I have an problem with SMC-3 Soft starter (150-c-135) 135 Amps. It is used to run a motor of 75 kw, 130 amps full load amps of a aeration compressor at ETP. The problem was with the Internal bypass contactors. There were 3 nos. of contactors of 50 Amps rating and 48V, 50 Hz coil voltage which were welded and due to that the main MCCB of 150 Amps was tripping. I replaced all 3 contactors with new once of 50amps, 48V, 50Hz coils. Now, there is another problem.

Now, when i start the soft starter with 10 second, soft start mode, initial torque 15% and kick start off - the motor starts, takes current of 190 amps and after 10 second current goes up to 550-600 amp and the main MCCB (150 amp) trips.

i tired with different settings in soft start mode by increasing the time, torque but the result is the same. The main MCCB trips after the time limit.

I also tried with current limit start, 10s, current limit %FLA 350 & 450 Amps, but it behaves the same. At start up current remains at 350-400 amps and after the time delay instead of dropping, the current goes upto 500-600 amps and the main MCCB trips.

what could be the reason?

1. Is it because the SCRs are not able to give initial start up torque to the motor and after that, when bypass contactors are on, due to high current the motor trips?

2. we did the DIP switch changes several times within a minute time after tripping of MCCB. Can due to that, the SCRs got heated and are not functioning well at start up?

Please note that, when I was doing the changes of the DIP switch (for time, torque, current limit) in current limit start mode, 10 second delay, 350% current limit once the soft starter worked well. But all the three internal bypass contactors where starting & stopping frequently at 130 amps so we got affraid and stopped it.

3. Shall the internal bypass contactos becomes ON permanently after the set time delay? Or they will start stop to do what?

Please guide...

## Comments rated to be Good Answers:

Re: SMC-3 Allen Bradly Soft Starter Problem" by JRaef on 02/26/2017 11:40 AM (score 3)## Comments rated to be "almost" Good Answers:

Re: SMC-3 Allen Bradly Soft starter problem" by JRaef on 02/25/2017 12:15 PM (score 1)Re: SMC-3 Allen Bradly Soft Starter Problem" by Vulcan on 02/27/2017 3:24 AM (score 1)