Electrical Engineering Q/A 51-to-60

 51: Explain the working principal of the circuit breaker?

Circuit Breaker is one which makes or breaks the circuit.It has two contacts namely fixed contact & moving contact.under normal condition the moving contact comes in contact with fixed contact thereby forming the closed contact for the flow of current. During abnormal & faulty conditions(when current exceeds the rated value) an arc is produced between the fixed & moving contacts & thereby it forms the open circuitArc is extinguished by the Arc Quenching media like air, oil, vaccum etc.

 52: In the motors starting purpose why the armature rheostats at maximum position while the field rheostat is kept in minimum position?

At the time of starting a motor, the field rheostat is kept in minimum state for the high starting torque.
At the time of starting a motor, the armature rheostats are used to control or reduce the high starting current. This high starting current can damage the motors starting systems.

53: What is the significance of vector grouping in Power Transformers?

Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN means Delta primary, Wye Secondry and the current is at o clock reffered to the voltage.

54: Advantages of vvvf drives over non vvvf drives for EOT cranes?

1. smooth start and stop.
2. no jerking of load.
3. exact posiitoning
4. better protection for motor.
5. high/low speed selection. 6. reliability of break shoe.
7. programmable break control.
8. circutry
9. reduction in controls
10. increases motor life

55: How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil?

It's possible by means of Electronic chokes,otherwise it's not possible to ionize the particles in tube light with normal voltage.

56: What is electric traction?

Electric traction means using the electric power for traction system (i.e. for railways,trams, trolleys etc). Electric traction means use of the electricity for all the above machines. Now a days, magnetic traction is also used for bullet trains.and basically dc motors are used for electric traction systems.

57: Why computer humming sound occurred in HT transmission line?

This computer humming sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.

58: What's the one main difference between UPS & inverter ? And electrical engineering & electronics engineering?

Uninterruptible power supply is mainly use for short time. means according to ups VA it gives backup. ups is also two types: on line and offline. online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 12v dc with 7 amp. but inverter is startwith 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup.

59: What is meant by armature reaction?

The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

60: What is Potential Transformer (PT)?

The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. This transformer step down the voltage to a safe limit value which can be easily measured by the ordinary low voltage instrument like a voltmeter, wattmeter and watt-hour meters, etc.