Star delta starter replacement

----- Star delta starters - in fact- may be much more efficient than any electronic equivalent. More clunky perhaps- but the "efficiency will be determined by the motor and its load. I suggest that you review the behavior of a motor when starting - and note that for the short starting period- Also efficiency (in terms of power out/power in) is not a factor of concern (for both star and delta connections, at standstill - it will be 0 ) when starting. So- please clarify what you mean by "efficiency: if it is not the standard definition then one can provide an answer. --

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

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Depending on the application, a motor may take 2 seconds to start and then run for a long time. The _efficiency_ of the start up mode is rarely an issue. There Were two issues, 1. that the starting torque was enough to get the load moving and 2. that the startup was fast enough since in motors like capacitor start, there was some serious overheating going on in the starter coil. In part since the start up stuff was designed to use the thinnest (cheapest) wire that we could get away with.

At least those were the issues with single phase motors. I suspect those sane issues were also of concern for 3 phase motors.

There are no 'start' windings in a star-delta motor, at least not dedicated ones. The motor starts with the windings in 'Star' and then changes to 'Delta' connection.

Rheilly P

What do you mean by "not efficient"? What exactly is the problem?

Torque and risk of overheating will still be issues, I suspect.

I still do not understand the reason for wanting to change from a star-delta starter. Can you please try and explain why you want to change?

BillB

Leeds Lad in exile

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1) If started as star, the starting line current in the winding will be 1/3 of the starting current for delta connection- The winding current will be about 58% of the delta current in the winding. The starting torque will be 1/3 of the "normal" starting torque and this will cause slower acceleration and, depending on the load, the motor may not start. You do need to know the speed torque characteristic of the motor and the load to apply this properly. If it is a fan or pump motor- there should be no problem. If it is a load that needs high starting torque there may be a problem. If the motor is unloaded, there should be no problem in starting or with overheating - The current may be below rated current for the complete starting period. Overheating should not be a problem- even if it takes 2 to 3 times as long to come up to the speed where you switch to delta.

2)Three phase motors don't have starter coils (which are relatively high resistance and intended for short duty. They are inherently self starting.

In either case, considering that the star/delta starter works- why change it? Efficiency and losses are not a concern as, in terms of the total time that the motor is operating- the start time is negligable.