MIL-HDBK-1003/11
c)
Bus voltmeter.
d)
Incoming voltmeter.
8.3.3 Permissive Control. Local policy synchronization may dictate the use
of a permissive type synchronism check relay (ANSI Device 25) which is
provided in series with the synchronizing switch to prevent closure when the
two sources are too far out of synchronization. This devices checks voltage
on both sides of a circuit breaker, this providing protection against
operating errors.
8.3.4 System Monitoring. System monitoring is provided to aid the operator
in avoiding system abnormalities. The amount of reporting, alarming, and
control can vary from alarms reporting there is a problem at a certain
location, or reporting only of electrical quantities and control as
previously discussed, to complex microprocessor-based Supervisory, Control,
and Data Acquisition Systems (SCADA).
8.3.4.1 Type of System. The operating duties of the plant should be
considered in system selection. Large prime duty plants in remote locations
or cogeneration plants may require SCADA. Where plants are continuously
manned, requiring only the minimum monitoring is usually adequate, refer to
Section 1, NFGS specifications.
8.3.4.2 SCADA. This system provides a master station which utilizes input
from equipment-mounted, field interface panels normally in conjunction with
a record-keeping printer. The selected reporting, alarm, and control
functions should consider those required for Energy Management Control
systems (EMCS) either by utilizing an existing EMCS or providing a new
system.
8.4 Generator Protection. Surge protection, neutral grounding, and
protective relays are used to protect the system from electric power system
disturbances whose abnormality could damage equipment or harm personnel.
8.4.1 Surge Protection. Some form of surge protection is usually necessary
within a generator plant. Surge arresters in parallel with surge protective
capacitors may need to be installed at the terminals of each generator.
Surge protective capacitors reduce steep wave fronts, which if imposed on
rotating machinery could result in stresses exceeding insulation impulse
strength of a machine. Small units supplying emergency loads within a
building which are not subject to lightning or switching surges usually do
not require surge protection.
8.4.2 Generator Neutral Grounding. Generator neutrals are grounded to
provide service reliability and reduce fault stresses in equipment. For
low-voltage systems, the neutral supplies phase-to-neutral loads as well.
The method of connecting the neutral to the station ground system is
selected as required to limit the available ground fault current.
8.4.2.1 Solid Grounding. For generators having a ground return path which
limits the ground current to safe values and where harmonic currents are
small, a solid ground connection is acceptable. Low-voltage generators are
usually provided with additional phase-to-neutral bracing so that the less
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