Define Insulation Resistance and its calculation!

A very significant maintenance procedure for checking out the working condition of an electrical system is called IR test or Insulation resistance. It can be said that ht system or equipment is fine when insulation resistance is high.

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Megger is an insulation resistance measurement tools for finding the equipment’s insulation resistance. Let us see how is the IR calculated?

Define Insulation resistance

There is an application of direct current (DC) and not alternating current (AC) and this is the first thing while doing the Insulation resistance test.

A permissible level of DC voltage is applied on the device and thus there will be current flow. While checking the insulation test for the earth equipment, there is no means of physical connection to them. The micro amps amount of current will be present between them.

As we all know that R= (V/I), this equation is for calculating the insulation resistance R. Another important point to note is that the total value of measured insulation resistance is small internal resistance of equipment + insulation resistance. The value of R will be low if the strength of the insulation is high you will have low value of R and if the insulation is weak there will be higher current with low IR.

Insulation resistance is affected by the following factors:

Conductive leakage current (IL)

It is a small amount of current that flows through normal insulation, from a conductor to ground or between conductors. You will find an increase in current as there is a deterioration in the insulation and becomes predominant after the absorption current vanishes. It is time independent and fairly steady this is the most significant current for measuring insulation resistance.

LEAKAGE CURRENT AND CAPACITIVE CHARGING (IC)

In a raceway two or more conductors run together and they act like a capacitor. A leakage current flows through the conductor insulation because of this capacitive effect.

As the DC voltage is applied the current lasts only for a few seconds and falls out after the insulation is charged with full test voltage.

The capacitive current is higher than the conductive leakage current in a low-capacitance device but it vanishes usually by the time we start recording the data. It is significant for letting the reading settle out before recording it.

While testing higher capacitance equipment the capacitance leakage current charging can hold on for a longer duration before settling out.

Leakage current and Polarization absorption (IA)

Polarization of molecules inside the dielectric medium causes absorption current. There is a higher current for the first few seconds in a low-capacitance equipment and reduces slowly to zero. The higher capacitance device or wet and contaminated insulation dealing will have no reduction in the absorption current for a longer duration.

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Basics of distribution and Power transformer! Definition of Distribution transformer?

For transferring the electrical energy from a primary distribution to a secondary distribution circuit or a user circuit is the purpose of a distribution transformer.

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They are referred for the purpose of electric power distribution electric power distribution and are also termed as step down transformers. There are various types of transformer used in the distribution system like single phase transformer, three phase transformer, pad mounted transformer, pole mounted transformer, and underground transformer. They are basically compact devices and filled with insulating oil. There are various sizes and efficiencies available in the market. Depending on the purpose and budget the distribution transformers are chosen from the user end.

Distribution transformer and its special need?

Since it is energized for 24 hrs even without load; there is a low iron loss as a distribution transformer.

As the distribution transformer is working at full load; the maximum efficiency is very low at load.

For availing minimum voltage regulation the leakage reactant is kept low and hence a higher efficiency is achieved. Top changers do not have any such provisions.

Definition of Power transformer?

For transferring electrical energy in any parts of the electrical circuit between generator and primary distribution circuit. The distinction between power and distribution transformers must not be as per KVA rating according to IEEE standards

It is composed of a coil wrapped around an electromagnet which transfers the electricity. They operate at 100% efficiency unlike distribution transformer. One more difference between power and distribution transformers is that power transformers is for handling high voltages and distribution transfer is for dealing with the low ones. Distribution transformers are fed with power from the Power transformers thereby providing small amounts of power to each and every home.

What Does a Power Transformer Do?

Electrical induction is the process of transforming the current from a power transformer along with electric voltage running into a current and voltage that is used for a specific system. Running is backed up by it. The frequency of the electricity remains the same but transformed at a different value for both the voltage and current. Along with distribution transformer power works together for regulating power in transmission networks by decreasing or increasing the voltage levels relying on the requirement of the consumer.

Power transformer and its special requirements

It has cooling and a higher insulation.

Voltage regulation and tap changer to cope up with.

Higher mechanical and electrodynamic stress needs to be maintained.

Applications of Power transformer

Various kinds of electronic circuits use this transformer. Transmission and distribution of electric power are used in these transformers widely in power plants, traditional electric utility companies, etc.

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ALSO READ : What are the main differences between Power transformer and distribution transformer?

Why transformer oil is used and what are its types?

High voltage and current is carried in a core-coil of transformer. Core-coil is secluded and isolation from other surrounding construction. Core-coil has a certain distance maintained known as Electrical Clearance. Surrounding isolated medium and it cannot pass electric current through it.

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The electrical clearance would be high for airy environment as a dielectric medium. This is th reason transformer is large and bulky. Air would loose its dielectric property thereby putting heavy stresses during fault condition becoming ionized or electrically conductive.

Cooling property and dielectric of transformer oil is much higher when compared to air. For transformer’s dielectric medium the compact design of transformer oil is an apt choice.

Define dielectric

An electrical insulator polarized by an applied electric field and dielectric material. If in an electric field a dielectric is placed, there is no flow of electric charge through the material.

Reason for using transformer oil in a transformer

Transformer oil or the mineral oil around a transformer core-coil assembly improves the dielectric strength of the winding and defends oxidation of the core. Enhancement in dielectric occurs due to oil and a greater electrical stability than air due to constant dielectric of oil closer to that of insulation.

Thus insulation stress is reduced when air is replaced by oil in a dielectric system. Heat is picked up by oil when in touch with the conductors and carries the heat out of the tank surface by self convection.

Therefore there are smaller electrical clearances when a transformer is inserted in oil and smaller conductors for the same voltage and kVA ratings.

Transformer oil types

Here are few coolant used here:

1. HIGH-TEMPERATURE HYDROCARBONS

High-molecular-weight hydrocarbons also known as high-temperature hydrocarbons (HTHC) are considered as coolants by National electric and is very less flammable when reached a fire point above 300 degree Celsius. They are very costly and have a disturbing cooling capacity from the higher viscosity accompanying higher molecular weight and this its only disadvantage.

2. Esters

Europe uses synthetic esters with high temperature capability and biodegradability. The cost is highly justified and biodegradability is of more importance. For instance, in rail road transformers. US Transformer manufacturers and esquiring now with the use of esters naturally obtained from vegetable seed oils.

Benefits of Transformer oil

Because of the generation of electrical power transformers are very critical. There can be total shut down or failure and can lead you to huge comprises and losses. Such transformer oils can prevent break downs and failures.

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What are the main differences between Power transformer and distribution transformer?

Power transformers

For transmitting networks of higher voltages for step-up and step-down application (400 kV, 200kV, 110kV, 33kV) and are generally rated above 200MVA in power transformers.

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For lower voltage distribution networks as a means for connecting end users among 11 kV, 3.3kV, 440V, 230V is basically rated less than 200MVA in distribution transformers.

Transformer Size/ Insulation Level:

Power transformer is for heavy load transformation load, it has 100% efficiency and high voltage greater than 33 kV. Distribution transformer is lesser in size when compared to this transformer and the main uses of this device can be found in generating station and Transmission sub station and higher level insulation.

The distribution transformer is used for the electrical energy distribution at low voltage less than 33kV for works related to industry and 440V-220V for household purposes. A lower efficiency of 50-70% size is enough , lower magnetic losses, easier installation, without full load.

Iron Losses and Copper Losses

Transmission network uses Power transformer as they do not directly connect with the users, there is very less load fluctuation. Throughout the day for 24 hrs they are loaded and the specific weight that is the division of iron weight by copper weight is very less.

In distribution network a power transformer is used and so they are connected to the consumer which leads to higher load fluctuations. The iron losses takes place 24 hrs a day and copper losses depends on the load cycle as it is not loaded fully and the specific weight is more as average loads are about 75% of full load and these are made in such a way that efficiency occurs at its maximum of 75% of full load. All day efficiency is defined in order to calculate the efficiency with power basis.

The main use of power transformers are in step up devices for I2r loss minimizing a given power flow. For utilizing the core to maximum these transformers are designed and it will operate with more clarity near the B-H curve.
The above kind of design cannot be applied for distribution transformers. While designing it the efficiency throughout the day comes into the picture. Typical load cycle for supply depends on its supply. For taking care of the peak load the core design will be done along with all-day-efficiency.

Power transformer commonly works on full load. Hence, its design has a motto to reduce the copper loss. The core losses are less because the distribution transformer is working on loads less than full load most of the time.

The flux density is higher in Power transformer when compared to distribution transformer.

Maximum efficiency

The major distinction between distribution transformer and power transformer is its design for maximum efficiency at 60 to 70 % load but power transformer has 100 % load with maximum efficiency because it works at 100% load near the generating station.

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ALSO READ:  Electrical Power transformer, definitions and its types.

What Is MATLAB?

A highly efficient language for technical computation is called MATLAB. It combines visual, computations, and programming in an easy-to-use environment where problems and solutions are given in well-known mathematical expressions. It is used for:

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Algorithm development

Scientific and engineering graphics

Modeling, simulation, and prototyping

Application development, including Graphical User Interface building

Math and computation

Data analysis, exploration, and visualization

The data element is considered as an array in a MATLAB interactive system that does not need dimensioning. It solves many issues regarding technical and computations especially the ones which include vector and matrix expressions, by using languages like C or Fortran you can write this program in no time.

Matrix laboratory is supported by MATLAB and it was created for giving a user-friendly access to matrix software written by LINPACK and EISPAKC projects, that together gives the state-of-the-art in matrix computation software.

There has been a periodic evolution of MATLAB over the years with many users providing input. For basic and advanced mathematics, science, and engineering it is the general instruction tool used in a university environment. For development, analysis, research, and higher productivity MATLAB is the apt choice used by the industry.

A group of application-specific solutions namely tool boxes is the main feature of MATLAB. It permits you for learning and applying specialized technology. There are vast collections of MATLAB functions in Toolboxes that enhances the ambiance of MATLAB to solve problems of a particular class. Signal processing, neural networks, wavelets, simulation, fuzzy logic, control systems and much more are the areas where tool boxes are available.

The MATLAB System

It comprises of five main parts:

The MATLAB language:

It is an array or matrix language at a higher level with control flow statements, functions, input/output, data structures, object-oriented programing features, etc. It permits both small programming for creating fast and junk throw-away programs, and big programming for creating difficult and big application programs.

The MATLAB ambiance:

It has a set of tools offering lots of provisions that perform with as the MATLAB user or programmer. It provides help for variable management in your workspace and data transfer. Developing, managing, debugging, and profiling M-files can be done using the tools of MATLAB.

Graphics management:

Offering higher level commands for two dimensional and three-dimensional data visualization, animation, image processing, and presentation graphics are included in the Graphics management. Low-level commands for allowing full customization view of graphics for building Graphical User Interfaces on your MATLAB applications.

Mathematical library function of MATLAB:

There are various basic operations like sum, cosine, sine, and complex operations collection of computational algorithms for more sophisticated functions like matrix eigenvalues, inverse, fast Fourier transforms, and Bessel functions.

The MATLAB Application Program Interface (API):

C and Fortran programs for interacting with MATLAB is permitted by the library. There are other facilities included for calling routines from MATLAB (dynamic linking), calling MATLAB as a computational engine, MAT-files with reading and writing facility.

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3 Significant ways for DC motor speed control

One of the most useful features of DC motor control is the speed control. If you control the speeds of the motor, you need to vary the speed of the motor according to the requirements for getting the required operation. There are many applications like the movement of the robotic vehicles, motors in paper mills, and elevators use the speed control mechanism.

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DC Motor’s working principle

When a conductor carrying current is placed in a magnetic field it is controlled by a mechanical force and this is the simple working of the DC motor. The current carrying conductor and the field is the armature in a DC motor.

The magnetic flux is produced on its own with a supply of the current to the conductor (armature). Due to field windings it either adds up to the magnetic flux at one direction or rejects the magnetic flux due to field windings. The rotation is because of the accumulation of magnetic flux at one direction compared to the other.

Faraday’s law of electromagnetic induction shows that the rotating action of the conductor generates an EMF. The supplied voltage or the cause is opposed by the EMF according to Lenz’ law. In case of varying load due to the EMF, the torque is adjusted and this is the speciality of DC motor.

3 ways of controlling DC motor speed control

1 Flux Control Method

The magnetic flux of the winding is varied for varying the speed of the motor. By changing the current flowing through the field windings the magnetic flux can be changed as it depends on the current flowing through the windings. This is achievable with the help of a variable resistor in a series with the field winding resistor. The variable resistor kept at the minimum position flows through the windings due to the speed voltage keeps the speed normal. The current through the field winding is reduced when the resistance increases slowly. Thus the flux voltage produced is reduced in turn. Beyond a particular normal value the speed of the motor increases.

2 Control Method of the Armature

By controlling the resistance of the armature the speed of the DC motor is controlled leading to voltage drop across the armature. A changeable resistor in series with the armature is used in this method. The armature resistance is at normal one when the changeable resistor reaches to a minimum value thus the armature voltage drops. The voltage across the armature decreases as the resistance value is increased gradually. The speed of the motor is decreased because of this.

3 Voltage Control Method

Speed control cannot be provided at a required range from the above mentioned methods. The armature control leads to huge power loss because of the usage of the transistor in series with the armature. Commutations happen because of magnetic flux control. It is always good to have an alternative method for controlling the speed of the motor.

The field winding receives a fixed voltage and the armature receives a variable voltage in the new method. The switch gear system is used for such purposes for the provision of changing voltage to the armature. And the other one has a provision of AC motor driven Generator for providing variable voltage to the armature. This method is very efficient as it keeps the power loss at its minimum. It does not include the use of complex equipment.

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What is Insulated Gate Bipolar Transistor?

Insulated Gate Bipolar Transistor is the abbreviation of IGBT and it is actually a semiconductor device. It has a wide range of bipolar current carrying capacity and has three terminals. It has CMOS input and bipolar output and most of the experts think that it is a voltage controlled bipolar device. Both BJT and MOSFET in monolithic form the design of IGBT can be done. Power circuits, pulse with modulation, interruptible power supply, power electronics, and much more are the applications of the insulated gate bipolar transistor. For reducing the audible noise level and for increasing the performance efficiency this device is used. Resonant mode converter circuits also uses it. For both low conduction and switching loss optimized insulated gate bipolar transistor is used.

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Insulated Gate Bipolar Transistor

A 3 terminal semiconductor device with each terminal named as gate, emitter, and collector. Conductance path and gate terminal is associated with emitter and control terminal of the IGBT. The ratio between the input and output signal is called the calculation of the amplification attained. The sum of the gain is equal to the ratio of the output current to the input current named Beta for the conventional BJT. Mosfets or BJTS are the amplifier circuits where IGBT is mainly used. The combination of lower conduction loss in an amplifier circuit there is an occurrence of ideal solid state which is ideal in many uses of power electronics.

Basic diagram of IGBT

In the N channel IGBT the Si section is almost the same as vertical power of MOSFET without P+ injecting layer. There is a share of metal oxide semiconductor with P- wells though N+ regions. There are 4 layers in N+ layer and the one’s situation in the upper layer are called the source and the lower one’s are the drain.

IGBT

There are two types of IGBT

Non Punch Through IGBT

Punch Through IGBT

If the IGBT is with N+ buffer layer then it is called NPT IGBT

If the IGBT is without N+ buffer layer then it is called PT IGBT

The working of an IGBT is faster than the power BJT and power MOSFET.

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Circuit of an IGBT

PNP , JFET, MOSFET, and NPN transistors are used for a simple IGBT driver circuit depending on its basic construction. The JFET transistor is used for connecting the collector of the NPN transistor to the base of the PNP transistor. There is also a negative feedback loop in it. Among the neighboring IGBT cells the transistor denotes the structure of the current. Emitter, gate, and collector are the terminals of the IGBT shown.

Characteristics of IGBT

It is a voltage controlled device and therefore a small amount of voltage is enough on the gate terminal for continuing the conduction through the device unlike BJT where there is a continuous supply of base current for keeping it in saturation.

IGBT has only one directional switch, forward from collector to emitter. MOSFET is bidirectional.

The working principle of IGBT and MOSFET are the same but when the current flows through the device and the conducting channel offers resistance and the device is in the active state and current supplied is very small in IGBT whereas in MOSFET the current supply is higher. Thus the article has been completed and for further information join the institute of electrical engineering to make your career as an electrical engineer in this field.

 

Explain the different types of modulation!

In the digital era, transferring the data is very easy for example audio, video files are sent in the form of electrical signals to the desired device or a person. For a lay man it sounds easy, but actually it is not as its complexity is very tough.

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Modulation is the important factor with respect to communication system any data to be transferred as to be modulated for sending them over long distance without any disturbance or loss of data.

Define Modulation

It is the process of changing the features of the wave to be transmitted with message signal on a higher frequency. Data signals, voice, and, video are converted into high frequency signal also called as carrier wave. This wave AC or DC or pulse chain which relies on the application used. A carrier wave signal is basically a high frequency sine wave.

Reason for the use of modulation in communication

For the purpose of transmission the message frequency signal is increased to a range. If you consider signal transmission there are lots of sources ready to transmit via common medium so if everything is transferred in the same frequency then it will lead to disturbance and interference. Therefore modulation concept is used over here for instance the sound file is transferred at a particular modulation frequency and from the receiver it is decoded from the given set of frequency transmissions.

The antenna size is also another factor which is inversely proportional to the radiation frequency signal. If the size of the signal is just 6khz then it is not usable therefore it has to be modulated and increased thereby reducing the size of the antenna.

It is not possible to send low frequency signal over longer distance and therefore modulation is important over here.

For avoiding any disturbance and allocating more channels to the users, modulation is mandatory.

Different Types of Modulation

There are different types of modulation they are”

Analog

Digital

The baseband information is converted into Radio Frequency Signals in both the techniques and the only difference is RF signals are in continuous state in Analog and discrete state in digital.

Analog Modulation

For carrier wave a continuous sine wave is used over here for modulating message signal over data. There are three types of Analog modulation they are:

Amplitude Modulation: Only the amplitude of the carrier wave is varied with respect to the message signal. It requires greater bandwidth and more power.

Frequency Modulation: Frequency of the carrier wave is varied with respect to the message signal. Modulation index and modulating frequency governs the efficiency and bandwidth.

Phase Modulation: Phase of the carrier wave is varied with respect to message signal but frequency is also varied with respect to phase therefore this also comes under frequency modulation.

Drawback: Disturbance till the receiver end.

Digital Modulation:

It is preferred a lot when compared to analog modulation. The main benefit lack of disturbance, available bandwidth. After the conversion of message signal from analog to digital format it is modulated using a carrier wave. Here also there are three types of digital modulation amplitude, frequency, continuous phase modulation, Trellis coded modulation, and phase.
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What are batteries and explain its types and working?

As a power back up for hand held devices to big applications, batteries are used for back up. It is a combination of one or more electrochemical cells and they convert chemical energy into electrical energy.

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Battery Working:

Lots of voltaic cells are composed together into a battery device. There are two half voltaic cells with a series connection with a conductive electrolyte capturing anions and cations. Electrolyte and the electrode to which anions move in other words negative electrode or an anode is contained in one half cell. And in the other half cell contains electrode and the electrolyte which attracts cations called as the cathode or positive electrode.

At the cathode, reduction occurs to cations in the redox reaction that charges the battery and oxidation occurs at anode. There is no physical connection between the electrodes and the only mode of connection is through the electrolyte. There are different electrolytes for each half cells.

An electromagnetic force EMF for each half cell is given by the capacity of the electric current to be drawn. The difference between the emf of the half cells is called the net emf of the cell. If electrodes have particular emf, the difference between the reduction potentials of the half-reactions is called the net emf.

Battery Maintenance:

For having a good battery condition, equalization of battery is required. As time passes by there is no charging of cells done in a routine fashion as some of them charge slowly and some of them charge very fast. Overcharging the battery for charging the weaker cells completely is called marginal equalization. Charged battery has a terminal voltage of 12 V and automobile battery shows 13.8 V and a tubular battery will show 14.8 V. For avoiding shaking, automobile batteries needs to be firmly fixed.

2 Types of Batteries

1) Primary Batteries:

It is a one time use battery or in other words use and throw battery as per the name. After the discharge of these batteries it cannot be recharged and bring its components to its original forms. It is not advised to recharge the primary cells . Some examples of the batteries are AA, AAA batteries and they are normally used in remote controls, torches, walk clocks etc. They are also called as disposable batteries.

2) Secondary Batteries:

Standard rechargeable batteries also known as Secondary Batteries are those which are reusable after getting discharged by charging it back using electric power. They are composed of active materials in the active state of discharge. Electric currents are applied for recharging the batteries with the use of charger. There are some examples of secondary batteries like the one used in mp3 players, mobile phones, Ipod etc. Miniature cells are used in wristwatches and hearing aids and large batteries are used in computer data centers and telephone exchanges.

There are Various types of Secondary Batteries:

SMF Battery: reliable, consistent, low maintenance

Lithium Battery: for portable devices like laptop, cell phone

Lead Acid Battery: for inverters, automobiles, power systems

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Significance of Reactive Power in System network

The significance of reactive power is shooting up with high demands for electric power by many industrial and domestic utilities, in the system of a power network. Reactive power management is the basis for stability and reliability of electric power system.

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For generating power in a more efficient, cost effective, and reliable way the effective way of delivering electrical energy utilizes techniques like FACTS (Flexible AC Transmission System), (Static Voltage Composition) SVC for maintaining high power factor, reducing transmission losses, voltage stability maintenance etc.

Reactive and Active powers are the two powers that AC power supply system consume and produce. Load receives the true power called active power or real power. Most of its applications are like lighting lamps, rotating motors etc.

An apparent or imaginary power by nature, reactive power has no useful work but it simply moves back and forth in the lines of a power system. AC systems are the predecessor of reactive power and it is produced from inductive and capacitive loads. The phase displacement between voltage and current is measured in units of volt-ampere reactive.

3 Importance of reactive power

1. Voltage control

Within ±5% of the nominal currents power system equipment are designed. Change in voltage levels leads to poor functioning of various appliances. Hollywood damages the insulating material of windings where as low volts cause poor performance of the various accessories like the low illumination of bulbs, heating up of induction engines, etc. If it has high voltage then it melts the insulation of windings and if it has low voltage it causes the poor efficiency of various equipment like overheating of induction motors, low illumination of bulbs, etc.

If the demand for the power is more than transmission lines supply than the current drawn from the supply reaches to a higher level and thus the receiving side voltage drops drastically. The amount of apparent power to be supplied is the basis of capacity for these reactors.

To get over this, the load should be provided with the reactive power by putting reactive inductors or reactors in transmitting lines. The amount of apparent power supplied decides the capacity of these reactors.

If the reactor power supplied is more than the power supply demand than the load voltage rises to a higher level with direct tripping of equipment, low power factor, cables and windings of mechanical devices gets insulation failures.

2. Electric Shortage

Many electrical shutdowns, like that at France during 1978, northeast countries in 2003, many parts of India during 2012, have seen inadequate reactive power on power production and it is the main cause for shutdown situations. Due to long distance transmitting the demand for apparent power is high and it is raised. Various equipment is shut down due to low voltages finally. Therefore it should have a continuous and adequate supply of reactive power.

3. Good condition of various devices

Generators, motors, transformers and other electrical devices need reactive power for producing magnetic flux. For doing useful works generation of magnetic flux is necessary. It helps for creating magnetic field in the motor but it results in decreasing the power factor. The inductive reactive power by supplying capacitive reactive power and that is the reason a capacitive reactive power is placed for compensation.

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