0
0 List of Frequently asked interview questions with answers under the subjects like electrical machines, Transmission and distribution, Power electronics and some general basic questions.
Part 2 : Question 26 to 50.
26. Define IDMT relay?
It is an inverse definite minimum time relay.In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates.It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.
27. What are the transformer losses?
TRANSFORMER LOSSES – Transformer losses have two sources-copper loss and magnetic loss. Copper losses are caused by the resistance of the wire (I2R). Magnetic losses are caused by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measurable loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss, however, is different for each frequency passed through the transformer.
28. what is the full form of KVAR?
We know there are three types of power in Electricals as Active, apparent & reactive. So KVAR is stand for “Kilo Volt Amps with Reactive component.
29. Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?
Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is constant across the bulb(P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is more (V=IR) so 40W bulb will glow brighter.
30. Why temperature rise is conducted in bus bars and isolators?
Bus bars and isolators are rated for continuous power flow, that means they carry heavy currents which rises their temperature. so it is necessary to test this devices for temperature rise.
31. 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 windmills.
32. What is Automatic Voltage regulator(AVR)?
AVR is an abbreviation for Automatic Voltage Regulator.It is important part in Synchronous Generators, it controls theoutput voltage of the generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator.
33. Difference between a four point starter and three point starter?
The shunt connection in four point stater is provided separately form the line where as in three point stater it is connected with line which is the drawback in three point stater
34. Why the capacitors works on AC only?
Generally capacitor gives infinite resistance to dc components(i.e., block the dc components). it allows the ac components to pass through.
35. How many types of Cooling system in transformers?
1. ONAN (oil natural,air natural) 2. ONAF (oil natural,air forced) 3. OFAF (oil forced,air forced) 4. ODWF (oil direct,water forced) 5. OFAN (oil forced,air forced)
36. Operation carried out in Thermal power stations?
The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine , the turbine which is coupled with the generator generates the electricity.
37. 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.
38. What is the principle of motor?
Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.
39. What is meant by armature reaction?
The effect of armature flux to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.
40. 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 windmills.
41. What’s MARX CIRCUIT?
It is used with generators for charging a number of capacitor in parallel and discharging them in series.It is used when voltage required for testing is higher than the available.
42. What are the advantages of speed control using thyristor?
Advantages : 1. Fast Switching Characterstics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate.
43. What is ACSR cable and where we use it?
ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.
44. What’s the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?
Uninterrupt 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.
45. What will happen when power factor is leading in distribution of power?
If their is high power factor, i.e if the power factor is close to one: a)Losses in form of heat will be reduced, b)Cable becomes less bulky and easy to carry, and very cheap to afford, & c)It also reduces over heating of tranformers.
46. What are the advantages of star-delta starter with induction motor?
(1). The main advantage of using the star delta starter is reduction of current during the starting of the motor.Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.
48. 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.
49. What is rated speed?
At the time of motor taking normal current (rated current)the speed of the motor is called rated speed. It is a speed at which any system take small current and give maximum efficiency.
50. If one lamp connects between two phases it will glow or not?
If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow.
50 Electrical Interview Questions with Answers updated on Sep 2019 Part 1
