Each generator shall be of the synchronous type, one or two bearing,
conforming to NEMA MG 1, equipped with winding terminal housings in
accordance with NEMA MG 1, equipped with an amortisseur winding, and
directly connected to the engine. Insulation shall be [Class H][Class F].
Generator design shall protect against mechanical, electrical and thermal
damage due to vibration, 25 percent overspeeds, or voltages and
temperatures at a rated output capacity of 100 percent. Generator
ancillary equipment shall meet the short circuit requirements of NEMA MG 1.
Frames shall be the drip-proof type.
2.12.1
Current Balance
At 100 percent rated load, and load impedance equal for each of the three
phases, the permissible current difference between any two phases shall not
exceed 2 percent of the largest current on either of the two phases.
2.12.2
Voltage Balance
At any balanced load between 75 and 100 percent of rated load, the
difference in line-to-neutral voltage among the three phases shall not
exceed 1 percent of the average line-to-neutral voltage. For a
single-phase load condition, consisting of 25 percent load at unity power
factor placed between any phase and neutral with no load on the other two
phases, the maximum simultaneous difference in line-to-neutral voltage
between the phases shall not exceed 3 percent of rated line to neutral
voltage. The single-phase load requirement shall be valid utilizing normal
exciter and regulator control. The interpretation of the 25 percent load
for single phase load conditions means 25 percent of rated current at rated
phase voltage and unity power factor.
2.12.3
The deviation factor of the line-to-line voltage at zero load and at
balanced full rated load at 0.8 power factor shall not exceed 10%. The RMS
of all harmonics shall be less than 5.0% and that of any one harmonic less
than 3.0% at full rated load. Each engine-generator shall be designed and
configured to meet the total harmonic distortion limits of IEEE Std 519.
2.13
EXCITER
The generator exciter shall be of the brushless type. Semiconductor
rectifiers shall have a minimum safety factor of 300% for peak inverse
voltage and forward current ratings for all operating conditions, including
110% generator output at 4O degrees C 104 degrees F ambient. The exciter
and regulator in combination shall maintain generator-output voltage within
the limits specified.
2.14
VOLTAGE REGULATOR
Each generator shall be provided with a solid-state voltage regulator,
separate from the exciter. The regulator shall maintain the voltage within
a bandwidth of the rated voltage, over a steady-state load range of zero to
100% of rated output capacity. Regulator shall be configured for safe
manual adjustment of the engine generator voltage output without special
tools, during operation from 90 to 110% of the rated voltage over the
steady state load range of zero to 100% of rated output capacity.
Regulation drift shall not exceed plus or minus 0.5% for an ambient
temperature change of 20 degrees C 36 degrees F. The voltage regulator
SECTION 16264A
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