problem with soft starter

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a.bisnath

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Electrical worker
Weg soft starter ssw-03 series usually used on 100 h.p. motor trip on thyristor failure/motor leg open, motor and cables checked ok works with another starter.
starter in question ramps up smaller motors,eg 0-15 h.p. normally with larger motor ramps then vibrates and trips
 
Re: problem with soft starter

not enough information--but sounds like you have lost a thyristor and the unit is starting and ramping up single phase..............
 
Re: problem with soft starter

mother board of starter has single phasing protection via feedback of current transformers forgive my ignorance but i have always believed that a 3 phase motor can run single phase but not stat single phase, at least for hard wired systems,can you clarify?
 
Re: problem with soft starter

Is the thyristor failure an open or a short?

In my experience, most thryistors fail shorted which would allow your motor to have full voltage on one leg and reduced voltage on the other two. This is a method of soft starting employed on many inexpensive small HP starters.

The single phase protection is typically for the loss of an incoming line not the loss of an output line. Also many soft starts will trip if there is not enough current flow through them giving a pratical lower HP size of 50% unless a protective feature is disabled (usually used for testing purposes only).
 
Re: problem with soft starter

What is the status of the mechanical portion of the system? Torque requirements for starting the mechanical load could have changed in the driven equipment, thus making it look like a soft start issue.
 
Re: problem with soft starter

All thyristors have checked out o.k.by component tester(radio shack),
'battery and bulb,touch the gate method
' and with simple anlogue meter,checked for shorts,none present-soft starter,checked votages and current on small motor all are balanced, problem still existed when big motor was reconnected.starter is used for motor in high torque application -a rock crushing plant in a quarry, motor never gave trouble before and starts with another soft starter none the less overhauled motor and changed bearings
 
Re: problem with soft starter

(Additon to last reply) when the starter is energised it gives the 'rdy" or ready display, on small motors it ramps and runs with all currents and voltages on line and load side balanced,this is done on a test bench whenit was returned to its original location in a 20 foot container and reconnected to the original motor it ramps and then begins to vibratethen stalls on the E03 errorwhich is thyristor failure/motor leg open
 
Re: problem with soft starter

So the motor will run as it should with another soft start and the suspect soft start will start smaller motors but not the big one and you have verified that there is nothing wrong with the mechanics of the driven system.

At this point... I would suspect the semi-conductors in the soft start. The thyristers might carry the current of a smaller motor with no problem only to die on you when under a larger load. This has happened to me before on large size Siemens VFDs.

It appear you have no options left but to change the semi-conductors in the faulty soft start and try it again - OR - try it on another motor of the same size and see what it does. In any case... I think you are going to be changing the semi conductors and or other components in the soft start. What about the rest of the power circuit in the soft start, as in capacators and inductors? Any visible damage or heating showing up? Send it back to the manufacturer with all of the data and see what they say.
 
Re: problem with soft starter

I thank you Rick you have given the info I needed the thyristors can be bad after all, there are no inductors in this weg designed starter the snubber circuit are a resistor/capacitor arrangement which checked ok,the only other component is an integrated motherboard and the fans,I like your other idea -use it on another motor of same size,it leads me to wonder why the protective fuses did not blow instead of the thryristors being damaged ,I was always taught in the early days of being a trainee that a motor should not burn, a starter should not fail if protected correctly
 
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