Electronic Soft Starter for 3 Phase Motor

How many SCR'S are you using 3 or 6?

Probably , the Voltage Ramp and/or the Current Ramp Settings are incorrect.

Most probably, the 'Initial Voltage' setting is low or the 'Start Ramp' setting is high. Try changing both of the settings.

See page 36 (Common Settings) of this document (Softstarter Handbook)

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/2985284834bcff7fc1256f3a00274038/$file/1sfc132002m0201.pdf

- MS

I think we need to know if you are trying to USE a commercially available soft starter made by someone else, or you are trying to MAKE YOUR OWN soft starter. Two totally different aspects of the problem you describe.

What is your application? You'll usually find these type of starters used to power conveyor or some type of gear sets. The starter slowly takes up the slack in the system before coming up to full speed, rather than a hard 3 phase start that can damage your equipment. So it should be starting slow! That's what its for.

How many phases are controlled in the troublesome system?

One phase at reduced voltage was offered in an SCR soft starter via RS components some 20 years ago but better electrical balance will result from more complex starters.

If one of an inverse-parallel pair of SCR's misfires DC will flow braking the motor, this could cause the 'stalling' trouble. If pulse firing (one ca 0.01ms pulse) is too early (during current flow through the other SCR) missfire follows. DC gate drive (say 6.0ms) is resistant to this trouble and the SCR will not backfire if the winding current has reversed. A gated pulse train (@ca 10kHz) may be used in lieu of DC gate drive and can be cheaper to build.

Hi

I would suggest looking at the startup voltage boost settings, incresae this setting to improve startup break away torque. But I am not sure if the soft starter you are using has this facility.

Best Regards

Joe