operation.
(2) Reduction of input winding(from current transformers) turn number(2U1  2U8) :
The exciting current proportional to the load current of generator decreases during on-load
operation.
(3) Reduction of output winding(the winding at static rectifier side) turn number(2U1  2U8) :
The exciting current proportional to the output voltage and proportional to the load current of
generator increases at the same time during no-load or on-load operation.
At any case the amount of exciting current is inversely proportional to the turn number of output
winding(the winding at the static rectifier side) and proportional to the turn number of input
winding(primary winding during no-load operation, input winding at CTs side during on-load operation).
7.5. Static rectifier(V1 or V29):
It rectifies the AC power supplied via Rectifier transformer(T6) to DC power which is supplied to exciter
field.
7.6. Measuring(Step down) transformers(T7, T8): (HFx5 only)
The high voltage(generator output voltage) is step downed by these transformer to the sensing
voltage(near to 24 [V]) and supplied to the AVR which measures this voltage to control the by-pass
current to keep the generator output voltage at the constant value.
7.7. Intermediate transformer((Droop compensation current transformer: T4, T5 or T4):
They add the sensing voltage via tandem potentiometer(‘R2’/HFx5, ‘S’/HFx6) by supplying the
transformed current proportional to the load current. This additional voltage(proportional to the load
current) and the sensing voltage supplied through measuring transformer from output voltage of
generator are compounded in vector and compounded voltage is supplied to the AVR as final sensing
voltage. The sensing voltage increases(The output voltage of generator decreases) according to
increasing of reactive load current because the sensing voltage increases to the maximum value at cos
Φ = 0 and minimum value(almost same as before) at cosΦ = 1.
Fig.(4) Vector Diagram of sensing voltage for HFx5 series generator
Sensing voltage (cosΦ = 0)
Sensing voltage (cosΦ = 1)
U
Line – line voltage
W
Phase
sequence
V
of
Phase
voltage
Voltage drop at R2 (cosΦ = 1)
Voltage drop at R2 (cosΦ = 0)
7.8. Series(By pass) resistor(R1 or R48):
The output voltage of the generator can be controlled by controlling the bypass current which flows
through the bypass circuit with this series resistor. And some of U phase current of three phases
currents supplied to the static rectifier(V1 or V29) from Rectifier Transformer(T6) bypasses through
this series resistor. The bypass amount of U phase current is controlled by the thyristor, which makes
the ON or OFF circuit by the pulse signal supplied by voltage regulator. The voltage regulator(A1)
compares the sensing voltage value and the reference value given by reference value setter, and
makes the pulse according to the comparison result and supplies the time controlled pulse to the
thyristor.
Fig. (5) Bypassing the exciting current by bypass resistor(HFx5 Type generator)
w
v
u
Ju
A.V.R. (A1)
Jb
R1
1
5
Jua
Js
Jef
F1
F2
Jb
Jef = Js - Jb
Jua = Ju - Jb
Jef = exciter field current
Js = total current of rectifier bridge (-) line
Jb = bypass current
Jua = ‘u’ phase current of rectifier bridge
Ju = total current of ‘u’ phase
7.9. Series(By pass) Thyristor(V28):
It makes the bypass circuit as ON or OFF state by the gat pulse supplied by Voltage regulator(A1).
8. The cause and trouble shooting for each fault of the machine including excitation
equipment
Several different causes can produce same abnormal result during setting of excitation equipment. So,
it is recommended that the trouble shooting should be started to check one by one from the most
possible cause.
8.1. The generator(T/O) can not be started due to severe mechanical vibration during
starting as motor. :
● Short between phases by main stator lead cable
If the T/O is run by loading machine, measure the unbalance of the phase voltages under low voltage
(1 ~ 3[%] of rated value) by supplying low separate exciting power with low speed under 50% of
rated speed. There must be more than 20[%] unbalance between phase voltages if there would be
short circuit between phases by main stator lead cable.
8.2. Current meter for exciter field does not work.
● No connection from static rectifier(+) to the current meter. Check the connecting pins.
● Incomplete connection of the pins(F1, F2 for 12 pin connector/HFx5 series, F1, F2 for connector
X4/HFx6 series)
8.3. Voltage meter for exciter field does not work.
● No connection from the cables for exciter field to the auxiliary terminal block F1, F2.
● Short circuit break(S/W) for exciter field is closed. 용 short circuit break 가 close 되어있다.
8.4. Reverse action of exciter field Ammeter(current meter)
● Reverse(Exchanged) connection of the (+), (-) pins for the cables from the static rectifier(+, -) to
the exciter field(F1, F2).
8.5. Reverse action of exciter field Voltmeter
● Reverse(Exchanged) output of the cables for pre-exciting(initial charging) terminals F1, F2.
● Reverse(Exchanged) connection of the (+), (-) pins for the cables from the static rectifier(+, -) to
the exciter field(F1, F2).
8.6. No voltage built-up or too low voltage built-up during no-load maximum voltage setting
● Opened circuit(misconnection) with the cables or pins between exciter field(F1, F2) and Static
rectifier(+, -) terminals
● The ammeter cable from the static rectifier(+) for exciter field current is not connected to the
ammeter terminal.
● Opened circuit(misconnection) with the cables or pins between the input terminals(U1,V1,W1) of
reactor(L1) and main bus.
● Opened circuit(misconnection) with the cables or pins between the output terminals(U2, V2, W2) of
reactor(L1) and the primary winding terminals(1U1, 1V1,1W1) of rectifier transformer(T6).
●
Opened
circuit(misconnection)
with the
cables or pins
between the
secondary winding
terminals(2UV, 2VV, 2WV) of rectifier transformer(T6) and the terminals(U, V, W) of static rectifier(V1
or V29).
● The failure(open or short) of the diode for static rectifier(V1 or V29)
● The failure(open or short) of the diode for rotating rectifier(V2)
● Insulation failure between turns on the primary winding of rectifier transformer(T6)
● Insulation failure between turns on the secondary winding of current transformers(T1, T2, T3)
8.7. The exciting currents between the generators with same type and same condition are
different from each other.
● Magnetic center(the coincidence of the center lines) between stator and rotor of main machine or
exciter machine
● The air gap(the gap between stator core and rotor core) of main machine or exciter machine is
different from that of other same generator.
● Inverse polarity with one or several coils for exciter pole
8.8. Too High voltage built up during no-load maximum voltage or on-load maximum
voltage setting
● Short failure with the diode for rotating rectifier
● Insulation failure between turns on the reactor (L1) winding
● Insulation failure between turns on the secondary winding of rectifier transformer(T6)
● The air gap of Reactor(L1) is too large
● No-load taps for rectifier transformer(T6) is set on too high numbers
8.9. During on-load maximum voltage setting,
voltage increases rapidly according to load current increase
or sudden load on at the time when the exciting is changing from the lagging
exiting(cosΦ = laging) to the leading exciting(cosΦ = leading).
● Setting too low turn number(too large secondary current) of secondary winding of current
transformers(T1, T2, T3)
● Setting too low turn number(too large output current) of output winding for load tap of rectifier
transformer(T6) rectifier transformer(T6)
● Setting too large turn number(too large output current) of input winding for no-load tap of rectifier
transformer(T6) rectifier transformer(T6)
8.10. The voltage decreases with light load and then increases with higher load during onload maximum voltage setting.
● Inverse polarity or interchanged connection of 2.1 and 2.2 cables with current transformer(T1, T2,
T3)
● Interchanged connection between two of the 3 phases cables from the secondary winding(2.2) of
current transformer(T1, T2, T3) to the rectifier transformer(2U, 2V, 2W).
● Interchanged connection between two of the 3 phases cables from the main bus to the input(U1, V1,
W1) of reactor(L1).
● Interchanged connection between two of the 3 phases cables from the output(U2, V2, W2) of
reactor(L1) to the primary winding(1U1, 1V1,1W1) of the rectifier transformer(T6).
8.11. Sudden voltage drop during on-load maximum voltage setting.
● Opened circuit(misconnection) with one or several cables or pins between the secondary winding
terminals(2.2S) of current transformers(T1, T2, T3) and the input terminals(2U, 2V, 2W) of rectifier
transformer(T6).
● Insulation failure between turns on the secondary winding of current transformers(T1, T2, T3)
● Insulation failure between turns on the secondary winding of rectifier transformer(T6)
8.12. The voltage droop is not linear and suddenly dropped with higher load during on-load
maximum voltage setting.
● There would be magnetic saturation due to the lack of capacity or quality with
current
transformer(T1, T2, T3) or rectifier transformer(T6).
8.13. Voltage rise or no voltage variation during voltage droop setting with load
● Inverse polarity or incorrect wiring of drop compensator current transformers(T4, T5 for HFx5 series
or T4 for HFx6 series)
● Inverse polarity or incorrect wiring of measuring(step down) transformers(T7, T8) for HFx5 series
● Incorrect phase(different phase voltage) connection to voltage sensing plug connector(X1) on AVR
for HFx6 series
● Incorrect phase rotation of Generator itself
8.14. Generator voltage not adjustable or too narrow control range by reference value
setter or A1(Usoll for HFx5 series or U for HFx6 series).
● No wiring for reference value setter or S/W off for reference value setter
● The S/W ‘ON’ for reference value setter and together with Micro S/W(S1-3) on AVR ‘ON’ for
HFx6series.
● Opened circuit(misconnection) with one or several cables or pins between the terminals 17, 18, 19
on AVR and secondary winding(2.1, 2.2) of sensing(step down) transformers(T7, T8) or between main
bus and primary winding(1.1, 1.2) of sensing transformer for HFx5 series
● Sensing of higher than normal U-W phase voltage by incorrect wiring or polarity of sensing(step
down) transformers(T7, T8) for HFx5
● Opened circuit or incomplete connection for voltage sensing plug connector(X1) on AVR for HFx6
series
● Opened circuit or incomplete connection of the cable(1, 5) for bypass cables of AVR for HFx5
● Opened circuit or incomplete connection for bypass plug connector(X3) on AVR for HFx6 series
● Setting no-load maximum voltage at too high value
● Setting bypass resistor(R1 or R48) at too high resistance value
● Failure of thyristor(V28) for HFx6series
● Failure of AVR
8.15. Hunting of output voltage or exciting current with load or without load
● Hunting of speed of driving machine(loading machine, engine ….)
● Incomplete contact of connecting pins or cable
● Loosened locking nut of potentiometer on AVR for HFx5 series
● Incorrect adjusting of potentiometers(Vr, Tn for HFx5 series, K, T, 47 for HFx6 series) on AVR
● The wiring cable between AVR and reference value setter is too long or the reference value would be
infected by external magnetic noise.
● The resistance value with bypass resistor(R1 or R48) is too low.
● External power for initial charging is connected to the auxiliary terminals(F1, F2) for exciter field.
● Out of control by AVR because of too low no-load exciter current
● Failure of AVR
8.16. Incorrect load sharing between generators in parallel operation
●
Incorrect active load(KW) sharing due to different speed variation ratio of each prime
mover(engine).
● Incorrect reactive load sharing due to different no load voltage setting by reference setter. ●
Voltage droop values by droop potentiometer(R2 or S on A1) are different from each other.
● The accurate load sharing is impossible if the voltage droop values by droop potentiometer(R2 or S
on A1) are too low.
● Voltage droop values are different from each other due to the long power cable(due to voltage drop
by high line resistance) from the generator to the circuit breaker.
8.17. The circuit breaker is opened due to high circulation current between generators
during synchronizing(‘break on’ for parallel operation).
● High variation of active power due to instability of governor of prime mover
● Different voltage droop setting from each other paralleling generator
●
Excessive
series
winding
compensation
with
current
transformers(T1,T2,T3)
or
rectifier
transformer(T6)
● Lack of bypass compensation by current transformers(T1,T2,T3) or rectifier transformer(T6).
When the lagging current due to any reason(different voltage setting by reference value setter, voltage
droop of loaded generator during synchronizing) flows(under exciting status) the phases of the
current supplied by Reactor(L1) and the current supplied by Current transformer(T1, T2, T3) are
opposite to each other. So the exciting current decreases according to the increase of circulating
current(leading current) and the AVR cannot control the exciting current if this exciting current
decreases to the meaning value. Then the circuit breaker will be opened due to increased circulating
current.
This phenomena can be happened with the generators which has lower no-load exciting
current, which voltage generator set at low value during no-load maximum voltage setting or set at
higher value during maximum voltage setting with load.
This kind of unstable situation can be
avoided by prolonging the powering time of bypass current, which can be achieved by setting the
bypass resister to higher value or by setting no-load maximum voltage to higher value within limited
value. And also it can be avoided by increasing the stability of exciter current control, which can be
achieved by setting ‘load maximum voltage’ to higher value(decreasing the exciting current.)
But more important points than resetting the excitation equipment are to confirm whether the noload voltage is adjusted at the same value by reference value setter before starting parallel operation
and to avoid the parallel operation under light load.
We can see the variation of current value supplied by excitation equipment according to the different
current value supplied by reactor on Fig.(6).
(a) Reduced current supplied by Reactor -> The current supplied by CTs increases. -> The
dramatically decreased exciting current to almost same as or lower than required value(Jf(n)) is
supplied if leading current load is applied. -> The AVR cannot bypass the control current due to
lower current supplied by reactor and CTs. -> Unstable Synchronizing.
(b) Increased current supplied by Reactor -> The current supplied by CTs decreases. -> The lightly
decreased exciting current(higher current than required value(Jf(n)) is supplied if leading current
load is applied. -> The AVR can bypass the control current due to higher current supplied by
reactor and CTs. -> Stable Synchronizing.
If this kind of problem happens during operating on site, try to secure it according to
following procedure.
But keep in mind that this procedure is not the absolute one for the troubleshooting.
(1) Confirm the normal operating status(voltage status, single operation status) of each generator with
excitation equipment.
(2) Confirm the normal operation of governor of prime mover during single and parallel operation if
possible.
(3) Confirm the same no-load voltage adjusting with each generator.
(4) If you could not find the cause of problem by above (1) ~ (3) procedure, reduce the current for
excessive series compensation(CT or T6) or increase the current for 보상 compensation. Generally it is
enough to change one(1) to three(3) taps of T6 in almost all the cases.
(5) If the problem could not be cleared by above procedure, try to find any other reason of the
problem except excitation equipment.
If you thrust that there is not any other reason except excitation equipment until yet, try to
follow Ex. Eq. resetting procedure as below.
(6) Resetting the exciting current for no-load maximum voltage(108 ~ 112 % of rated value) by T6
and L1 without connection of AVR .
(7) Measure the bypass current(A.C portion) by using clamp-meter after connecting AVR during
running at no-load rated voltage.
(8) During single operation, reset the CTs or T6 taps to keep the bypass current under full load
operation at about 100 ~ 150 % of bypass current under no-load operation. that 단독 운전 상태에서
(9) Try synchronizing and check the condition.
If the problem could not be cleared by above procedure, try to find any other reason of
the problem except excitation equipment.
Fig. (6) Vector diagram for exciting current with leading power factor load
ua: terminal voltage(phase)
Ja: armarture currrent
Jf(L1): supplyed curent from reactor
Jf(CT): supplyed curent from current transformer
Jf(s) = summation of two component = [ Jf(L1) + Jf(CT) ]
Jf(n) = rated field curent
Φ = power factor angle
Ua
Φ
Ua
Jf(s)
Jf(CT)
Φ
Ja
Φ
Jf(s)
Jf(CT) Φ
Ja
If(L1)
If(L1)
(a) reduced reactor current setting
(b) increased reactor current setting
9. Other useful information for setting in shop or operating at site for the excitation
equipment of the generators
9.1. The load voltage can be increased to the slightly higher than no-load voltage due to lower
sensing voltage by impedance drop of T9(step down transformer) for HSR7 series(High voltage
generator series). But that variation could be ignored because it cannot effect to normal operation of
the generator.
9.2. At site the indicated voltage is generally lower than actual voltage measured at generator
terminal box because of resistance voltage drop due to the cable length between generator terminal
box and control panel on which main breaker(ACB or VCB..) is equipped. This voltage drop could be
seen by large value with high capacity(current) generators.
9.3. Sometimes the purpose of resetting of T6 taps could be completed only by changing the tap
numbers of ‘u’ and ‘v’ or ‘w’. But this try is not recommended because the overheating of T6 winding
could be seen sometimes by unbalance between phases.
(ex.1) To increase the stability of AVR by increasing bypass power during no-load operation, the power of ‘u’ phase
shall be increased and ‘v’ or ‘w’ phase be decreased. (ex. T6 taps : from 5.6.6 – XXX to 6.5.6 – XXX
(ex.2) To reduce the heating of bypass resister and to increase the powering time of thyristor by decreasing
bypass power, the power of ‘u’ phase shall be decreased and ‘v’ or ‘w’ phase be increased. (ex. T6 taps : from X.X.X
– 4.4.4 to X.X.X – 5.4.3)
9.4. If it is difficult or impossible to adjust by bypass resister, the no-load maximum voltage and the
voltage control range shall be increased by increasing the current of ‘u’ phase of rectifier
transformer(T6).
(ex.) T6 tap: from 6.6.6 – X.X.X to 7.6.6 –X.X.X (increased no-load maximum voltage with enlarged
control range)
9.5. No-load maximum voltage could be decreased if there is insulation failure between turns with
one of three windings s of current transformer. This failure can be found by confirming the increase of
no-load voltage when the load cable on the rectifier transformer(connected to troubled CT) and the
cable for ‘2N’ are disconnected.
9.6. The voltage control range for the generator with lower no-load exciting current could be changed
after test due to high residual magnetism(specially for 4 poles generator). The exciting current shall
be increased or the ratio between exciter field resistance(by increasing) and the resistance of bypass
resister shall be changed during design.
The voltage control range is reduced from d1 to d3 after increasing the exciting current but it was from
d1 to d2 before increasing the exciting current.
If this is not considered during design, measure again the no-load maximum voltage after no-load
setting and load setting or temperature rise test. If there is any difference from initial setting value
more than 1.5%, no-load maximum voltage setting shall be performed again from that stage. It is not
required to confirm on-load maximum voltage in this case.
Fig.(7) variation of Voltage control range due to residual magnetism
Ifmax.
ⓐ
ⓑ
ⓓ
d2
voltage
ⓒ
d3
Ifmax.
d1
Ifmin
Ifmin
ⓐ: original saturation curve
ⓑ: changed saturation curve due to residual magnetism
ⓒ: original saturation curve (increased excitation)
ⓓ: changed saturation curve due to residual magnetism(increased excitation)
d1: voltage adjustable range of curve ⓐ and ⓒ
d2: voltage adjustable range of curve ⓑ
d3: voltage adjustable range of curve ⓒ
ΔIf: equivalent excitation current du to residual magnetism
exciting current
ΔIf
9.7. Optimistic setting of rectifier transformer(T6), Reactor(L1) and current transformers
(T1,T2,T3)
[Refer to Fig. (8)]
The winding ratio one(1) between input and output one has the highest efficiency because the
secondary winding of rectifier transformer(T6) acts as auto-transformer during on-load operation. If
possible it is better to keep the turn numbers of input and output of secondary winding of T6 near to
the same ones.
The variation of exciting current or output voltage according to changing one(1) number of T6 output
taps is high if no-load taps(primary winding) for T6 were chosen at high tap number(reduced number
of turns).
But accurate adjusting of output voltage is not so easy.
The variation of exciting current or output voltage according to changing one(1) number of T6 output
taps is high if load taps(CTs side secondary winding) of T6 were chosen at high tap number(reduced
number of turns). But total output current is increased due to reduced number of turns and accurate
adjusting of output voltage is very difficult.
The variation of exciting current or output voltage according to changing one(1) number of T6 output
taps is low if no-load taps(primary winding) for T6 were chosen at low tap number(increased number
of turns).
In this case the large variation of output voltage cannot be easily gotten by changing one
tap of T6 but accurate adjusting of it is so easy.
The variation of exciting current or output voltage according to changing one(1) number of T6 output
taps is low if load taps(CTs side secondary winding) of T6 were chosen at lower tap number(increased
number of turns). In this case the large variation of output voltage cannot be easily gotten by
changing one tap of T6 but accurate adjusting of it is so easy. And output exciting current by load
current is decreased.
If it is necessary to reduce the number of turns of T6 output winding(static rectifier side) for the
generator which has already set completely, the power supplied from Reactor(L1) and Current
transformers(T1,T2,T3) shall be increased by decreasing the number of turns at input winding(CT side)
of T6.
Fig.(8) example of wiring for Rectifier transformer(T6)
CT
CT
1N = 0
2N = 0
2.10 = 400
2.8 = 600
2.6 = 800
2.4 = 1000
1.1 = 2000
main bus
Static rectifier
(a) changing of no-load tap
main bus
2.1 = 1200
Static rectifier
(b) changing of no-load tap
(c) Number of turns for T6
The variation of exciting current can be estimated by calculating output current i(rectifier) according to
following two equations.(단 CT 이차 전류에 의한 T6 이차 여자 전류는 무시 하였다)
i(rectifier) = i(reactor) * T(primary) / T(rectifier) ................ eq.(2)
for no-load calculation
i(rectifier) = i(ct) * T(ct) / T(rectifier) .............................…eq.(3) for on-load calculation
note
: i(rectifier) = the current out to static rectifier(V1, V29) from T6
i(reactor) = the current supplied from reactor(L1) to the primary winding of T6
i(ct) = the current supplied from CT to secondary winding of T6(input current from CTs to T6)
T(primary) = number of turns for primary winding of T6
T(rectifier) = number of turns at the tap of static rectifier side for secondary winding of T6
T(ct) = number of turns at the tap of CT side for secondary winding of T6
Cal. Ex. 1) If i(reactor) = 1A on Fig. (8)-(a);
Connecting to tap 2.1 :
i(reactor) = 1 * 2000/1200 = 1.67A
Connecting to tap 2.2 : i(reactor) = 1 * 2000/1100 = 1.82A (increased 8.99% from that of tap 2.1)
Connecting to tap 2.9 : i(reactor) = 1 * 2000/500 = 4.00A
Connecting to tap 2.10 : i(reactor) = 1 * 2000/400 = 5.00 (increased 25.0% from that of tap 2.9)
i i(ct) = 5A on Fig. (8)-(b);
Connecting to tap 2.1 : i(rectifier) = 1 *1200/1200 =5.00A
Cal. Ex. 2) If
Connecting to tap 2.2 :
Connecting to tap 2.9 :
Connecting to tap 2.10:
i(rectifier) = 1 * 1100/1200 = 4.58A (decreased 8.4% from that of tap 2.1)
i(rectifier) = 1 * 500/1200 = 2.08A
i(rectifier) = 1 * 400/1200 = 1.67A (decreased 19.7% from that of tap 2.9)
Cal. Ex. 3) What are the on-load tap numbers(x.x.x) in 9.9.9 – x.x.x if we want to get the same exciting current
with that with the tap numbers 5.5.5 – 3.3.3 ?
It is assumed that i(rectifier) under no-load is same as before by
adjusting the air gap of Reactor(L1).
if i(CT) =5.0A : according to the eq.(3) for on-load calculation
i(rectifier) with the tap numbers
i(rectifier) with the tap numbers
5.5.5 – 3.3.3 :
9.9.9 – x.x.x:
i(rectifier) = i(ct) * T(ct) / T(rectifier)
5.0 * 1100/900 = 6.11A
5.0 *
T(ct) / 500 = 6.11A ---> T(ct) = 6.11 * 500 /5
= 611 [turn]
We can select the taps 9.9.8. – 8.8.8 to have the nearest to 611 turns or 9.9.9 – 7.7.7 to have
second nearest ones.
And we get the result that T6 load taps shall be changed according to the
variation of T6 no-load taps.
Fig. (6) Process map for the setting of excitation equipment
As generator
As motor
Different voltage from system
Pre-setting
Pre-setting
Pre-setting
Pre-exciting
Pre-exciting
Pre-exciting
No-load max. voltage w/o AVR
No-load max. voltage w/o AVR
No-load max. voltage w/o AVR
No-load rated voltage w/AVR
On-load max. voltage w/o AVR
No-load rated voltage w/AVR
No-load min. voltage w/AVR(RVS)
No-load rated voltage w/AVR
No-load min. voltage w/AVR(RVS)
No-load rated voltage w/AVR(RVS)
No-load min. voltage w/AVR(RVS)
reduced No-load max. voltage w/o AVR
On-load max. voltage w/o AVR
No-load rated voltage w/AVR(RVS)
Reduced no-load rated voltage w/AVR(RVS)
Voltage droop under load w/AVR
Voltage droop under load w/AVR
On-load rated voltage w/AVR(RVS)
* RVS: Reference Value Setter
On-load rated voltage w/AVR(RVS)
Reduced on-load max. voltage w/o AVR
Reduced voltage on-load droop w/ AVR
reduced voltage on-load rated voltage w/ AVR(RVS)
Procedure for the trouble shooting of ‘Hunting of output voltage or exciting
current with load or without load’
Estimated causes
● Hunting of speed of driving machine(loading machine, engine ….)
● Incomplete contact of connecting pins or cable
● Loosened locking nut of potentiometer on AVR for HFx5 series.
● Incorrect adjusting of potentiometers(Vr, Tn for HFx5 series, K, T, 47 for HFx6 series) on the AVR.
● The wiring cable between AVR and reference value setter is too long or the reference value would be
infected by external magnetic noise.
● The resistance value of bypass resistor(R1 or R48) is too low.
● External power for initial charging is connected to the auxiliary terminals(F1, F2) for exciter field.
● Out of control by AVR because of too low no-load exciting current.
● Failure of AVR
Check points
1. Check whether the speed of prime mover has the hunting or not.
2. Check the connecting status on the taps with secondary windings of current transformers.
3. Retighten the locking nut of potentiometers(Vr, Tn, Usol)l on the A.V.R kit of HFx5 series.
4. Check
whether
there
would
be
any
coloring
point
by
excessive
heating
with
all
the
transformers(T1,T2,T3, L1, T6, T4,T5, T7,T8..).
5. Check the bolting status on the auxiliary terminals in the terminal box and retighten them.
6. Try test after exchanging the A.V.R with that of normal operating generators.
7. Check the variation result by tester during adjusting ‘reference value setter’ installed on the control
panel.
Procedure for the trouble shooting of ‘Lower output Voltage’ of No.3
generator.<HFx5 series>
The lower voltage comes from any power loss in the excitation equipment or rectifiers(Static or Rotating
Rectifier).
A. If the lower voltage comes just after any transient condition by other abnormal condition, the
rectifiers
could
be
damaged
because
the
weakest
part
by
transient
shock
is
electronic
components(rectifiers or AVR....)
So, we would like to ask you to give keen attention to the Static Rectifier(V1) and Rotating
Rectifier(V2) with Varistor first of all.
B. If the lower voltage comes during normal operation, there must be any power loss by opening with
one of the lines(disconnection or improper contact on the terminals with one of the components) in the
excitation equipment.
So, we would like to ask you to give keen attention to the connecting status in the excitation equipment.
So, you are kindly requested to check the circuit and equipment according to the following instruction
step by step.
1. Check the ‘rectifier module(V1, static rectifiers)’ by multi-meter. If there is any ‘short’ or ‘open’ circuit
with one of the diodes on the rectifier module, the output voltage is lower than normal value. If there is
any failure with it, replace by new one.
If you are not sure whether there is any failure with V1, try to exchange it with the other one equipped
on the other generator(No.1 or No.2).
#Caution 1. During checking the resistance, stop the generator to avoid the defect of the equipment or
personal damage.
# Caution 2. Be careful not to touch live lines during measuring the voltage of each point.
2. Checking procedure to define whether there would be any failure on the Rotating Rectifiers(V2):
2.1 Adjust ‘no-load voltage value’ of No.1 or No. 2 Generator to the same with ‘no-load voltage value’ of
No. 3 Generator.(Before adjusting the voltages, record the present voltage value in order to return after
the test.)
2.2 Measure the D.C Voltage of No.1 or No.2 Generator at no-load by multi-meter at the terminal block
‘F1-F2’ at the Generator terminal box.
2.3 Measure the D.C Voltage of No.3 Generator at no-load by multi-meter at the terminal block ‘F1-F2’
at the Generator terminal box.
2.4 Compare the voltage values given by 2.2 and 2.3.
2.4.1
If there is any pointed difference between the D.C Voltage values of No.1 or 2 generator and
No.3 generator, there would be failure on any of the rotating rectifiers(V2). Then replace the damaged
rectifier by spare one.
If you cannot whether there would be failure on the rectifiers, please inform us all the voltage values
measured during above procedure.
2.4.2 If there is not any big difference between the D.C Voltage values of No.1 or 2 generator and No.3
generator, perform following procedure(3 ~ 6)
2.5 If you could not define by the difference, please inform us the measured result.
3. Check the excitation equipment for No.3 generator according to following procedure.
3.1 Disconnect the cables connected at the terminals 17,18,19(for sensing) and 1,5(for bypass) and
then measure the output voltage of No.3 generator.
3.2 If the output voltage is around 480V~500V, there is not any failure except Voltage regulator(A1).
Then Voltage regulator(A1) should be replaced by new one.
4. If the output voltage is below about 440V, the other equipment or lines should be checked as below.
4.1 During no-load operation, measure the voltage at the terminals U1-V1-W1 on the Reactor(L1).
4.2 The measured voltage must be same as the output voltage of the Generator.
4.3 If these voltages(measured voltage) are different from the output voltages, there must be any
disconnecting points between Reactor and Current transformers(T1,T2,T3). Check the connecting status
on the connecting points with Current transformers(T1,T2,T3) and secure failed points if any. Then
operate the generator and measure the output voltage.
5. If the output voltage is still lower than rated value, continue following procedure.
5.1 During no-load operation, disconnect the cables between current transformer(T1,T2,T3) and
secondary winding of Rectifier transformer(T6) at the points marked as 2U,2V,2W,2N.
And measure the output voltage.
5.2 If the output voltage would be increased above rated value, there must be any failure with one of
the ‘Current Transformers(T1,T2,T3) and should be replaced by new one.
But this case could hardly happen.
6. If the output voltage is still lower than rated value, continue following procedure.
6.1 Check the connection status between Reactor(L1) and primary winding of Rectifier Transformer(T6)
– between the terminals U2,V2,W2 on Reactor(L1) and 1U1, 1V1, 1W1 on Rectifier Transformer(T6)
If there is any troubled point or loosen point, secure it.
6.2 Measure the resistance value between the terminals 1U1, 1V1, 1W1 on Rectifier Transformer(T6)
after disconnect the lines connected to those terminals.
If there is the difference more than 0.5 Ohms between each terminals(1U1-1V1, 1V1-1W1, 1W1-1U1)
there would be any failure with the primary winding of Rectifier Transformer.
Then Rectifier Transformer should be replaced by new one.
But this case could hardly happen.
6.3
Check the
connection status between secondary winding
side(2UV,2VV,2WV) of Rectifier
Transformer(T6) and the terminals U,V,W on Rectifier module(V1).
If there is any troubled or loosen point, secure it.
6.4 The lower no-load output voltage would be generated if there would be insulation failure
between turns of Current transformer(T1,T2,T3). So, we can catch that there might insulation
failure between turns of Current transformer(T1,T2,T3) if the no-load output voltage
increases when the load tap of Rectifier transformer(T6) is opened.
6.5 The lower no-load output voltage would be generated if there would be insulation failure
between turns of primary winding of rectifier transformer(T6). And, there must be insulation
failure between turns of winding of rectifier transformer(T6) if there would be resistance
unbalance more than 4% between phases of winding of rectifier transformer(T6).
#Caution . After checking the connecting status or any disconnecting and reconnecting trial, all the
connecting points(terminals) must be tightened(the loosen pins must be carefully retightened).
If you could not find any troubled point by above detailed procedure, please inform us the checked
result in detail(step by step on above procedure).
Procedure for the trouble shooting of ‘Lower output Voltage’ of No.3
generator.<HFx6 series>
The lower voltage comes from any power loss in the excitation equipment or rectifiers.
A. If the lower voltage comes just after any transient condition by other abnormal condition, the
rectifiers
could
be
damaged
because
the
weakest
part
by
transient
shock
is
electronic
components(rectifiers or AVR....)
So, we would like to ask you to give keen attention to the Static Rectifier(V1) and Rotating
Rectifier(V2) with varistor first of all.
B. If the lower voltage comes during normal operation, there must be any power loss by opening with
one of the lines(disconnection or improper contact on the terminals with one of the components) in the
excitation equipment.
So, we would like to ask you to give keen attention to the connecting status in the excitation equipment.
So, you are kindly requested to check the circuit and equipment according to the following instruction
step by step.
1. Check the ‘rectifier module(V29, static rectifiers)’ by multi-meter. If there is any ‘short’ or ‘open’
circuit with one of the diodes on the rectifier module, the output voltage is lower than normal value. If
there is any failure with it, replace by new one.
If you are not sure whether there is any failure with V29, try to exchange it with the other one
equipped on the other generator(No.1 or No.2).
#Caution 1. During checking the resistance, stop the generator to avoid the defect of the equipment or
personal damage.
# Caution 2. Be careful not to touch live lines during measuring the voltage of each point.
2. Checking procedure to define whether there would be any failure on the Rotating Rectifiers(V2):
2.1 Adjust ‘no-load voltage value’ of No.1 or No. 2 Generator to the same with ‘no-load voltage value’ of
No. 3 Generator.(Before adjusting the voltages, record the present voltage value in order to return after
the test.)
2.2 Measure the D.C Voltage of No.1 or No.2 Generator at no-load by multi-meter at the terminal block
‘F1-F2’ at the Generator terminal box.
2.3 Measure the D.C Voltage of No.3 Generator at no-load by multi-meter at the terminal block ‘F1-F2’
at the Generator terminal box.
2.4 Compare the voltage values given by 2.2 and 2.3.
2.4.1
If there is any pointed difference between the D.C Voltage values of No.1 or 2 generator and
No.3 generator, there would be failure on any of the rotating rectifiers(V2). Then replace the damaged
rectifier by spare one.
If you cannot whether there would be failure on the rectifiers, please inform us all the voltage values
measured during above procedure.
2.4.2 If there is not any big difference between the D.C Voltage values of No.1 or 2 generator and No.3
generator, perform following procedure( 3 ~ 6)
2.5 If you could not define by the difference, please inform us the measured result.
3. Check the excitation equipment for No.3 generator according to following procedure.
3.1 Disconnect the multi-connector X1, X3 and the cables connected to thyristor(V28) and then
measure the output voltage of No.3 generator.
3.2 If the output voltage is around 480V~500V, there is not any failure except Voltage regulator(A1) or
Thyristor(V28).
Then Voltage regulator(A1) or Thyristor(V28) should be replaced by new one.
4. If the output voltage is below about 440V, the other equipment or lines should be checked as below.
4.1 During no-load operation, measure the voltage at the terminals U1-V1-W1 on the Reactor(L1).
4.2 The measured voltage must be same as the output voltage of the Generator.
4.3 If these voltages(measured voltage) are different from the output voltages, there must be any
disconnecting points between Reactor and Current transformers(T1,T2,T3). Check the connecting status
on the connecting points with Current transformers(T1,T2,T3) and secure failed points if any. Then
operate the generator and measure the output voltage.
5. If the output voltage is still lower than rated value, continue following procedure.
5.1 During no-load operation, disconnect the cables between current transformer(T1,T2,T3) and
secondary winding of Rectifier transformer(T6) at the points marked as 2U,2V,2W,2N.
And measure the output voltage.
5.2 If the output voltage would be increased above rated value, there must be any failure with one of
the ‘Current Transformers(T1,T2,T3) and should be replaced by new one.
But this case could hardly happen.
6. If the output voltage is still lower than rated value, continue following procedure.
6.1 Check the connection status between Reactor(L1) and primary winding of Rectifier Transformer(T6)
– between the terminals U2,V2,W2 on Reactor(L1) and 1U1, 1V1, 1W1 on Rectifier Transformer(T6)
If there is any troubled point or loosen point, secure it.
6.2 Measure the resistance value between the terminals 1U1, 1V1, 1W1 on Rectifier Transformer(T6)
after disconnect the lines connected to those terminals.
If there is the difference more than 0.5 Ohms between each terminals(1U1-1V1, 1V1-1W1, 1W1-1U1)
there would be any failure with the primary winding of Rectifier Transformer.
Then Rectifier Transformer should be replaced by new one.
But this case could hardly happen.
6.3
Check the
connection status between secondary winding
side(2UV,2VV,2WV) of Rectifier
Transformer(T6) and the terminals U,V,W on Rectifier module(V29).
If there is any troubled or loosen point, secure it.
6.4 The lower no-load output voltage would be generated if there would be insulation failure
between turns of Current transformer(T1,T2,T3). So, we can catch that there might insulation
failure between turns of Current transformer(T1,T2,T3) if the no-load output voltage
increases when the load tap of Rectifier transformer(T6) is opened.
6.5 The lower no-load output voltage would be generated if there would be insulation failure
between turns of primary winding of rectifier transformer(T6). And, there must be insulation
failure between turns of winding of rectifier transformer(T6) if there would be resistance
unbalance more than 4% between phases of winding of rectifier transformer(T6).
# Caution.
After checking the connecting status or any disconnecting and reconnecting trial, all the
connecting points(terminals) must be tightened(the loosen pins must be carefully retightened).
If you could not find any troubled point by above detailed procedure, please inform us the checked
result in detail(step by step on above procedure).
Procedure for the trouble shooting of ‘Higher output Voltage’ of the generator
on the site. <HFx5 series>
The output voltage of HFx5 series generator is set at the higher but limited value than the
rated voltage without connecting the AVR from excitation equipment system. And the AVR
acts to make bypass the excessive exciting current to keep the output voltage at the
reference value(neat to the rated value).
It means that the higher output voltage could comes from the loss of any connection from
any equipment to AVR or the loss of function of AVR.
A. The loss of sensing voltage(lowest sensing voltage):AVR acts to increase the output
voltage.
B. The loss of reference value(highest reference value):AVR acts to increase the output
voltage to the highest value.
C. The loss of Function as AVR due to failure of AVR, failure of thyristor or discontinuity of
bypass circuit.: The output voltage is kept at the same value with no-load maximum voltage
without AVR.
D. There could be any other cause than above for the higher output voltage rarely.
So, you are kindly requested to check the circuit and equipment according to the following
instruction step by step.
1. During standstill of the generator, check the connections from power output(1U,1V,1W for HFx5
series) to AVR(17,18,) via the measuring transformer(1.1, 1.2 and 2.1, 2.2 : for HFx5 series only).
Opening at one of the connections means the loss of sensing voltage.
2. Check the connections from AVR(20,21) to Reference value setter(A20,A21). All the connecting points
including the auxiliary terminal board equipped in the terminal box(20,21) and control panel shall be
checked with keen attention.
3. Check the connection of AVR(1) – R1(1,2) – static rectifier(U-F2) – AVR(5) for HFx5 series.
4. Check the connection of AVR(5) – R48(1,2), thyristor(A) – static rectifier(U-F2) – thyristor(K) AVR(6) and AVR(3) - thyristor(G) for HFx6 series.
5. Try the test after exchange the AVR with the other new AVR or that of the other generator operating
in normal.
6. The higher no-load output voltage would be generated if there would be insulation failure
between turns of secondary winding of rectifier transformer(T6).
And, there must be insulation failure between turns of winding of rectifier transformer(T6)
if there would be resistance unbalance more than 4% between phases of secondary
winding of rectifier transformer(T6).
#Caution 1. During checking the connection, stop the generator to avoid the defect of the equipment or
personal damage.
# Caution 2. Be careful not to touch the live lines during measuring the voltage of each point.
# Caution 3. After checking the connecting status or any disconnecting and reconnecting trial, all the
connecting points(terminals) must be retightened(The loosen pins must be carefully
retightened.).
If you could not find any troubled point by above detailed procedure, please inform us the checked
result in detail(step by step) on above procedure.
Procedure for the trouble shooting of ‘Higher output Voltage’ of the generator
on the site. <HFx6 series>
The output voltage of HFx6 series generator is set at the higher but limited value than the
rated voltage without connecting the AVR from excitation equipment system. And the AVR
acts to make bypass the excessive exciting current to keep the output voltage at the
reference value(neat to the rated value).
It means that the higher output voltage could comes from the loss of any connection from
any equipment to AVR or the loss of function of AVR.
A. The loss of sensing voltage(lowest sensing voltage):AVR acts to increase the output
voltage.
B. The loss of reference value(highest reference value):AVR acts to increase the output
voltage to the highest value.
C. The loss of Function as AVR due to failure of AVR, failure of thyristor or discontinuity of
bypass circuit.: The output voltage is kept at the same value with no-load maximum voltage
without AVR.
D. There could be any other cause than above for the higher output voltage rarely.
So, you are kindly requested to check the circuit and equipment according to the following
instruction step by step.
1. During standstill of the generator, check the connections from power output(= V1,W1 for HFx6
series) to AVR(1,3).
Opening at one of the connections means the loss of sensing voltage.
2. Check the connections from AVR(20,21) to Reference value setter(A20,A21). All the connecting
points including the auxiliary terminal board equipped in the terminal box(20,21) and control panel
shall be checked with keen attention.
3. Check the connection of AVR(1) – R1(1,2) – static rectifier(U-F2) – AVR(5) for HFx5 series.
4. Check the connection of AVR(5) – R48(1,2), thyristor(A) – static rectifier(U-F2) – thyristor(K) AVR(6) and AVR(3) - thyristor(G) for HFx6 series.
5. Try the test after exchange the AVR with the other new AVR or that of the other generator operating
in normal.
6. The higher no-load output voltage would be generated if there would be insulation failure
between turns of secondary winding of rectifier transformer(T6).
And, there must be insulation failure between turns of winding of rectifier transformer(T6)
if there would be resistance unbalance more than 4% between phases of secondary
winding of rectifier transformer(T6).
#Caution 1. During checking the connection, stop the generator to avoid the defect of the equipment or
personal damage.
# Caution 2. Be careful not to touch the live lines during measuring the voltage of each point.
# Caution 3. After checking the connecting status or any disconnecting and reconnecting trial, all the
connecting points(terminals) must be retightened(The loosen pins must be carefully
retightened.).
If you could not find any troubled point by above detailed procedure, please inform us the checked
result in detail(step by step) on above procedure.
Procedure for the trouble shooting of ‘Improper Reactive Load Sharing during
Parallel Operation’ on the site. <HFx5 series>
The main reasons of ‘improper load sharing’ are described below.
1. Improper
Active
Load
Sharing
in
parallel
operation
could
be
seen
by
different
rotating
speed(revolution) variation ratio of each prime mover(engine) under same rate of rated active
load(KW or active current) in single operation. So, the supplier of prime mover(Diesel Engine,
Turbine…) should support to clear the problem.
2. Improper Reactive Load Sharing could be seen by the difference of output voltage variation
ratio of each alternator at no-load or at the same rate of rated load.
2.1. Incorrect load sharing between generators in parallel operation
●
Incorrect active load(KW) sharing due to different speed variation ratio of each prime
mover(engine).
● Incorrect reactive load sharing due to different no load voltage setting by reference setter.
● Voltage droop values by droop potentiometer(R2 or S on A1) are different from each other.
● The accurate load sharing is impossible if the voltage droop values by droop potentiometer(R2 or S
on A1) are too low.
● Voltage droop values are different from each other due to the long power cable(due to voltage drop
by high line resistance) from the generator to the circuit breaker.
8.17. The circuit breaker is opened due to high circulation current between generators
during synchronizing(‘break on’ for parallel operation).
● High variation of active power due to instability of governor of prime mover
● Different voltage droop setting from each other paralleling generator
●
Excessive
series
winding
compensation
with
current
transformers(T1,T2,T3)
or
rectifier
transformer(T6)
● Lack of bypass compensation by current transformers(T1,T2,T3) or rectifier transformer(T6).
When the lagging current due to any reason(different voltage setting by reference value setter, voltage
droop of loaded generator during synchronizing) flows(under exciting status) the phases of the
current supplied by Reactor(L1) and the current supplied by Current transformer(T1, T2, T3) are
opposite to each other. So the exciting current decreases according to the increase of circulating
current(leading current) and the AVR cannot control the exciting current if this exciting current
decreases to the meaning value. Then the circuit breaker will be opened due to increased circulating
current.
This phenomena can be happened with the generators which has lower no-load exciting
current, which voltage generator set at low value during no-load maximum voltage setting or set at
higher value during maximum voltage setting with load.
This kind of unstable situation can be
avoided by prolonging the powering time of bypass current, which can be achieved by setting the
bypass resister to higher value or by setting no-load maximum voltage to higher value within limited
value. And also it can be avoided by increasing the stability of exciter current control, which can be
achieved by setting ‘load maximum voltage’ to higher value(decreasing the exciting current.)
But more important points than resetting the excitation equipment are to confirm whether the noload voltage is adjusted at the same value by reference value setter before starting parallel operation
and to avoid the parallel operation under light load.
We can see the variation of current value supplied by excitation equipment according to the different
current value supplied by reactor on Fig.(6).
(c) Reduced current supplied by Reactor -> The current supplied by CTs increases. -> The
dramatically decreased exciting current to almost same as or lower than required value(Jf(n)) is
supplied if leading current load is applied. -> The AVR cannot bypass the control current due to
lower current supplied by reactor and CTs. -> Unstable Synchronizing.
(d) Increased current supplied by Reactor -> The current supplied by CTs decreases. -> The lightly
decreased exciting current(higher current than required value(Jf(n)) is supplied if leading current
load is applied. -> The AVR can bypass the control current due to higher current supplied by
reactor and CTs. -> Stable Synchronizing.
If this kind of problem happens during operating on site, try to secure it according to
following procedure.
But keep in mind that this procedure is not the absolute one for the troubleshooting.
(1) Confirm the normal operating status(voltage status, single operation status) of each generator with
excitation equipment.
(2) Confirm the normal operation of governor of prime mover during single and parallel operation if
possible.
(3) Confirm the same no-load voltage adjusting with each generator.
(4) If you could not find the cause of problem by above (1) ~ (3) procedure, reduce the current for
excessive series compensation(CT or T6) or increase the current for 보상 compensation. Generally it is
enough to change one(1) to three(3) taps of T6 in almost all the cases.
(5) If the problem could not be cleared by above procedure, try to find any other reason of the
problem except excitation equipment.
If you thrust that there is not any other reason except excitation equipment until yet, try to
follow Ex. Eq. resetting procedure as below.
(6) Resetting the exciting current for no-load maximum voltage(108 ~ 112 % of rated value) by T6
and L1 without connection of AVR .
(7) Measure the bypass current(A.C portion) by using clamp-meter after connecting AVR during
running at no-load rated voltage.
(8) During single operation, reset the CTs or T6 taps to keep the bypass current under full load
operation at about 100 ~ 150 % of bypass current under no-load operation. that 단독 운전 상태에서
(9) Try synchronizing and check the condition.
If the problem could not be cleared by above procedure, try to find any other reason of
the problem except excitation equipment.