[Guide]The rated transformation ratio of the transformer KN refers to the rated voltage ratio of the voltage transformer and the rated current ratio of the current transformer. The former is defined as the ratio of the rated voltage U1N of the primary winding to the rated voltage of the secondary winding U2N, and the latter is the ratio of the rated current IIN to 12N.
That is KN=U1N/U2N (for voltage transformer)
KN=I1NI2N (to current transformer) voltage (or current) transformer primary voltage (or current)
When it changes within a certain range, it is generally specified as 0.85~1.15U1N (or 10~120%I1N), the secondary voltage (or current) should change proportionally, and the primary and secondary voltage (or current) should be in phase. However, due to the internal impedance, excitation current, and loss of the transformer, the ratio and phase errors are called ratio differences and angular differences, respectively. The ratio difference is the ratio of the difference between the converted secondary voltage (or secondary current) and the magnitude of the primary voltage (or primary current) to the latter, that is, fU is the ratio difference of the voltage transformer, and fI is the current transformer The ratio is worse.
When KNU2>U1 (or KNI2>I1), the ratio difference is positive, otherwise it is negative. The angle difference is the angle between the secondary voltage (or secondary current) phasor after 180% rotation and the primary voltage (or primary current) phasor, in cents. It also stipulates that when the secondary side’s concubine 2 (or one to 2) is ahead of concubine 1 (or to be 1), the angle difference is positive, and vice versa. For voltage transformers that have not been compensated, 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 iron core is saturated, the ratio difference and the angle difference Both increase with the increase of voltage.
For current transformers without compensation measures, the ratio difference is negative and the angle difference is positive. Both the absolute value and the angle difference of the ratio difference decrease with the increase of current. Using compensation methods can reduce the error of the transformer. Generally, it is compensated by adding additional windings or adding additional iron cores on the transformer, and connecting corresponding resistance, inductance, and capacitance elements. Commonly used compensation methods include turns compensation, fractional turns compensation, small iron core compensation, shunt capacitance compensation and so on.
