# General Electrical Engineering Questions – 1

1. Insulated cables are usually rated by their :

The operating voltage decides the breakdown capacity of the cable and due to the current flowing through the cable; the temperature can be raised in that insulating medium. So, once it goes beyond the over limit the insulation medium burns immediately. That is why the insulating cables are usually rated by their operating voltage and the highest operating temperature.

2. What is cable tray?

Cable tray is nothing but the shield or cover for protecting the number of separate cables from outer side forces. Hence, all cables are presented inside the tray and finally the top cover can be closed.

3. _________ cannot sustain much voltage fluctuations.

Other than the incandescent lamp, all the above mentioned lamps are having the booster chock coil. The incandescent lamp is directly connected with the power supply. So, the filament coil is affected a lot by this fluctuation. Thus, it cannot be sustained much voltage fluctuations.

4. Class B insulators can bear temperature (in degree centigrade) upto

The temperature rating for different insulation class are following -
B 130°.
E 120°.
A 105°.
Y 90°.

5. Excess 3 code is known as?

The self complementing is a key feature of the excess – 3 code. That is, the 1's complement of an excess - 3 number is the excess - 3 code for the 9’s complement of the corresponding decimal number. The 1's complement can be easily produced with the logic circuit by inverting it. The self complementing property makes the excess - 3 code useful in some arithmetic operations, because subtraction can be performed using the 9’s complement method.

6. Permittivity of free space is equal to

Permittivity of free space is equal to 8.84 × 10-12 F/m.

7. Capacitor banks are connected with ac induction motor

We know that the induction motors are inductive loads. So, the power factor is lagging in nature. Hence, we are provided the capacitor banks for improving the power factor and maintaining it in good rating. For that, the capacitor banks are connected in parallel with the terminal of the induction motor.

8. By looking at which part of the motor it can be easily confirmed that a particular motor is D.C motor?

Commutator is the part of a DC motor (or) DC generator that serves the following dual functions. The first one is the commutator is providing the electrical connections via brushes to the armature winding. The second one is the commutator acts as a rotary converter to convert the DC power into AC power (or) the AC power into DC power. So, in the motor mode, the commutator acts as an inverter and in the generator mode, the commutator acts as a rectifier. Thereby, we can identify a DC motor which has the commutator in it.

9. In regenerative braking which of the following is true?

In the regenerative braking (during braking period), the armature winding of the DC motor is kept open and the field winding is kept in power supply connection. Due to that, it is operated as a generator and its output is supplied to the connected electrical loads. Hence, the transfer of energy to the load provides the braking effect and finally the shaft of the motor comes to rest position.

10. Which of the following statements regarding single-phase induction motor is correct?

When the single phase power supply is connected with the motor, the main winding is excited from a single phase supply and it produces an alternating magnetic field instead of rotating magnetic field. According to double field revolving theory any alternating vector can be resolved into two vectors rotating in opposite directions, each having magnitude equal to one half the magnitude of the actual vector. The vectors will be rotating in such a way that their resultant will be zero at every instant. Thus a single phase induction motor fails to produce a net starting torque. Hence it is not a self starting motor.

11. 25 kV, 50 Hz, 1 - φ supply is used for supplying power to the locomotives throughout India except which zone ?

The west zone of the Indian railway is coming under the Mumbai suburban railway Ltd. They are using the 1500 Volts DC electric traction system. Since, it is being converted into 25 KV, 50 Hz, single phase AC system.

12. Three resistors, each of R ohms, are connected to form a triangle. The resistance between any two terminals will be

The three resistors are connected in delta connection (as triangle). So, in delta connection, two series resistors are connected across with one resistance in between any two terminals in that circuit. Now we have 2R || R. Therefore, the equivalent resistance is equal to [(2R × R) / (2R + R)] = (2/3) R.

13. A 100 W bulb is connected in series with a room heater. If now 100 W bulb is replaced by a 40 w bulb, the heater output will

Compared to the 100 Watts bulb, the 40 Watts bulb has greater resistance. So, the voltage drop across the 40 Watts bulb is more than the 100 Watts bulb. Since, the bulb is connected in series with the heater. So, the voltage across the heater is reduced. Hence, the output heat generation from the heater will decrease.

14. Which of the following statements is false in case of a series circuit?

In a series electric circuit, the current is same and the voltage drops across the connected loads are varied depends on the internal resistance of each load. So, the "option B" is wrong.

15. Which of the following quantities are same in all parts of a series circuit?

In a series electric circuit, the current is same and the voltage drops across the connected loads are varied depends on the internal resistance of each load.

16. Conductance is the reciprocal of what?

Conductance means that allows the electric current to flow through a electric current carrying conductor. So, the reciprocal of conductance is that the opposition of the electric current flow through a conductor. It is nothing but the resistance which opposes the electric current flowing through the conductor.

17. You have to replace 1500 Ω resistor in radio. You do not have any 1500 Ω resistor but have several 1000 Ω ones which way you would connect them ?

If we connect two 1000 Ω resistors in parallel, then the total resistance is the 500 Ω. Now, if we connect this parallel combination of two 1000 Ω resistance in series with another 1000 Ω resistance, then the total resistance is 1500 Ω. Hence, we need three 1000 Ω resistors with the connection of two in parallel and one in series.

18. Bulbs in street lightning are all connected in which format?

We need to apply full rated supply voltage to all street lights. So, the voltage should be same across the terminal of the lights. If we connect all the lights in parallel, then the voltage across each bulb is same. That is why all street lights are connected in parallel.

19. 1 newton metre (N - m) = ?

The Newton meter is nothing but that is equal to torque resulting from a force of one Newton applied perpendicularly to an arm which is one meter long. It is also used less commonly as a unit of work or energy. Another unit of energy or work is joule. Therefore, the one Newton meter is equal to one joule.

20. In a delta network each element has value R. The value of each element in equivalent star network will be equal to

The formula for getting the equivalent resistance REQ = (Rb + Rc) / (Ra + Rb + Rc). Now, all the resistances are same. Hence, REQ = (R × R) / (R + R + R) = (R2) / (3R) = R / 3.