Bus Transfer Equipment -141200106

procedures in this manual. In general, certain control

examined to determine that they are in good

circuits, such as those for the starting of motors or

mechanical condition and that there are no loose or

missing parts. The size of overload heaters installed

motor generator sets, or voltmeter switching circuits,

are best tested by using the circuits as they are intended

should be checked to determine that they are of proper

to operate. When testing such circuits, the precautions

size as indicated by the motor nameplate current and

listed in NSTM, chapter 300, should be observed to

heater rating table. Any questionable relays should be

guard against damage to the associated equipment.

checked for proper tripping at the next availability and

replaced. If necessary a description of the various

Protective circuits, such as overcurrent or reverse

types of overload relays can be found in NSTM,

current circuits, usually cannot be tested by actual

chapter 302, "Electric Motors and Controllers."

operation because of the danger to the equipment

involved. These circuits should be visually checked

Circuit Breakers, Contractors, and Relays

and, when possible, relays should be operated

manually to make sure that the rest of the protective

circuit performs its desired functions. Exercise

Circuit breakers should be carefully inspected and

extreme care not to disrupt vital power service or

cleaned at least once a year and more frequently if

damage electrical equipment. Reverse power relays

subjected to unusually severe service conditions; that

should be checked under actual operating conditions.

is, during ships overhaul period. A special inspection

With two generators operating in parallel, the

should be made after a circuit breaker has opened a

generator whose reverse power relay is to be checked

heavy short circuit.

should be made to take power from the other

To test normally operated circuit breakers, simply

generator. The reverse power relay should trip the

open and close the breaker to check mechanical

generator circuit breaker in 10 seconds or less after the

operation. For electrically operated circuit breakers,

reverse power relay starts to operate. If the relay fails

the test should be made with the operating switch or

to function, the generator circuit breaker should be

control to check both mechanical operation and

tripped manually to prevent damage to the prime

control wiring. Care must be exercised during these

mover. To make a generator act as a load, it is

operating tests not to disrupt any electric power supply

necessary to restrict the flow of steam or fuel. This can

vital to the operation of the ship, nor to endanger ship's

be accomplished by reducing the speed control setting

personnel by inadvertently starting or energizing

slowly until the generator begins to absorb power and

equipment being repaired.

act as a motor.

POWER REMOVAL.-- Before working on a

circuit breaker, control circuits to which it is

Bus Transfer Equipment

connected should be de-energized. Drawout circuit

breakers should be switched to the open position and

Bus transfer equipment should be tested weekly.

removed before any work is done on them.

For manual bus transfer equipment, manually transfer

Disconnecting switches ahead of fixed-mounted

a load from one power source to another, and check

circuit breakers should be opened before any work is

the mechanical operation and mechanical interlocks.

done on the circuit breaker. Where disconnecting

For semiautomatic equipment, the test should also

switches are not provided to isolate fixed-mounted

include operation by the control push buttons. For

circuit breakers, the supply bus to the circuit breaker

automatic equipment, check the operation with the

should be de-energized, if practical, before inspecting,

control switches. The test should include operation

adjusting, or replacing parts or doing any work on the

initiated by cutting off power (opening a feeder circuit

circuit breaker. If the bus cannot be de-energized,

breaker) to see if an automatic transfer takes place.

observe the safety precautions of working on an

When testing bus transfer equipment, you should

energized circuit, These precautions can be found in

follow the same precautions given for testing circuit

NSTM, chapter 300.

breakers. The tests and inspections are normally

outlined on MRCs.

CONTACT CLEANING.-- Contacts in circuit

breakers, contractors relays, and other switching

Overload Relays

equipment should be clean, free from severe pitting or

burning, and properly aligned, Occasional opening

During periodic inspections of motor controllers,

and closing of contacts will aid cleaning and sealing.

Remove surface dirt, dust, or grease with a clean cloth

or at least once a year, overload relays should be

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