# What is burden in current transformer

FAQ | Feb 06,2023

The burden of the current transformer refers to the total impedance of the instrument, relay and connecting wire connected to the current transformer twice。

The impedance (current transformer) or admittance (voltage transformer) of the secondary circuit. Impedance or admittance within the transformer (the secondary winding itself) is not included. The load is usually expressed in terms of apparent power volt-ampere.

The burden of the current transformer is calculated as follows:
When calculating the burden of the CT, pay attention to the impedance conversion coefficient under different wiring modes and fault conditions.

The secondary burden of the CT can be expressed as impedance Z2(Ω) or capacity S(VA). The relationship between the two is: S=I2*I2*Z2

When the secondary current of the CT is 5A, S=25Z2

When the secondary current of the CT is 1A, S=Z2

The secondary burden rating (S) of the current transformer can be selected as 5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100VA.

Load calculation of current transformer for measurement.

Generally, the phase difference between impedances can be negative in engineering calculation. The calculation formula of secondary load Z2 is as follows:

Z2=Kcj.zkZcj+Klx.zkZlx+Zc

Where: Zcj——- Impedance of meter coil (Ω)

Zlx——- one-way impedance (Ω) of the connecting wire. Generally, the reactance can be ignored and only the resistance can be calculated.

Zc——- Contact resistance (Ω), generally 0.05~0.1(Ω).

Kcj.zk—- Impedance conversion factor of the meter

Klx.zk—- Impedance conversion factor of connecting wire

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