GENSET DRIVING A UPS LOAD
GENSET DRIVING A UPS LOAD
(OP)
Dear All ,
Since i work for five years on Power generation business , i have a question to make in the forum .
Fist of all i live in Greece , and the mains supply here is rated at 400/240 Volts - 50 Hz.
I have to size a diesel generating set , able to provide power in 2 parallel connected UPS rated at 40 KVA each (that means total 80 KVA). UPS brand name is Liebert.
Can somebody propose a gooud source to retrieve data for my calculations ?
Liebert refers a Harmonics distortion better that 4% (no load) .
UPS , do not have a Starting current to take into account when sizing generating sets , but they are having a lot of Harmonics.
How do i have to proceed in order to calculate the correct KVA size of my Diesel Generating Set ?
Best Regards
George
Since i work for five years on Power generation business , i have a question to make in the forum .
Fist of all i live in Greece , and the mains supply here is rated at 400/240 Volts - 50 Hz.
I have to size a diesel generating set , able to provide power in 2 parallel connected UPS rated at 40 KVA each (that means total 80 KVA). UPS brand name is Liebert.
Can somebody propose a gooud source to retrieve data for my calculations ?
Liebert refers a Harmonics distortion better that 4% (no load) .
UPS , do not have a Starting current to take into account when sizing generating sets , but they are having a lot of Harmonics.
How do i have to proceed in order to calculate the correct KVA size of my Diesel Generating Set ?
Best Regards
George






RE: GENSET DRIVING A UPS LOAD
A safe approach may be to contact 2 or 3 genset manufacturers for recommendations.
RE: GENSET DRIVING A UPS LOAD
Thank you busbar anyway for your help.
Any other ideas to make my clalculations ?
Regards
George
RE: GENSET DRIVING A UPS LOAD
GenSet KVA = 2 times x UPS KVA (minimum !)
Does anybody knows why ?
RE: GENSET DRIVING A UPS LOAD
The reason includes:
1. Generator will heat more with harmonics.
2. Some generator's voltage regulators do not react well to harmonic voltage distortion.
However this assumes 100% UPS load, all harmonics. Also consider the following and you will see why there is no strating answer. In my opinion if the motor load equals the UPS loads, the effect of the UPS harmonics is pretty much negated. This assumes no VFDs.
UPS loads, usually have associated cooling and need to be suppported by the generator. The cooling (motor) loads acts as dampner for total harmonics.
Also it is important to know what order harmonics are invlolved. Different generator pitch winding eliminates or permits different harmonics (for example, 2/3 pitch will eliminate circulation of triplen harmonics). Ask gen mfrs.
Also incorporation input isolation transformer for UPS also help emliniate triplen harmonics.
Digital voltage regulators on generator are not (or much less) sensitive to harmonics. Using a isolation transfomer for voltage sensing circuits for AVR is also helpful.
RE: GENSET DRIVING A UPS LOAD
RE: GENSET DRIVING A UPS LOAD
Smaller gensets tend to have less expensive regulators so I would be cautious and carefully consult with the suppliers' engineering folks as previously suggested. You may have difficulty getting a definitive answer.
Ron was alluding to UPS input filters which have very large capacitors. Under light load conditions, if the filter stays connected, the generator may well see leading power factor if there are not enough inductive loads to absorb the VARs. This can cause problems with genset votlage regulators as well. Some UPS mfg's have recognized this problem and include switching to disconnect the filters automatically when load is light.
RE: GENSET DRIVING A UPS LOAD
RE: GENSET DRIVING A UPS LOAD
Then you wont have (ANY) problems with dirty power, or (Harmonics)! They are a bit pricy but they done require hardly any maintenance and certainly no batteries to deal with. Check into them you can fine info at most Cat web sites.
I've installed them an I'm pretty sceptibale at new things especially when they are so small for what they do. But after going to the school on them I was really surprised at them and I also found out after going through the electronics that they are virtually unbreakable! They are that good.
RE: GENSET DRIVING A UPS LOAD
Caterpillar rotary UPS is still a static UPS (rectifier/inverter) and equally susceptible to harmonics as any.
The rotary part there in is spinnig DC generator in lieu of battery (lasting a few seconds). This is different than a conventional rotary UPS consisting of a motor-generator such as a piller Uniblock.
I only stated this response to the last post. I have nothing against Caterpillar 'rotary ups' but it is important to know the difference.
RE: GENSET DRIVING A UPS LOAD
Please take a look at the following supplied link and scroll down slightly to the section heading "Product Benefits" in particular (Harmonics.
Sometimes it pays to take a second look. Your input is appreciated.
RE: GENSET DRIVING A UPS LOAD
No offence..but read again what I wrote...and I am familiar with it..and one who really makes them..Active Power.
CAT is a Static UPS with rotary "battery" (a dc generator)not a conventional rotary UPS which includes a M-G set in essence. M-G sets isolate back up generators from harmonics as motor is electrically isolated from UPS generator. I am not disputing your "battery" time..
RE: GENSET DRIVING A UPS LOAD
Have a look for the a true rotary UPS made by a company called EuroDiesel. They were sold to GE by Seghers group in the last year or so - I'm not sure of the current website.
It is a very interesting design of electrical machine with a diesel generator and clutch. No electronics in the power circuit. They are popular with the financial institutions, who are among the few people who can afford them, but they are an exceptional product.
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If we learn from our mistakes,
I'm getting a great education!
RE: GENSET DRIVING A UPS LOAD
We have quite a UPS here on site - Piller made and its something worth seeing. Basically a rotary double wound that uses power to turn the machine to give out on the critical services bus. when the mains fails the battery supplies the machine to keep it turning and there is no dip in output. If it exceeds the duration of time then the diesel kicks in and turns the machine through a clutch. While this is happening the motor windings that were used to turn the machine now act as a generator and supply the non critical supported load.
These machines are so rock solid in construction and can take some abuse without affecting the critical load.....
When something depends on secure power Piller do some good units but they are pricy....
http:
Rugged
RE: GENSET DRIVING A UPS LOAD