MIL-HDBK-1003/11
Section 7:
ENGINE CONTROLS AND INSTRUMENTS
7.1 General. Controls and instruments assist in economical operation,
supervision, and maintenance of a generating plant. Instruments sense
changes in operating conditions and provide data to measure operating
economy. An operator can control the changes in operating conditions to
some extent by remote equipment. Continuous duty electric generating
plants, provided with 24-hour manned operation are usually arranged for
manual starting, synchronizing, and stopping and with only automatic
protective controls. Standby/emergency generating plants are usually
completely automated and controls are unattended. Remote monitoring devices
and controls may be limited to system status indication and start/stop
controls.
7.2 Speed Governing System. Speed governing systems maintain the same
operating speed (frequency) after load increase or decrease by adjusting the
fuel delivered to the engine in proportion to the load regulated. As long
as the specified performance characteristics are met, the type of the speed
governing system provided (i.e. mechanical-hydraulic, electric hydraulic,
electric, etc.) should be left to the engine manufacturer's discretion.
7.2.1 Speed Regulation. Speed regulators can be either speed droop or
isochronous type. Droop operation permits engine speed to increase as load
is removed. Isochronous operation maintains the same speed at any load.
Some governors can be operated in either mode.
7.2.2 Governor Operation. Governors consist of hydraulic or servo systems
used for fuel control in conjunction with speed sensing elements. Hydraulic
governors utilize the centrifugal force produced by rotating fly-weights to
actuate the hydraulic servo system. The electric-hydraulic type uses
electric signals for actuation of hydraulic servo mechanisms. There are
also completely electronic governing systems. Electric signals can also be
initiated by changes in frequency (speed) or respond even faster, if
initiated by load changes.
7.2.3 Performance Requirements. Industry-recognized performance
requirements are given in Table 9. These requirement provide uniform
concepts for the appropriate application classification without introducing
unwarranted technical refinements and augmented costs. The referenced guide
specifications and the industry specification from the Institute of
Electrical and Electronics Engineers (IEEE) 126, Speed Governing of Internal
Combustion Engine-Generator Units provide systems for independent or
parallel operation.
7.2.4 Modifications. Generally the use of the appropriate NFGS
specification (refer to Section 1) is all that is necessary. However, when
paralleling with the local utility company is a requirement, NFGS approval
of the performance characteristics and the type of load sharing control
specified is required. Special applications such as another incoming
service or more precise frequency and voltage requirements must be evaluated
on a case-by-case basis. Values given in Table 9 may not be available for
all engine sizes, duties, or manufacturers and may either be excessive or
not exacting enough for a specific requirement. It may be more economical
to
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