not possible such as when paralleling to a large
electrical utility grid network. When paralleling
two or more droop units with a utility grid (or with
other droop units), to achieve load sharing, the
unit governors must be compatible, their speed
settings must be matched, and the droop must be set
the same on all units. Droop adjustment range of 0
to 7% is typical for mechanical-hydraulic governors,
and 0 to 10% is typical for electro-hydraulic
governors. Isochronous units should not be
paralleled with an infinite bus (utility grid
system) without also specifying synchronizing and
governor-load sharing controls. Delete speed droop
adjustment for isochronous governors in non-parallel
applications.
defines the allowable steady state variation in
frequency as is typically quite small for
commercially available governors (typically less
than + 0.4% with + 0.25% readily available). The
predominant type of device loads which are
susceptible to steady state frequency deviations
less than + 0.4% are those which employ switching
power supplies (computers and variable frequency
drives). The designer should select the least
restrictive value for bandwidth for the application.
Voltage Regulators. Solid state regulators are
readily available which maintain the voltage level
(regulation or voltage droop) to + 2% from no load
to full load, while some manufacturers offer
regulators which limit the droop to + 0.5%. Voltage
regulator bandwidth is important relative primarily
to transient response. EGSA Standard 100R-1992
defines three performance classes for voltage
regulators: standard (2% bandwidth); high (1%
bandwidth); and precision (0.5% bandwidth). Select
the least restrictive bandwidth necessary to satisfy
the application requirement.
Generator frequency and voltage should be shown on
the engine-generator set schedule. (For example:
208Y/120 volts, 3-phase, 4-wire).
Subtransient Reactance. The subtransient reactance
determines current during the first cycle after a
system short circuit condition is presented to the
generator. Therefore, it is used to determine the
necessary interrupting capacity of the genset
circuit interrupting device. It also is utilized to
predict generator response to non-linear loads.
Typical values for generator subtransient reactance
are found in IEEE Std 141. Subtransient reactance
is specified in per unit of the generator rated kVA.
Also, see the following discussion on non-linear
loads.
SECTION 16263A
Page 20