Loosing Power Supplies

[Strahan]

Any suggestions? We have 4 identical machines in our plant and the problem exists with all. Here is the problem 480v 3phase 225A supply for each machine within each machine there is a Siemens SITOP Power 40 DC power supply Input 3phase AC 400-500v Output 24vdc 40A. Per specs, on the supply side we have a motor protection circuit breaker set at 3A ahead of the breaker we have it fused at 20A. Everytime (ok not everytime but atleast 80% of time) the power is shut off to these machines due to power outage or shutdown for repair we loose this power supply. Has anyone had experience with these supplies are they too sensitive and or is there sometype of surge suppression we can put ahead of this supply? Ground connections have all been inspected and are fine.

 

[brian john]

1. Utilize a line disturbance analyzer to determine the source/cause.
2. It could be impulses and like a fight the first punch may not take out the power supply but numerous hits may. TVSS.
3. Is there another option for power supplies?
4. How do they power up the machines let the power just slam back on, the whole plant hits the bus at one time? Or in a systematic approach, power up the plant then the machines one at a time?

 

[Strahan]

Thanks Brian. When we have the option we power equiptment up one at a time not all at once, but this still has proven to be an issue. When we really get hit is during power outages which of course do not occur all the time but when they do we can count on changing a few of these supplies. Once the power goes down if were able to get there before it comes back on we will pull each individual disconnect. These supplies are located in a control cabinet isolated to a particular peice of equiptment and there is a need for the 24vdc at a higher capacity. This has been a problem since we brought this machine into our facility but of course the way we work we never made the manufacturer address the issue (German manufacturer) so now we are left to deal with and come up with a solution.

 

[dbuckley]

My suspicion is you have an inductive element that is in parallel with the power supply, and when the breaker opens the collapsing magnetic field causes a back EMF voltage pulse.

 

[ELA]

Any suggestions? Here is the problem 480v 3phase 225A supply for each machine within each machine there is a Siemens SITOP Power 40 DC power supply Input 3phase AC 400-500v Output 24vdc 40A. Ground connections have all been inspected and are fine.

Are you saying you are feeding the machine with 480VAC and the DC power supply within the machine is rated for 400-500VAC input?

Isn't that an issue right there? 480+/- 10% ?

 

[Strahan]

Are you saying you are feeding the machine with 480VAC and the DC power supply within the machine is rated for 400-500VAC input?

Isn't that an issue right there? 480+/- 10% ?

Yes feed 480vac power supply rating is 400v-500v ac per nameplate. I'm not sure if I'm following you. DC out is adjustable from 22.8 to 26.4.

 

[Strahan]

My suspicion is you have an inductive element that is in parallel with the power supply, and when the breaker opens the collapsing magnetic field causes a back EMF voltage pulse.

Would this explain why sometimes we can get away with cycling the power and the next time we burn the supply? Depending on where in the cycle we are at when we throw the switch (maybe)

 

[robbietan]

Am I correct in reading that you are supplying motor loads? during a voltage sag (or before a total loss of voltage) there is current inrush. this current surge may be enough to fry your inverter. sometimes it takes one event, sometimes more than one - depending on how severe the sag is.

I can recommend putting line reactors so that you can protect your power supplies from hauling intoo much current to compensate for a voltage sag.

however, I also recommend that you try to get an analyzer installed so that you can be sure its current inrush before buying reactors.

 

[Strahan]

Yes there are motor loads but the DC power supply is not being used for them they are all 480vac. The control cabinet for this machine has everything from 480vac to 24vdc to 120vac. These are all being used for different apps including PLC device-net field wiring etc.. I understand what you are saying with the motor loads causing an inrush of current that will play havoc when loss of power occurs while running but when we pull the disconnect to perform maintenance all loads are shut off and problem still occurs not everytime but atleast 80% of time. Yes I agree with the analyzer idea I believe this is where we are headed the only way to really know whats going on.

 

[ptonsparky]

FWIW a local supplier suggests we do not use their 3ph 480 to 24v DC power supplies. To many failures. He recommends a 480 to 120 control transformer, then a power supply.

 

[Strahan]

FWIW a local supplier suggests we do not use their 3ph 480 to 24v DC power supplies. To many failures. He recommends a 480 to 120 control transformer, then a power supply.

Other than the analyzer this seems like the direction we may be heading in thanks

 

[ELA]

Yes feed 480vac power supply rating is 400v-500v ac per nameplate. I'm not sure if I'm following you. DC out is adjustable from 22.8 to 26.4.

My point was 480 V + 10% = 528 Volts
Max nameplate input rating is 500V!

So if the utility voltage is high you exceed the nameplate acceptable input voltage.
Depending upon the power supply design it may get destroyed when you exceed much over 500V. (of course it is always nice to define what destroy means?)

It may be that the line voltage increases over the 500 volt point when you decrease the load.

Based only on nameplate ratings alone I would say this is a problem. It could be corrected by adding a transformer to reduce the 480 volt input to the power supply to something closer to 440V or so.

 

[76nemo]

When you say "destroys", is it taking out anything other than the MOV's, assuming it is an overvoltage problem?

 

[weressl]

Any suggestions? We have 4 identical machines in our plant and the problem exists with all. Here is the problem 480v 3phase 225A supply for each machine within each machine there is a Siemens SITOP Power 40 DC power supply Input 3phase AC 400-500v Output 24vdc 40A. Per specs, on the supply side we have a motor protection circuit breaker set at 3A ahead of the breaker we have it fused at 20A. Everytime (ok not everytime but atleast 80% of time) the power is shut off to these machines due to power outage or shutdown for repair we loose this power supply. Has anyone had experience with these supplies are they too sensitive and or is there sometype of surge suppression we can put ahead of this supply? Ground connections have all been inspected and are fine.

Could be a bad batch. Contact Siemens.

I would not put the DC power supply on the same source as your machinery. When you say 'supply' side, what does that mean? Line side or load side? 480V/225A service disconnect can produce some nasty switching surges. I would have a separate 480V AC service for all the power supplies with a decent isolation transformer or individual isolating 480/120VAC transformers in the machinery.

What is the machinery involved. Does that produce high surges?

In case you don't have the manual I am enclosing the specs. Seems to be a robust device.

 

[weressl]

My point was 480 V + 10% = 528 Volts
Max nameplate input rating is 500V!

So if the utility voltage is high you exceed the nameplate acceptable input voltage.
Depending upon the power supply design it may get destroyed when you exceed much over 500V. (of course it is always nice to define what destroy means?)

It may be that the line voltage increases over the 500 volt point when you decrease the load.

Based only on nameplate ratings alone I would say this is a problem. It could be corrected by adding a transformer to reduce the 480 volt input to the power supply to something closer to 440V or so.

Voltage tolerance (340/360 to 550 V)​

 

[Strahan]

Could be a bad batch. Contact Siemens.

I would not put the DC power supply on the same source as your machinery. When you say 'supply' side, what does that mean? Line side or load side? 480V/225A service disconnect can produce some nasty switching surges. I would have a separate 480V AC service for all the power supplies with a decent isolation transformer or individual isolating 480/120VAC transformers in the machinery.

What is the machinery involved. Does that produce high surges?

In case you don't have the manual I am enclosing the specs. Seems to be a robust device.

Sorry for the misunderstanding I mean line side. The machine is a Kister Caser lots of inductive loads motors, heaters and 10 servo motors. We have came to the conclusion that it is a surge or spike that is taking our supply out other than following your recommendations of isolating this supply I was curious if there was anything out there we could put on the line side to help obsorb some of these spikes? I'm not real familiar with 3phase surge suppression.

 

[ELA]

Voltage tolerance (340/360 to 550 V)​

That sounds better

 

[gar]

080725-1928 EST

Strahan:

Analyze one or more of the failed supplies and see what failed. If you check several supplies and it is the same component, then this will greatly assist you in determining the cause.

If this is a switching power supply then it is usual to used diode rectification directly from the input line(s) to a capacitor input filter. If the capacitor is good and one or more input diodes failed, then it is most likely input line transients that failed the diodes. If this is the case, then are there input line transient limiters? What kind of limiters. What are the diode PIV (peak inverse voltage) ratings?

If the input transient limiters are properly rated relative to clamping voltage in relationship to the diode PIV, then input inductors might be very useful.

You are talking about a relatively small power supply, 1 KW.

If you do not really need tight output voltage regulation, then a single phase Sola regulated voltage transformer, followed by a stepdown transformer, bridge rectifier, and capacitor input filter can provide an extremely reliable supply. This regulates within about 1% for input line voltage changes and thus your primary voltage variation at the output would be determined by the ouput internal impedance and load current variations.

.

 

[Strahan]

I am trying to attain the last supply that failed our management team is really quick to package them up and send them out for repair with out letting us look at them. To answer a question that will probably follow the answer is no we never get good info back from the manufacturer as to what they found wrong during the repair. I have also tried shedding loads prior to pulling the main and then turning them back on individually after the main has been turned back on and this still didn't help.

 

[charlietuna]

we have run into this type of problems on large printing presses and large chillers. we changed out the power supplies to 120 volt source voltage using 480/120 volt step down transformers and then installed small power conditioners to supply the dc power supply. solved our problems!