Author: V. Tudora, Autonomous Electricity Management (RENEL)
Year of publication: 1994
Checking the protection relays
The operation of electrical equipment and installations is largely ensured by the efficiency in operation of the protection by relays. For this reason, when commissioning and then periodically, the protection installations are subjected to complex checks, after which it can be established whether they correspond to the purpose for which they were provided, as well as the remedial measures in case of defects.
Joint checks performed on relays
The tests and verifications to which the relays are subjected depend mainly on the type and category to which they belong. However, a number of common checks can be established, usually valid for any type of relay.
This category includes:
a) General verification of the relay, which consists in verifying the concordance between the type and characteristics of the relay mounted with the project data, the condition of the mechanical or electrical part visible to the naked eye, without further investigation;
b) Checking the insulation, is done to detect possible points where there has been a weakening of the insulation; the maintenance in operation of an equipment for which an inadequate insulation has been found, can lead to its deterioration, with the decommissioning of other installations.
The insulation check is done in two stages:
- insulation resistance measurement;
- testing the insulation with increased alternating voltage.
The insulation resistance measurement is performed with the 1000V inductor. The relay is considered appropriate if after one minute from the application of the voltage, the value of the insulation resistance is higher than 10 MOhm. If the insulation resistance has been adequate, the insulation test with increased alternating voltage is tested.
This test is performed by means of the kit for testing the insulation with increased alternating voltage or with 2500V inductor. In both cases, the relay must withstand the applied voltage for one minute.
If no punctures, sparks or effluents are found during the test, the relay is considered appropriate for this test. After charging with increased alternating voltage, a new test will be performed to check the insulation resistance, in order to detect any weakening of the insulation as a result of the test.
c) Mechanical verification, in this test it is aimed that the mechanical parts of the relay have a proper operation, without friction, that there are no illegal games of the moving parts, loose screws, insecure connections, etc.
Particular attention must be paid to the correct operation of the clockwork components of the time relays; the contacts to ensure a firm closing, to work without vibrations, to return after actuation.
Among the main topics discussed:
- Checking the protection relays
- Joint checks performed on relays
- Specific checks performed on the relays
- Calculation of distance protection settings
- Checking the operation of the RD 110 remote protection