Page 372 - Offshore Electrical Engineering Manual

CHAPTER
4
Protection and Control

PRECOMMISSIONING
Before commissioning, it is essential that the installation work has been properly
checked before any equipment or cables are energised. Cable connections are ‘rang
through’ and cable insulation is checked where possible. Hard-wired logic and con-
trol and monitoring software must be checked, although this may be limited to criti-
cal circuits if the factory acceptance tests are comprehensive and well documented.
The ‘sense’ of any current transformers (CTs) must be checked to ensure terminals
are not reversed.
All such work is termed precommissioning.

PROTECTION SCHEME COMMISSIONING
The satisfactory operation of protection relays is important for the prevention of
danger to equipment operators and local damage to equipment. By preventing an
electrical fire, it may also have prevented growth of an incident to platform-threat-
ening proportions. Therefore, great care should be exercised by the commissioning
engineer to ensure that the protection devices will respond to electrical system dis-
turbances as the designers intended. If the commissioning engineer considers that he
or she has found design errors or omissions during commissioning, they must not be
shrugged off but must be discussed with the designers and/or operators.
The testing of voltage transformers (VTs), CTs and protection relays is described
in detail in the following sections.
The general procedure for the commissioning of protection schemes is to perform
the following checks and tests:

1. obtain a full set of wiring diagrams, schematics and the protection relay setting
schedules for the equipment to be tested;
2. ensure that you are in possession of the manufacturer’s technical data and com-
missioning procedures;
3. carefully inspect the overall scheme, checking all connections and wires on
CTs, VTs and protection relays;
4. measure the insulation resistance of all circuits;
5. carry out ratio, polarity and magnetisation curve tests on the CTs;
6. carefully inspect each relay before testing it by secondary injection in accor-
dance with the manufacturer’s installation instructions;
Offshore Electrical Engineering Manual. https://doi.org/10.1016/B978-0-12-385499-5.00043-1 359
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