Klockner Moeller Electric Parts from KlocknerMoeller.net
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Representing
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All about Motors
Star-delta switching of three-phase motors |
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| Star-delta starters
with overload relay |
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Arrangement in the motor line
The star-delta starter with overload relay, including a thermally delayed overcurrent relay are situated in a standard circuit
configuration in the leads leading to the motor terminals U1, V1, W1 or V2, W2, U2. The overload relay is also operational in the star
connection as it is in series with the motor winding and the relay current flowing through it = rated motor current × 0.58.
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Arrangement in the mains supply line
Instead of the arrangement in the motor line, the overload relay can be placed in the mains supply line. For drives where the F2 relay trips out
when the motor is starting in the star circuit, the F2 relay rated for the rated motor current can be switched in the mains line. The tripping
delay is thus increased by approximately four to six times. In the star circuit the current also flows through the relay but here the relay does
not offer full protection since its limit current is increased to 1.73 times the phase current. It does, however, offer protection against
non-starting.
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Configuration in the delta circuit
Instead of the arrangement in the motor line or mains supply line, the overload relay can be placed in the delta circuit. When heavy,
long-starting procedures are involved (e.g. for centrifuges) the F2 relay, rated for relay current = rated motor current × 0.58, can also be
connected in the connecting lines between the delta contactor Q15 and the star contactor Q13. In the star circuit no current then flows
through the F2 relay. The motor is therefore not protected when starting. This circuit is always used when exceptionally heavy and long
starting procedures are involved and when saturable core current transformer-operated relays react too quickly.
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