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ETL 1110-8-5(FR)
26 Jul 91
Figure 1. Breaker auxiliary contact
5. Preventing Induction Motoring
not applied and should be considered as fast-acting
supplemental protection where excitation relays are
Induction motoring occurs when a unit is on-line
applied.
without excitation. The schemes described in the
following paragraphs can be in addition to the other
a. While a unit would not automatically come
schemes in this ETL. These schemes involve permis-
on-line without excitation, it could be done acciden-
sive contacts that prevent a unit breaker from being in
tally in manual mode. A 41"a" contact in the "Main
a closed position while the excitation breaker (AC
Breaker" circuit of Figure 2 prevents this from
supply breaker 52E or field breaker 41) is open.
happening.
Paragraphs a and b relate to conditions which would
be served by loss of excitation relaying. They should
b. If the field breaker trips for whatever
be implemented where loss of excitation relays are
reason, a 41"b" contact in the "Field Breaker" circuit
Figure 2. Field breaker control circuit
2
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