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
Electrical Machines
Current Transformer (CT) – Construction and Working Principle
A current transformer (CT) is a type of transformer that is used to measure AC current. It produces an alternating current (AC) in its secondary which is proportional to the AC current in its primary. Current transformers, along with voltage or potential transformers are Instrument transformer. Current transformers are designed to provide a scaled-down replica of the current … [Read more...] about Current Transformer (CT) – Construction and Working Principle
Practical Transformer on No Load
Please read Ideal Transformer and Practical Transformer before continuing. Consider a practical transformer on no load i.e., secondary on open-circuit as shown in figure below. The primary will draw a small current I0 to supply (i) the iron losses and (ii) a very small amount of copper loss in the primary. Hence the primary no load current … [Read more...] about Practical Transformer on No Load
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 … [Read more...] about Ideal Transformer and Practical Transformer