Search Previous Year Questions

The correct answer is option 1): AC; AC

Concept:

• AC Voltage Controller is a thyristor-based device which converts fixed alternating voltage directly to variable alternating voltage without a change in frequency.
• The ac voltage controller is a static power electronic circuit that converts fixed ac to variable ac.
• It accomplishes this task without a change in frequency. It finds application in heating, lighting circuits, speed control of ac machines, fan regulators, etc, similar to the applications of an autotransformer.
• The circuit of the ac voltage controller is based on either thyristors, TRIACs, SCRs, or IGBTs.

Additional Information A Single-phase full-wave ac voltage controller using SCR’s Shown below.

The correct answers are option 3): Unpolarized

Concept:

Electrolytic capacitor is a polarized,unidirectional capacitor are specially designed for operate in Direct current circuits.

Unpolarized capacitor:

A non-polarized capacitor is a type of capacitor that has no implicit polarity.

It can be connected either way in a circuit.

It operates on pure AC circuits.

They are mainly used in circuits of coupling, decoupling, feedback, compensation, and oscillation.

The symbol for polarized and non polarized capacitor  are

​

Economic load dispatch

• In power system analysis and optimization, the B-coefficient loss formula is frequently used to estimate network losses.
• The losses are expressed in terms of the penalty factor.
• The penalty factor in the power system is a factor (greater than unity) by which the incremental cost of power production of the plant must be multiplied to accommodate for transmission losses.
• The penalty factor is given by:

Penalty factor = \({1\over 1-{dP_L\over dP_n}}\) 

where, \({dP_L\over dP_n}=\) Loss factor

In a transmission line, the capacitors are installed in a parallel (admittance) branch.

The problem associated with Series capacitors are:

• The series compensated line produces series resonance at frequencies lower than power frequencies. This is known as sub-synchronous resonance. The sub-synchronous produces mechanical stress due to which high torsional stress occurs in the rotor shaft.
• Series capacitors produced high recovery voltages across the breakers contact.
• If the degree of compensation and location of capacitors are not proper, the distance relays used for line protection may not function properly.
• Switching in of an unloaded transformer at the end of a series compensation of the line may produce non-linear resonance or Ferro resonance. This may result in uninterrupted oscillations.

The correct answer is option 4):(from the input of the inverter)

Concept:

• The inverter is a power electronics device used to regulate the flow of electrical power
• The inverter is used to accomplish the DC-to-AC conversion by switching the direction of a DC input back and forth very rapidly.
• As a result, a DC input becomes an AC output.
• The battery used in an inverter is connected to the input of the inverter
• The diagram for ups is drawn given as

The correct answer is option 2):(on the stator)

Concept:

• The stator has pairs of poles
• each pair of which is activated and made into an electromagnet by a current being passed through the coils wrapped around it.
• When one pair of poles is activated, a magnetic field is produced that attracts the nearest pair of rotor teeth so that the teeth and poles line up.
• The Dc machine Diagram is shown as

The correct answer is option 2):(TRIAC)

Concept:

• TRIAC is a three-terminal electronic component that conducts current in either direction when triggered
• Triac is a non-linear device, a switch. That means it has no predominant linear region to amplify a signal, and is not used as an amplifier.
• TRIAC is designed to carry high currents. The control terminal is used to control the power to the load by varying the phase angle.
• A transistor has a predominant and useful linear region and can amplify voltage/current
• when supplied by a voltage source. The control terminal of the transistor is used to vary the output amplitude. The  SIT, MOSFET, IGBT are Transistor

Additional Information

The correct answer option 1):(HVDC)

Concept:

• HVDC stands for High Voltage DC transmission system
• HVDC allows power transmission between AC transmission systems that are not synchronized.
• Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power.
• HVDC also allows the transfer of power between grid systems running at different frequencies, such as 50 and 60 Hz.
• This improves the stability and economy of each grid, by allowing the exchange of power between incompatible networks

Neural network laying is not used for laying underground cables.

Laying Of Underground Cables

1.) Direct Laying Of Underground Cables

• A trench of about 1.5 meters deep and 45 cm wide is dug.
• Then the trench is covered with a 10 cm thick layer of fine sand.
• The cable is laid over the sand bed. The sand bed protects the cable from moisture from the ground.
• Then the laid cable is again covered with a layer of sand about 10 cm thick.
• When multiple cables are to be laid in the same trench, a horizontal or verticle spacing of about 30 cm is provided to reduce the effect of mutual heating.
• Spacing between the cables also ensures a fault occurring on one cable does not damage the adjacent cable.
• The trench is then covered with bricks and soil to protect the cable from mechanical injury.

2.) Draw-In System

• In this method, cast iron or concrete pipes or ducts are laid underground with manholes at suitable positions along the cable route.
• The cables are then pulled into the pipes from the manholes.
• Usually, an additional pipe/duct is also provided along with the three cable ducts for carrying relay protection connections and pilot wires.

3.) Solid System

• In this method, the cable is laid into troughing of cast iron, stoneware, asphalt, or treated wood.
• When the cable is laid into the position, the troughing is filled with bituminous of asphaltic compound and then covered over.
• Cables to be laid in this manner could be just lead-covered as the troughing provides good mechanical protection.

Commutator pitch winding

The distance between the two commutator segments to which the two ends of a coil are connected is called commutator pitch (Y_C).

In commutator pitch winding:

• Number of commutator segments = number of armature coils
• The diameter of the commutator will generally be about (60 to 80)% of the armature diameter.
• The segments of the commutator are insulated from each other and the armature shaft.
• The purpose of the commutator is to rectify the waveform.