VAR sharing issues with cross current circuit compensation between Basler SR4A and CDVR

[michelin3x]

I am having a problem with the sharing of VARS between these 2 kinds of regulators!! I shall explain the system in detail, hope you can help!

Firstly,
I have three generators of 1000 kVA rating wired to a Basler SR4A regulator. As I recently required a power upgrade, I added a fourth generator of a 1400kVA rating wired to CDVR. The CDVRs voltage bias is fed by a Easygen 3500.

I added the fourth gen CTs to the cross current compensation circuit of the other 3 gens(note: without the burden resistor as specified in the CDVR manual).

My problem is that the VARs are not sharing, as soon as I parallel the two gens, either one of them takes all the kVARS and the other goes negative. I try increasing the voltage of the lower one, it brings the kVARS but within little time it either goes to maximum and the other one goes to negative kVARS and keeps fluctuating one way or the other.

Kindly help!

Thanks,
Mike

 

[catserveng]

Well first off I have personally had VERY poor experience doing cross current compensation with different type units, even with the "correct" burden resistors installed, depending on length of CT wiring, how you wire in shorting contacts, etc, you will find that even small differences will drive the VAR share apart. Without the right input burdens at each voltage regulator you will get erratic results, as everytime you bring a unit into the network it won't be at exactly the same voltage, so if it comes in a bit high it may hog the VAR's, if it comes in low, the other unit may hog the VAR's.

So a couple of specific questions,

Are the Cross current CT's proportionally the same? Without more specific info hard to be exact, but say the 1000kVA machines have a 1200:5 CCCT, ideally the 1400kVA machine would have a 1700:5 CT But since they don't make that size, which way would you go???).

Is the CCCT on the 1400kVA machine with the CDVR a 5 amp secondary? Some CAT generators ship with a droop CT that is not a 5 amp secondary.

Have you "dummied down" the dynamic settings in the CDVR? The default settings in a CDVR make them way more responsive than the SR4A. Where are the Stability pots on the SR4's set to (usually mid-scale).

Did you match the droop settings on all the units, ideally you would set all the voltage droops to zero, however in practise I find a little bit of droop improves stability?

What is the EasyGen voltage bias doing? Voltage matching for parallel? The EasyGen can be setup to trim voltage, is that feature active? You may want to monitor the voltage bias output and make sure it is not contributing to your problem.

Have you tried paralleling in droop? One of the most common problems in cross current compensation setups is one or more of the droop CT's wired backwards. The results of this are not always consistant, sometimes the VAR's will drift apart very slowly, other times the oncoming unit will either grab it all or dump it all.

I am assume you've looked at the Basler Tech Pub on Paralleling voltage regulators? I've attached a copy just in case.

Hope that helps, MikeL.

 

[redlinej]

Hello
how are the basler SR4A been bias.

Julian.

 

[michelin3x]

Thank you guys for the prompt response!

@redlinej The SR4A has a bias from a voltage pot

@MikeL I shall try replying to most of your questions as my knowledge on the droop logic is less.

We have 1600:5 CTs on all. So yes, a 5 amp secondary.

Initially the droop setting was off on the CDVR, I switched it on, tried all settings from 0 to 10%, I noticed the kVARS dropping down on 4(Considering engine 4 is taking all the kVARs). I bring them to as close equal and then within sometime again they go hay wire and the amps and kVARS start shooting up and I have to trip it off.

I removed the bias from the Easygen and tried but that did not help too. I switched off all the settings for voltage control on the easygen and tried that too while the bias was connected but again that didn't help.

http://files.engineering.com/getfil...c-4b53-a3cf-5cae57c8bab9&file=CCC_DRAWING.pdf

http://files.engineering.com/getfil...ebd-96a1-acfe1075b64f&file=2301021540edit.pdf

These are links to the drawings if that might help.

Thanks again guys,

Cheers,
Mike

 

[Parchie]

@michelin3x,
Reverse your CT connection on Gen 4. Cross-compensation CTs should be in series (X1 of Gen 1 connected to X2 of Gen 2--> X1 of Gen 2 connected to X2 of Gen 3--> X1 of Gen 3 connected to X2 of Gen 4--> X1 of Gen 4 back to X2 of Gen 1).

 

[michelin3x]

Parchie
The generators are wired in this order
Gen 4-Gen 1-Gen 2-Gen 3.Gen 4 is the first Gen actually.

I just checked the CT connections, they are wired exactly as your said. Could you check again.

 

[Parchie]

@michelin3x,
I did as requested and here's my trace:
X1 of Gen 4 CT ->TB5-> 1-63 --> TB1(1-65)-->35 (1812)--> TB2 of VR4-->SB3-1-->X1 of CT for Gen 3!
That's the reason why sharing don't work, IMO.