Kvar Stepping Controller on GENSET for PF control - Page 1
Forum section: electronics / general

author: rixtalbert
author_rank: Newbie
timestamp: November 27, 2017, 04:01:51 pm
content: Dave suggested I drop my comment here , so no stones Please! I know it is off topic somewhat!Problem: I started gathering information about 15 years ago, on applying power factor correction capacitors on large 850 KW and more , to save fuel. At the time it seemed logical.That was 15 years ago. I never did it due to issues I have seen with hardwired applications on main grid power. On grid power you pay the penalty for low PF. So it works.I could see that the caps could help a little in certain areas , but the maintenance to keep this running smoothly were not applicable. No maintenance programs for this bunch!I could never find and engineering brief on the subject of fuel savings regarding portable generator sets. Did find very few mentions, but the Dave "BullShit", kicked in.Well about a year ago , I heard that someone was adding 800 Kvar switch bank on a portable plant with a 2000 amp main at generator. So i put my ear to the ground for a year or so to seewhat kind of results were achieved. From what little data I can obtain , the customer states that a fuel savings of 25% have been obtained. Wow, I thought. All the studies I did 15 years indicated only 3 to 5%. And you had to maintain the hell out of that and really keep and eye on its operations.I did not ever install them on a genset because I was concerned of damage or runaway speed control of the genset.Over the last 6 months, I have heard the genset has had 3 or 4 main Catipillar, 2000 amp circuit breaker failures. It was an electronic controlled circuit breaker and all were brand new! Why did these breakers fail? I immediately thought back to some of my research and wondered if the Kvar or magnetic Flux was flowing back and forth between the genset windings or stator and causing the trips. But why a breaker failure where the unit would not reset. No word as yet from Cat. The engineer that programmed the auto step capacitor bank had it cranked right up to 97% for the caps. I have heard of many problems once unity was crossed, leading pf over 1. Still what would cause this. Or does it really happen that way as far as flow back and forth between cap and windings.I do remember reading one article regarding megawatt generators where a design engineer demanded the capacitor be removed from the system before switching in and out of grid power contacts. He never stated why. Also there are some articles where UPS systems do not like all the caps or switching.My conclusion is,,(just a thought), if the portable plant is running at max or average load of 80% or so and a certain amount of capacitors are switched in,ONLINE, and someone in the field activated the ESTOP button, All currently loads are opened immediately, the genset is running wide open and the banks of Kvar are pulled in.All of a sudden that magnetizing current flows into the genset windings or stator causing all kinds of crap. Strangely , no other damage has been reported. But after a few of these trips , it seems the new circuit breakers cannot handle the condition. ( They will not manually reset), The large flat platted blades of the circuit breaker appear to have some heat thermal color change on line and load bus.Anyone have some hard core DAVE TYPE evidence of this or what is really happening?Thanks to you all,PS if this tread takes off a little , I will add a picture of the Circuit Breaker for funnzies.Rix

author: G7PSK
author_rank: Super Contributor
timestamp: November 27, 2017, 04:38:04 pm
content: In 1979/80 I was building and servicing gen sets. I had one client who wanted to run a small weliding transformer from a 4KW Lister lighting set. They had been sold the transformer as it was only 3KVA and would obviously therefore run on a $KW set, some sales people will say anything or are ignorant. Anyway they wanted to know if I could do anything they did not want to replace the genset so I looked into power correction as the 4KW was at unity, the set was designed for lighting basically.I had some power correction capacitors made up by Phillips who at the time had a capacitor factory in the local town.The result of putting the power correction capacitors on the welder was to raise the generators voltage to nearly 400 volts until the transformer was under load and when the arc broke the voltage went even higher briefly but at the time I had no way of measuring such a transient voltage. If there was a light left on it was blown instantly the arc was broken and was insanely bright otherwise and soon failed.I did sort of sort the problem in the end, I removed half the capacitors and put a small electric fire as a shunt load, they could weld but not at full capacity and everything else had to be switched off especialy electronics.No real help to you I guess but your post reminded me of the time.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 27, 2017, 06:27:49 pm
content: QuoteThat would be disastrous. The capacitor bank should be at the consumer, switched off with the estop.The problem with capacitive loads on generators is that the leading current creates flux in the stator, before the flux of the rotor. This amplifies the total flux and results in an overshoot of voltage. Especially in load dump conditions. The excitation system can't do anything about this.I also fail to see how a capacitor bank will save you fuel on a genset, since only the losses and real power output are load for the engine. A short for example, does not load the engine.Normally capacitor banks are placed since to correct the consumers, so you are able to have more real power output. Maybe the engine is more efficient at higher power?

author: rixtalbert
author_rank: Newbie
timestamp: November 27, 2017, 11:26:36 pm
content: Thanks guys for those post . Jeroen3 and G7PSK.I usually have another way of looking at things I dont understand or lack in knowledge.My first thought 15 years ago was, Hey if PF caps on a Genset can save fuel cost, why the heck isn't every generator manufacturer on earth doing it or making a Cap bank you can slap on your old tired 1200 KW genset! Problem solved! "Dave Quote HERE". It would be the GREENeST invention of the whole world. Billions of gallons of fuel saved and carbon footprints reduced.Does anyone know of a way to measure Kvar circulationg between a genset and a cap bank?Would I need 3 Fluke 1750's hooked up at the same time to measure the three directions of the flow. Genset winding to load side breaker, capbank to load side breaker, loadside breaker to actual load.Thanks again.ok, back to MircoPython,nite

author: Jeroen3
author_rank: Super Contributor
timestamp: November 28, 2017, 07:32:47 pm
content: Quote from: rixtalbert on November 27, 2017, 11:26:36 pmAny three phase power monitor should be able to provide you with these fundamentals. The genset should already have one of those, on it you can see all the numbers.

author: rstofer
author_rank: Super Contributor
timestamp: November 28, 2017, 11:52:57 pm
content: Just to drive a stake in the ground, consider that for many utilities, they don't start penalizing customers until their overall power factor drops below 0.8. There is no bonus for going higher than 0.8 and they almost certainly don't want to see a leading power factor.I have always thought that leading power factor would result in some kind of oscillation. I don't want to be bothered to prove it because I never got much higher than 0.8 lagging.The circuit breaker sees amps and, more to the point, kVA. As the power factor approaches 1.0, the kVA approaches kW and the current falls. So, yes, with poor power factor, the circuit breaker is seeing a higher current. As to why the breaker doesn't reset, who made the breaker? Assuming the breaker tripped on 'long time', there is no reason why it shouldn't reset. Tripping on 'instantaneous' (short circuit), the UL requirement doesn't state that the breaker has to survive. It just can't self-disassemble. This applies to 'bolted faults' right at the breaker terminals.I never could cost justify power factor correction at the loads for low voltage equipment. The penalty for poor power factor just isn't enough for any reasonable value. I can justify correction at the high voltage service but while that may reduce the bill a little bit, it does nothing for recapturing capacity at motor control centers and such.

author: rixtalbert
author_rank: Newbie
timestamp: November 29, 2017, 01:06:35 am
content: Guys,Attached somewhere is the pic of the 2000 amp Cat electronic circuit breaker about 3 months old. Load on this breaker is normally running at 750 amps. Softstarts on a few 200HP motors. 480VAC in the USA.Now , the discoloration may be due to oxidation , however, it sure looks thermal to me! ( 3 to 4 months old)My brainfart idea is that when and ESTOP is pressed in the field, All power loads are immediately stopped and contactors open. Then I suspect the autocapacitor bank is slow switching and since in is at 97% PF at the time of the ESTOP, about of 600 Kvar or more , are hanging on the load side of that breaker. Since the Kvars now have no place to go, I think they migrate,,, very very rapidly into the windings or stator and Wham, You get a trip on the CB and maybe some crazy action at the contact openings of the CB. I would love to hear what others think. I wonder if the electronic trip mechanism is destroyed or freaked out when this happens cause you cannot ever reset that breaker again. ( I wish I had it to tear it apart for myselt) but they always replace them by the time i hear it happens.The autocap bank is the slow switching type Cheap. So its not one of those Thyristor or other fast switching type.I have never been around the breaker when this "MAY" occur, and if it wasn't for blowing another 8 thousand dollar breaker, I would for fun , video and Fluke the thing while I pressed the estop about 100 foot away from the action.Thanks again guys and happy holidays or how ever you celebrate!Rix

author: Jeroen3
author_rank: Super Contributor
timestamp: November 29, 2017, 08:10:12 am
content: It looks like is has been used in a very moist environment. What is the IP rating on the cabinet?

author: G7PSK
author_rank: Super Contributor
timestamp: November 29, 2017, 08:20:42 am
content: If you have to much capacitance the power factor will go to leading with huge surge currents and raised voltage, been there done that on a much smaller scale and learnt the lesson.

author: rstofer
author_rank: Super Contributor
timestamp: November 29, 2017, 03:12:55 pm
content: How many years do the capacitors need to function before the user recovers the cost of a circuit breaker?Who makes that breaker?

author: rixtalbert
author_rank: Newbie
timestamp: November 30, 2017, 04:07:04 am
content: Schneider micrologix breaker, it had only been installed for less than 4 monyhsGood question on IP,I am positive Schneider would comment !as you can see from the load wire direction, the breaker has a front cover. It is strutually mounted on the generator enclosed in a trailer.If the breaker had a bottom with conduit connections i think that dust problem could be reduced. However, when the genset is running a negative pressure is created around the wires passing through the trailer floor. This means a hell of a lot of airborn dust passes this way to the radiator cooling fan. They do not run in rain, but high humidity they will. I think this ,the pic , is a pretty bad design , and the breaker protected greatly.This may though off any thermal charastics of the breaker rating. Since electronic , may not be an issue.The middle top bus of the breaker does ,to me, looks like a corona or plasma type pattern. Maybe the load of kvar dumping into the genset windings.

author: jmelson
author_rank: Super Contributor
timestamp: November 30, 2017, 11:41:20 pm
content: Quote from: rixtalbert on November 30, 2017, 04:07:04 amOh, the breaker is on the generator! It could possibly be a VIBRATION problem. Lots of electronic gear can suffer from vibration issues if it was not designed and tested to be used in a high vibration environment.Jon

author: rixtalbert
author_rank: Newbie
timestamp: December 01, 2017, 12:37:48 am
content: No, even though I am a friend of the vibration theory on a lot of issues, This particular Cat Gen set was specifically designed with the main mounted this way! It is very common. And actually , this thing runs very smoothly. The breaker is a spec,ed Caterpillar replacement and no equal , straight from the Caterpillar Parts wear house. All of the real hubub on this issue is the effects of power factor correction capacitors on stator windings or other components.Thanks GuysRix

author: G7PSK
author_rank: Super Contributor
timestamp: December 01, 2017, 08:22:54 am
content: Seeing as most large alternators are designed to run at point eight power factor and cope with high motor starting loads it does not make much sense to put correction capacitors on them.