Page 534 - Industrial Power Engineering and Applications Handbook

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pressure interlock
by - p a s s
v
AMF scheme (continued)

Figure 16.10 Typical control and annunciation scheme for an AMF panel

both active and reactive powers. The basic principle take corrective action, by promptly shedding a part
of the relay is to compare the current in any one of the load. The current setting of the OK alarm
phase with the voltage output across the other two relay is kept lower than the setting of the OK trip
phases. When the operating parameters exceed the relay, say, 105% for the alarm and 110% for the trip.
pre-set values, the generator is switched OFF after a A single-pole overcurrent relay with a setting of 50-
pre-set delay in case the operating conditions have 200% and a time delay of 2.5-5 seconds may be
not improved. considered ideal. Figure 16.13 illustrates a typical
(c) Differential protection (Relay Code 87) To detect protection and metering scheme and Figure 16.11
a stator phase-to-phase fault by a three-pole differential shows the provision of these relays on the panel.
protection relay, current setting 1040%. For scheme
diagrams, refer to Section 15.6.6( 1). For a large power station
(d) Overcurrent alarm (Relay Code 51A) This may
be provided to warn the operator of a likely This is a complex subject and requires detailed engineering
overloading on the generator to prevent a trip and and application of the various protection schemes for