dear all,

I came across a control panel which is controlling a 50 hp motor (hydraulic pump is attached to it), and for this all the star delta wiring is done in it, and in the same panel PLC is mounted on the top.

basically i am a plc guy and have very low idea of 3 phase connections. the customer told me that plc is not working...but when i went on the site and opened the panel smoke came out which is originating from the bus bars.

i just want to know the reasons for that heating..the only thing which i noticed is the incoming is very high around 550v instead of 440v.

please reply soon.

 

Smoke coming from inside a control panel is generally considered bad.

Having 550V coming into a system designed for 440V is also generally considered bad.

Have you measured the current coming into the cabinet while the smoke is being generated?

--
Bob

 

When Bob said that the situation is bad, I think what he meant was "Stay far away from the panel". Most Industrial equipment is rated at +- 10% of rated nominal voltage. You are talking about +25% or more. This is sufficient to cause insulation failures if ambient temperature is also high.

Smoke coming from any panel is an indication of a latent fire. Once again, stay far away when the panel is energized as mentioned.

Regards,

Tomy Zacharia

 

As some of the previous posters indicated, smoke coming out of a panel is not a good sign. You did not indicate how you measured the bus voltage - voltage to ground or phase to phase or if all of the three phases had high voltage. 550 Vac is a standard equipment voltage specification for a 600 Vac service like 440 Vac is for a 480 Vac service. If all three phase-phase voltages were 550v, this would probably indicate an incorrectly specified transformer somewhere, however, this is inconsistent with the symptoms of overheating bus bars in motor service but the motor may not like it. If the measurement were to ground, it would probably indicate a cross connection with a higher voltage level somewhere, still inconsistent with motor service but the insulation may not like it somewhere in the system (the source of the smoke may not be in the panel). In motor service under constant load, the current would go down not up if the voltage goes up. A phase to phase voltage of 550v itself should not be an issue as the panel should be nominally rated for 480 Vac and 550 Vac is only 14.6% over that nominal rating and while a bit over is unlikely to cause burning as the motor stuff and wire-in the panel should be rated to 600 volts at typically 60 deg. F. High current on the other hand can cause burning of insulators or insulation. High voltage on the one or two phases to ground or phase to phase on a delta service may indicate potentially a fault of some sort on one of the legs of the motor circuit.

The first thing to do, is to shutdown the panel at its power sources (LOTO). The following steps can be used to troubleshooting the problem.

1. Inspect the panel for signs of burning, arcing, etc.

2. All the incoming source voltages (phase to phase & phase to ground) should be checked upstream of the isolating device.

3. If there is indication or burning on the motor conductors in the panel, see if there is evidence of conductor overheating or burning at the motor peckerhead. If present, megger the motor.

4. If there is no evidence of evidence of conductor overheating or burning at the motor peckerhead, megger the motor conductors.

5. If 4 is done and no problems found, megger the motor.

6. If none of this helps, carefully and with proper PPE, turn the system back on. Use a thermographic imager like a Fluke Ti27 and look in the panel, at the motor, at every connection point from the voltage supply source to the motor or any other load serviced by the panel, etc..

William (Bill) L. Mostia, Jr. PE
Sr. Consultant
SIS-TECH Solutions, LP
Any information is provided on Caveat Emptor basis.

 

Just a quick question, are you seeing 550V plant-wide? This is a little alarming, but I have seen things like this in the past- the utility had a faulty regulator and we had some crazy variations. It sounds like the panel is not functioning, so ask an electrician to safely power it down and determine the cause of the smoke. Could be a loose connection, or something resulting from the high voltages.

 

While others are giving practical advice here, I'd like to stress that if you are a PLC guy, please request the help of experienced and qualified technicians/electricians.

One thing we can almost certainly guarantee is that this is NOT a PLC fault (unless there are some very serious design errors) therefore you should refer this to someone else.

 

one of the electroplating machine. voltage is around 12 and current is around 2000 Amp. The bus bars got heated very soon. I have checked the m/c in stop condition there is no continuity in between the m/c body and busbars. But while the m/c is in running condition the cathode and anode at different ends showing continuity. Is this the reason for the heating up of the bus bars. I checked but not getting the clue of this continuity. Or if anybody could suggest better d reason behind this heating up.

 

you need to show a sketch with the m/c
and define what is hot in Deg C

you also need to buss bar rating and or dimensions

 

I's say the 2000 Amps is what's heating the busbars.

Regards
cww

 

some warmth might well be normal. you would need a cross sectional area of about 2 square inches of copper for that kind of current.

--
Bob
http://ilbob.blogspot.com/

 

two rails with dimension 10 x 100 mm. Now just one contact is heating up. Temp. is around 85 C. ambient is around 45 C. All other bars at ambient only. Why just one contact is heating up?

 

There is resistance at that contact, obviously.

Regards
cww

 

inadequate compression in the buss connection and poor contact preparation are the major causes of heating.

it is always a concern in corrosive environments.
About the only recourse is to establish proper joining practices and inspections, otherwise all you can do is monitor the buss temps.