Inverter/ Generator Problem 1

[sparks22222]

We have a new asphalt plant set up in the last year and production has been good, but last week came across a problem with a 75 kw inverter controlling a skip.
At present the plant is being powered by a big generator.
Six months ago, the electronic card in the compressor packed up, and now the power supply card packed up on the inverter.
Any solutions to stop this happening again?

 

[abeltio]

When electronic cards start to go... my first questions are:
Q1.Is the equipment (control system) grounded per manufacturers specifications?
Q2. Did the failures coincide with storms (i.e. lighting bolts), then: do we have a suitable lighting arrestor system?
Q3. Is the controlled equipment (in your case the compressor) properly grounded per manufacturers specs? rotating equipment can generate a lot of static electricity which is not so good for electronic cards.
Q4. What changed lately? any connections modified?
Q5. Do we have grounds in the wiring?
Q6. If the connected wiring is shielded, are all the shields grounded at the shield ground bar @ the control system only? (i.e. having more than one ground on the shield can cause a return path through ground inducing high currents).
Q7. Are there any alarms, diagnostic alarms present on the control system?
Q8. Are AC and DC wiring segregated (AC voltage running paralell to DC can induce serious voltage)?
Q9. Did the constructor properly segregate voltage levels?
Q10. Are the power supply voltages within spec?
Q11. Are we blowing fuses?
Q12. What about junction boxes? any flooded?
Q13. In hot areas, check the terminal boards...sometimes the cables are rated for high temp but the boards are not ...therefore they just desintegrate creating shorts.
Q14. High vibration zones: check that the wiring insulation is ok (vibration would cause frettage of the insulation, baring the conductor and creating ground faults).

You did not provide much data... but if electronics are starting to fail those would be my prime suspects as a starting point.
Hope this helps.
a.

 

[jbartos]

Suggestion: It appears that there are some flaws affecting the cards MTBF or MTTR. The cards can last a long time, if properly designed, e.g. 50000hours or more. Therefore, a root cause analysis is justified. The previous posting gives a very meaty content to think about, at least. Another approach is more related to analyses and tests of the defective card. This is where the card manufacturers normally provide the tech support. A second opinion from an electronic engineer with a small laboratory could help. There are some on Web.

 

[sparks22222]

Thanks guys for the replies, sorry i was a bit vague with the question.
anyway, there is an input and output chokes before and after the inverter so its well protected from overvoltage.
Everthing was properly checked and earthing is ok.
We are not sure of lightning yet, but we have decided to use a power monitor on the incoming supply to monitor and download the voltage from the generator, in case there is any overvoltage coming from this generator.
No fuses are blowing.
All that happened was the inverter failed and there was no display even on the inverter.
its just a coincedence that two electronic cards have failed in six months on a one year old plant from a generator supply.
We have a seperate electric supply we use at night for tank heating which is not big to run the whole plant but maybe enough to change to this supply for the inverter to prevent any overvoltage.
any more suggestions please pass them on.
thanks

 

[jbartos]

Suggestion to sparks22222 (Electrical) Aug 2, 2002 marked ///\\Thanks guys for the replies, sorry i was a bit vague with the question.
anyway, there is an input and output chokes before and after the inverter so its well protected from overvoltage.
///These chokes are essentially for harmonic mitigation, that may eventually produce some overvoltages. However, the normal protection for overvoltages or spikes is a Transient Voltage Suppressor.\\Everthing was properly checked and earthing is ok.
We are not sure of lightning yet, but we have decided to use a power monitor on the incoming supply to monitor and download the voltage from the generator, in case there is any overvoltage coming from this generator.
///If you are in an area with lightnings, the proper lightning protection is recommended, e.g. air terminals according to NFPA 780.\\No fuses are blowing.
All that happened was the inverter failed and there was no display even on the inverter.
its just a coincedence that two electronic cards have failed in six months on a one year old plant from a generator supply.
We have a seperate electric supply we use at night for tank heating which is not big to run the whole plant but maybe enough to change to this supply for the inverter to prevent any overvoltage.
any more suggestions please pass them on.
///There also may be Electromagnetic Interference (EMI). EMI measurements are suggested.\\thanks

 

[sparks22222]

Transient Voltage Suppressor.\\I may check up on these for protection.

 

[bigamp]

Sparks22222,

When you say the plant is being powered by a big generator does that mean you are generating your own power (diesel,
GT?) and are not on grid power?

Have you had any problems with generator volts going high? If the generator voltage regulator (AVR) is poor quality or defective, you can get into a high voltage situation if there is a sudden loss of electrical load. Possibly check the operation of the AVR.

Some years ago, I had a similar problem on a site in a third world country. The plant UPS (which provided power to "delicate" control equipment) was destroyed by high input voltage from the site diesel generators following a large load rejection (there was no grid power on the site). My fix was to power the UPS (when a replacement turned up) via a power conditioner to stop the volts applied to the UPS going high. Lots of equipment was damaged/destroyed the day the volts went high. Mostly input transformers on equipment power supplies (printer and laptop computer battery charger amongst others).

Regards

 

[jraef]

Just an anecdotal possibility.
I have worked on many generator powered systems in the rock crushing industry and have had similar problems. In most cases, they were from older generators having AVR (Automatic Voltage Regulator) systems too old to be used with modern harmonic generating industrial electronics. The old AVR interacts with the harmonics and starts allowing high or low voltages and frequencies during periods of peak loading. No one has been willing to spend the $ necessary to isolate the exact problem, but newer gensets have filtering on the inputs of the AVRs and avoid this. If you have a Catepillar genset I heard that they have a retrofit solution for older systems that works. The trick is to find one of their service techs that knows of it. Maybe they just put in a new AVR, I don't know because I wasn't there for the solution.

I also see that you are shutting this power system down at night. Another common problem with genset operation is on start-up. I have seen several users who start the generator engine with the main breakers closed, thinking this is OK since the loads are not turned on. A VFD however is powering up the DC bus, and the low frequency and low voltage present as the engine ramps to full speed can have detrimental effects on PC boards. The same holds true for anything with a switch mode power supply, which is just about everything now. If you are doing this, it is a simple solution to make sure the main breakers are open until the generator is at full speed.

Good luck.
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