Download 3. APPLICATION OF NON-PROTECTION FUNCTIONS

Application Notes
P34x/EN AP/F33
MiCOM P342, P343
Note 4:
Page 135/176
For the P343, the IA/IB/IC Current magnitudes are IA-1
Magnitude, IB-1 Magnitude, IC-1 Magnitude.
2.27.4 Setting guidelines for current loop outputs
Each current loop output can be selected as Enabled or Disabled. One of four types
of analogue output can be selected for transducers with ranges of 0-1mA, 0-10mA,
0-20mA or 4-20mA. The 4-20mA range is often used so that an output current is still
present when the measured value falls to zero. This is to give a fail safe indication
and may be used to distinguish between the analogue transducer output becoming
faulty and the measurement falling to zero.
The Maximum and Minimum settings allow the user to enter the measuring range for
each analogue output. The range, step size and unit corresponding to the selected
parameter is shown in the table above. This allows the user to “zoom in” and
monitor a restricted range of the measurements with the desired resolution. For
voltage, current and power quantities, these settings can be set in either primary or
secondary quantities, depending on the ‘CLO1/2/3/4 Set Values – Primary /
Secondary’ setting associated with each current loop output.
The relationship of the output current to the value of the measurand is of vital
importance and needs careful consideration. Any receiving equipment must, of
course, be used within its rating but, if possible, some kind of standard should be
established.
One of the objectives must be to have the capability to monitor the voltage over a
range of values, so an upper limit must be selected, typically 120%. However, this
may lead to difficulties in scaling an instrument.
The same considerations apply to current transducers outputs and with added
complexity to watt transducers outputs, where both the voltage and current
transformer ratios must be taken into account.
Some of these difficulties do not need to be considered if the transducer is only
feeding, for example, a SCADA outstation.
Any equipment which can be
programmed to apply a scaling factor to each input individually can accommodate
most signals. The main consideration will be to ensure that the transducer is capable
of providing a signal right up to the full-scale value of the input, that is, it does not
saturate at the highest expected value of the measurand.
3.
APPLICATION OF NON-PROTECTION FUNCTIONS
3.1
VT supervision
The voltage transformer supervision (VTS) feature is used to detect failure of the ac
voltage inputs to the relay. This may be caused by internal voltage transformer faults,
overloading, or faults on the interconnecting wiring to relays. This usually results in
one or more VT fuses blowing. Following a failure of the ac voltage input there
would be a misrepresentation of the phase voltages on the power system, as
measured by the relay, which may result in maloperation.
The VTS logic in the relay is designed to detect the voltage failure, and automatically
adjust the configuration of protection elements whose stability would otherwise be
compromised. A time-delayed alarm output is also available.
There are three main aspects to consider regarding the failure of the VT supply.
These are defined below:
P34x/EN AP/F33
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Application Notes
MiCOM P342, P343
1.
Loss of one or two phase voltages
2.
Loss of all three phase voltages under load conditions
3.
Absence of three phase voltages upon line energisation
The VTS feature within the relay operates on detection of negative phase sequence
(nps) voltage without the presence of negative phase sequence current. This gives
operation for the loss of one or two phase voltages. Stability of the VTS function is
assured during system fault conditions, by the presence of nps current. The use of
negative sequence quantities ensures correct operation even where three-limb or ‘V’
connected VT’s are used.
Negative sequence VTS element:
The negative sequence thresholds used by the element are V2 = 10V
(Vn = 100/120V) or 40V (Vn = 380/480V), and Ι2 = 0.05 to 0.5Ιn settable
(defaulted to 0.05Ιn).
3.1.1
Loss of all three phase voltages under load conditions
Under the loss of all three phase voltages to the relay, there will be no negative
phase sequence quantities present to operate the VTS function. However, under such
circumstances, a collapse of the three phase voltages will occur. If this is detected
without a corresponding change in any of the phase current signals (which would be
indicative of a fault), then a VTS condition will be raised. In practice, the relay detects
the presence of superimposed current signals, which are changes in the current
applied to the relay. These signals are generated by comparison of the present value
of the current with that exactly one cycle previously. Under normal load conditions,
the value of superimposed current should therefore be zero. Under a fault condition
a superimposed current signal will be generated which will prevent operation of the
VTS.
The phase voltage level detectors are fixed and will drop off at 10V
(Vn = 100/120V), 40V (Vn = 380/480V) and pick-up at 30V (Vn = 100/120V),
120V (Vn = 380/480V).
The sensitivity of the superimposed current elements is fixed at 0.1Ιn.
3.1.2
Absence of three phase voltages upon line energisation
If a VT were inadvertently left isolated prior to line energisation, incorrect operation of
voltage dependent elements could result. The previous VTS element detected three
phase VT failure by absence of all 3 phase voltages with no corresponding change in
current. On line energisation there will, however, be a change in current (as a result
of load or line charging current for example). An alternative method of detecting 3
phase VT failure is therefore required on line energisation.
The absence of measured voltage on all 3 phases on line energisation can be as a
result of 2 conditions. The first is a 3 phase VT failure and the second is a close up
three phase fault. The first condition would require blocking of the voltage
dependent function and the second would require tripping. To differentiate between
these 2 conditions an overcurrent level detector (VTS Ι> Inhibit) is used which will
prevent a VTS block from being issued if it operates. This element should be set in
excess of any non-fault based currents on line energisation (load, line charging
current, transformer inrush current if applicable) but below the level of current
produced by a close up 3 phase fault. If the line is now closed where a 3 phase VT
failure is present the overcurrent detector will not operate and a VTS block will be
applied. Closing onto a three phase fault will result in operation of the overcurrent
detector and prevent a VTS block being applied.
Application Notes
P34x/EN AP/F33
MiCOM P342, P343
Page 137/176
This logic will only be enabled during a live line condition (as indicated by the relays
pole dead logic) to prevent operation under dead system conditions i.e. where no
voltage will be present and the VTS Ι> Inhibit overcurrent element will not be picked
up.
ALL POLE DEAD
IA>
IB>
IC>
VA>
VB>
VC>
1
&
&
V2>
I2
ANY POLE DEAD
240ms
DIA>
DIB>
DIC>
1
VTS_MANRESET
VTS_AUTORESET
MCB / VTS OPTO
&
1
&
&
S
R
1
tVTS
0
S
R
Q
1
&
1
&
SLOW BLOCK
FAST BLOCK
Q
&
VTS_BLOCKING
ANY VOLTAGE
DEPENDENT FUNCTION
ACCELERATE IND
&
&
&
S
R
1
Q
&
S
R
1
INDICATION
Q
20ms
0
P2226ENa
Note: The accelerated ind input is not used in the generator protection.
Figure 49: VTS logic
Required to drive the VTS logic are a number of dedicated level detectors as follows:
•
ΙA>, ΙB>, ΙC>, these level detectors operate in less than 20ms and their settings
should be greater than load current. This setting is specified as the VTS current
threshold. These level detectors pick-up at 100% of setting and drop-off at 95%
of setting.
•
Ι2>, this level detector operates on negative sequence current and has a user
setting. This level detector picks-up at 100% of setting and drops-off at 95% of
setting.
•
∆ΙIA>, ∆ΙB>, ∆ΙC>, these level detectors operate on superimposed phase
currents and have a fixed setting of 10% of nominal. These level detectors are
subject to a count strategy such that 0.5 cycle of operate decisions must have
occured before operation.
•
VA>, VB>, VC>, these level detectors operate on phase voltages and have a
fixed setting, Pick-up level = 30V (Vn = 100/120V), 120V (Vn = 380/480V),
Drop Off level = 10V (Vn = 100/120V), 40V (Vn = 380/480V).
•
V2>, this level detector operates on negative sequence voltage, it has a fixed
setting of 10V/40V depending on VT rating (100/120 or 380/480) with pick-up at
100% of setting and drop-off at 95% of setting.
P34x/EN AP/F33
Application Notes
Page 138/176
MiCOM P342, P343
3.1.2.1 Inputs
Signal Name
Description
ΙA>, ΙB>, ΙC>
Phase current levels (Fourier Magnitudes)
Ι2>
Ι2 level (Fourier Magnitude).
∆ΙA, ∆ΙB, ∆ΙC
Phase current samples (current and one cycle
previous)
VA>, VB>, VC>
Phase voltage signals (Fourier Magnitudes)
V2>
Negative Sequence voltage (Fourier
Magnitude)
ALL POLE DEAD
Breaker is open for all phases (driven from
auxiliary contact or pole dead logic).
VTS_MANRESET
A VTS reset performed via front panel or
remotely.
VTS_AUTORESET
A setting to allow the VTS to automatically
reset after this delay.
MCB/VTS OPTO
To remotely initiate the VTS blocking via an
opto.
Any Voltage Dependent Function
Outputs from any function that utilises the
system voltage, if any of these elements
operate before a VTS is detected the VTS is
blocked from operation. The outputs include
starts and trips.
Accelerate Ind
Signal from a fast tripping voltage dependent
function used to accelerate indications when
the indicate only option is selected.
Any Pole Dead
Breaker is open on one or more than one
phases (driven from auxiliary contact or pole
dead logic).
tVTS
The VTS timer setting for latched operation.
3.1.2.2 Outputs
Signal Name
Description
VTS Fast Block
Used to block voltage dependent functions.
VTS Slow block
Used to block the Any Pole dead signal.
VTS Indication
Signal used to indicate a VTS operation.
Application Notes
P34x/EN AP/F33
MiCOM P342, P343
3.1.3
Page 139/176
Menu settings
The VTS settings are found in the ‘SUPERVISION’ column of the relay menu. The
relevant settings are detailed below:
Menu Text
Default Setting
Setting Range
Min
Max
Step Size
GROUP 1
SUPERVISION
VTS Status
Blocking
Blocking, Indication
VTS Reset Mode
Manual
Manual, Auto
VTS Time Delay
5s
1s
10s
0.1s
VTS Ι> Inhibit
10Ιn
0.08Ιn
32Ιn
0.01Ιn
VTS Ι2> Inhibit
0.05Ιn
0.05Ιn
0.5Ιn
0.01Ιn
The relay may respond as follows, an operation of any VTS element:
•
VTS set to provide alarm indication only (DDB 292 VT Fail Alarm);
•
Optional blocking of voltage dependent protection elements (DDB 736 VTS Fast
Block, DDB 737 VTS Slow Block);
•
Optional conversion of directional SEF elements to non-directional protection
(available when set to blocking mode only). These settings are found in the
function links cell of the relevant protection element columns in the menu.
Time delayed protection elements (Directional SEF, Power, Sensitive Power, Field
Failure) are blocked after the VTS Time Delay on operation of the VTS Slow Block.
Fast operating protection elements (Neutral Voltage Displacement, System Backup,
Undervoltage, Dead Machine, Pole Slipping) are blocked on operation of the VTS
Fast Block. Note, the directional SEF and neutral voltage displacement protection are
only blocked by VTS if the neutral voltage input is set to Derived and not Measured.
Other protections can be selectively blocked by customising the PSL, integrating DDB
736 VTS Fast Block and DDB 737 VTS Slow Block with the protection function logic.
The VTS Ι> Inhibit or VTS Ι2> Inhibit elements are used to overide a VTS block in
event of a fault occurring on the system which could trigger the VTS logic. Once the
VTS block has been established, however, then it would be undesirable for
subsequent system faults to override the block. The VTS block will therefore be
latched after a user settable time delay ‘VTS Time Delay’. Once the signal has
latched then two methods of resetting are available. The first is manually via the front
panel interface (or remote communications) provided the VTS condition has been
removed and secondly, when in ‘Auto’ mode, by the restoration of the 3 phase
voltages above the phase level detector settings mentioned previously.
A VTS indication will be given after the VTS Time Delay has expired. In the case
where the VTS is set to indicate only the relay may potentially maloperate, depending
on which protection elements are enabled. In this case the VTS indication will be
given prior to the VTS time delay expiring if a trip signal is given.
Where a miniature circuit breaker (MCB) is used to protect the voltage transformer ac
output circuits, it is common to use MCB auxiliary contacts to indicate a three phase
output disconnection. As previously described, it is possible for the VTS logic to
operate correctly without this input. However, this facility has been provided for
P34x/EN AP/F33
Application Notes
Page 140/176
MiCOM P342, P343
compatibility with various utilities current practices. Energising an opto-isolated input
assigned to “MCB Open” on the relay will therefore provide the necessary block.
Where directional SEF elements are converted to non-directional protection on VTS
operation, it must be ensured that the current pick-up setting of these elements is
higher than full load current.
3.2
CT supervision
The current transformer supervision feature is used to detect failure of one or more of
the ac phase current inputs to the relay. Failure of a phase CT or an open circuit of
the interconnecting wiring can result in incorrect operation of any current operated
element. Additionally, interruption in the ac current circuits risks dangerous CT
secondary voltages being generated.
3.2.1
The CT supervision feature
The CT supervision feature operates on detection of derived residual current, in the
absence of corresponding derived or measured residual voltage that would normally
accompany it.
The CT supervision can be set to operate from the residual voltage measured at the
VNEUTRAL input or the residual voltage derived from the 3 phase-neutral voltage
inputs as selected by the ‘CTS Vn Input’ setting.
The voltage transformer connection used must be able to refer residual voltages from
the primary to the secondary side. Thus, this element should only be enabled where
the 3 phase VT is of five limb construction, or comprises three single phase units, and
has the primary star point earthed. A derived residual voltage or a measured
residual voltage is available.
Operation of the element will produce a time-delayed alarm visible on the LCD and
event record (plus DDB 293: CT Fail Alarm), with an instantaneous block (DDB 738:
CTS Block) for inhibition of protection elements. Protection elements operating from
derived quantities, (Neg Seq O/C) are always blocked on operation of the CT
supervision element; other protections can be selectively blocked by customising the
PSL, integrating DDB 738: CTS Block with the protection function logic.
CTS block
I N>
&
Time delay
t
CTS alarm
V N<
P2130ENa
Figure 50: CT supervision function block diagram
The following table shows the relay menu for the CT supervision element, including
the available setting ranges and factory defaults: