Electrical Engineering Q/A 10 To 20

 1: What is load in Electrical Eng?

Any device which consumes electricity and converts it into another form of energy is called load. For e.g all the devices connected in our homes which runs on electricity are called as loads.

2: Give two basic speed control scheme of DC shunt motor?

By using flux control method:in this method a rheostat is connected across the field winding to control the field current.so by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled .armature control method:in this method a rheostat is connected across armature winding by varying the resistance the value of resistive drop(laRa) can be varied,and since speed is directly proportional to Eb-laRa the speed can be controlled. 

3: How to Reduce the Ferranti Effect in a Transmission Line?

Ferranti Effect in a transmission Line is reduced using voltage compensation which in turn is accomplished by Shunt Reactor. Shunt Reactor is just like a Transformer but it has only primary and no secondary. Shunt Reactor is connected to all the three phases i.e. R, Y and B phase.

4: What is 2 phase motor?

A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.

5: What is the difference between synchronous generator & asynchronous generator?

In simple, synchronous generator supply's both active and reactive power but asynchronous generator(induction generator) supply's only active power and observe reactive power for magnetizing. This type of generators are used in windmill's.

6: Define IDMT relay?

IDMT relays are protection relays. They are used on transmission lines to see that the line current doesn't exceed safe values and if it does, triggers the circuit breaker. IDMT means inverse definite minimum time. So as the current keeps increases, the relay takes minimum time to trip the circuit Inverse means "higher the current value, lesser the time taken for the relay to trip the circuit Current in the line and the time taken for the realy to trip the CB follow an inverse proportonality.

7: What is Latching current?

Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor starts conducting the forward current above the minimum value, called Latching current, the gate signal which is applied to trigger the device in no longer require to keep the scr in ON position. 

8: How is electrical energy produced?

Production of Electrical Energy is based on law of energy conservation that energy can neither be created nor destroyed. It can only be converted from one form to another.

Electricity is produced by converting different energies like solar, wind, hydro, nuclear, thermal, biogas to Electrical.

9: What is the purpose of transient analysis?

Transients means a sudden change. I.e whenever a disturbance is created in a system such as when equipments are turned on/of, so it results in suddent change in energy, this short burst of energy is called as transients. Transients means temporary i.e. something that comes and go. Like in a laymen term, imagine you are travelling in a bus, and suddenly bus stops and you move forward in bus due to inertia. That state will be your transient state.

Transient analysis is done to find out the impact of transients on our system. Although transients exists for very short duration but they can cause severe damage in that short time if our systems are not properly protected. So transient analysis is done to find out effect of transients on our system.

10: What is stranding and how it reduces skin effect to some extent?

Stranding means that instead of making wire as single solid conductor, we make it in the form of small wires that are called as strands. Basic purpose of doing stranding is to improve flexibility of conductor because a solid cable cannot be layed easily on a larger distance. By doing Stranding, conductor becomes flexible and can be layed easily over long distance.

Another reason of doing stranding is that it reduces skin effect. Because we know that, resistance is jinversely proportional to area. So, by doing stranding, net area of wire is reduced to some extent and resistance increases. When resistance increases so lesser skin effect will exist.