Banging noise from transformer

Was hoping you'd chime in Jraef, the model is PST210-600-70.

DrOrpheus said:

Was hoping you'd chime in Jraef, the model is PST210-600-70.

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Should be OK then. Don't bother testing the output without the motor connected, that's not going to tell you anything useful. For the PST, ABB copied a soft starter starter I helped design years ago, so assuming they reverse-engineered the logic in the control board, it likely works the same way. As you ramp, once the current goes above a threshold (for mine it was 200%), after 3 seconds if it is not still increasing or drops below that threshold, the assumption is that the motor has finished accelerating and the SCRs are gated full on. With no motor connected, the inrush current on the transformer can possibly be tricking the soft starter into this situation.

I can't quite make out what you are saying with the purple and orange wires, that sounds like a control circuit issue. If something in your control circuit is "bouncing", you may be getting these weird effects from that.

Purple/orange is control wiring on the face of the unit. Orange wires coming out of the start and stop terminal and purple (supplying 24Vdc?) coming out of some other terminal. What do you mean by bouncing? Could we be getting some interference from another source, maybe check full length of these low voltage wires and look for chaffing grounding?

DrOrpheus said:

Purple/orange is control wiring on the face of the unit. Orange wires coming out of the start and stop terminal and purple (supplying 24Vdc?) coming out of some other terminal. What do you mean by bouncing? Could we be getting some interference from another source, maybe check full length of these low voltage wires and look for chaffing grounding?

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By bouncing, I mean that whatever is giving you a start/run command is closing, then opening, then closing, then opening ion rapid succession. A bad contact, a bad relay somewhere, anything like a sensor, whatever is supposed to call for the fan is not staying steady. So the soft starter is being told to run/stop/run/stop/run and it resets the ramp every time.

Separate issue, although possibly related to the unit overloading; Has anything changed with thre fan mechanically? For example, many people mistakenly believe that if a damper for a fan is closed, it loads the fan more, when in fact that is exactly the OPPOSITE. A fan load is air flow; less flow, less load. So it may be that the fan and soft starter have been EXPECTING the dampers to be closed until AFTER the motor is at full speed, and someone has misinterpreted that, opening the damper before the fan even starts. So when the soft starter is done ramping, the fan is already overloaded because it has been trying to move air without enough torque.

Thought about a chattery relay, however I was told it got replaced. Physically the fan and motor has not changed, except after the problem started, the whole combo got changed out like I said earlier. This is a cooling fan on a vacuum furnace, it's load is circulating nitrogen or argon gas around. You know, I'll have to look into that, there is a manually actuated damper that "should" be fully open.

Is there a contactor supplying in the soft starter?
Have you megged out the transformer and the motor to make sure there are no shorts?
Is the inside of the transformer housing clean?

Maybe motor issue... Have you taken apart the cooling blower can and inspected the motor and blown it out? If your furnace is graphite insulated, you could have a lot of graphite dust in the motor and cooling exchanger can. Also... the vacuum tight power connectors for bringing in the leads to the motor could be shorted inside due to the graphite powder.
Have you tried wiring in another motor on the floor to see if the system can start it okay?

Have you tried removing the soft start and doing a direct start on the motor to see if the rest of the system is okay?

On the secondary of the transformer........are there amp meters and an overload unit for monitoring 240V motor current?

Transformer has been checked/megged by outside company and passed. It is dirty. I believe it's a moly heat zone. Motor/fan has both been replaced a couple weeks ago. I didn't personally see what it looked like inside. I'm off this week, so I can't verify some of these things, nor am I normally involved in maintenance of the furnace. I did hook up a different motor on the floor and it did start normal. I think it has been determined that the transformer makes that noise under a large inrush current under heavy load, was told we had a normal contactor and noisy starts were normal back in the old days. Now Im starting to suspect dirty heat exchanger/debris/faulty butterfly valve. It does seem to start up and end up tripping an OL breaker we have post transformer at the motor. Watched the current rise after it should have been on it's way back down.

DrOrpheus said:

Transformer has been checked/megged by outside company and passed. It is dirty. I believe it's a moly heat zone. Motor/fan has both been replaced a couple weeks ago. I didn't personally see what it looked like inside. I'm off this week, so I can't verify some of these things, nor am I normally involved in maintenance of the furnace. I did hook up a different motor on the floor and it did start normal. I think it has been determined that the transformer makes that noise under a large inrush current under heavy load, was told we had a normal contactor and noisy starts were normal back in the old days. Now Im starting to suspect dirty heat exchanger/debris/faulty butterfly valve. It does seem to start up and end up tripping an OL breaker we have post transformer at the motor. Watched the current rise after it should have been on it's way back down.

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I wouldn't suspect butterfly valve (you mean the backfill valve or the heat exchanger water valve)?
However.... you may want to check the flow switch on the exchanger water flow. It may be intermittent.
I am serious about checking the vacuum tight power connections that carry the motor power thru the exchanger can. They can short out across the plate on the inside and the power connections are pretty close together. Are they Auburns (look like a large spark plug)? When you inspect this plate...look for arch flashes on the back side of the plate and inside the pipe.
Some if these systems used a junction block mounted below the motor. The motor leads went from the vacuum tight connections to this junction block consisting of 3 connections with high voltage insulators. If it exists I would check it out and maybe replace the insulated connectors.

What is the HP of the motor and the KVA of the transformer?

Now..... I use only a transformer specifically wound for drives (Drive Isolation Transformer). We do a lot of cooling blower systems with VFDs.
https://www.hammondpowersolutions.com/product/hps-drive-isolation-transformer/

I have also done a lot of systems that run the motor at 480V. I can do this overseas, but in the US "NFPA 86" prevents me from doing this...

3-10.3 Fans and Motors for Gas Quenching Systems.

3-10.3.1 Fans shall not be exposed to any temperature in
excess of their design temperature rating.

3-10.3.2 Electric fan motors shall be interlocked to prevent
operation below a chamber pressure of 7 psi (48 kPa) absolute
to prevent motor failure.

3-10.3.3 Where motor windings are exposed to argon gas or
other ionizing gases, the voltage on the motor shall be limited
to 260 volts maximum.

If you run Nitrogen only....you can go 480 on the motor.