Unbalance Current Detection

[Humble2000]

I am looking for a meter to detect unbalanced current. This means if one phase current is more than 10% in difference with other two ,the unit initiates a trip.
I also have one set of CT’s which are source for Crompton Ammeters. There is diagram for connecting two meters in series, is this going to be accepotabel and provide enough current for proposed meters. I apprecite any feedback on this.

 

[Humble2000]

I forgot to mention that I am looking for an inexpensive solution.

 

[rbulsara]

Look up current balance relay 46D or negative sequence relays, device 46 on websites of protective relay mfrs like Basler, ABB, GE, SEL etc. They are made for this.

While I am not sure of this, you may want to look up some highend Power quality meter from leading switchgear mfr like SQ D, GE, Eaton etc. to see if they include such a functionality.

 

[rbulsara]

what is inexpensive?

 

[dpc]

You first need to define unbalance. For motors, NEMA defines unbalanced current based on the maximum deviation of any one phase current from the AVERAGE of all three phase currents.

There is no easy way to do this with conventional meters. A digital power meter of some kind is probably your best option.

You may need to extract the current data and calculate the imbalance in a computer or PLC.

For inexpensive, I'd take a look at meters from Electro Industries, such as the "Shark" meter.

 

[rbulsara]

You may want to look up some electronic overload relays. Not sure they do what you are looking for.

 

[cranky108]

Usually meters don't provide a trip function, use a relay for that.

For industrial applications I would look into the Basler 200 and 300 series relays. These are not quite utility standard, but should be priced such.
For a utility application, spend the money needed.

What is unbalance? Negative sequence? Zero sequence? What is the application?

 

[slavag]

Hi.
I don't think that power meter is good solution for the protection. As posted above, you can use very simple relay:
motor protection or broken conductor detection.
Regards.
Slava

 

[waross]

Look for a refrigeration type motor protector. They are cheap and give adjustable phase unbalance protection. If you can use one in your application it may be the cheapest solution.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Humble2000]

Basler relays are very expensive around $1500.00
Most other relays do not detect the unbalanced for current difference less than %40.00.
My budget is around $500-$700.
I would call 10-20% current imbalance.
does anybody know any other manufacturer I can check?

 

[waross]

How about three CTs with suitable load resistors across each CT. Connect the resistors in broken delta. Unbalanced currents will show up as a voltage across the broken delta.
What and why are you protecting? It does make a difference to the solution to the problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[slavag]

Hi.
Try

http://startco.ca/

Best Regards.
Slava

 

[Humble2000]

Well, Most these units work based on zero sequence current. Here I have three legs of phases which I need to detect the unbalance current. There is no ground. Voltage level is 600V. Unit is an AVC. So three diffent cap banks on each stage, if one stage doesnt provide the required reactive power meaning the scr blown or something like that, the upstream breaker would trip which is not desirable. I need to disable the AVC.
Warros, your suggestion might work, although I prefer using a unit with adjustable settings.
I called Startco, they dont have a unit I am looking for.

 

[rbulsara]

Humble2000:

As Bill implied, if there were a cheap method someone would be selling it by now. There is a reason why this is not a commnly applied protection on small installations: the cost is not justified.

You are the only judge as to what is justified. Anything you will build will require current sensing and a sort of a meter/comparator and decision maker and it can't possibly cost you within the range you specified in the USA.

 

[davidbeach]

Basler relays are very expensive around $1500.00

That would be the BE1 line of relays. Look at the BE3 line. I don't recall exactly what is available, but if there is a relay in that line that will do what you want, it will be around your price range.

 

[Humble2000]

BE3 line doesnt have 46 function. Thats all I am looking for. A relay with 46 function.

 

[davidbeach]

OK, try the BE1-700C. More than the BE3 line, but last I checked well less than $1500.

 

[Humble2000]

Thank you. Price is half.

 

[slavag]

Hi.
Please see attached

http://www.buyeng.co.uk/store/product.php?productid=16156&cat=265&bestseller=Y

for my pinion you can found this relay in US.
Best Regards
Slava

 

[waross]

Hi slava
The refrigeration industry uses protectors with similar features. About 1/10th the cost. Several manufacturers to choose from.

Bill
--------------------
"Why not the best?"
Jimmy Carter