Generator output filter 2

[gepedo]

Hello all,

For short power outages, some of our equipment is backed up by a UPS. During (known) extended outages, critical areas (i.e. servers) are supplied via generators. In some cases, these generators are not producing a clean enough output and are causing key computer equipment to reboot (time and time again). My question is: Do you know of any type of filter that is relatively cheap and can be placed between the generator and the equipment that it is supplying (I'm looking for some sort of plug and play approach) ?

The voltage that I'm considering is 120 V and 208 V.

Thanks in advance

 

[rbulsara]

It's not the generator producing clean power, but the lousy UPS (rectifiers) procuding too much harmonics and 'polluting' the generator source, and driving its AVR crazy.

The remedy to this may include:

1. Make sure the generator is atleast sized 1.6 to 2.0 times the UPS kVA rating.

2. The generator has digital voltage regulator.

3. Gen AVR voltage sensing circuit has a isolation transformer.

4. If the UPS is lightly loaded and has input filters, disconncet the input filters of the UPS (yes, disconnect).

5. If UPSs are old, more than 10 yrs, replace them with newer one with better technology.

6. If the generator is made to serve (provided it has capacity) other motor loads, such as HVAC it will help dampen some harmonics produced by the UPS, reflecting on the generator bus.

 

[torslum]

As explained by rbulsara it might very well be that the harmonics created by the UPS and other equipment is making the AVR go mad, because it is not suited for operation with such large amount of disturbancies.

Some manufacturers providing input filters for their AVRs. I guess this is doing somewhat the same as a isolation transformer for AVR voltage sensors as explained by rbulsara, maybe even more efficient?

Check with you generator supplier for such filters.

 

[bacon4life]

gepedo,
For extended outages, are you supplying computers directly from the generator?

 

[fsmyth]

An idea for a (relatively) cheap solution:
Add a 3-phase idler motor that starts before the
load is switched. Phase angle adjusted with caps.
Size it as large as possible, where the idle current
is within the margin left by the load. Works best if
the generator has ample headroom. Connect Y or delta
depending on the which harmonic levels are the worst.
<als>
P.S. I have not tried this with generators, but have
used the method to clean up power in other instances.
(The motors were cheap and available). __