Download EXERCISE #1 To measure the tripping time of maximum

EXERCISE #1
To measure the tripping time of maximum-current (over load and
short-circuit) in a three-phase network with different current values,
1-THEORETICAL NOTIONS
a) When performing the function of maximum current (overload)
protection, a three-phase current relay enables to set a limit for the
current output by variable load (its rated power), or the current value
which can be borne normally by a power transmission line. The
values of these currents, as well as the delay of tripping time, are
adjustable.
b) When performing the function of short-circuit protection, a threephase current relay will trip instantaneously (times below one
second) as soon as the controlled current exceeds the set value.
Current values are adjustable.
Objective:- Both the values of (overload, short-circuit) current and of delay
times must be controlled and checked during the testing of the device and
even in the periodical checks to make sure of the functionality of the
protection device. The values of current and of delay times are tested and
marked in table to be check with design data.
2- MATERIAL NEEDED
1- Module SR1: three-phase maximum-current (overload and shortcircuit) relay.
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OL current
OL time
SC current
SC time
Caution! The operating range is 0.5 – 2 Input current; and Iinput of the
relay is equal to 1 A
1.1 TEST. When kept in position of test on the left it enables the LEDs;
when kept in position of test on the right it also enables relays I1 and I2 to
trip. Observe that relay I2 will trip rapidly (Time T2), whereas relay I1
depends on the selected delay time (selectors T1).
1.2 Relay Colors codes indication:Green LED NORMAL: indicates that the relay is powered and OK
Red LED TRIP I1: signals tripping for overload current
Yellow LED TRIP I2: signals tripping for short-circuit currents.
1.3 Tripping time
- Short-circuit tripping time adjustable (by selectors T2) from 0.05 to 0.8 s by
steps of 0.05 s
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- Overload tripping time adjustable (by selectors T1) from 1 to 16 s by steps
of 1 s.
2- Three-phase variable power supply unit with current of 5 A
3- Ammeters for measuring three alternating currents with range 5 – 10 A
4- Three-phase rheostat - 3 x 500 W, 3 x 50 Ω, or an equivalent one, for
regulation of currents
5- Digital stopwatch with resolution of one tenth of a second (normal watch
with chronometer)
6- Ohmmeter for tests of electrical continuity.
Module SR11: three Current step-down Transformers (CT) with primary
winding of 10 A and secondary winding of 5 A
N1 = 15 coils
N2 = 29.5 coils
Section S1 = 2 x 0.90 mm2
Section S2 = 2 x 0.71 mm2
10 A Input terminals of the amperometric transformer I1 = 10 A.
5 A Output terminals of the amperometric transformer I2 = 5 A
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Performance (Sn) 3 VA in cl. 0.5 - 6 VA in cl. 1
OPERATIVE MODE (experiment steps)
1. Refer to the wiring diagram of fig. 1.1 for the check of overload tripping,
and to the diagram of fig. 1.2 for the check of short-circuit tripping.
2. Connect the auxiliary power line of 110…230 Vac with the relay, without
powering it.
3. Connect the relay between the variable power line and the load rheostat
RC (see circuit diagram).
4. Connect an ammeter in series with each current input (an ammeter can
be sufficient if voltages and load – and consequently currents –are
surely symmetrical).
5. Power the relay with the auxiliary supply voltage and check whether the
green LED in the frontal panel goes on. (Using a multimeter with Ohm
scale, make sure that the state of the contacts of output relay complies
with the diagram shown on the panel, in normal conditions), that is with
device correctly powered and current within the controlled limits.
6. adjust the device with the following design data:
- overload threshold = 1.5 A;
- tripping delay time = 10 s;
- short-circuit threshold = 5 A
- tripping delay time = 0.1 s
8. Connect the multimeter with Ohm scale alternately with the NC contacts
of output relays.
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9. Adjust the voltage of the variable power line and the load rheostat to
obtain a current lower than 2 A. In this condition the current relay will not
trip.
10. Increase the test current over 2 A, record the time elapsing from the
moment of “overcurrent” to the moment when output relay I1 will trip
(that is signalled in the multimeter by the interruption of continuity). If
the delay time and the value of tripping current are not equal to the
values supposed, adjust the device with the corresponding settings.
11. Increase the test current over 5 A (diagram of fig. 1.2) and check the
rapid tripping of output relay I2 (signalled in the multimeter by the
interruption of continuity). If the value of tripping current is not equal to
the value supposed, adjust the corresponding setting in the device.
12. As demonstration, repeat the test with other values (design data).
13. RESETTING manually the device by pressing the RESET button will
enable to clear the information from the memory .
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Figure 1.1 Wiring diagram for the check of a maximum-current fixed-time relay in a three-phase line.
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Figure 1.2 Wiring diagram for the check of a short-circuit protection relay in a three-phase line.
The CTs indicated in the diagram are connected as “step-up transformers”
(primary winding of 5 A, secondary winding of 10 A).
A similar configuration can be used for the check when no power supply
unit nor any corresponding load are available to obtain a current equal to
(or higher than) that provoking the short-circuit tripping.
As soon as current exceeds the set value (5 A), the relay I2 will trip.
Caution! If the test is not carried out rapidly and current does not exceed
the threshold value I2, after the delay time, the threshold relay I1 will trip.
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For current setting of over load starting from 0.5 to 2 ampers we have
1,2,4,8 combinations and time from 1…16 second as:
Combination pins Overload current
Time combination
(A)
Triping
time(sec.)
1
0.5
0
1
2
0.6
1
2
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0.7
3
0.8
4
0.9
5
1
6
1.1
7
1.2
8
1.3
9
1.4
10
1.5
11
1.6
12
1.7
13
1.8
14
1.9
15
2
16
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For current setting of short circuit starting from 1 to 16 ampers we have
1,2,4,8 combinations and time from 0.05…0.8 second as:
Combination pins Overload current
Time combination
(A)
Triping
time(sec.)
1
1
0
0.05
2
2
1
0.1
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3
0.15
4
0.2
5
0.25
6
0.3
7
0.35
8
0.4
9
0.45
10
0.5
11
0.55
12
0.6
13
0.65
14
0.7
15
0.75
16
0.8
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1-What is the combination for OL triping on 1.6A and time of 6 second?
2- What is the combination for SC triping on 12A and if what is the time
coresponding the combination of 4+2+2 ?
3- Comper between current of triping and the load current in case of shor
and over current situation.
Dr Audih al faoury
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