AMIE INDIA Students Forum

[sarathlal]

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[yadavblue]

Restricted Earth Fault Relay:

This relay uses an attracted armature element energized by a low pass filter ciruit and a full wave rectifier. The relay has a pre set setting of 15 V. Here a restricted earth fault relay-5B3 (Easun Reyrolle make) is being used which has single voltage setting of 15-270 V. This relay is directly calibrated in operating volts, which is the main criterion of high impedance. The operating current setting of the relay is significant only from the point of view of the primary fault setting of the protection, which in turn determines the sensitivity of the protection.
C.T. requirements -
a) All CTs should have identical turn ratios.
b) The knee point voltage of each CT should be at least 2xVs.
c) The CTs should be of the low leakage reactance type.

Commissioning

Test Equipment Required
1. 500 V insulation test set.
2. Secondary current injection arrangement (CFB set).
3. Multimeter to measure AC/DC voltage.
4. A suitable double pole switch for making and breaking the secondary injection circuit.
5. Suitable test leads.

Inspection
Ensure that all the connections are tight and in accordance with the relay wiring diagram and the scheme diagram. Check that the relay is correctly set and the relay is fully inserted into the case.
Precautions
Before testing commences, the equipment should be isolated from the current transformers and the CTs to be short circuited, in line with the local site procedures. The tripping and alarm circuits should also be isolated, where practical. Also ensure that trip links are removed.

TEST PROCEDURE

INSULATION
Connect together all relay voltage terminals and measure the insulation resistance between these terminals and all the other relay terminals connected together to earth.
Connect together all the output relay terminals and measure the insulation resistance between these terminals and all other terminals connected together to earth.
A minimum value of 2.5 to 3 MΩ can be considered as satisfactory value.

SECONDARY INJECTION

Use correct wiring diagram for relay connection.
Increase the voltage slowly and check that the output relay operates at appropriate voltage setting of the relay. The pick up value shall be ±10 % of the setting. Voltage ssetting is to be done by selecting DIL switch in 5B3 relay.
To check operating current, select the voltage setting in minimum. Connect 6 kΩ, 10 W resistor in series with the circuit and measure the operating current as 20 mA ± 1 mA.

PUTTING IN TO SERVICE
After completing the tests satisfactorily, the relay should be put into service as below follows:
1. Insert the DC supply fuse.
2. Replace the relay cover.
3. Insert the trip links.
4. Perform trip test by secondary injection.
5. Remove all test conductors.
6. Make a final check of the secondary wiring and tightness of all terminal connections.

[yadavblue]

Overcurrent And Earth Fault Protection

For overcurrent and earth fault protection, Easun Reyrolle make MIT 114 relay which is a four pole over current earth fault relay with high set is being employed. This relay is suitable for various inverse characteristics and also for definite time lag characteristics, any one of them selectable at site independently for phase and earth fault. This relay also combines the power and flexibility of microcontroller technology. This relay is also provided with the DC transient free high set instantaneous elements, which will not over reach for DC transient condition. This relay has a reset time setting which can be user programmed to be either instantaneous or delayed from 1 to 60 seconds. This relay is suitable for 1 A or 5 A application. To set its installation for 1 A, check the connection of CT wires connected to the bottom terminal block at the rear of the chassis as per following table-
Phases Terminal No. of TB Ferrule No. of CT wire (Black)
R 5 5 A
Y 7 7 A
B 9 8 A
E/F 11 11 A





COMMISSIONING

Required Test Equipments:
1. 500 V insulation test sets.
2. Variable secondary injection current source rated 10 A or greater.
3. Time interval meter.
4. Primary injection equipment.
5. A DC supply with a nominal voltage within the working range of the relay DC auxiliary supply ratings.

Applying Settings
The relay settings for the particular application should be applied before any secondary testing is started. This relay has a MMI (Man Machine Interface) for setting purpose.

TESTS

a. Pick up and Reset

The test checks accuracy of the current settings for the relay’s main over current characteristics. Apply single-phase current into one of the current inputs. Slowly increase the current until the starter LED (yellow) operates and record the pickup current. Reduce the current until the LED goes off and record this as the reset level. Repeat this test for each pole. Check that all the pickup current levels are measured within 104% ± 4% or ± 10m A of the applied setting. Check that the reset levels are ≥ 94% of the setting.
b. IDMTL / DTL Characteristics This test checks the accuracy of the main time delay characteristics (IDMTL/DTL). Select the relay current setting characteristics and time multiplier settings as required and then inject a level of current which is a multiple of the relay setting . A time interval meter should be connected to the correct output contact terminals. The timer should be started by the source and stopped by the relay trip contacts. Each pole should be tested. The secondary injection test equipment should be made 'OFF', once the relay contact is closed. Check that the measured times are within ±5% or ± 30-m.secs.of theoretical value.

c . Highset
Program the current settings for the highset characteristics to the required level. Inject a level of current below the setting of the relay, then increase the current until the output operates. Record the pick up level for each pole, and confirm that in each case it occurs within 100% ± 4% or ± 10 ma of applied setting. When the highset setting is above the continuous thermal rating of the relay, care should be taken, such that the duration of the applied current should not damage the relay. Refer catalogue for thermal rating.

Putting into service

After completing all tests satisfactorily, the relay should be put into service as follows:
1. Make a final check of the secondary wiring and tightness of all terminal connections.
2. Insert the DC supply fuse.
3. Check the relay healthy indication/display.
4. Replace the relay cover.
5. Insert the trip links.
6. Perform trip test by secondary injection.
7. Remove all test connections