Keep Blowing 30A fuses?

AC VFD or DC drive? Are they Time Delay fuses or Semiconductor fuses? Are the fuses feeding only the drive? If so, what is the 2.5A load, is it just the cooling fans and control board power for the drive? Is the enclosure sealed, i.e. NEMA 12 or 4 (IP54 +)?

The three 30A fuses are time delay fuses that feed 3 phase 480V to 3 Main Contactors (Siemens 3RT1035-1BB40) that in turn serve 18 B&R Acopos Servo Amplifiers (8V1010.00-2). The first contactor feeds 5 Servo Amplifiers, the second contactor feeds 8, and the third feeds 5. Each servo amplifier has it own 6A fuse (none of which have blown).

The input to the servo amplifiers is 400 to 480Vac 3 phase, 1.35kVA. The output of the servo amplifiers is 0 to 480Vac 3 phase, 0...1-0.75A.

The equipment is contained in a Nema enclosure that is air conditioned to 76F but I have noticed that the drive cabinet is around 85F. I don't think the air conditioner is working right. Would that have anything to do with fuses blowing over the weekend? I wouldn't think so. The fuses are in another cabinet that is cool.

We have verified that the fuses blow over the weekend when nothing is in operation because we tested them prior to startup this week.

Just a guess. I'm wondering if it could be that the starter contacts on your piece of equipment aren't worn and arcing at start up, causing the fuses to blow. I had a similar problem on my air conditioner at home, I thought my compressor was going bad, it was blowing fuses at start up, turned out to be the contact points on the starter relay.

Everything is less than a year old. The machine isn't really in full production yet.

Everything is less than a year old. The machine isn't really in full production yet.

Assume nothing, you have a problem even if its a new machine, crap happens, check the contactors. You'll have to do a trace anyways.

You did not supply the specs on this, you have a supply of 485V, what is the requirement?

p911

The contactors are Siemens 3RT1035-1BB40. They stay closed during the weekend and the servo amps are kept energized. The contactors don't operate over the weekend so I don't believe they are the problem.

Based on the information provided it sounds like perhaps the fuses are opening upon production startup, not over the weekend.

So many things it could be, possibly something as simple as a faulty drive (it is the same one isn't it?). I would advise checking the fuses before starting the suspect drive first (it sounds like the fault is at least regular).

Additionally you do not indicate if the drive is constantly powered and just in stop mode, or if the input power side of the drive is controlled by a contactor and the contactor is open during the weekend. If the latter is the case then I would suspect leaky capacitors in the suspect drive causing excessive startup currents when the contactor powering the drive closes.

Can you provide any more information?

We keep the drives powered but in stop mode.

We have confirmed that the fuses are blown before attempting to start up.

Each drive has its own 6A fuse as well. See my other comments above.

Off the top of my head, with very little information to go on, I'd bet the mortgage on a bearing, assuming this is something that has bearings?

sounds to me with the limited Info we have here you have worn startup contacts or assuming this is a motor driven machine your brushes need replacing or your armature needs reconditioning or booth . keep on keeping on K

It seems that the machine mentioned by you is connected to a common switch board/ bus bar , to which the AC is also connected. However if the AC of the cabinet is connected to the switchgear/ switch board the current cannot be so low which is 2.5 A. This 2.5A may be the current drawn for lighting etc.

You check the O/p OR shaft of the Machine. The shaft may be struck up a little or a problem in bearing. Check the temperature at the M/c end if the fuses are found blown after 10 to 15 min of start up.

As you are stating for any voltage surges etc, it shall be taken care by the main incomer or the incomer switch of the subject switch board.

The three 30A fuses are time delay fuses that feed 3 phase 480V to 3 Main Contactors (Siemens 3RT1035-1BB40) that in turn serve 18 B&R Acopos Servo Amplifiers (8V1010.00-2). The first contactor feeds 5 Servo Amplifiers, the second contactor feeds 8, and the third feeds 5. Each servo amplifier has it own 6A fuse (none of which have blown).

The input to the servo amplifiers is 400 to 480Vac 3 phase, 1.35kVA. The output of the servo amplifiers is 0 to 480Vac 3 phase, 0...1-0.75A.

The equipment is contained in a Nema enclosure that is air conditioned to 76F but I have noticed that the drive cabinet is around 85F. I don't think the air conditioner is working right. Would that have anything to do with fuses blowing over the weekend? I wouldn't think so. The fuses are in another cabinet that is cool.

We have verified that the fuses blow over the weekend when nothing is in operation because we tested them prior to startup this week.

OK, so if none of the 6A fuses downstream of the 30A fuses are clearing, then it cannot be the result of anything downstream of them , i.e. the suggestions of motor bearings, jams etc.

So that only leaves the power circuit between the 30A fuses and the 6A fuses. Being that the contactors are constantly energized, it doesn't appear to be related to closing the contactors. That leaves the power distribution system, i.e. conductors / bus bar (you didn't say). Remaining possibilities:

1. If, as you say, the AC unit is having trouble maintaining the temperature at the setting, that means it is either inadequately sized, or defective. If it is defective and it is powered from behind the 30A fuses, then there's a possibility that when you start up the system, the temperature in the box increases due to the added heat rejection of all of those drives. This causes the compressor on the A/C unit to cycle on, and being defective, the added load of the drives plus the defective A/C compressor is enough to blow the fuses. If the A/C is not getting power from behind the fuses, forget this.
2. A/C units also dehumidify.The A/C unit not working properly is allowing a buildup of condensation in the cabinet. That moisture would collect on un-powered circuit components (because powered ones would be warm), so when you start up, one of those circuits goes to ground across the moisture path. Once up and running, everything remains warm enough to keep moisture off, until the weekend when it gores idle again. Spray everything with WD-40 prior to start-up after the weekend. If the problem goes away, that was it. Then fix / replace that A/C unit.
3. Similar to above, but you have a nick in a conductor insulation that can only conduct to ground when moisture is present, i.e. after being idle all weekend.
   

Suggestion on trouble shooting: (maybe you already have done these but I need to enumerate them in case ...)

1- Possible cable damage from the fuses to any of the 3 contactors:

- Check the cables for any wound that might be shorting to ground (if single cores are used)... maybe a cable was crushed by a part of the machine panels/doors etc. For 3 cores cables (flexible?), maybe a break within ... bad piece of cable.

- Check the connection points on the contactors, both IN and Out: Some stray strands?

- Check cable after the contactors also for the same

** You are saying that the machine is kept energized and the contactors are energized... and the fuses downstream of the contactors are OK ** Then your problem will have to be between the 30A fuse holders and the contactors, OR with in the fuse holder:

1) Have you been running these machines during the week continuously and without any problem? I mean that these have been commissioned and running for production?

2) If Yes then look for some interfeering during the week end: Is this happening every week end ?

Try shutting down all the components down stream on the week ends.

IF not yet running fully, then the cables and connections should be trouble shooted AND the fuse holders checked for good contact (Some bad contact pressure will heat the fuses and provoke their breakdown even for a small load: The body and the wires will heat if partial contacts are there. Eliminate that possibility.

This is a very good possibility if the drives are protected against high voltage like this.

For curiosity: Did you experience failure of any of these drives during these incidences or they just blew the fuses because of temporary shorts due to protective devices within them?

I second your idea! We installed voltage monitoring relays in front of our feeds to some new servo systems after spending $20K to replace them after an extended overvoltage of 10.1% on the 480V line. These relays detect 'overvoltage', 'undervoltage', 'phase loss', 'phase reversal', etc. for about $85 from Automation Direct.

Haven't lost any since.

The B&R ACOPOS drives are European, but they claim to be able to handle 400V to 480V +10%.

My thoughts exactly, had the same problems at weekends when our intake was on low load.

We had 4 X 33/11KV 20MVA transformers, unbeknown to us the motor for the one of the tap changers had tripped. Any VSD fed of it would go up in smoke over the weekend.

About thirty drives toasted and to fix it, I pressed the O/L reset button. End of problem.

Back to our friends problem, a simple way would be power the drives down over the W/E.

The drives didn't blow any fuses and we didn't lose any drives. It did just about drive me nuts finding the problem.

Whoops, now I remember, old age, we did lose one drive, it looked like it got hit by lightning. We also had bigger drives than what is being used here.

Yeah, the fuses on our drives didn't blow. They just melted the heavy duty resistors used to shed off energy during a stop.

Your other solution would be to disconnect the drives over the weekend. What a pain that is....

I am guessing power interuption over the weekend. On re-establishment of power, all the drives powering up at once overload the 30A "Master Fuses", but the 6 A individule fuses are not over loaded. Wire a small relay ahead of the "Master Fuses" (with a small local fuse) with its N.O. contact in series with its own coil and a push button to activate it. Activate Friday evening, check Monday AM, if relay is open, you had a power interuption. -- JHF

The thing is, though, the fuses are blowing over the weekend while the line is idle. So, even if there is a power interruption, the drives are not calling for much current.

Besides, a power interruption would cause many other things to fault plantwide, which is not the case.