HARMONICS

[smur]

I have come across an interesting unresloved problem.
A gas cleaner keeps tripping on or around 80% loading. The transformer that feeds this unit is 40kva and the max load kw is around 15kw. The waveform from the unit on the input to the equipment shows chopped waveform on the AC. THere is switching power supply in it I believe. As it attains 80% load, a sudden trip is initiated. I have not done any load study on the transformer yet. Is it possible that some kind of resonance occurs between the caps in the switcher and the inductance created resonance ? I raised the taps on the transformer and the problem goes away. I suspect for some reason the reactive power needs shoot up and this causes the trippings. Any ideas ?

 

[waross]

When you were looking at the waveforms, did you note the peak current. With a distorted waveform, you may have high peak currents that are tripping the magnetic trips in the breaker. As a test procedure, I would try adjusting the magnetic trips in the breaker up or down and see what the effect is on the percentage load that causes the breaker to trip.
respectfully

 

[rbulsara]

I think you are on the right track.

If raising tap makes the problem go away, I would think it is because at higher tap, the voltage is high and current goes down. I would suspect the "trip" setting in your "power supply controller" is set at "80%" or it is true RMS sensing and sees higher rms at "80%" you are measuring.

I do not think this is any "problem", but the matter of right settings and voltage.

 

[rbulsara]

How does the waveform look like when you raise the tap?

 

[smur]

Hello
The breaker is not tripping but the power limiter safety device in the tool is tripping. Looking at the power waveform that is drawn into the tool shows power spikes and this happens only during higher power draw close to 14.7kw
When I hooked this device to 45kva transformer it starts tripping at high power levels. When I hook it to larger transformers above 45 kva, there is no trippings. Is it possible that some kind of resonance between the instrument and the transformer is causing sudden power spikes?
The instrument is a plasma generator that takes AC in and converts to DC and then to a DC to DC converter for plasma.
When I increase tap on the 45 kva transformer, there is no tripping.

 

[unclebob]

I would suggest to put a power recorder for some time, with each transformer, and look for voltage and/or current spikes and harmonics..

 

[rbulsara]

You need to find out at what conditions the power supply is designed to shut down. Current? power? waveform or power quality?. Peak voltage?. Compare the waveforms and other paramenters when it trips and when it does not. And try to narrow down the probable causes.

I still think this has to do with voltage and/or the impedance. Does the device draw power in high current pulses? May be at very high current, the tansfromer with lower tap or high impedance can not provide a desired peak voltage, a necessary parameter for proper DC voltage conversion. The unit probably shuts down when it sees lesser peak voltage or chopped voltage. Higher tap or lower impedance source is able to maintain the peak voltage duting a high current draw.

 

[Skogsgurra]

A "gas cleaner"? Are you talking about an electrostatic precipitator (aka electric dust filter)? The plasma you mention is not a proper plasma, but ionized air (OK, it is almost plasma). The efficiency of such devices is at its peak when you are close to a flash-over in the filter chamber and that's why most filter controllers keep the electrode voltage close to flash-over (usually 65 - 70 kV). If your controller is not correctly set up, you will get repeated trips whenever you try to run higher than this voltage.

Of course, we do not know what kind of "gas cleaner" you are talking about. It would help a lot if you describe what you have. And try to forget about resonance for a while. You seem to have fallen in love with that thinking and that makes other thinking difficult for you.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[victa1288]

Skogsgurra,

Very good point. The setup of the voltage levels can definitely change the efficiency of the motors or other types of machines, which would cause different current outputs.I always go higher settings in order to avoid nuisance trippings. We need to consult with manufactures regarding the machine performances.