Protection Engineering Basics and Schemes Protection Engineering | Page 271

9.4 Overload Protection: It is provided by means of
bimetallic relay, fuses and motor protection relay with
thermal overload function. Bimetallic relay is connect
in series with load circuit, these relay work on the
principle of thermal expansion, when load current
increases the metallic contact in relay expand to close
circuit and send signal to breaker. If motor rating is
high then current transformer is installed with bi
metallic relay.
Fuses uses in motor may be depend on starting current
of motor, for higher rating we uses high rupturing
current.
pg. 271