Simens Simoreg 6RA - 23

Fuses protect against over current, but sometimes when you have power failures or even brief interruptions, the problem is voltage spikes that come down the line due to grid switching or capacitors somewhere else that are discharging when power comes back on. Fuses will do nothing for that. If your thyristors are exploding, that is usually indicative of a voltage problem; what is called dV/dt (delta voltage over delta time), meaning too rapid of a change in voltage in too short of a time. It can cause the thyristors to self commutate, in other words they fire on their own and usually at the worst possible time. The fuses then blow after the fact because the thyristors are shorted. If this has happened more than a few times I would look at replacing your capcitors on the drive now as well, they have likely been damaged.

What you probably need is some good quality surge/spike protection, something that will work more than once.

Siemens TPS link - Tpsbroch.pdf

Thanks.

I have visited Siemens TPS link. I will be contacting their sales persons shortly.

Mean while, I have changed the Thyristors and Fuses. I have checked the pcb for any signs of damage. I have also checked RC connected across thyristors. They appear to be OK. Resistance is as mentioned on it. Capacitors rating was 0.15 uf, but with my lcr meter it is showing all 0.25 uf.

When we stared our drive it is immidiately tripping on fault F16, which is I> or =I max. There is no movemet of motor. Checked the voltage on Dc out put. It was just 18 v for that fraction of secound. Motor remains dead! All the parametrs set are as per previous data. There is no change.

Apparently during starting there is no backemf for considerable amount of time,therefore dead short is occurring across the phases,therfore the fuses and the thristers are blowing.Please examine why motor is not rotating when voltage is applied.

Checked the system and founthat there existed a loose contact in field circuit.

On setting it right,

the motor started.

Thanks all.

good experiance!