# How to install and use the current transformer terminal block?

How to install and use the current transformer **terminal block**?

The principle of current transformer is based on the principle of electromagnetic induction. The current transformer consists of a closed core and a closed core. Its primary winding turns are very few, and they are connected in the circuit of the current to be measured. Therefore, it often has all the current flowing through the line, and the number of secondary winding turns is relatively large. It is connected in series in the measuring instrument and protection circuit. When the current transformer is working, its secondary circuit is always closed. Therefore, the impedance of the series coil of the measuring instrument and the protection circuit is very small The working state is close to short circuit.

Current transformer connection mode

Rated transformation ratio and error: rated transformation ratio kN of transformer refers to rated voltage ratio of voltage transformer and rated current ratio of current transformer. The former is defined as the ratio of rated voltage u1n of primary winding to rated voltage u2n of secondary winding, while the latter is the ratio of rated current i1n to I2n. Namely, kn = u1n / u2n (for voltage transformer) kn = i1n / I2n (for current transformer)

When the primary side voltage (or current) of voltage (or current) transformer changes within a certain range, it is generally specified that it is 0.85-1.15u1n (or 10-120% i1n). The secondary side voltage (or current) should change proportionally, and the primary and secondary side voltage (or current) should be in the same phase. However, due to the internal impedance, excitation current, loss and other factors of the transformer, the ratio and phase errors appear, which are called ratio difference and angle difference respectively.

The ratio difference is the ratio of the difference between the converted secondary voltage (or secondary current) and the primary voltage (or primary current) to the latter, that is, Fu is the specific difference of voltage transformer and fi is the specific difference of current transformer. When knu2 > U1 (or kni2 > I1), the ratio difference is positive, otherwise it is negative.

For the voltage transformer without compensation measures, the ratio difference is negative, and the angle difference is generally positive. The absolute value and angle difference of the ratio difference decrease with the increase of voltage; when the core is saturated, the ratio difference and angle difference increase with the increase of voltage. For the current transformer without compensation measures, the ratio difference is negative and the angle difference is positive. The absolute value and angle difference of the ratio difference decrease with the increase of current. The error of transformer can be reduced by means of compensation. Generally, additional winding or core is added to the transformer, and the corresponding resistance, inductance and capacitance components are connected to compensate. The common compensation methods include turn number compensation, fractional turn compensation, small core compensation, shunt capacitor compensation, etc.