Inside Delta Connected Starter
7.7 Inside Delta Connected Starter
There are differences between a line connected soft starter as shown in Figure 39 and the inside delta connected soft starter as shown in
Figure 40 that need to be considered.
By observation of Figure 40, access to all six stator-winding terminals is required for an inside delta application. For a 12-lead motor, all
12 stator terminals must be accessible. In the line connected soft starter of Figure 39, access to only three leads of the stator windings of
the motor is required.
One failed SCR on any phase of the inside delta soft starter results in a single-phase condition. A shunt trip circuit breaker is
recommended to protect the motor in this case. A programmable relay can be configured as a shunt trip relay and can be used to trip the
breaker. When certain faults occur, the shunt trip relay energizes.
The SCR control for an inside delta application is different than the SCR control for a standard soft starter. The Starter Type parameter
needs to be properly set so that the SCRs are gated correctly.
If a circuit breaker is the only means to disconnect the soft starter and motor from the line, then one leg of the motor leads in the inside
delta soft starter is always electrically live when the circuit breaker is closed. This requires caution to ensure these leads of the motor are
not exposed to personnel.
7.7.1 Line Connected Soft Starter
In Figure 39, the power poles of the soft starter are connected in series with the line. The starter current equals the line current.
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7 - THEORY OF OPERATION
Figure 39: Typical Motor Connection
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