Star-Delta Advantage Over DOL

GA to you JRaef. In another forum, you have given a more detailed and valid argument for soft starters vs ΥΔ.

However, this bane of ΥΔ is not going to go away. At least in countries where there may be a substantial difference in cost or, ignorance of the negative points of open-transition ΥΔ starting.

Perhaps there is a comparison out there somewhere which brings out the 1:1 comparison of the two. i will look for it sometime.

The starting current for motor started with DOL starter is about 5-6 times full load current which causes voltage drop in supply lines thereby affecting other equipments.

The use of DOL or star delta starter basically depends on the load requirements. For loads requiring starting torque of 70-75% of full load torque, it is imperative to use DOL starter.

In rich countries whose power grid is very strong, DOL starter could be used even for 100hp motors. In poor countries where the power grid is weak ,up to 5hp motors only are allowed to use DOL starting. If you use S/D starter it is advisable to use the closed transition type as it avoids current/torque surges.

Dear Mr.pnaban,

I have seen 2000 H.P. MOTOR (11 KV) started by DOL STARTER it is in mines.

DHAYANANDHAN.S

Was it fed by genset or grid,if grid- is the country's grid very strong? The current taken by 2000hp at 11kV will be less than if at 400volts.

Dear Mr.pnaban,

Yes. This is during the year 2001.

The particular state had very great SURPLUS POWER to the extent of 60% over and above the Demand. It was exporting Power to neighbouring states - even though, the entire nation faced Power deficiency in supply from 16% to 23%

The Full Load current at 11 KV is 105 Amps, starting current is 252 Amps, Motor takes 160 Seconds to reach Rated speed of 742 RPM.

DHAYANANDHAN.S