HRC Fuse Operation,Types And Characteristics

Operation,Types And Characteristics Of HRC Fuse

Fuse is a common switch gear device which we see even at our homes. It is used to protect a device or circuit from over currents.  For household purpose usage of HRC fuse is more economical than usage of circuit breakers. Let see a clear picture about what is fuse? , how a fuse works?

What Is Meant By HRC Fuse?

HRC fuse means high rupturing capacity fuse which is a modern type fuse. It interrupts current flow and protects from over current.  It is used to provide protection from short circuit damages in low voltages and medium level voltages.

Construction Of HRC Fuse:

The body of HRC fuse is made of ceramic which is highly heat resistant. It has two end caps to this caps a silver current carrying element is welded. The internal space of fuse is filled with powder material such as plaster of paris, marble, chalk, cooling media etc. as shown in the following diagram.

The above diagram shows the cross-sectional diagram of a HRC fuse.

Working Of HRC Fuse:

The fuse wire inside the HRC fuse conducts the short circuit current for a period of time safely. During this time if the fault is removed the fuse doesn't blow off. But if the fault is not removed the fuse will melt and isolates the circuit from the electrical supply as shown in the below figure.

This is how a fuse works

Controlling Of Arc In HRC Fuse:

The inner portion of HRC fuse consists of cooling medium which helps to carry normal current by the fuse wire without heating. When over current flows then heat is produced in the current carrying fuse wire because of high I2Rf loss. This heat vaporizes the silver metal element and a chemical reaction takes place between this silver metal and filling powder which produces a high resistance substance. This high resistance substance helps in arc quenching.

Characteristics Of HRC Fuse:

As discussed for normal current the fuse wire doesn't melt but when over current flows due to high I2Rf loss the fuse wire melts.So fuse wire melts faster for higher fault currents and takes more time to melt for lower fault currents. This gives the time-current characteristics of HRC fuse. This is shown in the following figure.

Types Of HRC Fuse:

We have different types of HRC fuse. They are:

1.Semi- enclosed or rewireble type.

2.Totally enclosed or cartridge type.  

3. Current limiting fuse link. 

4. Drop-out fuse.

5. Explosion fuse.

6. Striker fuse.

7. Switch fuse.

Now let us see each of them in detail.

1. Semi- enclosed Or Rewireble Type Fuse:

In this type of fuse the carrier of fuse can be pulled out and the melted fuse wire can be replaced with the new wire. Carrier has to be replaced in the fuse base. This type of fuse is used in our houses. Its diagram is shown below.

2. Totally Enclosed Or Cartridge Type Fuse:

In this type we have a fuse wire inside a totally closed container and it has metal contacts on either sides. This is further divided into two types.

1. Bolted type 2. D-type.

The above diagram is cartridge type fuse. 

3. Current Limiting Fuse Link:

This fuse link brings the current to a value lower than a prospective value.

4. Drop Out Fuse:

After fault current flows,fuse-carrier drops out. Now there will be isolation between the terminals. This diagram is shown below.

5. Explosion Fuse:

In this type of fuse the arc is quenched when produced arc produces heat which vaporizes the metal and chemical reaction is established between this vapors and powdered filling. This produces a high resistance substance which helps the produced arc to quench.

6. Striker Fuse:

This type of fuse consists of combination of a fuse and a mechanical device. This fuse releases a striker after fuse operation with a certain displacement and pressure. The following figure shows diagram of striker fuse before and after fuse operation.

7. Switch Fuse:

This is a fuse which contains both switch and fuse. This is shown in following figure.

                                            

In this post we have discussed about the operation, types and characteristics of HRC fuse.

January 29, 2017 at 07:36PM by EEE, ADBU

Differences between electrical degree and mechanical degree

Differences between electrical degree and mechanical degree

Many people get confused about what is electrical degree and mechanical degree. Well, to get a clear idea about this we have provided the following post.

We consider an alternator with two poles once and four poles once to clearly understand about electrical degree and mechanical degree.An alternator consists of conductors on stator and poles on rotor. But for understanding purpose we consider conductors are rotating and poles are stationary. Because of relative motion between conductors and poles emf is induced inside the conductor.

Two pole alternator:

Consider a two pole alternator with a conductor as shown in the following figure.

Position 1 :At this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of a conductor i.e, 360 degrees there will be two maximum positions of emf this is indicated in the following figure.

Induced emf inside the alternator is sinusoidal in nature.Two maximum peaks is 360 degrees.Conductor rotation angle is mechanical degree and emf wave cycle degree for one complete rotation of conductor gives electrical degree.

Here mechanical degree is equal to electrical degree which is 360 degrees. Since for one complete rotation of conductor one complete emf cycle is produced.

Four pole alternator:

Consider a four pole alternator with a conductor as shown in the following figure.

Position 1 :At this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 5: Now conductor rotates to position 5.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 6: Now conductor rotates to position 6.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 7: Now conductor rotates to position 7.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 8: Now conductor rotates to position 8.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of a conductor i.e, 360 degrees there will be four maximum positions of emf this is indicated in the following figure.

°

Induced emf inside the alternator is sinusoidal in nature.Four maximum peaks is 720 degrees.Conductor rotation angle is mechanical degree and emf wave cycle degree for one complete rotation of conductor gives electrical degree.

Here mechanical degree is 360 degrees and electrical degree is 720 degrees.  Since for one complete rotation of conductor two complete emf cycles are produced.

This says that electrical degree depends on number poles inside the alternator. Now we can obtain relation between mechanical degree and electrical degree as

360° mechanical = 360° ✕ P/2 electrical

P = number of poles

1° mechanical = (P/2)° electrical.

In this post we have discussed about difference between mechanical degree and electrical degree.

To download this post on difference between mechanical degree and electrical degree as PDF click here.

January 29, 2017 at 04:16PM by EEE, ADBU

Generation of electrical energy

GENERATION OF ELECTRICAL ENERGY

Energy exists in different forms in nature but the most important form is the electrical energy.Now a days usage of electricity is very high it has become a basic need for everyone. 

Why electrical energy why not other energy sources?

Well, the simple answer to this is the modern technology has developed in such a way that electrical energy can be easily converted into all other energy forms. It also has other advantages  as mentioned below.

1.Greater flexibility: As it can be easily transported with the help of conductors from one place to other it has great flexibility.

2.Convenient : As it can be easily converted into other forms of energy it is very convenient form.  If we take the example of converting electrical energy into heat energy  all we need to do is just pass electricity through a resistor then electrical energy converts o heat energy. Similarly, all the others forms of energy like light,mechanical etc can be obtained easily from electrical energy.

3.Cheapness: When compared to other forms of energy electrical energy is much cheaper . Thus it is  economical to use for any purpose.

4.Cleanliness: Electrical energy doesn't produce  smoke,ash or poisonous  gases. So it maintains cleanliness.

5.Easy control: The electrically operated machines can be controlled easily by switching on or off the switch. For example we can turn off or on the fan by switching off or switching on the switch. And speed can also be easily controlled for example speed of fan can be adjusted by using a regulator. So it is easy to control.

6.High transmission efficiency:  Consumers of electrical energy are located away from the electricity generation stations generally.But with the help of over head line conductors and by using transformers and few other equipment's electricity can be supplied efficiently with less amount of losses.

The above mentioned advantages made usage of electrical energy popular than other energy forms.

Generation of electrical energy:

Converting  different forms of energy that are present in nature into electrical energy is known as generation of electrical energy.

To get the basic idea of generation of electrical energy observe the following figure. 

Energy from any of the sources like heat, wind, hydro, fossil etc can be given as input to the prime mover. For example take hydro energy, Water at certain head  when falls on the prime mover which is a rotating part rotates the prime mover in this way the potential energy exerted on it is converted to mechanical energy. This prime mover drives generator and the generator converts mechanical energy to electrical energy.

Sources of energy:

1. Fuels: Fuels like  coal,  oil and natural gas are the main sources of energy. The heat energy produced  by these fuels is converted into mechanical energy by certain type of  prime movers like steam engines, steam turbines etc. The prime mover drives the alternator which converts mechanical energy into electrical energy. Although these fuels play main role in the electrical energy production now a days we need to see other alternatives as there quantity is diminishing due to increase in the usage of electrical energy. The alternative to them is renewable energy sources likes solar, wind, hydel.

2.Solar energy:  Sun is the major source of energy. Electrical energy can be produced from sun by focusing the heat energy produced  by sun on reflectors and heating water which produces steam which in turn rotates the turbine which is coupled to the generator and this generator converts mechanical energy to electrical energy. As it has limitations like availability of solar energy is not possible all the time it can be used as alternative wherever other sources of energy are not available abundantly.

3.Water:  When water present at certain head falls down on turbine the potential energy possessed by water is converted into mechanical energy by a water turbine. This turbine drives the generator which converts mechanical energy to electrical energy.

4. Wind: To generate electrical energy from wind energy a wind mill is established. This runs the generator which produces electrical energy. Wind mills are generally placed at hilly areas.It is cheaper way to generate electrical energy.

5.Nuclear energy: Very large amount of heat can produced by nuclear fuels like uranium. This heat energy is utilized to produce steam. This stem rotates the steam turbine and runs the generator which can produce electrical energy.

This helps you to understand the basics of generation of electrical energy from different power plants.  

Efficiency:

Some energy is lost i.e converted to other form of energy other than electrical energy  while converting any input energy to output electrical energy. Efficiency gives you how efficiently the input energy given is converted to output electrical energy. Efficiency is generally calculated in percentage.

Efficiency of power plant =  output energy / input energy = output power / input power.

Power is rate of flow of energy.

In this post we have learnt about electrical energy importance and generation of electrical energy from different power plants.

To download this post on generation of electrical energy as PDF click here

January 28, 2017 at 01:46PM by EEE, ADBU

Electrical Machinery [ Electrical Machines ] By Ps Bimbhra Pdf Download

You all know we recently launched free electrical engineering pdf books to all. In this post we are sharing a very good book on electrical machines by ps bimbra , he is a very good author of so many electrical engineering books some of them are mentioned below,

1. Electrical Machinery by ps bimbhra

2. Power electronics by ps bimbhra

3. Generalised theory of electrical machines by ps bimbhra

Electrical Machines PS Bimbhra  PDF Free Download 

User Ratings: *****A Lecturer - Abhishek TiwariI have referred to this for many topics in Electrical Machines. This books gives a detailed explanation of design and working of electrical machines. It a good book to refer for undergraduate students.

Electrical machinery ps bimbhra will cost us around Rs.400 /- in india. To provide this book for students who can't afford we are sharing  "electrical machinery by ps bimbhra".you can download this pdf directly into your computer or mobile phone easily.You need to have any pdf reader to read this book.

Download Here: Link 1 | Link 2

Note: Due to space on server some times file may get deleted.Please mail us at electricaledition@gmail.com if you face any problem.

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January 17, 2017 at 05:41PM by EEE, ADBU

Welding Transformer Working Principle and Applications

Welding Transformer Working Principle and Applications 

Now a days we have many ac power supplies. So the usage of welding transformer has significant role in welding compared to a motor generator set. When we need to use a motor generator set for welding we need to run it continuously which produces a lot of noise. With the help of welding transformer weld is done with a less noise. Now let us see in detail about welding transformer.

Construction of welding transformer:

1. Welding transformer is a step down transformer.

2. It has a magnetic core with primary winding which is thin and has large number of turns on one arm.

3. A secondary winding with less number of turns and high cross-sectional area on the other arm.

4. Due to this type of windings in primary and secondary it behaves as step down transformer.

5. So we get less voltage and high current from the secondary winding output. This is the construction of ac welding transformer. 

6.A dc welding transformer also has same type of winding the only difference is that we connect a rectifier(which converts ac to dc) at the secondary to get dc output. 

7.We also connect a inductor or filter to smooth the dc current. This will be construction of dc welding transformer. The diagrams are shown below.

Fig 1.DC welding transformer

Fig 2.AC welding transformer

Note:

Many people have a doubt which is primary winding and which is secondary winding. The winding which is connected to power supply is called primary winding and the winding to which load is connected is called secondary winding.

Working of welding transformer:

1.As it is a step down transformer we have less voltage at secondary which is nearly 15 to 45 volts and has high current values which is nearly 200 A to 600 A it can also be higher than this value.

2. For adjusting the voltage on secondary side there are tappings on secondary winding by this we can get required amount of secondary current for welding.

3. These tappings are connected to several high current switches.

4. Now one end of secondary winding is connected to the welding electrode and the other end is connected to the welding pieces as shown in fig 2. 

5.When a high current flows a large amount of  I2R heat is produced due to contact resistance between welding pieces and electrode. 

6.Because of this high heat the tip of electrode melts and fills the gap between the welding pieces.

This is how a welding transformer works.

Volt - ampere characteristics of welding transformer:

Figure given below shows the volt - ampere characteristics of welding transformer.

Arc control of welding transformer:

The impedance of welding transformer must be higher than the normal transformer to control arc and also to control current. 

We can use different reactors for controlling the arc. They are

1.Tapped reactor.

2.Moving coil reactor.

3.Magnetic shunt reactor.

4. Continuously variable reactor.

5. Saturable Reactor.

Now let us see each of this methods for arc control of welding transformer in detail.

1.Tapped reactor:

Below is the circuit for arc control using tapped reactor is given below.

  

With the help of taps we control the current. It has limited current control.

2. Moving coil reactor:

Below is the circuit for arc control using moving coil reactor.

The distance between primary and secondary decides the amount of current. If the distance between the primary and secondary is high then the current is less.

3. Magnetic shunt reactor:

Below is the circuit for arc control using magnetic shunt reactor.

By adjusting the central magnetic shunt flux is changed. By changing the flux current can be changed.

4. Continuously variable reactor:

Below is the circuit for arc control using continuously variable reactor.

By varying the height of reactor core insertion is changed. If core insertion is greater reactance is higher so output current will be less.

5. Saturable reactor:

Below is the circuit for arc control using saturable reactor.

The reactance of the reactor in this is adjusted by changing the value of d.c. excitation which is obtained from d.c. controlled transducer. Higher the d.c. currents, reactor approaches to saturation. This changes the reactance of reactor. By changing the reactance current can be changed.

By using above reactors current can be controlled which helps to control the arc.

In this post we have learnt about welding transformers.

To download this post on welding transformers as PDF click here.

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January 12, 2017 at 08:07PM by EEE, ADBU

Operational Amplifier as Integrator and Differentiator/OP Amp Differences between Integrator and Differentiator

Operational amplifier as integrator and differentiator

Operational amplifier which is called also called as op-amp has a key role in many electronic applications due to its special characteristics. Name itself indicates that it can perform operations. By using op-amp we can perform different operations like addition, subtraction, multiplication, differentiation and integration. Of these op-amp application as integrator and differentiator is very common.

                  Before going to see op-amp as integrator and differentiator let us first understand working principle of operational amplifier.

Operational amplifier working principle:

Let us see the symbol of operational amplifier and its terminals before going to see working of op-amp.

It has two input terminals one is marked negative and other as positive and one output terminal. The input terminal which is marked negative is called inverting input because when we apply an input signal to this inverting input we get a phase shift of 180° in the amplified output signal with respect to the applied input signal. The input terminal which is marked positive is called Non-inverting input because when we apply an input signal to this Non-inverting input there is no phase shift between input signal and amplified output signal.

                             It has two input power supply terminals +Vs and -Vs. +Vs is connected to positive terminal of battery and -Vs is connected to negative terminal of other battery. If we require a ground we need to provide ground separately as there is no common ground provided in op-amp.

Open loop operation of op-amp:

In this open loop operation we apply two input signals one at inverting input and other at Non-inverting input as shown in the figure.

 So it has differential input(since one is + and other is -) which means difference of two applied input signals and one output is obtained. The gain of open loop operation of op-amp is given by

Gain = output / input

Aol = Vo / V1 - V2

so output voltage is

Vo is output voltage

V1 is voltage at non-inverting terminal 

V2 is voltage at inverting terminal 

V1 - V2 is differential input voltage

Aol is open loop gain

Open loop gain is very high even a small signal given at input amplifies to large amount but its value will not exceed the supply voltage of op-amp as it obeys law of conservation of energy.

Closed loop operation of op-amp:

If we introduce a feed back in the circuit it is called closed loop operation. Here a part of output signal is fed back to one of the input terminals. The terminal where feed back is given two signals are present simultaneously one is feed back signal and the other is original applied signal it can be seen in the following diagram.

If we apply feed back signal from output to non-inverting terminal it is called positive feed back which is used in oscillator circuits. And if we apply feed back signal from output to inverting terminal it is called negative feedback here phase shift is present between applied signal and feed back signal. This negative feed back is used for amplifier circuits. Closed loop gain of op-amp is given by

Acl = Vo / V1 - V2

 Now output voltage will be

where Vd = V1 - V2.

Acl = closed loop gain.

As we have learnt operation of op-amp now we can clearly understand the application of op-amp as differentiator and integrator.

Op-amp as integrator:

When an operational amplifier work as integrator we get output as integration of voltage with respect to time. Here we use capacitors at a right place in the circuit which helps to perform integration of applied input voltage. The arrangement can be seen from the following diagram.

                           

The above circuit is called an ideal op-amp integrator circuit.

Here the negative feed back is taken and a capacitor is connected between output terminal and inverting input terminal. Because of negative feedback node X is at virtual ground and if the input voltage is 0 V then no current flows through input resistance Rin then the capacitor will remain uncharged. So we get output as 0 V.

                          Now if we apply a constant positive DC voltage at the input then  we get a linearly falling voltage at output. If we apply a constant negative DC voltage at input then we get a linearly raising voltage at output. And this rate of change of output voltage will be directly proportional to input voltage. 

Output voltage calculation:

Now we calculate the output voltage of this circuit.

According to virtual ground concept as non-inverting terminal is grounded then node X will also be at ground potential

                                                            VX = VY = 0

For an ideal op-amp input impedance is high so input current is very less and the current flowing through resistor R1 also flows through capacitor C.

Input current equation is given by,

I = (Vin – VX) / R1 

I = Vin / R1.

output current equation is given by

I = C [d(VX – Vout)/dt] = -Cf[d(Vout)/dt]

Now we equate both current equations as current flowing through resistance R1 (input) and capacitor C (output) are same(since op-amp has high input impedance all current flows through capacitor). We get,

                                         [Vin / R1] = – C [d(Vout)/dt]

Apply integration on both sides, now we get,

The above equation clearly says that output voltage is - 1 / R1 . C times the integration of input voltage. This shows that op-amp acts as an integrator by this circuit arrangement. Here R1.C is called integrator time constant and negative sign shows that there is a phase shift of 180° between input and output voltage. The phase shift is because we have applied signal to inverting terminal.

                        We use integrator circuit to convert a square wave input to triangular wave output as shown in the following circuit.

As discussed when we apply constant positive dc voltage we get a falling output voltage at linear rate and if we apply constant negative dc voltage we get a rising output voltage at linear rate(if a step signal is integrated we get ramp signal).

An integrator op-amp circuit acts as low pass filter it attenuates high frequency signals.

OP-amp as differentiator:

A differential op-amp has output voltage which is proportional to rate of change of input voltage. This op-amp can act as differentiator by keeping a capacitor in series with the input voltage source. This can be seen from the diagram given below 

The capacitor acts as open circuit for dc input. Here we ground the non-inverting terminal of op-amp and the inverting input terminal is connected to output through a feed back resistor Rf. This makes the circuit to behave as voltage follower. The input current to op-amp is very less due to high input impedance of op-amp we have same current through capacitor and resistor Rf.

Output voltage calculation:

Now we calculate the output voltage of this circuit.

According to virtual ground concept as non-inverting terminal is grounded then node X will also be at ground potential

                                                            VX = VY = 0

Input current is given by,

                            I = C [d(Vin-Vx)/dt] = C [d(Vin)/dt]

output current is given by,

                            I = -{(Vout-Vx)/Rf} = -{Vout/Rf}

 Now we equate both equations as current through capacitor and resistor are same.

                            C{d(Vin)/dt} = -Vout/Rf

                            Vout = -C.Rf {d(Vin)/dt 

The above equation clearly says that output voltage is - C.Rf  times the differentiation of input voltage. This shows that op-amp acts as adifferentiator by this circuit arrangement.     Here    Rf.C is called differentiator time constant and negative sign shows that there is a phase shift of 180° between input and output voltage. The phase shift is because we have applied signal to inverting terminal.

                Here if we give a square wave input to differentiator the output has to be zero( since differentiation of constant is zero) but we get negative and positive spikes because input signal takes time to change from 0 to Vm. At constant positive DC input we get negative spike at output and at constant negative DC input we get positive spike at output. This can be seen from the following diagram.

 If we give a sin wave as input to differentiator we get cos wave as output.

                              Vout = -C.Rf {d(Vm sin ωt)/dt}

                               Vout = – Vm. ω. cos ωt consider(C.Rf = 1)

This can be seen in the following diagram

A differential op-amp circuit acts as high pass filter it attenuates low frequency signals.

In this post we have learnt op- amp as integrator and op-amp as differentiator.

To download this post on operational amplifier as integrator and differentiator as PDF clik here

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January 12, 2017 at 08:05PM by EEE, ADBU

Conversion from binary code to gray code and gray code to binary code

Conversion from binary code to gray code and gray code to binary code

 In this post let us see conversion from binary code to gray code and gray code to binary code.

Purpose for converting binary code to gray code?

Gray code has occupied a prominent role now-a-days because of its special characteristics. It is, there is change in only one bit for two successive values. This gray code is widely used for error correction in digital communications.

Steps to convert from binary code to gray code:

Let us consider an example to clearly understand the conversion from binary code to gray code

Consider binary code = 1110

Now represent this binary code as b3 b2 b1 b0 = 1 1 1 0

Let the representation of this binary code in gray code be g3 g2 g1 g0

Here b3, g3 are called most significant bits(MSB) and b0,g0 are called least significant bits(LSB).

Step 1: The most significant bit(MSB) of gray code is equal to most significant(MSB) bit of binary code.

In this example g3 = b3 = 1.

Step 2: Now the second most significant bit i.e,which is adjacent to most significant bit(MSB) in the gray code is equal to the sum of most significant bit(MSB) and second most significant bit of binary code. If addition produces any carry ignore the carry.

Note:

Carry is produced when we add two 1's i.e, 1 + 1 = 0, 1 is carry( from Boolean algebra) 

In the following example

g2 = b3 + b2

g2 = 1 + 1 = 0, carry 1 is neglected.

Step 3: The third most significant bit of gray code i.e, which is adjacent to the second most significant bit in the gray code is equal to the sum of second most significant bit and third most significant bit of binary code. If any carry is generated ignore it.

In the considered example:

g1 = b2 +b1

g1 = 1 + 1 = 0, carry 1 is neglected.

Step 4: The above process is continued until the least significant bit(LSB) of gray code is obtained. This least significant bit (LSB) of gray code is obtained by adding last most significant bit and the least significant bit of binary code.If any carry is produced that has to be neglected.

In the following example we have,

g0 = b1 + b0.

g0 = 1 + 0 = 1.

So finally we get the gray code as g3 g2 g1 g0 = 1 0 0 1

Diagrammatically conversion from binary code to gray code  can be represented as follows,

Example can be represented diagrammatically as follows,

 Hence by following above steps conversion from binary code to gray code is done.

Steps to convert from binary code to gray code:

Let us consider an example to clearly understand the conversion from gray code to binary code. 

Consider gray code = 1001.

Now represent this gray code as g3 g2 g1 g0 = 1 0 0 1.

Let the representation of this gray code in binary code be b3 b2 b1 b0.

Here b3, g3 are called most significant bits(MSB) and b0,g0 are called least significant bits(LSB).

Step 1: The most significant bit(MSB) of binary code is equal to most significant(MSB) bit of gray code.

In the example,

b3 = g3 = 1.

Step 2: Now the second most significant bit i.e,which is adjacent to most significant bit(MSB) in the binary code is equal to the sum of most significant bit(MSB) of binary code( It is obtained from step 1) and second most significant bit of gray code. If addition produces any carry ignore the carry.

In this example,

b2 = b3 + g2.

b2 = 1 + 0 = 1.

Step 3: The third most significant bit of binary code i.e, which is adjacent to the second most significant bit in the binary code is equal to the sum of second most significant bit of binary code(It is obtained from step 2)and third most significant bit of gray code. If any carry is generated ignore it.

In the considered example,

b1 = b2 + g1.

b1 = 1 + 0 = 1.

Step 4: The above process is continued until the least significant bit(LSB) of binary code is obtained. This least significant bit (LSB) of binary code is obtained by adding last most significant bit of binary code and the least significant bit of gray code. If any carry is produced that has to be neglected.

In this example,

b0 = b1 + g0.

b0 = 1 + 1 = 0, 1 is carry it is neglected.

So finally we get the binary code as b3 b2 b1 b0 = 1 1 1 0.

Diagrammatically conversion from gray code to binary code can be represented as follows,

Example can be represented diagrammatically as follows,

Hence by following above steps conversion from  gray code to binary code is done.

Today in this post we have learnt conversion from binary code to gray code and gray code to binary code.

This post on conversion from binary code to gray code and gray code to binary code can be downloaded as PDF here.

January 11, 2017 at 06:36PM by EEE, ADBU

Synchronization of alternator and methods of synchronization of alternator

Synchronization of alternator and methods of synchronization of alternator

What is meant by synchronization of alternator?

Connecting a group of alternators parallel to a bus bar and the alternators should have same voltage and frequency as that of bus-bar. This is called synchronization of alternator. There are some conditions to be satisfied by the alternators which are to be connected in parallel to bus-bar to be in synchronization.

Conditions for synchronization of alternators: 

1. The terminal voltage of incoming alternator must be equal to the bus bar voltage.

2. The frequency of voltage generated by incoming alternator must be equal to busbar frequency.

3.The phase sequence of the three phases of the incoming alternator must be same as phase sequence of bus-bars.

4. The phase angle between the voltage generated by incoming alternator and voltage of bus-bar must be zero.

5. Always connect running alternator to bus-bar. If a stationary alternator is connected to bus-bar it will result in short circuit of stator winding.

The above conditions are to be satisfied by alternators to satisfy synchronization.

Why synchronization of alternators is necessary?

1.An alternator cannot deliver power to electric power system until its voltage,frequency,phase sequence and other parameters matches with the network to which the the alternator is connected.

2. The case of synchronization arises because we are connecting many alternators in parallel to supply the demanded load. So we need to match all the parameters of connected alternators with bus-bar to deliver power to load.

3. By synchronization we can match all the parameters of one alternator with the other alternator and also with the bus-bar and deliver the required power to load.

4. Synchronization of alternator is also called as paralleling of alternators.

Advantages of paralleling of alternators: 

We get a common doubt why we need to supply the load by paralleling small units of alternator rather than using a single larger unit? This is because we have many advantages by doing so. They are:

Continuity of service: 

In case of any damage to one of the alternators it can be removed.Supply to load is not interrupted because other alternators can supply the required load. But if u use a larger single unit even a small damage causes the interruption of supply.

Requirement of load:

As the load demanded is not same all the time, during light load periods we can run two or three alternators in parallel. When the demand is high we can add the required amount of alternators in parallel to meet the load demanded.

Reliability:

Several single units connected in parallel is more reliable than single larger unit because if a single unit gets damaged it can be removed and its work is compensated by other units which are running.

High efficiency:

An alternator runs efficiently when it is loaded at their rated value. By using required number of alternators for required demand i.e, light load or peak load we can load an alternator efficiently.

So because of above advantages we use paralleling of alternators.

Steps to connect alternators in parallel or synchronization of alternators:

1.Consider an alternator-1. It is supplying power to bus bar at rated voltage and frequency.

2. Now we need to connect another alternator let it be alternator-2 in parallel with the alternator-1. In order to match the frequency of alternator-2 with the frequency of bus-bar or alternator-1 (since alternator-1 and bus-bar are already in synchronism) we need to adjust the speed of alternator-2. Now the voltage of alternator-2 is to be matched with the voltage of bus-bar or voltage of alternator-1 (since alternator-1 and bus-bar are already in synchronism). For this purpose we need to vary the field rheostat until the voltage matches.

3. The three phase voltages generated by alternator must be same as the three phase voltages of bus-bar or alternator-1(since alternator-1 and bus-bar are already in synchronism).This can be achieved by matching the phase sequence and frequency of alternator-2 with bus bar or alternator-1(since alternator-1 and bus-bar are already in synchronism) phase sequence and frequency.

By following these steps synchronization of alternators is possible.

Methods for synchronization of alternators:

There are three methods for synchronization of alternators. These methods check whether the above mentioned conditions for synchronization of alternators is satisfied or not. The three methods are.

1. Three dark lamps method.

2. Two bright, One dark method.

3. Synchroscope method.

Three dark lamps method for synchronization of alternators:

Let us study synchronization of alternators using three dark lamps method in detail.

Circuit diagram for synchronization of alternators using three lamp method:

Procedure:

1. Consider alternator-1 is supplying power to load at rated voltage and rated frequency which means alternator-1 is already in synchronism with bus-bar.

2. Now we need to connect alternator-2 in parallel with alternator-1.

3. Across the 3 switches of alternator-2 three lamps are connected as shown in the figure.

4. To match the frequency of alternator-2 with the bus-bar frequency we need to run the prime mover of alternator-2 at nearly synchronous speed which is decided by the frequency of bus-bar and number poles present in alternator-2.

5. To match the terminal voltage of alternator-2 with bus-bar voltage we need to adjust the field current of alternator-2 until terminal voltage of alternator-2  matches with the bus-bar voltage. The required value of voltage can be seen in the voltmeter connected to bus-bar.

6.To know whether the phase sequence of alternator -2 matches with the bus-bar phase sequence we have a condition. If all the three bulbs ON and OFF concurrently then we say the phase sequence of alternator-2 matches with the phase sequence of  bus-bar. If the bulbs ON and OFF one after the other then the phase sequence is mismatching.

7. To change the connections of any two leads during the mismatch of phase sequence first off the alternator and change the connections.

8. ON and OFF rate of bulbs depends upon frequency difference of alternator-2 voltage and bus-bar voltage. Rate of flickering of bulbs is reduced when we match the frequency of alternator-2 with bus-bar voltage by adjusting the speed of prime mover of alternator-2

9. If all the conditions required for synchronization are satisfied then the lamps will become dark. 

10. Now close the switches of alternator -2 to synchronize with alternator-1.

11. Now the alternators are in synchronism.

Disadvantage of three dark lamps method for synchronization of alternators:

Flickering only says difference between frequency of voltages of alternator and bus bar but correct value of frequency of voltage of alternator cannot be found.

For example, if the bus bar frequency of voltage is 50 HZ and difference in frequency of voltage of bus-bar and alternator is 1 HZ the alternator frequency of voltage can be either 49 HZ or 51 HZ.

Two bright and one dark lamp method for synchronization of alternators:

Let us discuss synchronization of alternator using two bright and one dark lamp method.

Circuit diagram for synchronization of alternators using two bright and one lamp method:

Procedure:

1. Consider alternator-1 is supplying power to load at rated voltage and rated frequency which means alternator-1 is already in synchronism with bus-bar.

2. Now we need to connect alternator-2 in parallel with alternator-1.

3. Here lamp L-2 is connected similar to the three dark lamp method.

4. Lamps L-1 and and L-3 are connected in different manner. One end of lamp L-1 is connected to one of the phases other that the phase to which lamp L-2 is connected and the other end of lamp L-1 is connected to the phase to which lamp L-3 is connected.

5.Similarly one end of lamp L-3 is connected to a phase other than the phase to which lamp L-2 is connected and other end of lamp L-3 is connected to the phase to which lamp L-1 is connected as shown in the following circuit.

6. To match the terminal voltage of alternator-2 with bus-bar voltage we need to adjust the field current of alternator-2 until terminal voltage of alternator-2  matches with the bus-bar voltage. The required value of voltage can be seen in the voltmeter connected to bus-bar.

7. Depending upon the sequence of lamps L1,L2, L3 becoming dark and bright we can decide whether the alternator-2 frequency of voltage is higher or lower than bus-bar frequency.

8. If the sequence of bright and dark of lamps is L1-L2-L3 then the frequency of voltage of alternator-2 is higher than the bus-bar voltage. Now until the flickering reduces to a low value decreases the speed of prime mover of alternator-2.

9. If the sequence of bright and dark of lamps is L1-L3-L2 then the frequency of voltage of alternator-2 is less than the bus-bar voltage. Now until the flickering reduces to a low value increase the speed of prime mover of alternator-2.

10. When the  L1 and L3 are equally bright and lamp L2 is dark then close the switches.

11. Now the alternators are in synchronism.

Disadvantage of two bright and one dark lamp method for synchronization of alternators:

Phase sequence of the alternator cannot be checked by this method.

Synchroscope method for synchronization of alternators:

Let us discuss synchronization of alternator using synchroscope method.

Circuit diagram for synchronization of alternators using synchroscope method:

Procedure:

1. A synchroscope is used to achieve synchronization accurately.

2. It is similar to two bright and one dark lamp method and tells whether the frequency of incoming alternator is whether higher or lower than bus bar frequency.

3. This contains two terminals they are a) existing terminal b) incoming terminal.

4. Existing terminals are to be connected to bus-bar or existing alternator here in the diagram it is alternator-1 and incoming terminals are connected to incoming alternator which is alternator-2 according to the diagram which we have considered.

5. Synchroscope has a circular dial inside which a pointer is present and it can move both in clockwise and anti clockwise direction.

6. To match the terminal voltage of alternator-2 with bus-bar voltage we need to adjust the field current of alternator-2 until terminal voltage of alternator-2  matches with the bus-bar voltage. The required value of voltage can be seen in the voltmeter connected to bus-bar.

7. Depending upon the rate at which the pointer is rotating the difference of frequency of voltage between incoming alternator and bus-bar can be known.

8. And also if the pointer moves anti clockwise then the incoming alternator is running slower and has frequency less than the bus bar or existing alternator frequency and if the pointer moves clock-wise then the incoming alternator is running faster and has frequency greater than bus-bar or existing alternator frequency. So by adjusting the speed of prime mover of incoming alternator we can match the frequency with bus bar or existing alternator frequency. Frequency matches when the pointer is straight up-wards. At this point close the switch.

9. Now both the alternators are in synchronism.

So by these three methods synchronization of alternators is checked.

Today in this post we have learnt what is meant by synchronization of alternator and methods of synchronization of alternator.

To download this post on synchronization of alternator and methods of synchronization of alternator as PDF click here.

January 11, 2017 at 06:33PM by EEE, ADBU