DC Drive Prob

JRaef as you said may be its prob with 1 thyristor, because previously also this drive was tripping with over current fault without load,when machine was suddenly stopped.

i think that it was problem with regenerative thyristor or with that circuit.now there is totally 2 thyristors r damaged. but pls let me know is it possible to test firing circuit with multimeter? if yes how can i do? because i am in Kuwait (arab country) where we cant find any good dealers and technicians to do all this jobs.so we only do all this things in our company.also we cant find spare parts also for many things here.

Take several detailed pictures...with close-ups of the controls. Maybe we can save you a little time.

are you a certified maintanence engineer?

The PIV of SCR's do degrade with time and use.

You state this is a 4 quadrant drive - therefore you may have had an inverting fault. That can be a drive failure, cross fire, low mains voltage, poor cml loop tuning, even a bad tachometer can cause havoc.

Rockwell, and ABB both protect their 4 quadrant bridges with fuses an the mains and on the DC side if it uses only three line fuses. If the drive uses 6 leg fuses then the DC side fuses are not used.

If you are not comfortable with commissioning this equipment (from the ground up), then get a qualified service tech.

at Epke yes i am certified maintenance engineer,but i am looking all plant maintenance including mechanical works so i didnt went fully inside the drive maintenance.

and GW. this design is working well from 15 years.this is 15 yrs old machine.as u said i also feel that its prob with regenerative circuit.so now i am purchasing the thyristor module and will see the result.but again here in original design they only used 3 fuses at the drive i/p which is 80amps.so now i want to place 2 fuses at the drive o/p. but what type of fuse will act fast and clear fault? and what i am thinking is right or wrong? if right what type fuse u recommand?

ABB uses the same size and type as the three line fuses which are semiconductor current limitting fuses. Rockwell tends to use fuses about 1.25 times larger on the DC side, but again semiconductor type fuses similar to the ones used on the AC side. These fuses must have a DC interupting rating.

Reliance electric often used molded case circuit breakers on the dc side with the three poles in series to get the DC interupting capacity. Magnetic trip only, with trip setting about 200% to 250% of motor full load amps. Again, the CB must have a DC rated interrupting rating. The DC rated interrupting capacity will be much lower than the AC rating.

That would be 3 poles in parallel to get the higher interrupt capacity. Right?

No, in series! To get a higher DC voltage interupting. Your typical MCB will only have 250VDC rating. Put the 3 poles in series lengthens the arc better. MCB has to be rated for the full load amps x 1.25

Roger that.

Ratings and capacities jumbled here. In my head at least.

I hear what you're saying.

Hope this helps. This was for a 540HP 500V armature. 300/1200 RPM field range.

Well, sometimes it is a good idea to read the manual.

Have you considered using a circuit breaker between the drive and motor instead of the fuses you suggested?

You can compare the interupt time of different fuses and CBs with a bit of research on the internet.

Reason for SCR damage? They do fail and the failure of one can lead to a cascaded fault of the others. Are the SCRs correctly attached to their heatsinks? Is there adequate cooling of the heatsinks?

First failure in 15 years is a pretty good service history. What has changed?

If you have an Oscilloscope you can check this thoroughly.

JRaef is right you need a new Drive. (and the Service Manual with it)

The nice thing about DC drives is they tend to be very reparable.

With the 590 drive there may be some MOV's on the main board. My experience has been when fuses blow the MOV's also explode damaging the printed circuit board. If the PC board is damaged you are out of luck. If the SCR's shorted then replacing them and the fuses (not a big job) will get you up and running.

The MOV's are round discs about 3/4 to 1 inch in diameter about 3 mm thick with 2 leads. When they blow the tend to rupture out the side and spew ionized gas around causing colateral damage. Again, not an expensive part by itself.