EXERCISE 2

EARTH LEAKAGE RELAY TEST

EXERCISE 2

EARTH LEAKAGE RELAY TEST LEARNING OUTCOME

1. To identify the setting of Earth Leakage Relays. (C2-LO2)

2. To study the protection of equipment and system by relays in conjunction with Low Voltage Switch Board. (P5-LO5)

3. To explain briefly how the test is conducted. (A2-LO9)

CONTENT

2.1 THEORY

Earth leakage relays ensure the protection of electrical installations and persons against direct and indirect contacts. Earth leakage relay are designed on an electronic basis, which ensure the monitoring of earth fault currents. When the fault current rises above the selected level, the outputs of the product operate depending on the relay selected, it can have either fixed or adjustable settings for selectivity purposes. In the case of a ground fault occurring in any one of the phases, the Zero Current Transformer (ZCT) will produce a flux and in turn develops a current in the secondary. This current when passed through a burden produces a voltage. This voltage is amplified, precision rectified and filtered. This voltage is compared with a pre-set voltage in a comparator. When this voltage exceeds the pre-set voltage, the comparator output changes level. This is fed to a time delay circuit before feeding to the relay driving circuit. With the help of the dipswitches the trip current can be set. Pressing the ‘Reset’ button after the clearance of the fault can reset the relay. The red LED provided on the front panel will glow in case of a fault. Pressing the ‘Test’ button the healthiness of the unit gets checked. The green LED indicates the healthiness of the unit.

Figure 2.1: Earth Leakage Relay

2.2 Equipment list

2.2.1. Low Voltage Switchboard 1 unit 2.2.2. Multimeter 1 unit 2.2.3. Hand tools Necessary 2.2.4. Secondary Current Injection Test Set 1 unit

ACTIVITIES

Activity 1 (Current Injection)

1. Tests on the ELR protection relay are carried out using the Secondary Current Injection Test Set with the wiring connections as shown in Figure 2.2.

2. Alternatively, a single-phase primary current can be injected into one of

the primary conductors to induce a secondary current on the ZCT. Before the tests, ensure that the primary circuit of CT’s is de-energized.

3. Supply the ELR with external 240V source.

4. Set up the Secondary Current Injection Test Set at 0 - 10 A; 0 - 240 V AC

operation.

5. Check and record all particulars of the relay to be tested and its operational settings, using test report as shown in Table 2.1.

6. Increase the output current of the test set gradually until the ELR element

picks up. Record the pick-up current reading (Io) in test report as shown in Table 2.1.

7. Switch off the Secondary Current Injection Test Set.

Activity 2 (Operating Time Check)

1. The following tests are carried out to verify the relay operating time. Connect a relay trip contact to Secondary Current Injection Test Set timer terminals. Referred to Figure 2.3.

2. Switch on the Secondary Current Injection Test Set and set the output

current to 2.0 x Io and 3.0 x Io (tripping current setting).

3. Switch off the test set with control knob remaining in the set position. Switch the Secondary Current Injection Test Set to the ‘Test’ position to inject the set current and start the timer at the same time.

4. After the relay trip contact has operated, record the relay operating time in the above-mentioned test in the test report as shown in Table 2.1.

5. Finally, disconnect all wiring between test set and relay and ensure that all connections to relay are returned to the normal operational conditions.

6. Switch off the test set.

Figure 2.2: Current Injection Test circuit.

Figure 2.3: Operating Time Check Test circuit.

Table 2.1: Earth Leakage Relay Test Report. Relay Details:

Make: Auxiliary Voltage:

Type: Serial No:

Relay Settings:

Service Setting

Leakage Current, Is (mA)

Time Delay, Ts (s)

Current Injection: Minimum operating current recorded for relay operation.

Expected Relay Operation Current (mA)

Recorded Relay Operation Current (mA)

Operating Time Check.

Injected Current (A) Expected Operating Time

(s)

Measure Operating Time

(s)

2 x Io

3 x Io

Tripping Circuit : Remarks : Tested by : Date :

Figure 2.4: Connect the testing wiring.

Figure 2.5: Yellow LED, indicate 60% to trip.

Figure 2.6: Red LED, indicate tripping.

Figure 2.7: Typical ELR circuit.

Activity 3 (Questions)

1. Briefly explain the function of Earth Leakage Relay (ELR).

2. Briefly explain the function of Shunt Trip Coil.

REFERENCE

1. Paul Gill; Electrical Power Equipment Maintenance & testing; Taylor & Francis (1998).

2. Robert W. Seaton; William H. Ubert; Switchgear & Control Handbook (3th Edition); McGraw Hill )1998).