Please clear my problem on DOLs

[pssdeepak]

we use star/delta starter to minimise the starting current but even by using star/delta we are getting the same high current which reduces the life of the contactor. Then why using Star/delta?

For our crusher application we used 200KW Star/Delta which has a maximum current of 350A. But we are getting starting current of 1800A. Why is this happening?

 

[oldtimer]

Star / Delta start on a motor should be looked at assisted start in other words the motor is too big for Direct on Line and needs a 2 stage start up the other way to get arounfd this is fit a invertor so you can have a linear start up

 

[bomjac]

The accepted norm for start currents in star connected motor is typically 2.5 times FLC (For Delta start up to 6 times). However, what this does not take into account in your case is the initial inertia in the system. For a crusher I would say that the reason for the high start currents is down to this. Best thing to do would be get some means of recording the start currents involved in this, and then look at what can be done to provide a solution.

Bear in mind the reason for using star/delta is to reduce the starting current of the application, but the torque produced by the motor in star connection is not as high as that in delta connection. It very much looks as if your motor is not capable of producing sufficient torque to run the machine up top speed (70-80%) before switching to Delta, and due to this you are experiencing high start currents.

Also when you state start current is 1800 amps, is this the initial spike when the star contactor comes in or is it the average current over the start time ? If its the spike current, then your start current will actually be closer to 900 amps.

Another option could be to try to start the motor DOL in Delta (assuming your electricity supplier is happy with this) and measure the current then. I do not see that the start current should be any worse than it is already.

 

[Darkwood]

A few areas to look at here, as bomjac mentioned the reading your getting maybe a momentary spike but due to the high inertial load the motor starts up in you need to make sure the star /delta timer is allowing sufficient time for the motor to maintain full speed, a timer pulling in too early will lead to torque collapse and a high current in rush.
Another thing to look at is the feed to the crusher stops at a predetermined period depending on product to allow the crusher to clear itself before it stops itself, if their is any product left in the crusher after it has stopped the the motor will have a heavier duty on start up and may not reach full speed before delta pulls in..... rspv interested in what you find.
Im assuming the crusher in this case is a heavy rotating cylinder for the advice given above if its not then more info needed to how the motor does its job.....thx

 

[pssdeepak]

Thank u very much for your replies

 

[Knobhead]

What type of crusher? Hammer, impact, gyratory, jaw,,, they all start differently.