Current Transformers

Thank you Very Very Very Very!!!!!!! much. I appreciate your prompt response. In my MV board the terminal is connected to the respective phase bus bar on the CT installed to some phase line indication lights in front of the panel. My main question: How is the potential equalization realized, because of the connection on the CT capacitor terminal.

The terminal on the CT with capacitor symbol marking may probably be tapped from the outer wall of the CT's insulated enclosure. This outer end of the CT enclosure (and thus the terminal marked with the capacitor symbol) forms one plate of a capacitor. The inner wall of the CT which is in proximity to the live bus bar forms the other plate of a capacitor. There is a solid dielectric (may be epoxy resin) between these two plates. This construction of two plates seperated by a dielectric is called a capacitor. Isn't it? Now, when to short the outer terminal on the CT to the bus bar of the phase on which this CT is mounted, you are literally shorting the two plates of this capacitor (i.e.) the potential between the inner and the outer walls of the CT will be same. There will not eb any potential differenec and hence no capacitive leakage currents thro the CT insulation, thus saving the insulation deterioration.

And, the indication lights installed in the front of the panel are called "Live Line Indicators". They work on the principle of Capacitor Potential Divide. You take an insulator. One end of the insulator is at the bus voltage and the other end of the insulator is at ground potential (thro the mounting bolt). The insulator is a dielectric. Now, the two ends (the bus end and the panel end) of this insulator form plates of a acpacitor and the insulating medium of the insulator is the dielectrc, thus forming a capacitor. Even though you would see a solid insulator, it, in fact, is made up of discreet smaller cell capacitances. Now, if I tap a wire from the centre of the insulator, I can mesaure approximately half the phase voltage of the bus bar which is mounted on to this insulator. As the tapping point is nearer to the bus you would get more voltage and as you tap nearer to the panel end, you would get less voltage. Now, if can locate a point on the surface of the insultor, where if I tap, I can get, say, 110V, can I not use this to power an indication lamp? And, as the voltage on the bus bar varies, the tapped voltage also varies very linearly, thus indirectly performing the function of a Potential Transformer. The only problem in such an arrangement is that this capacitor potential divide cannot drive a large current thro the burden. SO, ot may work for smaller burdens like an LED lamp. In one of my previous employments, I have developed a digital voltmeter, which would work on signals from this capacitive potential divider. Such an arrangement, we used to call, "Voltage Sensors".

Thank you very much. Your immense contribution to this matter cannot be over stated. Thank you very much.

We just wrote to ABB to provide us with a logical explanation why they have made such changes. Presently, nothing has been said yet. Thank you very much and have a wonderful afternoon.

Good afternoon,

Please i am in search of professional certifiactions i need to better position myself as an elctrical and instrumentation engineer. I have been involved in the contruction and installation of gas turbine power station and presently i am involved in the revamping of an oil and gas flow station(electrical). I have been searching the internet for professional certifications i can obatin that will enable me work as a professional, internationally. Please can u help me with any information. Thank you in anticipation.

Presently, i only have a university degree in electrical electronics engineering.

Regards,

ifidon

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