that unnecessarily stringent requirements are not
specified.
Recovery Time Back to Bandwidth. The designer
should determine the required recovery time for the
loads served. The recovery time to bandwidth is not
critical to operation of most equipment if the
voltage and frequency do not deviate from the
critical limits, or if momentary interruption is
acceptable to the loads being served. The primary
importance of this requirement is to ensure that the
engine generator set recovers and stabilizes after
load changes. Most engine generator sets can
respond to 100% block loads and return to voltage
and frequency bandwidths within 15 - 20 seconds,
depending on the size of the machine (RPM, relative
mass of the rotating elements, and ambient
conditions).
Maximum Step Load Decrease (without shutdown). An
engine generator set should be capable of being
unloaded in a single step without tripping offline.
In these situations the voltage and frequency
transients are of no concern because there is no
load being served.
Nominal Step Load Decrease. Step load decrease is
used to account for dropping of block loads. This
affects engine-generator set frequency and voltage
output and usually initiates governor and regulator
response. The change in engine-generator set output
and the response of the governor and regulator
defines the transient loading response. Where the
load served may be sensitive to voltage and
frequency variation due to significant load
decrease, include the items below in the Parameter
Schedule. The Nominal Step Load Decrease provides
the genset manufacturer with the information
necessary to set the governor response for load
decreases such than an overspeed (over-frequency)
condition does not occur. The cost of
engine-generator sets increase by large percentages
for smaller frequency and voltage deviations from
bandwidth and improved recover times. Carefully
analyze the user's need for restrictions on
Nominal Step Load
[25] [50] [75] percent
Decrease
of Service Load at
[_____] PF
Transient Recovery
[_____] seconds
Time with Step Load
Decrease (Voltage)
Transient Recovery
[_____] seconds
Time with Step Load
Decrease (Frequency)
SECTION 16263A
Page 24
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