Aux CT ratio

[byrdj]

I'm trying to determine the ratio for an aux CT used to convert the 5A rated current from the main generator CTs for use with a control circuit. The manufacture of the equipment in which it is used has not been able to identify.

the numbers on the transformer are 8600K 4904. I'm thinking the ratio is something like 2500:1

any body reconize this number?

 

[DTR2011]

What is the maximum or nominal current required by the input device you intend to feed from the Aux CT?

In North America, most CT's have a 5A secondary. That will be the primary of your Aux CT. Whatever you input device needs to see (1A max, mA max, etc), will determine what your secondary should be and thus your Aux CT Ratio.

If you have another unit you can do a simple test on the CT available by testing the CT with the voltage method. You need a variac and 2 volt meters to do this.

 

[byrdj]

the generator CT is 5A near rated load. ( I forget its ratio at the monent)

The circuit on the secondary side of the aux CT rectifies current to derive 10VDC to be used by the control circuit. My reason for believing the ratio is 2500:1 is I calculated the secondary aux current needed to provide the desired voltage at each end of the trim adjustment resistor and 2500 was the "nominal" value between the two extremes.

Unfortunately the industry i'm currently in requires such extensive review of test procedures, asking to "let me find out" is not well recieved.

I am fairly sure, I have the value, but a manufactor's spec sheet of the transformer would be nice

 

[electricpete]

byrdj - is your first name Jim and did you ever work in Texas?


=====================================
(2B)+(2B)' ?

 

[byrdj]

No
Yes

not jim, but joe

I've visited several utility stations in Texas over the years

 

[waross]

A 2500:1 ratio will give you 2 mA at 100% load. 2 mA across a 5000 Ohm impedance will develop 10 Volts AC. Does this seem reasonable?
Re testing to find out: How about a good excuse to verify the ratio for preventative maintenance rather than testing it?

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

 

[byrdj]

the reason for desiring the AuxCT ratio is to perform a bench calibration of this circuit board. my recent project was to verify PCBs for a turbine control system were operable and ready if replacement was needed. actually the OEM was to perform the work with my observation for the plant.

I specified for them to used 2mA for the bench calibration for this card, since the OEM procedure did not address (nor could find any data about the input auxCT) from many years back, the plant has on file a work order where I performed an inservice loop trim calibration that is approved for use in the event this card is ever replaced.

In addition to the process of getting a planner to add instructions to the routine PM calibration, thne "purchase" the card from inventory, then return it, to perform a PM verification at the plant would require the coordination with the relay/transmittion group (not part of the plant) to provide the test equipment to drive the 5As.

so with the ability to perform the in service loop, the card will be performing proper if installed, I feel i can't justify spending the other resorces just to get the bench calibration a little better

I was just hoping some one reconized the transformers part number