Deviation in Current Transformer RCT Value while Converting Xmer Rating

Dear Sir

There more two cores in the CTs which are PS(Special Class) class and used for Restricted E/f & Transformer Differential Protection.will IT(Differ RCT value)affect in these protection ranges.

Suryakant Jatania

Dear Friend

Transformer terminal voltage will drop due to increased pri & sec winding voltage drop ( i*r, i increased by 25% due to increased capacity from 16 to 20 MVA, applied voltage remaining constant ). While cooling will take care of additional heat produced but just check the effect of reduced secondary voltage on connected equipment. If tapping is available then check feasibility of using the lower tap on secondary side to improve voltage, unless you have OLTC. Changing tap in pri. side will also increase iron loss.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Dear Mr. Ashok

Pl find herewith Transformer Tap position details for your comments,At present we run transformer with Tap position (OFF-Load-Tap changer)No. 2

TAP POSITION VOLTAGE

1 34650

2 33825

3 33000

4 32175

5 31350

We can go up to Tap position no.5 considering the Voltage Drop.

Regards

Suryakant Jatania

Dear Guest ,

From your case thatCore-2 of Both CT-1 and CT-2 are having Ps class which are used for Differential and E/F Ref protections.I also note that new CTs 2000A are having roughly twice RCt value of old 1500A CTsRct ValueI

These higher RCt values of the proposed CTs will give higher Knee point Voltsage (Vk) during fault condition than the knee point voltage produced by old CTS with less RCt values and the increased VK values are more than sufficient for operation of connected protective Differential Relay and Restriced E/F Relay .This highervalue of knee point voltage Vk should not cause any problem for the operation of these relays since giveing higher knee point voltage is always better and will not surely cause saturation of Cts during faults..Only cost of CTs increases.

Hope this clear

V.Ambarani

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Ever see an oil filled transformer blow up? It is spectacular! But... you are going to get to see it up close and personal. Buy a new transformer.

Dear Friend

While you have a valid point, I take it for granted, since it is a basic protection feature for this size of transformer, that oil over temp. protection equipment is provided & therefore blowing up of transformer is a remote possibility. But if such a catastrophic situation does arise, then it is like a bomb explosion!!! Very very serious problem.

Thanks and regards

Ashok Toshniwal, Bangalore, India