Isolation Transformer for "Dirty" Power

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I have received updated information recently with updated measurements - they said their current distortion exceeds the levels set by IEEE 519. They said that when they ran the calculations with 1500kVA transformer and 5% impedance, the Isc/IL value came out to 39.4 which puts a limit on TDD at 8%, but they need to know the exact transformer information to run the calcs with a precise Isc.
Is anyone familiar with this test and what it means? Honestly I have not done power quality analysis before.
 
elecshop said:
I have received updated information recently with updated measurements - they said their current distortion exceeds the levels set by IEEE 519. They said that when they ran the calculations with 1500kVA transformer and 5% impedance, the Isc/IL value came out to 39.4 which puts a limit on TDD at 8%, but they need to know the exact transformer information to run the calcs with a precise Isc.
Is anyone familiar with this test and what it means? Honestly I have not done power quality analysis before.
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The IEEE 519 standard is for the
Point of Common Coupling with the utility power system it was not intended for use with customer owned transformer secondaries or end use equipment thin at ion points even though many specifications refer to it.

I don't know that there is a good way to take a standard for one place and them misapplied at some other point.

For 1500kVA customer owned transformers you will not get any better %Z impedance than what is stamped on the unit's name plate. Certified transformer data is usually a special order item performed at the factory at an increased cost. Yes you can perform an impedance test in the field but it is rarely done just to determine Isc values.
 
with B leg dropping to zero for 50 minutes, I'm not buying this being any kind of distortion issue whether harmonics or power factor. Did the generator start and pick up the load when this happened? Did the voltage just suddenly reappear on B leg? Has anyone done a visual inspection of the transformer, it's terminations, and any switchgear?

One thing I can tell you from experience, when things seem really strange like this, don't trust reports coming from your Oompa Loompas out in the field. I've seen them miss blown primaries hanging down, and connections frying so bad I could smell them from 50 feet.
 
elecshop said:
The 17 dips are shorter durations but the particular 50min dip among them is the longest one.
I was thinking maybe there could be a problem with switching/contacting occurrence in the utility substation. I forgot to mention that those dips occur almost at the same time each day i.e., at around 2:20pm. Could it be that a non-zero voltage at the MV side during this event is causing this phase lag? Maybe capacitor banks become unsymmetrical/unbalanced when seen from the LV side? I'm not an expert in power on the utility side, but we can be almost sure that it is not an issue from the hospital.
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Any industrial plants nearby? Since it seems to be at the same time each day, could be a large piece of equipment starting up. Usually affects all phases though, unless it’s a defective regulator on the poco substation.
 
hillbilly1 said:
Any industrial plants nearby? Since it seems to be at the same time each day, could be a large piece of equipment starting up. Usually affects all phases though, unless it’s a defective regulator on the poco substation.
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I only ever skimmed IEEE 519 but I think it addresses distortions caused by customers at the PCC. I also think there is something in there specifically addressing power delivered to healthcare facilities
 
@elecshop,
IMO, that's a PoCo problem. The utility is obligated to deliver electricity at your POCC at a specified voltage range, frequency, and at specified quality. The hospital has the right to question the PoCo and demand they correct the problem. If you are working for the hospital, you could provide proof that the hospital side is not "dirty" and not the cause of the problem.
 
If the transformer is wye-wye with a three-leg core and the center connection of both the primary and secondary wye's is grounded (Yg-Yg), then with an open phase on the primary the normal voltage will be regenerated on the secondary winding corresponding to the open phase (as I mentioned in post #14 of this thread). In this case the utility should verify that the proper voltage level is present on all phases of the primary. An alternative measurement in this situation is to check the current on the primary neutral. With an open phase on the primary, this neutral current will be substantial even when the loads are balanced on the secondary. The primary neutral current could also be logged to check whether it might be getting excessive on an intermittent basis. Preferably, the phase B secondary voltage would also be logged concurrently to see if there's a correlation of the voltage dropouts with the primary neutral current.
 
230616-1556 EDT

If i have a 3 phase delta or wye source, then connect this source to two primaries of two transformers and connect the two secondaries as an open delta, then I still have a 3 phase output. Very common practice in our part of the country.

If i have a 3 phase wye secondary, and loose one transformer secondary, then I do not have a balanced 3 phase output. However, with some additional windings or transformers I can produce a balanced 3 phase output.

..
 
Updates:

Another round of measurements was performed on the main incoming service between the utility transformer secondary and the main switchgear, and the harmonics were analyzed.
It looks like the current distortion harmonics (TDD) exceeded the guidelines for the transformer there which sets a limit to 8% but the phases were approaching 15% of distortion several times. The voltage distortion was within limits (THD).

Can someone explain how the harmonics are related to the voltage dips events? I have read the TDD levels mean that the nonlinear loads are causing this issue, but I'm not sure how to align this with the previous results that voltage dips with no current swells indicate utility-power issues.

Someone suggested the use of harmonic filters and size them according to nonlinear loads to filter out the harmonics. But before going there, how can we confirm that this is a utility side problem or a load side problem?
 
elecshop said:
Updates:

Another round of measurements was performed on the main incoming service between the utility transformer secondary and the main switchgear, and the harmonics were analyzed.
It looks like the current distortion harmonics (TDD) exceeded the guidelines for the transformer there which sets a limit to 8% but the phases were approaching 15% of distortion several times. The voltage distortion was within limits (THD).

Can someone explain how the harmonics are related to the voltage dips events? I have read the TDD levels mean that the nonlinear loads are causing this issue, but I'm not sure how to align this with the previous results that voltage dips with no current swells indicate utility-power issues.

Someone suggested the use of harmonic filters and size them according to nonlinear loads to filter out the harmonics. But before going there, how can we confirm that this is a utility side problem or a load side problem?
Click to expand...
TDD means Total Demand Distortion not current distortion, it takes into account the size of the system feeding the load being measured.
THD is Total Harmonic Distortion the can be both voltage (THDv) and current (THDi) components. The current distortion is often the cause of the voltage distortion. The voltage distortion is what is usually measured and reported.
 
jim dungar said:
The current distortion is often the cause of the voltage distortion. The voltage distortion is what is usually measured and reported
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Generally true. It is equipment in your facility that causes current distortion, that causes voltage distortion, and the voltage distortion travels on the utility lines to the neighbors. But if you WERE getting more than 5% THDv from the utility, that could cause excess THDi in your facility. This is why the IEEE 519 specs go both ways: for both the user AND the utility. But if your THDv was within spec., then the THDi is internal.

Now, can excessive THDi cause voltage dips? Possibly. High THDi means there is more current flowing in the system than the actual working loads represent. So in effect, the CAPACITY of your system is reduced. So IF you have a transformer that is sized too close to the working load current, the high harmonic current is possibly causing saturation of that transformer to where the voltage dips. There are a number of “ifs” in that of course, so determining whether that is the cause is not a simple task.

But could this cause a 50 minute zero volt condition on one phase? Nope… move on from that idea.
 
Jraef said:
But could this cause a 50 minute zero volt condition on one phase? Nope… move on from that idea.
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Does this mean that because one of the phases is interrupted for a long duration then it is not likely the case of having the transformer size close to the loads?
On another note, the peak demand recorded was around 700kW which is less than half of the transformer rating (1500kVA).

Since current harmonic distortion is observed without voltage harmonic distortion, we could say that the internal loads are what causing this problem right?

What are your suggested solution(s) - maybe harmonic filters? Would a UPS at those nonlinear loads be effective?
 
elecshop said:
Updates:

Another round of measurements was performed on the main incoming service between the utility transformer secondary and the main switchgear, and the harmonics were analyzed.
It looks like the current distortion harmonics (TDD) exceeded the guidelines for the transformer there which sets a limit to 8% but the phases were approaching 15% of distortion several times. The voltage distortion was within limits (THD).

Can someone explain how the harmonics are related to the voltage dips events? I have read the TDD levels mean that the nonlinear loads are causing this issue, but I'm not sure how to align this with the previous results that voltage dips with no current swells indicate utility-power issues.

Someone suggested the use of harmonic filters and size them according to nonlinear loads to filter out the harmonics. But before going there, how can we confirm that this is a utility side problem or a load side problem?
Click to expand...
Care to give us a snapshot of the levels of the harmonics you have and which harmonic level is dominant? My understanding is that IEEE 529 specifies the limits as "TDD", not THDi. If you can compute for TDD (total demand distortion) and compare that figure with the IEEE 519 limits, you might be amazed you're below the specified limits. Last year, we did our harmonics scanning and we knew were not violating 519 (not harming other facilities by producing harmonics) but the best info we've gathered is that we now know how much load can be added to our system without getting into trouble.
All THDs affect others near your facility: by giving unwanted hum/ noise, malfunction of sensitive electronics equipment (capacitors will be damaged earlier compared to having low distortions), etc.
On your side, your system becomes more inefficient as the harmonics increase the currents drawn from your system compared to having no harmonics in your system. IsquaredR losses increase hence your substation capacity has to be derated.
 
I had a call a while back about some job. I really didnt have any real in depth knowledge but they heard I had worked on one fwiw, not much but they reading every meter invented and while its entertaining to use all that, different readings everywhere for they even splain all that I say, its busted and software isnt going to fix busted internal hard part.
Just a guess but the V meter going to 0 for almost an hour sounds like a problem bigger than a little wiggle in a wave form.
 
elecshop said:
Updates:

Another round of measurements was performed on the main incoming service between the utility transformer secondary and the main switchgear, and the harmonics were analyzed.
It looks like the current distortion harmonics (TDD) exceeded the guidelines for the transformer there which sets a limit to 8% but the phases were approaching 15% of distortion several times. The voltage distortion was within limits (THD).

Can someone explain how the harmonics are related to the voltage dips events? I have read the TDD levels mean that the nonlinear loads are causing this issue, but I'm not sure how to align this with the previous results that voltage dips with no current swells indicate utility-power issues.

Someone suggested the use of harmonic filters and size them according to nonlinear loads to filter out the harmonics. But before going there, how can we confirm that this is a utility side problem or a load side problem?
Click to expand...
Since you are not responding to the request to share the figures that you've got, if you said your TDD is over 8%, say 9%, do you mean to say your THDi is around 19% or so? (THDi = (TDD x max load)/load during testing)
 
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