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 should be as close as possible to transformers, lightning arresters, and ground switches, but
should not be spaced closer than ten feet. Cables shall be sized accordingly:
(a) Able to resist fusing and deterioration of electric joints for the worst case fault
current magnitude and duration possible.
(b) Mechanically rigged to a high degree. Normally 1/0 is adequate, mechanically, for
brazed joints and 2/0 for bolted joints.
(c) Have sufficient conductivity to prevent contribution to dangerous local potential
differences.
3.8.3 Preventive Maintenance. Proper maintenance of line and substation equipment will
reduce both unnecessary outages and operating costs. Preventive maintenance is also less costly
than maintenance that must be performed on already damaged or faulty units. Procedures for
maintaining the following apparatus are discussed in detail below:
3.8.3.1 Transformers. Transformer maintenance procedures may be divided into the
following service classifications:
(a) Distribution Transformers:
o
Check all the overhead connections monthly.
o
Check the oil content for PCB contamination annually.
o
Check oil level annually.
o
Check the bushings for cracks or loose contacts annually.
o
Obtain oil sample and perform lab tests for dielectric strength, neutralization
number, interfacial tension, and gas-in-oil analysis every two years.
(b) Substation Transformers:
o
Check all the overhead connections monthly.
o
Check the oil content for PCB contamination annually.
o
Obtain oil sample and perform lab tests for dielectric strength, neutralization
number, interfacial tension, and gas-in-oil analysis annually. For arc furnace,
rectifier, and on-load-tap changer type units, the frequency should be from
quarterly to annually, depending on the service and history of the individual unit.
o
Check the bushings for cracks or loose contacts annually.
o
Check the connections of incoming and outgoing overhead/underground
conductors at the bushings biannually.
o
Check the service transformer connection annually.
o
Check the fuses on the high side and the low side annually.
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