Synchronous motors are not self starting. Some additional devices should be used to start the motor. Basically there are two methods for starting synchronous motors: Induction motor starting (Damper winding) Auxiliary motor starting. Damper Winding Starting Most of the synchronous motors have salient pole structure. A winding consisting of heavy copper bars is … [Read more...] about Starting Methods for Synchronous Motor

# Electrical Machines

## Need of a Starter (3 & 4 Point) in DC Motors

We use 3 and 4 point starters in DC motors. What happens if a DC motor is started without a starter? Let's check it. Consider a dc motor at standstill. When a dc motor is at rest the speed of the motor is zero, therefore the back emf is zero. We know that Back Emf, Eb= V - IaRa Therefore, Ia = (V - Eb)/Ra Armature resistance Ra in a DC motor is very small. Now at rest … [Read more...] about Need of a Starter (3 & 4 Point) in DC Motors

## Why Current Transformer (CT) Seconday Should not be Open ?

Amazed why secondary of current transformer should not be open? If it is left open it may destroy the current transformer. So it is very important that the secondary of Current Transformer should not be kept open. The reason is quite interesting. Either it should be shorted or must be connected in series with a low resistance coil such as current coils of watt meter, coil of … [Read more...] about Why Current Transformer (CT) Seconday Should not be Open ?

## Ideal Transformer and Practical Transformer

Ideal Transformer An ideal transformer is one that has no winding resistance no leakage flux i.e., the same flux links both the windings no iron losses (i.e., eddy current and hysteresis losses) in the core Although an ideal transformer cannot be physically realized, yet its study provides a very powerful tool in the analysis of a practical transformer. In fact, … [Read more...] about Ideal Transformer and Practical Transformer

## Percentage Impedance of Transformer and Its Calculation

What is Percentage Impedance? The impedance of a transformer is the total opposition offered an alternating current. This may be calculated for each winding. However, a rather simple test provides a practical method of measuring the equivalent impedance of a transformer without separating the impedance of the windings. When referring to impedance of a transformer, it is the … [Read more...] about Percentage Impedance of Transformer and Its Calculation