Answer / kj

The star delta starter limits the starting current of the
motor by reducing the voltage across each winding. In star
the voltage is equivalent to the phase to neutral of the
power supply. In delta the phase to phase voltage is
applied across the windings.
With a DOL starter the phase to phase voltage is applied
across the windings. The starting current can be in excess
of 7 times the full load current.
The main reason for using star delta starters is that the
power supply system to the motor does not have to support
the high current needed for DOL starting. If the power
supply is not able to supply the current a voltage dip will
occur affecting all other users on the supply.

Answer / brd ganesh

We can use dol stater up to 5HP (dol stater can
not control starting current of motor but protect
by them up to 5HP). We have been using dol
staters to lower rating ac motors due to low cost.

Answer / vijendra joglekar

The Main purpose of using starter in motor to limit the
starting current as you know evry starter have there own
limitations i.e rating,inrussh current holding capacity as
you told 15 kw motor cant use DOL starter because of its
limitaions its not with stand motor rated current .

Sir We have a REF relay connected to 10MVA(Y-Y) Transformer.on External earth fault REF relay trips along with earth fault relay.The REF relay has no complant as we tested relay.Why is it happening?

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