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ETL 1110-8-5(FR)
26 Jul 91
inexpensive, reliable, and maintenance free; however,
trip circuit failure. For the single case of a coil fail-
their use may require special trip coils on some brea-
ure, secondary coils have been installed on some unit
kers. Loss of breaker trip coil dc control power
breakers to provide a backup in the case where the
causes undervoltage relay (Device 27) to drop out,
breaker itself is mechanically operable.
applying potential from the capacitor trip device to
the trip coil to trip the breaker. The breaker will trip
b. Remotely controlled plants use fail-safe unit
even though there is a simultaneous loss of ac power.
relaying to shut the units down on loss of dc control
Device 43 is a transfer switch to disable the auto-
power by dropping out start-stop solenoid 65S, which
matic trip function when desired.
trips the breaker as the turbine wicket gates pass
through the speed no-load position. Provisions have
8. Action
not been made at many plants, however, to trip the
generator breakers when there is a loss of the breaker
Control schemes for generator breakers of hydroelec-
trip dc control power. The scheme in Figure 4 has
tric plants should be reviewed. Personnel involved
been used at some plants to protect against this
are encouraged to contact a designated Corps of
possibility. Stored energy from a capacitor trip de-
Engineers Hydroelectric Design Center to discuss the
vice is used to trip the breaker in case of a loss of
schemes described in this ETL or alternate schemes.
control power. Capacitor trip devices are readily
available from the breaker manufacturers. They are
Figure 4. Scheme to trip generator breakers upon loss of breaker trip dc control power
FOR THE DIRECTOR:
JOHN A. McPHERSON
Acting Chief, Engineering Division
Directorate of Civil Works
4
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