Ground Wire / Sky Wire / Shield Wire in Transmission Line

Protection of Power Transmission Line from the effect of Lightening is achieved by using Sky Wire which is also known as Ground Wire or Shield Wire.   A direct Lightening Strike on a Power line or induced voltage from a nearby Lightening Strike may lead to the line flashover or insulation failure of transformers, arrestors … Read more

Difference between Isolator and Circuit Breaker

Isolator and Circuit Breaker both are switches to isolate a section of power system. But Isolator is off load device whereas Circuit Breaker is on load device. Off load device means, Isolator cannot be operated when load is connected i.e, current is flowing through the circuit. Therefore, Isolator shall only be operated when that circuit … Read more

Why Transformer Rated in kVA and not in kW?

Not only Transformers, even Alternators are rated in VA, kVA or MVA etc. The rating of a Transformer depends on the winding or oil temperature reaching the specified limiting value which is decided by the type of insulation minus a safety margin, something like 170 – 20 =150 °C. Now the temperature rises because of … Read more

Why Swamping Resistance in Ammeter?

Swamping Resistance in Ammeter can be well understood if we investigate the Effect of Temperature change in the Reading of an Ammeter. Ammeter is basically moving Coil instrument and flow of current through the coil decides the deflection of Ammeter. Now if there is change in the temperature then correspondingly there will also be a … Read more

Why we Replace Voltage Source with Short Circuit and Current Sources with Open Circuits in Thevenin’s and Norton’s Theorem?

We don’t really replace the voltage sources with shorts rather we make the voltage of the voltage sources zero volts.  An ideal voltage source has zero internal impedance by definition of being “ideal”, so if we reduce its voltage to zero, we are left with a zero impedance source, which is a short circuit.  An … Read more

Concept of Transient State and Steady State

The terms Steady State or Transient State is defined not only for electrical systems, but for many other physical systems also. The transient response does not depend on the source i.e. forcing function, applied. It is purely natural response. Mostly transient response is associated to on/off events. Previously the circuit is switched off. Now it … Read more

Purpose of Centrifugal Switch in Induction Motor

In the common Induction Motor which are used in drill presses, furnaces, table saws, pumps, grinders, washers and dryers, normally have a Centrifugal Switch. Centrifugal Switch is required together with an additional winding to start the motor. An induction motor has no copper windings in the turning rotor part; windings are only in the fixed … Read more

Why Inductor is Short Circuited in DC?

As we know that from, Faraday law that a varying current will induce voltage in a coil. When a current passes through a coil it will generate its own magnetic field and this field cuts the same coil producing an emf across it by self induction (L=Coefficient of self induction).     The current which … Read more