system protection

1. Testing and
Maintenance
J.C. Phiri

2. Introduction
• Every relay has to go through an acceptance test before it is
commissioned.
• Acceptance tests are those tests which are performed by the
manufacturer to satisfy the customer’s demand according to the
device’s specification.
• These tests are carried out by the manufacturer in the presence of
the customer at a standard laboratory.
• Organizations like Malawi Bureau of Standards can carry out
acceptance tests for equipment coming into the country (Before it is
sold in stores)

3. Relay Specifications-Relay Nnc68bvl

4. Types of Tests
Before a relay goes on the market, it has to undergo all the following tests
carried out by the manufacturer:
1. Operating or pick-up value test
2. Reset value or drop-off value
test
3. Operating time test
4. Resetting time test
5. Insulation test
6. Temperature rise test
7. Contact capacity test
8. Volt-Ampere test
9. Overload test
10. Mechanical test

5. 1. Operating Value Test
• The operating quantity whether it is current, voltage, frequency, etc.,
of the relay is changed towards its set value and the value at which
the relay unit just operates is noted.
• Generally, the pick-up value must be within 90% to 130% of the
declared nameplate value.
• For over and under-voltage relay, the permissible value should be
around ± 5% of the declared value.

6. 2. Reset Value Test
• In this test, the operating value is adjusted such that the relay remains
operated.
• Then the actuating quantity is changed towards a value when the
relay just fails to operate (when it stops sending a tripping signal)
• This value is the reset value and is normally expressed as a percentage
of the nominal set value of the relay.

7. 3. Operating Time Test
• The time interval between the energisation of the relay and the
operation of its contacts (sending a trip signal) is the operating time.
• For a single-input instantaneous relay, several sets of readings must
be taken and the average operating time chosen.
• For Inverse Definite Minimum Time (IDMT) relays the operating times
are taken for PSMs 2, 5, 10 and 20. Also, the times for different Time
Multiplier Settings (TMS) for the above PSMs have to be determined.
• The permissible deviation from the declared time should be within
12.5%, and within 5%. for PSM between 4 to 20.

8. 4. Reset Time Test
• The reset time is defined as the time taken by the trip contacts of a
relay to return from its energized position to de-energised condition.
• In this test, the relay is kept in the operated condition.
• The energizing quantity is removed suddenly and the time taken for
the relay contacts to completely return to its un-operated condition is
noted.

9. 5. Insulation Test
• All relays have to undergo this test whereby the safety of insulation
between coils, contacts and casing is checked.
• Test voltage obtained from an H.V. testing set is applied between
• All current-carrying terminals connected together and the casing of the relay
• The contact terminals shorted together and other coil terminals
• Between set of ‘NO’ and ‘NC’ contacts held open externally by operating the
relay mechanically
• The voltage applied must be sinusoidal and should be applied
gradually. The voltage equal to 2 kV ac is to be applied for one minute
during which insulation should not fail.

10. 6. Temperature Rise Test
• The current-operated relay must be energised for its setting current or
rated current whichever is lower, while voltage-operated relay should
be energised at 110% of its rated voltage.
• The test is carried until the circuits attain a final steady temperature,
as measured by a thermometer.
• The above test must be carried out at an ambient temperature not
exceeding 40o
C.
• The insulation should withstand a temperature rise as per its class of
insulation.

11. 7. Contact Capacity Test
• For the contacts of a relay meant for heavy duty, it is required that the
maximum VA capacity that it can successfully make, break or carry
continuously has to be determined.
• Both making and breaking capacities are to be determined by dc and ac
sources with resistive loading.
• Moreover, the breaking capacity has to be further determined for an
inductive load having p.f. (0.4±0.1) lag for ac and time constant of (40±5)
milliseconds.
• The relay has to undergo repeated make and break operations, 100 times in
succession with time interval not less than 30 seconds between 2
immediate operations.

12. 8. Volt – Ampere Burden Test
• To carry out this test, the relay must be energised at its rated current
or voltage and the voltage drop across or the current flowing through
the coil has to be measured.
• The product of rated quantity (current/voltage) and noted quantity
(voltage/current) gives the VA burden.

13. 9. Overload Test
• This test is applicable to all current-operated relays.
• In this test, at the highest time setting a current of 20 times the setting current is
injected.
• The temperature rise of the relay after undergoing this test must not exceed 200
o
C.

14. 9. Overload Test
• Three such operations are made in quick succession for instantaneous relays and
at intervals for time lag relays.
• For a thermal relay, 8 times the setting current is injected at the highest time setting and
the test as above is carried.
• For a voltage-operated relay, 115% rated voltage is applied during the operating time of
the highest time setting.
• In case of relays having current and voltage coils, 20 times the setting current is passed at
highest time setting with a rated voltage across the voltage coil.

15. 10. Mechanical Endurance Test
All relays having a mechanical moving system must undergo this test.
• It is carried out at the highest time setting and largest plug setting of a
relay.
• The relay coil is energized at twice the current setting for current-
operated relays and at the operating voltage setting for voltage
operated relays.
• 500 repeated operations are carried out. After the test, all mechanical
assemblies of the relay must be in sound order.

16. Maintenance Test
• Periodic maintenance of the relay is an absolute necessity.
• The manufacturer will give guidelines on how maintenance of their
components can be handled.
• Certain items are continuously tested, while others may be tested
once in a year.

17. Maintenance Test
A typical schedule has been suggested as follows:
a) Continuously checking
• Pilot supervision
• Trip circuit supervision
• Relay voltage supervision
• Battery emf supervision
• Busbar CT supervision

18. Maintenance Test
A typical schedule has been suggested as follows:
b) Monthly
• Earthing resistance
c) Yearly
• Checking and calibrating operating levels, sensitivity, tripping angle, etc.
• Secondary injection test on more complex relays
• Insulation resistance test
• Inspection of gas and oil actuated relays

19. THANK YOU