CT Saturation Test

[shkim2000]

I didn't see CT Saturation Test. Anybpdy tell me how CT saturation Test is conducted?

 

[DiscoP]

Basically you apply voltage to the CT terminals and measure the current. Do some googling and you will find some information on this - or talk to the person/company who did the tests.

 

[bjeservice]

if you need to know the ct saturation you need to do excitation current test.By this test you find the relation between the secondary voltage if ct and excitation current responsible for induced voltage. you will see that the curve of relation will have linear region and tend to saturate and then full saturate.

 

[RalphChristie]

I am not familiar with the term saturation test but it seems from the above posts like an exciting current test to obtain the knee-point of the CT. With this test you can also obtain the exciting curve (mag-curve) of the CT.

You'll need a variable voltage, (easiest obtain from a variac - must be able to obtain the suitable voltage) a voltmeter, an ammeter, a pencil and paper.You'll have to measure the voltage and the current while you do the test.
Apply the voltage to the secondary winding with the primary and other windings being open-circuited. Increase the voltage until you reach a point where a small increase in voltage results in a big increase in current.
Now slowly decrease the voltage to a few measuring points, while you measure the current. (write it down) Something like:

205V - 1.1A
200V - 0.6A
190V - 0.238A
180V - 0.149A
170V - 0.114A
150V - 0.08A
125V - 0.061A
100V - 0.049A
50V - 0.028V
25V - 0.017A
0V - 0A

You have to decrease your voltage slowly to zero volt to demagnetize the CT-core.

BEWARE The knee-point voltage will depend on the size and class of the CT, and it can be very high on some CTs (several hundreds of volts) Be very cautious, you will be working on live equipment during the test.

Now you can just plot the current and voltage values on a graph. This is the mag-curve of the CT. IEC classify the knee point voltage as the point where a 10% increase in voltage results in a 50% increase in current.



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[camo1978]

Totaly agree with the above posts. The easiest way to test a CT kneepoint(saturation test) is by use of some specialist test gear ie Omicron CPC100. This type of equipment makes life so easy. Open circuit primary and then connect voltage output to secondary. Then push GO!! the set will automatically increase the voltage and measure the primary open circuit current.Once the set finds the kneepoint it will automatically ramp back down to prevent magnitisation. It will then Plot a graph and record the V and I measured. To easy!!!

 

[RalphChristie]

The problem with this specialized equipment, like the Omicron, is that it is very expensive. If you are not testing protective devices everyday, you will not be able to justify its costs.
Many tests can be done manually with easily obtainable, everyday used, equipment.

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