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The correct answer is option 3):(two coils: one current coil and one potential coil)

Concept:

Wattmeter:

• A wattmeter is an electrical instrument that is used to measure the electric power of any electrical circuit.
• The internal construction of a wattmeter is such that it consists of two coils.
• One of the coils is in series and the other is connected in parallel. The coil that is connected in series with the circuit is known as the current coil and the one that is connected in parallel with the circuit is known as the voltage coil Wattmeter measures the average power.
• The reading of wattmeter will be,

Average power = Vpc Icc cos ϕ

Where,

Vpc is the voltage across the pressure coil

Icc is the current flows through the current coil ϕ is the phase angle between Vpc and Icc

• So, a wattmeter is a device capable of detecting voltage, current and the angle between the voltage and the current to provide power readings.

The correct answer is  option 3):(Same operating temperature)

Concept:

Essential and desirable conditions of parallel operation of DC generators are:

• Same drooping voltage characteristics
• Same voltage rating
• Same percentage of voltage regulation
• Same percentage speed regulation of the prime movers

The Same operating temperature is NOT a condition for parallel operation of DC generator

The correct answer is option 1):(Copper loss/Iron loss = 1)

Concept:

The efficiency of the transformer is defined as the ratio of  output to input power. 

efficiency = \(output:power\over input:power\)

= \(output:power \over output:power+loss\)

=\(output:power \over output:power+​​​​iron : loss +copper : loss\)

The maximum efficiency in a transformer that occurs at copper losses is equal to iron losses

Efficiency is maximum at some fraction x of full load.

x = \( \sqrt{Wi \over Wcu}\)

Where

Wi = iron losses

Wcu = copper losses

The correct answer is option 2):(0.03)

Concept:

Slip in Induction Motor is the relative speed between the rotating magnetic flux and rotor expressed in terms of per unit synchronous speed.

If N_s and N_r are the synchronous speed of rotating magnetic flux and rotor speed respectively, then the relative speed between them is equal to (Ns – Nr). Therefore, slip is defined as

\(N_s=\frac{120f}{P}\)

f is the frequency in Hz

P is the no of poles 

Calculation:

P = 6

f = 50 Hz 

\(N_s=\frac{120f}{P}\)

= \(120 × 50 \over 6\)

= 1000 RPM

Rotor speed N_r = 1000 ×  0.97 = 970 RPM

​\(s=\frac{N_s-N_r}{N_s}\)​

= \(1000 -970 \over 1000\)

=  0.03

The correct answer is option 1):(accumulator)

Concept:

• The secondary battery or charge accumulator is a cell or combination of cells in which the cell reactions are reversible.
• The secondary battery is rechargeble battery
• The basic electrochemical unit responsible for the actual storage of energy is called a Cell. A Cell, as just mentioned, is the fundamental electrochemical unit that is the source of electrical energy produced by the conversion of chemical energy.
• In its basic form, a cell typically contains three main components: two electrodes and an electrolyte and also consists of terminals, a separator and a container. Speaking of electrodes, there are two types of electrodes called the Anode and the Cathode.
• The Anode is the negative electrode (also called the Fuel Electrode or the Reducing Electrode). It loses electrons to the external circuit and in the electrochemical reaction, it gets oxidized.

The correct answer  is option 1):(Voltage control and reactivity electro-power control are related)

Concept:

Voltage Control:

• In power system networks, while supplying power through a transmission line,
• The voltage constant at the sending end. The voltage at the receiving end undergoes a change that does not depend on the load and power factor.
• Voltage control should therefore be considered in power system networks as the voltage changes while transmitting power from sending end to end.

Adjusting Reactive Power for Voltage Control

• For voltage control, reactive power flow should be adjusted and its reactive VAR is adjusted locally.
• In other words, locally adjusting the VAR means, generating the VAR in the system locally whenever it is required
• This could be achieved with the help of shunt capacitors or synchronous capacitors and also by shunt inductors in case of capacitive loads or light loads

The correct answer is option  4):(When neutral is not available)

Concept:

Grounding transformers are typically used to: 

• Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential.
• Limit the magnitude of transient overvoltages when restriking ground faults occur. Provide a source of ground-fault current during line-to-ground faults.
• The grounding transformer is used to provide a path to an ungrounded system or when the system neutral is not available for some reason.
• For example, when a system is delta connected. It provides a low impedance path to the neutral and also limits the transient overvoltage when the ground faults occur in the system.

The correct answer is option 4): (DC-DC converter)

Concept:

• A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another.
• It is a type of electric power converter. Power levels range from very low (small batteries) to very high (high-voltage power transmission).
• DC-DC converters are widely used to efficiently produce a regulated voltage from a source that may or may not be well controlled to a load that may or may not be constant
• DC Drives are functional circuitry designed to regulate the speed of the dc motor by offering precise control of the same.
• It facilitates starting, and stopping along with changing the direction and speed of the motor
• Choppers are used in speed-controlling dc motors. Generally, when a dc supply is given to the system than the case speed of the motor is controlled by the chopper. There are several advantages like high efficiency, controlling flexibility, lightweight, small size, fast response

The correct answer is option 1):Inductor 

Concept:

• A freewheeling diode is used to protect the circuit from unusual damage caused due to abrupt reduction in the current flowing through the circuit
• The purpose of the freewheeling diode is to overcome the impact of the inductive load at the output voltage,
• A freewheeling diode is used in parallel to the load that freewheels the energy stored in the inductor during the negative cycle of the input voltage as shown in Fig.

Bus bar Arrangements in Substations:

1.) Single bus-bar system

• It consists of a single bus-bar and all the incoming and outgoing lines are connected to it.
• The chief advantages of this type of arrangement are low initial cost, less maintenance and simple operation.
• However, the principal disadvantage of single bus-bar system is that if repair is to be done on the bus-bar or a fault occurs on the bus, there is a complete interruption of the supply.
• This arrangement is not used for voltages exceeding 33kV. The indoor 11kV sub-stations often use single Bus bar Arrangements in Substations.

2.) Single bus-bar system with sectionalization:

• In this arrangement, the single bus-bar is divided into sections and load is equally distributed on all the sections. Any two sections of the bus-bar are connected by a circuit breaker and isolators.
• Two principal advantages are claimed for this arrangement. Firstly, if a fault occurs on any section of the bus, that section can be isolated without affecting the supply from other sections.
• Secondly, repairs and maintenance of any section of the bus-bar can be carried out by de-energising that section only, eliminating the possibility of complete shut down. This arrangement is used for voltages upto 33 kV.

3.) Duplicate bus-bar system:

• This system consists of two bus-bars, a “main” bus-bar and a “spare” bus-bar. Each bus-bar has the capacity to take up the entire sub-station load.
• The incoming and outgoing lines can be connected to either bus-bar with the help of a bus-bar coupler which consists of a circuit breaker and isolators.
• Ordinarily, the incoming and outgoing lines remain connected to the main bus-bar. However, in case of repair of main bus-bar or fault occurring on it, the continuity of supply to the circuit can be maintained by transferring it to the spare bus-bar.
• For voltages exceeding 33kV, duplicate bus-bar system is frequently used.