Page 379 - Offshore Electrical Engineering Manual

366 CHAPTER 4 Protection and Control

3. the bimetallic thermal element,
4. electronic circuitry which replicates the characteristics of the above-mentioned
electromechanical devices.

One relay case may contain a combination of different elements to meet the par-
ticular protection requirements of the equipment it serves, and therefore a number of
different test procedures may be involved in the testing of one relay case. The follow-
ing sections provide only the general principles on relay testing, and the manufactur-
ers’ literature and the references given in PART 4 Chapter 1 should be referred for a
deeper appreciation of the subject. A guide to the principal applications of protection
relays offshore is given in PART 4.

MECHANICAL CHECKS ON INDUCTION DISC AND ATTRACTED
ARMATURE RELAYS
1. Check that all fixing and terminal screws are secure.
2. Check that air gaps are free of dirt and foreign matter.
3. Check that the hair spring on induction discs is reasonably spiral in shape, with
no turns touching.
4. Check that turn multiplier dials have a smooth action and show no sign of sticking.
5. Ensure that all the transit packing has been removed.
6. On attracted armature relays check that, when the armature is closed with a
finger, normally open contacts close and normally closed contacts are opened
properly by their push rods.
7. Ensure that any trip indicator flags and their latching mechanisms operate satis-
factorily and that they may be unlatched by pushing the reset rod.
8. With the aid of the system schematic drawing check that the relay wiring is as intended.

ELECTRICAL CHECKS ON ELECTRONIC (STATIC) AND INDUCTION
DISC RELAYS
Insulation Tests
A cautious approach is required when applying insulation test voltages to protective
relays, especially when they contain semiconductor devices.
However, secondary wiring insulation can usually be tested at 500 V DC, and
tests should be made on relay coils, contacts and between AC and DC circuits, with
secondary CT and VT connections removed. The resistance values obtained should
exceed 10 MΩ.

Secondary Injection Tests
These tests are normally carried out using test plugs. However, for relays which cannot be with-
drawn from their cases, the test connections must be made directly on to the relay terminals.
If secondary injection tests are to be carried out on relays whose CTs are ener-
gised, then care must be taken to ensure that the CT secondary connections on the