Excitation and Voltage Regulation

MIL-HDBK-1003/11

6.2.1 Rating. Regardless of the duty rating (i.e. for prime, standby, or

emergency use) NFGS specifications require that generators be capable of

carrying the gross kW of the diesel engine without exceeding the temperature

limits of NEMA MG 1 for continuous duty.

6.2.2 NEMA Temperature Limitation. Limitations are based on a 40 degree C

ambient and altitudes not exceeding 3,300 ft (1,000 m) utilizing the

specified insulation classes (B and F). Where these values are exceeded,

NEMA MG 1 stipulates a decrease in the allowable temperature rise.

6.2.3 NEMA Temperature Classifications. NEMA MG 1 has two temperature rise

classifications, continuous and standby. The NEMA MG 1 standby temperature

rise shall not be used as a basis for generator ratings used in standby or

emergency duty plants.

6.2.4 Generated (Terminal) Voltage. The generator voltage should be the

highest standard voltage commensurate with the load served and the electric

distribution or utilization system characteristics. NEMA standard voltage

ratings shall be used, except where special conditions prevail. The use of

stepup or stepdown transformers should be considered only under extending

circumstances. Standard generator voltages to be used are as follows:

a)

208Y/120 V

b)

480Y/277 V

c)

4,160 V

d)

13,800 V

6.3 Excitation and Voltage Regulation. The brushless exciter and static

voltage regulator combination is considered to provide the best performance

available as it provides all the features available from brush-type rotating

dc generators or brush-type static exciters while eliminating the

maintenance and radio-noise features of the brush type.

6.4 Paralleling and Synchronizing. All generators in a plant shall be

capable of operating in parallel with each other and shall be connected so

that any or all units can furnish power to the main bus at the same time.

Where plants may operate in parallel with commercial power, coordination

with the serving utility must be maintained. The plant shall be designed

with the capability for paralleling with an infinite bus.

6.4.1 Synchronization. Synchronizing operation can be performed manually

or automatically. For both methods, control of incoming voltage and speed

is required to match the system before closing the generator circuit

breaker. The use of a permissive synchronism-check relay series with the

synchronizing switch is suggested. Manual synchronizing is provided on most

attended electric generating plants. Automatic start up, synchronization,

and shutdown is normally only provided for unattended plants.

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