Got Anopther Power Reducer Scammer For you

Gotta love that scientific process! Hahaha. No controls. No metering. Wow, this guy needs to work in the medical field. He could put MRIs out of business.

If this is the best you have, you are in a sad state.

Charles Perry P.E.

You're most welcome.

Please do. I hope you fall off your flat Earth (Earth is a proper noun, BTW).

There's nothing wrong with the well known science and technology involved with capacitances for power factor correction. What is wrong are some of your claims and some of your version of the science (part of which is merely misleading and part of which is simply untrue. I could detail a number of points from your own literature but I have dealt with these before as have others who have shown far greater technical competence, knowledge of both practice and theory, (and honesty) than you have shown.

Oddly enough I am in the midst of a situation that bears some resemblance to the demonstration, albeit a much larger scale..

The load is about 60 kW with a PF of .991 (measured). It is 180 amps 3 phase. Everything is fine on mains power but when switched to generator power harmonic distortion of the AC rises to 10%. The equipment (load) DC power supply voltage drops 5 to 10%.

AC generator line voltage shows the same as line voltage with both standard and true RMS DVMs.

Here's the resemblance: although stuff seems to be working there is 5 to 10% less power transfer to a slightly reactive load.

The generator tests fine on an 80 kW non-inductive load. Rating is 130 kW.

This is a rectified load?

The harmonic distortion being measured is current or voltage?

The regulator is probably based on true RMS sensing.

By 'standard' DVM, you mean a peak reading unit with a 1/SQRT(2) fudge factor?

No. The science is fine. Its the economics that stink.

resemblance to

Yes, the usual six diode stacks on the secondary. 'normal' is 10 kV 5.2 amps.

The power co. was measuring both at the same time. (They dont usully test customers generators but they were being nice to me and I suspect he was intreagued by the problem.)

I think the waveform display was power but i'm not absolutely sure. It was an average of a 15 min sample.

Yes, both flukes. "The transmitters do not present a linear load, This causes harmonics as the transmitter wants more current when the Generator is ready to give it. The biggest problem occurs on the odd number harmonics as the even number harmonics will cancel each other. The triplet harmonics become additive, therefore a neutral line that would normally not have any current draw will suddenly have the current draw of these additive 3rd harmonics of all three phases. This will cause the neutral lines to over heat and the generator to over heat.

Possible solutions

1)Balance the load with more linear loads. The transmitter uses 51kW, what is being done with the remaining 79kw capacity of the generator? Some people put a purely resistive linear load on the generator to offset the harmonics coming back into the generator. The down side of this approach is that 51kW of resistance is going to add a lot of extra heat.

(in this case adding a resistive load showed no evidence of improving operation)

2) Install Harmonic line filters on the output of the Genset to filter out the harmonics. The manufacturers of the Harmonic filters should be able to calculate what is needed to clean up the lines. The Genset manufacturer may even be able to provide a recommendation."

It looks like option 2 is the way to proceed. It is a bitter pill as the project is already over budget do to cost increases.

but do the 0011 kind know BCD?

A few comments:

Gensets can handle only a relatively small amount of capacitive loading (leading pf), they go unstable. Rough rule of thumb, capacitive kVAR equal to 10% of kVA rating is the limit, IIRC. Could be more or less.

Gensets can handle only a moderate amount of harmonic current load.

The genset mfr can probably advise on capacitive current limitations and - somewhat - on harmonic current limitations.

Maybe the impedance of the genset is an issue. Trying to draw significant currents - at higher frequencies (5th, 7th, 11th, 13th) - through the synchronous (inductive) reactance of the genset may cause a fair voltage drop or flat topping of the voltage waveform and a reduction of RMS voltage.

You say the power factor is 0.991, do we know the displacement power factor, distortion power factor, and total power factor? Is the displacement pf leading or lagging? Do we have an idea of the harmonic spectra - mostly 5th, 7th, 11th, 13th? no dc? no even harmonics? no triplens? Nicely balanced between phases? These questions about harmonic spectra are just a bit of a fishing expedition.

I have some reservations as to the benefits of adding more resistive load. Mathematically this sounds nice because you are bringing the pf closer to unity and reducing the % harmonic current. However you are not reducing the actual number of amps of capacitive (or inductive as the case may be) current nor the actual number of amps of harmonic current and I suspect the actual number of amps of current is what is most critical in each case. It is worth a shot though, a genset company can bring around some resistive test loads easily enough, if you have a splitter, breaker, or some place to connect them to while the plant is still running.

If you put harmonic line filters on the output of the genset, be careful. Simple filters are normally quite capacitive and can be bad news for a genset as the genset does not like a capacitive load. Some filters come on in stages, some are active harmonic cancellation, I suspect these would be better suited to application with a genset. The UPS guys learned this the hard way. Gensets had to be drastically oversized to handle UPS because the gensets didn't like the harmonics that UPS drew. So the UPS guys put filters on the front ends. That cleared up the harmonics but now the gensets didn't like the capacitive load that the UPS filter presented.

First thing I would try is to get a generator mfr / service guy to come down and take a look for free, or for a bit of money if he's bringing test banks too. Next thing would be to check out costs to get filtering supplied and installed ($20-40k?). I would look for a power quality type consultant if one could come down cheap enough that it is worth the risk of getting non-conclusive results, maybe $5k. Look for one with tons of experience with gensets, UPS, transformers, harmonics, and power quality, and with a quality 3 phase power monitoring / waveform capturing / transient capturing logger like a Dranetz, BMI, RPM, or whatever.

Isn't 0011, 3? Then I guess the answer would be "no." :)

j

The buiilding measures .991 inductive. The major load is speced at .94. additional loads are lighting, obstruction beacons (1,800 W, flashing), 2 cell companies with a/c cooling, building HVAC and 5,400 watts of antenna deicers.

5th an 7th, no even

pretty well ballanced... the cell sites are single phase and were measuring

50 to 60 amps on a hot day with thier A/C running. The gen tests were on a cool day.

I realize i have incomplete data at this time. It's just a problem i am facing that seemed to relate to the way the gizmo that made the W-H meter slow down. Thats assuming the whole test jig wasnt rigged.

No noticable effect, still had 5 to 10% reduction in power supply voltage and the consiquent reduction in output power.

This location loses power several time a year. It also has had a couple of mysterious 'brownouts" the power co. can't or won't explain. voltage on all

3 legs drops from a nominal 208 to 190. My equipment just shuts itself down then. They told me their PF capacitor banks are non switching.

He was there. He pretty much demonstrated the that genset is performing to spec.

gulp

'Corporate says: "we have these things running all over the country and don't have this problem elsewhere"

well dosent that just half byte

That doesn't make much sense. What you are interested in is an instantaneous reading of both the harmonic currents and voltage distortion. That will give you an idea of the source impedance at the harmonic frequencies.

The neutral current is only one problem caused by harmonic currents. The above is correct, albeit somewhat poorly worded. But high harmonic currents drawn on the phases can result in voltage distortion. Particularly if the source has a higher impedance at harmonic frequencies. This voltage distortion will be seen by every load on the system and can cause strange load behavior.

The filter vendors will probably have the best ideas about what sorts of measurements need to be made to specify the correct solution.

At the time I didn't know what questions to ask. After talking to an applications engineer today I believe it was 10% voltage distortion.

The applications engineer of a filter vender spoke with me at length. I now have an assignment to query the generator's aplication engineer about a series inductor.

I appreciate the thoughtful comments. I was able to study some areas that are new to me which allowed me to communicate better with the ap eng.

With a large 3 phase diode rectifier I could believe a dispalcement power factor near unity if I had to. This rules out problems due to leading pf. (Strangely, yesterday as I read '0.991' power factor, and typed '0.991' power factor, I was thinking '0.911' power factor). However there ought to be a whole bunch of harmonic current, and a horrible distortion power factor. Normally that would be my first suspect. I would expect that a genset supplying a bare (no filters or harmonic mitigation) 3 phase rectifier might have to be rated between

1.4x and 4x the rectifier rating - these are derating numbers I had heard from UPS mfrs, maybe 6 years ago, in regards to sizing gensets that would feed UPS with their rectifying, high harmonic, front ends. If you have a step up transformer in front of your rectifier, this should act as a bit of harmonic filtering, like a series choke or series inductor. Sometimes large rectifiers are fed via TWO transformers, with some phase shifting (e.g. one Y-D transformer and one D-D transformer) as this tidily causes a bunch of harmonic cancellation. I think this would not be the case at your site as this setup should remove the 5th and 7th harmonics.

If there are similar sites around the country with the same rectifier and the same genset with the same controller, regulator, alternator, and excitation, and no voltage problems, then I would have to suspect a problem with THIS genset. If you know the current distortion you might be able to ask the genset mfr if the genset ought to be able to handle it. If the genset people say yes, the genset ought to be able to handle it, then maybe there is a problem with the unit. If the genset people say no, this genset can't handle those harmonics, then maybe they can tell you what exactly the difference is between this site and other sites where the gensets can handle it? (It's worth knowing for future installations).

Another possibility is a resonance condition. If there is a significant capacitor somewhere in the distribution (fed by the generator) there is a chance that it makes a parallel resonance with the genset inductive impedance at a critical frequency (e.g. somewhere around 5th to 7th harmonic or even 11th to 13th). Voltage distortion would be terrible (as it is seen to be). It is a slim chance and I don't see anything that looks like a capacitive load in your description of loads. I would continue to look into the genset first before investigating this. If you are able to run the convertor on genset power, with all the breakers to all other equipment open, and the voltage problems persist, then resonance is very likely not the problem.

Well, is 10% voltage THD and 10% voltage drop 'to spec'? Or did he show that the genset is operating 'to spec' under linear loads only? These are rhetoric, and are the same issue as discusse above re: should this genset be able to handle the current harmonics it is being subjected to.

Corporate has a point. I would discuss this with the genset people. Does this genset have a lesser spec, or a lesser controller, regulator, alternator, or excitation? Round up some detailed specs or shop drawings for a couple of similar installations (similar loads, similar load ratings, and similar genset) if you can.

yes, that nibbles, to use the parlance

I imagine that is correct, current distortion was probably way higher assuming a full diode bridge rectifier with little or no filtering / smoothing. Harmonic current could be equal to 40% or more of the fundamental.

Is there a convertor transformer that steps voltage up from 208V to 7 or 8kV or so? If so the transformer ought to be very much like a series inductor of a few percent - if the transformer is 5%IZ impedance then it is somewhat like a series inductor of around 5%. A little less inductive than a 5% inductor and a little more resistive, but in the neighborhood.

If an active cancellation filter is deemed to be required, and is horribly expensive, it may be worth asking the genset people if the genset can be modified to handle the harmonic current. If it is a matter of changing the controller it may be 'only' several thousand dollars.

By the way, when current harmonic distortion is discussed in 'percentages' (e.g. %THD or "40% current distortion) it is a little ambiguous as percent current distortion is sometimes measured as

current distortion = (combined total harmonic current of all harmonic frequencies) / (RMS of total current)

and sometimes as

current distortion = (combined total harmonic current of all harmonic frequencies) / (RMS of fundamental)

In the first case, a heavily distorted current can show up as, say,

80% harmonic distortion. In the second case the same current waveform could be way over 100% harmonic distortion. For your waveform at full load I would expect the discrepancy between the two measurements to be much less than this and hopefully small enough to not be a concern. If the utility technician can tell you the amps of harmonic current at each frequency then that is completely unambiguous.

Two more quick thoughts. It may be that adding a series inductor will add to the problem. The inductive impedance of the genset (and step up transformer (if there is one), and cabling) may be contributing to the poor voltage (low RMS value and heavy distortion) at the rectifier input. While more inductance may reduce harmonic current draw, I think it could only do so at an increase of voltage problems. Since it is the ac voltage peak that 'tops up' the dc capacitor in a rectifier, the dc voltage would probably be very sensitive to the peak value of the applied ac voltage. Your ac voltage is probably 'flat-topping', due to the impedances plus a possibly struggling genset, and causing the low dc voltage. I would mention this to the filter guy, he should be able to debunk this idea if it is bunk.

Also, you already have the genset people, filter people, and, somewhat, the utility people involved. You may also want to call up the vendor of the rectifier equipment. They may be able to say how much harmonic current the thing is expected to draw, and what voltages (RMS and distortion-wise) it may be able to tolerate. A four way teleconference may help get things rolling.

j

[snip]

Exactly right. Most nonlinear loads of this type draw nearly constant harmonic currents. If the voltage source is ideal (zero impedance at the harmonic frequencies), the system voltage will remain a pure sine wave. As the source impedance increases, harmonic currents will result in harmonic voltage drops.

If a blocking filter is placed between the system and the one offending load to block the currents, other loads may be protected, but the one producing the currents will see highly distorted voltages. The best filters offer a combination of a low impedance path for harmonics to flow (such as a transformer with a tertiary delta winding) plus high impedance to block the currents from being drawn from a common source (the generator).