Effect of Core Induction

By decreasing the iron core induction, the magnetization power, such as the loss power in the core, also decreases. The vacuum current is decreasing with an exponent greater than 1, so by decreasing the induction the CT errors decrease.

Thus, it is necessary to analyze the minimum allowed value of the induction. According to the norms, the current can vary between 10% and 120% of the nominal current, which means a ratio of 1:12. Essentially, the induction is within this ratio, but on the other hand the charge can vary from 25% to 100% of the nominal load, which means a ratio of 1: 4.        ORC4FJRMP36P61

The phasor representation shows that, neglecting the internal voltage drop due to the load variation, the induction (B) will vary close to the same ratio of 1: 4. Accordingly, between the ends one has to rely on a variation of the ratio of the induction of about 1:48.

The phasor representation shows how the nonlinear characteristic of the nucleus is causing the errors to increase, so the nucleus induction can not be unduly diminished. Between the ends of the 1:48 ratio, the errors must be within the specifications of the standard.

 

 

Effect of Core Induction