Rated Secondary Voltage

The nominal secondary voltage is defined according to ABNT [9] as “the voltage appearing at the terminals of a nominal load imposed on the CT at 20 times the rated secondary current, without the ratio error exceeding the specified value.” This means that the CT must withstand a maximum current in its secondary circuit proportional to 20 times its rated current without conducting errors higher than the one specified by its accuracy class.

The rated secondary voltage represents the maximum voltage that the CT must withstand under overcurrent conditions. The value 20 is set by the ABNT as the standardized value for the overcurrent factor. Only the protective duty CTs reach rated secondary voltage. In measuring CTs, the core saturates well before the secondary current reaches this value.

The ratio error depends on the impedance connected to the secondary circuit. The calculation of the total impedance of the circuit for practical purposes of specifying the

TC uses the nominal nominal loads as reference.

However, the CTs for protection service also have a consideration in calculating the impedance of the secondary circuit. ABNT subdivides these CTs into two classes for their impedance.


Synchronous Motors – Operation

Synchronous electric motors have two plausible excitation factors:

– direct current in the field winding;

– from the three-phase source of alternating current in the armature.    Gates Rubber 16/A42

The synchronous electric motor when operated in the overexcited and empty condition is called the synchronous capacitor and performs the same function as a capacitor bank, being more efficient than the static capacitors. If its field current is sufficient to compose the essential magnetomotive force, not requiring magnetization current or reactive power, the motor acts with unit power factor.

If your field current is less than is said necessary, saying that the motor is underexposed, the magnetomotive force deficiency needs to be completed by the armature, so the motor works with a delayed power factor. If your field current is greater than is declared necessary, we say that the electric motor is overexcited, the surplus of magnetomotive force must be carefully balanced in the armature and an advanced current device is present, the motor works with power factor in advance.