Shunt Reactor:

• A shunt reactor is a piece of electrical equipment used in high voltage power transmission systems to stabilize the voltage during load variations. 
• When a reactor is connected in series with an electrical system or circuit then it is called Series Reactor.
• Whereas, when a reactor is connected in parallel with an electrical system or circuit then it is called Shunt Reactor.
• The main function of a Shunt Reactor is to pass the current.
• Generally, the shunt reactor allows or passes the low-frequency signals or alternating current.
• A shunt reactor is also known as a current absorber.
• Shunt reactors have high internal resistance which blocks the current in normal conditions and passes the current in abnormal conditions.
• A three-phase shunt reactor is generally connected to 400 kV or above an electrical bus system for capacitive reactive power compensation of the power system and to control dynamic over-voltage occurring in the system due to load rejection.
• The shunt reactor should be capable of withstanding maximum continuous operating voltage (5% higher than the rated voltage in the case of a 400 kV system) under normal power frequency variation without exceeding the top spot temperature of 150°C at any part of the shunt reactor.

Shunt Reactor Use and Applications:

• Shunt Reactors are used to suppress the high capacitance effect in transmission and distribution systems.
• Shunt reactors are used in transmission and distribution systems, to adjust the high transient voltage.
• A shunt reactor is used as an excessive Reactive Power Absorber or compensator during low loads.
• Just like shunt capacitors, shunt reactors are also used in electrical substations for voltage balancing, power factor maintenance, improvement, etc.

Additional Information

Electrical Reactor:

• An electrical reactor is nothing but an inductor or inductive or magnetic coil.
• When an AC supply is applied across an inductive coil, it shows the inductive reactance property. The same does an electrical reactor.
• An electrical reactor works with an AC supply only, and it blocks the high-frequency signal and passes the low-frequency signal.
• Electrical reactors are designed in such a way that they have very low internal resistance and high inductance property. 
• The figure given below shows the different types of reactors in the power system.

Series Reactor Use and Applications:

• Series Reactors are used in electrical power transmission and distribution systems to limit the flow of high currents during abnormal conditions.
• Series Reactors are also used in parallel networks for load-sharing purposes.
• Series reactors are also used in electrical circuits for impedance balancing purposes.
• Series Reactors are used for neutral earthing purposes also.
• Series Reactors are used in some motor starter circuits to limit the high starting current.
• Series Reactors are used in Alternator Parallel operations to reduce the risk of the high short circuit during the abnormal condition.
• Series reactors are also used to limit fault current during harmonic and transient conditions.

Diversity Factor (F_D):

• The ratio of the sum of maximum individual demands to the maximum demand on the power stations is known as a diversity factor.

• • Where ∑MD is sum of individual maximum demand
  • MD is the Maximum demand on the system
• A power station supplies loads to various types of consumers whose maximum demands generally do not occur at the same time.
• Therefore, the maximum demand on the power station is always less than the sum of the maximum individual demands of the consumers.
• The diversity factors will always be greater than 1. 

Plant Capacity Factor (FPC):

It is the ratio of actual energy produced to the maximum possible energy that could have been produced during a given period.

Where, AD is average demand & PC is plant capacity

• The plant capacity factor is an indication of the reserve capacity of the plant.
• Reserve capacity = Plant capacity − Max. demand

Plant Use Factor (FPU):

It is ratio of kWh generated to the product of plant capacity and the number of hours for which the plant was in operation.

Where, Po 0s station output in kWh

PC is plant capacity

T is hours of use

Load Duration Curve:

When the load elements of a load curve are arranged in the order of descending magnitudes, the curve thus obtained is called a load duration curve.

Load flow analysis:

Schrage motor:

• Schrage motor is a polyphase commutator motor with shunt characteristics
• The rotor carries two windings, of which one receives current from the supply by means of collector rings, while the other is connected to the commutator
• It is a variable speed motor that was commonly used in low voltage applications
• It is treated as an inverted polyphase induction motor

• By varying the brush position the speed of the scharge motor can be obtained below and above synchronous speed
• Scharge motor can run on positive, negative, and unity slip therefore Scharge motor can work on all power factor
• Thus, scharge motor can be used for unity power factor

Additional Information

• Schrage motor is essentially a combination of wound rotor induction motor and frequency converter.
• The primary winding of schrage motor is on the rotor and three-phase supply is given to the primary with the help of three slip rings
• The secondary winding is on the stator and the secondary winding terminals are connected to the commutator via three sets of movable brushes
• Apart from primary and secondary, there is a third type of winding called tertiary winding which is connected to the commutator
• The primary and tertiary are housed in the same rotor slots and are mutually coupled
• The brush position can be changed by a wheel provided at the back of the motor
• The angular displacement between the brushes determines the injected emf into the secondary winding which is required for speed and power factor control

Concept:

Considered a sinusoidal Alternating wave of voltage and current

From the waveform:

Where Vm and Im are the maximum value of instantaneous voltage and current respectively.

v, i is the instantaneous value of voltage and current at any instant t.

ω is the angular frequency in radian/second.

And, ω = 2πf  

f is the frequency in Hz

ϕ is the phase difference between voltage and current

From the above three equations instantaneous value of voltage and current can be written as: is

Additional Information

PN Junction Diode:

• A unilateral device is a device that conducts only in one direction.
• p-n junction diodes conduct only when the p region is connected to higher voltage and n region is connected to lower voltage.
• When reverse biased, it acts as an open circuit.
• The symbol for a diode is as shown:

Schottky Diode: It is not a typical diode because it does not have a p-n junction.

It consists of a doped semiconductor (usually n-type) and metal, bound together as shown:        

Features:

• ​An important characteristic of a Schottky diode is its fast switching speed, as it doesn't allow the diode to reach saturation.
• This makes the Shottky diode useful for high-frequencies and digital applications.
• Schottky diode is also known as the Schottky barrier diode, surface barrier diode, majority carrier device, hot-electron diode, or hot carrier diode.
• Its symbolic representation is as shown:-

Tunnel Diode:

Symbol:

• It is a highly doped PN Junction diode, used for low voltage high-frequency switching applications.
• It works on the tunneling principle.
• When compared to a normal p-n junction diode, the tunnel diode has a narrow depletion width.
• In normal forward-biased operation, it exhibits the “Negative resistance region” as shown:
• The negative differential resistance in their operation, allows them to be used as oscillators, amplifiers, and switching circuits.
• Their low capacitance allows them to function at microwave frequencies.

​Varactor Diode:

• It is represented by a symbol of diode terminated in the variable capacitor as shown below:

• Varactor diode refers to the variable Capacitor diode, which means the capacitance of the diode varies linearly with the applied voltage when it is reversed biased.
• The junction capacitance across a reverse bias pn junction is given by

• As the reverse bias voltage increases, the depletion region width increases resulting in the decrease in the junction capacitance.

Zener diodes:

• Zener diodes are normal PN junction diodes operating in a reverse-biased condition.
• Working of the Zener diode is similar to a PN junction diode in the forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold/breakdown voltage.
• Zener diodes also called avalanche diodes or Breakdown diodes  are the heavily doped P – N junction diodes
• It is operated in a breakdown region.

The symbolic representation of the Zener diode is as shown:

• A Zener diode is used as a voltage regulator in reverse biased mode.
• The breakdown voltage in the Zener diode when connected in the reverse-biased is called Zener voltage.
• This Zener voltage is steady and constant and it has huge applications in circuits, most importantly, voltage regulation.
• From the above explanation, we can see that the Zener diode is fabricated by heavily doped p-side and lightly doped n-side, which helps it in operating in reverse bias.

Different Forms of Alternating Voltage:

The standard form of an alternating voltage is given by:

Where,

v is the instantaneous value of voltage

V_m is the maximum value of voltage

From the above equation following point can be noted:

• The maximum value of alternating voltage is given by the co-efficient of sine of the time angle i.e. Maximum value of voltage = Co-efficient of sine of time angle
• The frequency f of alternating voltage is given by dividing the co-efficient of time in the angle by 2π i.e.,
  f = Co-efficient of time in the angle/2π

Concept:

The forward slip (S) in a 1ϕ induction motor is given by:

When rotation of the rotor reverses, the slip produced is known as ip (S_b).

Hydro Power Plant:

• The Hydro-electric power plant has a high initial cost, least running & maintenance cost among all types of power generation plants.
• The initial cost of the hydro-electric power plant is very high due to the dam structure, and other essentials.
•  Because Hydro-electric power plant has fewer moving equipment, a rigid structure then the operating and maintenance cost reduces.
• Another factor in operations is the fuel cost which is practically free for hydro stations.
• Where a typical coal-fired plant is has a coal handling unit, a DM water unit, a generating unit, a cooling water unit, and an ash handling unit while a hydro plant has a generating unit only.
• The electricity produced from the kinetic energy of flowing water is called hydroelectricity and a plant that generates electricity on a large scale from flowing water is called a hydroelectric power plant.
• The requirements for a hydroelectric power plant are a strong, fast flow of water and a significant drop down in which the water can fall.
• In a hydroelectric power plant, more electrical power can be generated, if water falls from a greater height because the rise in water level causes the increase in potential energy of water.
• Thus, when it flows from a higher position more amount of kinetic energy is formed by the conversion of higher potential energy and this kinetic energy in the form of moving water can produce more electrical power.

Track Rask:

• It is used in hydro-electric power plant to filter the water before it flows
• towards turbine.
• The unwanted impurities (e.g. fish, plastics, etc.) present in the
• stored water is avoided to flow towards the turbine. 

Spillway:

• The excess water from the dam is discharging through the spillway at a permissible level.
• It is also known as the safety valve of the dam.

Surge tank:

A surge tank (or surge chamber) is a device introduced within a hydropower water conveyance system having a rather long pressure conduit to absorb the excess pressure rise in case of a sudden valve closure.

Surge tanks are usually provided in high or medium - head plants when there is a considerable distance between the water source and the power unit, necessitating a long penstock. 

The main functions of the surge tank are:
1. When the load decreases, the water moves backward and gets stored in it.

2. When the load increases, an additional supply of water will be provided by the surge tank

Forebay:

• Instead of a surge tank, some hydro-electric power plants used Forebay.
• The Forebay is useful as the surge due to a change in load occurs.
• Forebay is an enlarged body of water at the intake (dam) to store more quantity of water.
• It is nothing but regulating reservoirs.
• Forebay stores the rejected water as the load on the turbine decreases & supplies water immediately when loading on turbine increases i.e. it is nothing but a surge tank for a small capacity hydropower station.

In a three-phase induction motor, any one of the rotors is employed.

1) Double cage rotor

2) Wound rotor

In the slip ring induction motor, a wound rotor is used whereas, in the squirrel cage induction motor, a double cage rotor is used.

Additional Information

Slip Ring Rotor or Wound rotor:

• It consists of a laminated cylindrical core and carries a 3-phase star-connected winding.
• The open ends of the rotor winding are brought out and joined to three insulated slip rings mounted on the rotor shaft with one brush resting on each slip ring.

• The three brushes are connected to a 3-phase star-connected resistance by slip ring as shown.
• At starting, the external resistances can be added to the rotor circuit to give a large starting torque.
• These resistances are gradually reduced to zero as the motor runs up to speed.
• The external resistances are used during starting period only.
• When the motor attains normal speed, the three brushes are short-circuited so that the wound rotor runs like a squirrel cage rotor.

Squirrel cage rotor:

• It consists of a laminated cylindrical core having parallel slots on its outer periphery.
• One copper or aluminum bar is placed in each slot. All these bars are joined at each end by metal rings called end rings.
• This forms a permanently short-circuited winding which is skewed by some angle.

• The rotor is not connected electrically to the supply but has current induced in it by transformer action from the stator.
• Most of the 3-phase induction motors use squirrel cage rotors because of their simple and robust construction enabling them to operate in the most adverse circumstances.
• It suffers from the disadvantage of a low starting torque. It is because the rotor bars are permanently short-circuited and it is not possible to add any external resistance to the rotor circuit to have a large starting torque.