Looking at waveforms to determine if transients are coming from facility or utility

[mull982]

Recently we've been experiencing several voltage transients on our system that have lead to voltage spikes that have reaked havoc on several drives, electronics, etc...

I have set up a power meter to try to catch some of these transients and have seen some of these transients occuring. I'm trying to determine weather or not these disturbances are coming from the utility (cap switching etc..) or from within the facility (vaccum breakers etc..)

Someone once told me that you could look at both the voltage and current waveforms during a transient event and from these waveforms be able to determine what side of the metering device the transient is origonating from therefore determine weather or not its coming from the utility or within the facility.

Does anyone know how to determine what direction the transient is originating from by looking at the current and voltage waveforms during a transient?

 

[gar]

100722-1124 EST

mull982:

Make a power measurement during the time of the transient. If the change in power flow due to the transient is toward your loads it is from the power company. If negative using the above sense, the transient is from you.

It may be hard to detect this if the transient power is small compared to your load at the time of the transient.

Since instantaneous power is p = v * i it may be possible from waveform capture to determine the power flow direction.

.

 

[jghrist]

If you can measure the transient on both sides of the service transformer, then you might be able to tell the source. If the voltage spike is from the plant, it will have a much lower magnitude on the primary side of the transformer. I doubt that you would be able to tell much from the current during a voltage spike. The current would be a usefull measurement during a voltage sag. A high current at the time of the voltage sag would indicate a problem within the plant.

 

[hillbilly1]

I have been told by some engineers that if the amperage as well as voltage drops, it is on the utility side of the recorder, if the amperage rises, as the voltage drops, the problem is on the load side of the recorder. Since I'm not an engineer, I do not know how much truth there is in it.

 

[mull982]

100722-1124 EST

mull982:

Make a power measurement during the time of the transient. If the change in power flow due to the transient is toward your loads it is from the power company. If negative using the above sense, the transient is from you.

It may be hard to detect this if the transient power is small compared to your load at the time of the transient.

Since instantaneous power is p = v * i it may be possible from waveform capture to determine the power flow direction.

.

From what I'm seeing we are looking at sub-cycle transients or spikes.

So are you saying to look at the instantaneous power to see weather it is positive or negative to determine direction?

Would this be multiplying the voltage and current at the same point (x axis) on the waveform, or do you need to account for power factor too?

 

[mivey]

I have been told by some engineers that if the amperage as well as voltage drops, it is on the utility side of the recorder, if the amperage rises, as the voltage drops, the problem is on the load side of the recorder. Since I'm not an engineer, I do not know how much truth there is in it.

It is the general rule.

 

[gar]

100722-1334 EST

mull982:

Perform the integral of v * i over time where time starts at the beginning of the transient and ends at the end of the transient. Use these same start and end times relative to a voltage zero crossing on some other nearby cycles to determine the normal power during this period without the transient. If the difference power is positive, then the transient is external, and vice-versa.

If you do not divide by the integration time interval, then the result is energy and not power, but that does not matter. For the purposes here there is no need determine amount of average power.

I have never done this so I do not know the problems you may encounter. If it is an oscillating transient it may take more work.

If both your normal voltage and current are close to a sinewave, then a visual observation of the directional changes in each may immediately tell you what is happening.

Since you have a high frequency transient jghrist's suggestion may be effective and easy if you can make the measurements.

.

 

[ghostbuster]

Record the time of these events and correlate this with any utility switching(usually the utility groups will co-operate with this type of request)

 

[gar]

100723-0816 EST

mull982:

Can you provide simultaneous photos of the transient voltage and current from one of your transient events? Preferably with the largest transient voltage.

.

 

[mull982]

100723-0816 EST

mull982:

Can you provide simultaneous photos of the transient voltage and current from one of your transient events? Preferably with the largest transient voltage.

.

Here are two that I captured. I dont know if they are the best quality and size however.

 

[gar]

100723-1534 EST

mull982:

The voltage spike in both plots is somewhat similar. In what I can view in the current plots there is nothing significant with which to work. Are the voltage spikes always near a negative voltage peak? And always on Va?

This implies some other criteria to determine the source.

.

 

[mivey]

mull982,

In additon to answering gar's questions:

Can you move further upstream or are you at the service entrance? It looks like the effect of a sudden switching of load, fault, or capacitor. I thought there might be some current reaction if it was local so we could make some guesses but the current looks steady.

Have you captured transients with this same signature in several locations or just at one spot?

 

[boboelectric]

I don't see any benefit in chasing the cause to the ultility company.They are only providing power to you on an industrial scale.If you get into exotic drives,ect,I would look into power conditioners,u.p.s. ,ect.

 

[jghrist]

I don't see any benefit in chasing the cause to the ultility company.They are only providing power to you on an industrial scale.If you get into exotic drives,ect,I would look into power conditioners,u.p.s. ,ect.

I don't see any reason to rule out a utility problem. The voltage spikes are not inconsistent with utility capacitor switching.

 

[cadpoint]

I don't see any reason to rule out a utility problem. The voltage spikes are not inconsistent with utility capacitor switching.

Where are the capacitors sitting your statement; is it a situaion that they could at the plant sub-station or farther down the line?

Better yet could you explain utility capacitor switching? What exactly is that?

Am I wrong to think it's at a base substation where the power is brought down and this is where the power is monitored and/or conditioned, or just flat out something else?

 

[ELA]

A suggestion for isolating the source:

Install a temporary Surge protector near the service entrance using a "Y" connection to one side of the MOV. One upper leg of the "Y" connection goes to the source and the other to the loads. The other end of the MOV connects to the grounded conductor or ground.

Use two current probes, one to monitor each leg of the "Y".
The larger current transient recorded indicates the direction from which it came.

 

[topgone]

Here are two that I captured. I dont know if they are the best quality and size however.

Or comtrade files of those you captured?

 

[Besoeker]

Here are two that I captured. I dont know if they are the best quality and size however.

In both cases, the transient is an increase in voltage. This would happen with a sudden interruption of a significant current. However, the currents don't appear to show any appreciable change in amplitude. That could infer that it is external to your system i.e. upstream.
It also appears to be fairly long for a single transient - a bit over 1 ms.
I'd hazard a guess that there is ringing within that 1 ms but the limited resolution of the data capture doesn't show it.
Maybe you could get a picture of it over fewer cycles to improve the resolution of the event?

 

[gar]

100725-1520 EST

mull982:

Is your source a three phase Y or delta?

Assuming a Y. Why is Vb= 0?

On plot _er12 ---
Vc negative peaks seem to be fairly close to Ic peaks. But much less so with Va and Ia.

On plot _ 10_936 ---
Here the problem seems worse with Va and Ia differing by about 90 deg.

Both plots show a negative transient at or near a negative peak voltage of Va. This implies a cause with a phase correlation to the voltage peak and only on Va, and from this limited sample of two only on the negative peak.

We can assume that the cause is not at the location of your instrument. Therefore, there is both distributed inductance and capacitance, maybe some lumped inductance and capacitance, and lots of resistive load distributed at many points. The probably result is generally a low pass filter effect.

If you apply an impulse to a low pass filter its amplitude will be reduced and duration stretched. However, the filter might have resonances. In World War II there were a lot of vacuum tube failures aboard ship from the shock of guns being fired. Accelerometers were used to measure the shock at the guns. Shock levels of 1000 Gs were measured. From this information tubes were designed to be more resistant to this shock. No change in the failure rate. Then measurements were made at the tube locations and the shock levels were much lower in magnitude but much longer. The wrong design criteria had been used. Basically the ship between the guns and the equipment looked like a low pass filter.

For well designed electronic or electrical equipment the spike as you are showing it should not cause failures.

Suppose the cause is in your plant. What possible equipment might cause a transient at a negative voltage peak and only on line A?

You might move your test equipment to other locations that might be closer to a possible source and see if the transient voltage gets larger. Also monitor all three voltages.

.

 

[jghrist]

Where are the capacitors sitting your statement; is it a situaion that they could at the plant sub-station or farther down the line?

I was thinking in terms of capacitors on the utility primary system, either upstream or downstream from the plant substation.

Better yet could you explain utility capacitor switching? What exactly is that?

Switching a utility owned capacitor on or off.

Am I wrong to think it's at a base substation where the power is brought down and this is where the power is monitored and/or conditioned, or just flat out something else?

Flat out something else -see comment above.