Y-delta starters

Arrangement in the motor line

In a standard circuit configuration, the star-delta starter with overload relay, including a thermally delayed overcurrent relay are situated in the cables leading to the motor terminals U1, V1, W1 or V2, W2, U2. The overload relay can also be operated in a star circuit as it is usually connected in series with the motor winding and the relay current flowing through it = rated motor current × 0.58.      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.    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. The section shown here indicates the modified circuit diagram . 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 delta contactor Q15 and star contactor Q13. In the star circuit no current then flows through relay F2. This circuit is used wherever exceptionally heavy and long starting procedures are involved and when saturable core current transformer-operated relays react too quickly.