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I work in power plant, Can any body tell me about the burden of a C.T and P.T.


Hi Fuad,

Though I don't have experience in Power Plant (HT) CTs and PTs. But, what I understand from VA burden of a CT and PT is Power consumed by the instrument connected to it's output at full load.

For a PT, burden will decide how many instruments can be connected in paralle across it, provided burden of instruments are know. Similarly, for CT, it will decide how many instruments can be connected in series, provided its burden is know.




Asif Mansoori


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I work in power plant, Can any body tell me about the burden of a C.T and P.T.



Simple answer for CT's: CT (current transformer) Burden is the maximum load that the CT secondary can drive (e.g. meters or protection relays)


The below is excerpted from ... CURRENT TRANSFORMERS - The Basics and will provide you with a more accurate definition of CT burden. http://www.nktechnologies.com/pdfs/ct-tutorial.pdf



The third part of the CT Accuracy Class is the maximum burden allowed for the CT. This is the load that may be imposed on a transformer

secondary without causing an error greater than the stated accuracy classification. For Metering Class CTs burden is expressed as ohms impedance. For Protection-class CTs burden is express as volt-amperes (VA). Protection-class CT burdens are displayed as the maximum secondary volts allowable if 20 times the CT rating were to flow through the secondary circuit (100 amperes with a five-

ampere nominal CT secondary).



The PT—Potential Transformer is now referred to as VT—Voltage Transformer

Simple answer for PT's / VT's : The load connected to the secondary of the transformer is the burden.


The below is excerpted from ... http://www.uomschool.org/Meter_Book/Table%...%27s/VT%27s.htm


Burden Rating

The burden on a voltage transformer is the connected load. As more devices are connected to the voltage transformer the burden increases. This burden is usually calculated in volt amps. Two burden ratings are usually stated. The burden rating at the stated accuracy class is important for metering. Exceeding this rating will cause the voltage transformer to operate outside the required .3% accuracy class. The thermal burden rating is usually several times the burden rating stated for metering accuracy. Exceeding the thermal burden rating will shorten the life of the voltage transformer.



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