For combinations of linear and non-linear loads
where the percentage of non-linear loads is small
relative to the capacity rating of the generator
(25% or less), standard generator configurations are
normally acceptable.
Provide a list of the non-linear loads in the
parameter schedule, either on the drawings (and
denoted on the single-line diagram) or in tabular
form in the specification section. The list should
contain a description of the load including
equipment type, whether the rectifier is 6-pulse or
12-pulse, kVA rating, and frequency. Provide a
linear load value (kVA @ PF) which represents the
maximum linear load demand when non-linear loads
will also be in use. The generator manufacturer
will be required to meet the total harmonic
distortion limits established in IEEE Std 519.
Delete the non-linear load paragraph when non-linear
loads are not served from the engine-generator set.
Maximum Step Load Increase. Maximum step load
increase is used to account for the addition of
block loads. These affect engine-generator set
frequency and voltage output and usually initiate
governor and regulator response. The change in
engine-generator set output and the response of the
governor and regulator defines the transient loading
response. The designer should provide the actual
loads to be applied to the engine-generator set
because specification of maximum step load increases
of 75 or 100% requires significant oversizing of
engines and generators and/or addition of mass to
fly-wheel, all of which add cost. Additionally,
oversizing of engines causes maintenance problems
and increases operating costs. The following
percentages may be used when the actual load
acquisition rate cannot be determined. A maximum
step load increase of 25% should be used for prime
rated sets, 50% for optional standby rated sets with
step loading, and 100% for legally required standby
(emergency) service with no step loading.
Transient Response Criteria (short time duration).
Genset-set response and recovery times vary
according to the size of the set, the block load,
and the controls specified. Normal response to
addition of a block load will include dips in either
output voltage or frequency or both and possible
"overshoot" as the governor and voltage regulator
respond to bring the voltage and frequency back
within bandwidth. Normal response to loss of a
block load will include an upward spike in output
Maximum Voltage and Frequency Deviation apply to
undervoltage/underfrequency ("dips") from the
addition of block loads and any undershoot resulting
from the recovery of an upward spike, as well as
overvoltage/overfrequency (upward spikes) from the
SECTION 16263A
Page 22
Previous Page
