AVR - 3 Phase Sensing

[ccdubs]

Hi,

Could someone explain 3 phase sensing to me in terms of an automatic voltage regulator for grid generation purposes.

I know that it should be used when a load is non-linear and fluctuating, but I don't understand why this requires 3 phase sensing?

 

[ccdubs]

I guess I should also ask, if the generated supply is variable (ie., fluctuating prime mover like wind) should 3 phase sensing be used.

 

[dpc]

I don't think three-phase sensing is required for a generator voltage regulator.

 

[gjones33]

Hi ccdubs
Three phase sensing is not necessaty and most alternators I have been involved with have a single winding for the avr supply and sensing.
Cheers
G

 

[busbar]

As something that is not a protective element, and the ‘grid’ being fairly stiff and not subject to significant voltage or current unbalance in non-faulted conditions, I don’t see the point. It may be a tactic by the utilty to discourage or complicate the interconnection. Isn’t there only one DC field that equally affects all three phases?

This could backfire, but you may want to ask for a list of “approved/previously accepted” components that meet the specification. Maybe it’s worth posing the question to Basler or Beckwith. They both offer fairly complete technical support for their products, and seem to have their ear to the ground on distributed-generation trends. {I’m not sure 3-voltage/3-current excitation control exists for any size generator.}

 

[ccdubs]

3 phase sensing refers to the AVR control being determined by the voltage of all three (grid/stator) phases rather than two or one phase. The excitation on the rotor is definately DC.

 

[nitro]

ccdubs,
I have to input my thoughts on this subject.

Caterpillar has led the industry in regulators with three-phase voltage sensing. Most Caterpillar generators are equipped to sense three-phase voltage. Three-phase sensing averages all three-voltage phases, resulting in better regulation, especially when the load is unbalanced. The most significant benefit is the ability to handle the three-phase silicone controlled rectifier (SCR) drives used in systems such as un-interruptable power supplies (UPS).

I could go into this indepth but that would take up to much space so if you want more thoughts on the AVR send me your e-mail address. I have some great printed material on the subject.

 

[dpc]

Sorry nitro, I can't really agree, at least regarding the improved voltage accuracy. I think the three-phase sensing has more to do with obtaining three-phase power for the regulator, and not voltage monitoring.

I suppose for the small 480V standby applications, three-phase sensing might have some merit since you could have highly imbalanced systems. But for a typical generator application, I still don't think there would be much benefit. We have worked on several large generator projects lately and all used single-phase sensing for AVR.

 

[ccdubs]

Nitro,

I would appreciate any info on the subject. My email addy is ccdubs@hotmail.com this addy has limited space so if the publications are large I would be happy to give another email address but not on a public forum.

Thanks