The basic difference in 4 Point Starter as compared to 3 Point Starter is that in this a holding coil is removed from the shunt field circuit. This coil after removing is connected across the line in series with a current limiting resistance R. The studs are the contact points of the resistance represented by 1, 2, 3, 4, 5 in the figure below. The schematic connection diagram of a 4 Point Starter is shown below:

The above arrangement forms three parallel circuits. They are as follows:-

• Armature, starting the resistance and the shunt field winding.
• Variable resistance and the shunt field winding.
• Holding coil and the current limiting resistance.

With the above three arrangements of the circuit, there will be no effect on the current through the holding coil if there is any variation in the speed of the motor or any change in field current of the motor. This is because the two circuits are independent of each other.

The only limitation or drawback of the 4 point starter is that it cannot limit or control the high current speed of the motor. If the field winding of the motor gets opened under the running condition, the field current automatically reduces to zero. But as some of the residual flux is still present in the motor, and we know that the flux is directly proportional to the speed of the motor. Therefore, the speed of the motor increases drastically, which is dangerous, and thus protection is not possible. This sudden increase in the speed of the motor is known as High-Speed Action of the Motor.

Nowadays automatic push-button starters are also used. In the automatic starters, the ON push button is pressed to connect the current limiting starting resistors in series with the armature circuit. As soon as the full line voltage is available to the armature circuit, this resistor is gradually disconnected by an automatic controlling arrangement.

The circuit is disconnected when the OFF button is pressed. Automatic starter circuits have been developed using electromagnetic contactors and time delay relays. The main advantage of the automatic starter is that it enables even the inexperienced operator to start and stop the motor without any difficulty.

The post 4 Point Starter appeared first on Circuit Globe.

• L is known as the Line terminal, which is connected to the positive supply.
• A is known as the armature terminal and is connected to the armature windings.
• F is known as the field terminal and is connected to the field terminal windings.

The 3 Point DC Shunt Motor starter is shown in the figure below:

Contents:

• Working of 3 Point Starter
• Drawbacks of a 3 Point Starter

It consists of a graded resistance R to limit the starting current. The handle H is kept in the OFF position by a spring S. The handle H is manually moved, for starting the motor and when it makes contact with resistance stud one, the motor is said to be in the START position. In this initial start position, the field winding of the motor receives the full supply voltage, and the armature current is limited to a certain safe value by the resistance (R = R₁ + R₂ + R₃ + R₄).

Working of 3 Point Starter

The starter handle is now moved from stud to stud, and this builds up the speed of the motor until it reaches the RUN position. The studs are the contact point of the resistance. In the RUN position, three main points are considered. They are as follows:

• The motor attains the full speed.
• The supply is direct across both the windings of the motor.
• The resistance R is completely cut out.

The handle H is held in RUN position by an electromagnet energized by a no-volt trip coil (NVC). This no-volt trip coil is connected in series with the field winding of the motor. In the event of switching OFF, or when the supply voltage falls below a predetermined value, or the complete failure of supply while the motor is running, NVC is energized.

The handle is released and pulled back to the OFF position by the action of the spring. The current to the motor is cut off, and the motor is not restarted without a resistance R in the armature circuit. The no voltage coil also provides protection against an open circuit in the field windings.

The No Voltage Coil (NVC) is called NO-VOLT or UNDERVOLTAGE protection of the motor. Without this protection, the supply voltage might be restored with the handle in the RUN position. The full line voltage is directly applied to the armature. As a result, a large amount of current is generated.

The other protective device incorporated in the starter is overload protection. The Over Load Trip Coil (OLC) and the No Voltage Coil (NVC) provide the overload protection of the motor. The overload coil is made up of a small electromagnet, which carries the armature current. The magnetic pull of the Overload trip coil is insufficient to attract the strip P, for the normal values of the armature current

When the motor is overloaded, that is the armature current exceeds the normal rated value, P is attracted by the electromagnet of the OLC and closes the contact aa thus, the No Voltage Coil is short-circuited, shown in the figure of 3 Point Starter. As a result, the handle H is released, which returns to the OFF position, and the motor supply is cut off.

To stop the motor, the starter handle should never be pulled back as this would result in burning the starter contacts. Thus, to stop the motor, the main switch of the motor should be opened.

Drawbacks of a 3 Point Starter

The following drawbacks of a 3 point starter are as follows:-

• The 3 point starter suffers from a serious drawback for motors with a large variation of speed by adjustment of the field rheostat.
• To increase the speed of the motor, the field resistance should be increased. Therefore, the current through the shunt field is reduced.
• The field current may become very low because of the addition of high resistance to obtain a high speed.
• A very low field current will make the holding electromagnet too weak to overcome the force exerted by the spring.
• The holding magnet may release the arm of the starter during the normal operation of the motor and thus, disconnect the motor from the line. This is not a desirable action.

Hence, to overcome this difficulty, the 4 Point Starter is used.

Also See: 4 Point Starter

The post 3 Point Starter appeared first on Circuit Globe.

The armature flux causes two effects on the main field flux.

• The armature reaction distorted the main field flux.
• It reduces the magnitude of the main field flux.

Consider the figure below shows the two poles dc generator. When no load connected to the generator, the armature current becomes zero. In this condition, only the MMF of the main poles exists in the generator. The MMF flux is uniformly distributed along the magnetic axis. The magnetic axis means the centre line between the north and south pole. The arrow in the below-given image shows the direction of the magnetic flux Φ_M. The magnetic neutral axis or plane is perpendicular to the axis of the magnetic flux.

The MNA coincides with the geometrical neutral axis (GNA). The brushes of the DC machines are always placed in this axis, and hence this axis is called the axis of commutation.

Consider the condition in which only the armature conductors carrying current and no current flows through their main poles. The direction of the current remains the same in all the conductors lying under one pole. The direction of current induces in the conductor is given by the Fleming right-hand rule. And the direction of flux generates in the conductors is given by the corkscrew rule.

The direction of current on the left sides of the armature conductor goes into the paper (represented by the cross inside the circle). The armature conductors combine their MMF for generating the fluxes through the armature in the downward direction.

Similarly, the right-hand side conductors carry current, and their direction goes out of the paper (shown by dots inside the circle). The conductor on the right-hand sides is also combining their MMF for producing the flux in the downwards direction. Hence, the conductor on both sides combines their MMF in such a way so that their flux goes downward direction. The flux induces in the armature conductor Φ_A is given by the arrow shown above.

The figure below shows the condition in which the field current and the armature current are simultaneously acting on the conductor.

This happens when machines running at no-load condition. Now the machine has two fluxes, i.e., the armature flux and the field pole flux. The armature flux is produced by the current induced in the armature conductors while the field pole flux is induced because of the main field poles. These two flux combines and gives the resultant flux Φ_R as shown in the figure above.

When the field flux enters into the armature, they may get distorted. The distortion increases the density of the flux in the upper pole tip of the N-pole and the lower pole tip of the south pole. Similarly, the density of flux decreases in the lower pole tip of the north pole and the upper pole tip of the south pole.

The resultant flux induces in the generator are shifted towards the direction of the rotation of the generator. The magnetic neutral axis of poles is always perpendicular to the axis of the resultant flux. The MNA is continuously shifted with the resultant flux.

Effect of Armature Reaction

The effects of Armature Reaction are as follows:-

• Because of the armature reaction the flux density of over one-half of the pole increases and over the other half decreases. The total flux produces by each pole is slightly less due to which the magnitude of the terminal voltage reduces. The effect due to which the armature reaction reduces the total flux is known as the demagnetizing effect.
• The resultant flux is distorted. The direction of the magnetic neutral axis is shifted with the direction of resultant flux in the case of the generator, and it is opposite to the direction of the resultant flux in the case of the motor.
• The armature reaction induces flux in the neutral zone, and this flux generates the voltage that causes the commutation problem.

The MNA axis is the axis in which the value of induced MEF becomes zero. And the GNA divides the armature core into two equal parts.

The post Armature Reaction in a DC Generator appeared first on Circuit Globe.

A motor operates in two modes – Motoring and Braking. A motor drive capable of operating in both directions of rotation and of producing both motoring and regeneration is called a Four Quadrant variable speed drive.

In motoring mode, the machine works as a motor and converts the electrical energy into mechanical energy, supporting its motion. In braking mode, the machine works as a generator and converts mechanical energy into electrical energy and as a result, it opposes the motion. The Motor can work in both, forward and reverse directions, i.e., in motoring and braking operations.

The product of angular speed and torque is equal to the power developed by a motor. For the multi-quadrant operation of drives, the following conventions about the signs of torque and speed are used. When the motor is rotated in the forward direction the speed of the motor is considered positive. The drives which operate only in one direction, forward speed will be their normal speed.

In loads involving up and down motions, the speed of the motor which causes upward motion is considered to be in forward motion. For reversible drives, forward speed is chosen arbitrarily. The rotation in the opposite direction gives reverse speed which is denoted by a negative sign.

The rate of change of speed positively in the forward direction or the torque which provides acceleration is known as Positive motor torque. In the case of retardation, the motor torque is considered negative. Load torque is opposite to the positive motor torque in the direction.

The figure below shows the four-quadrant operation of drives:

In the I quadrant power developed is positive and the machine is working as a motor supplying mechanical energy. The I (first) quadrant operation is called Forward Motoring. II (second) quadrant operation is known as Braking. In this quadrant, the direction of rotation is positive, and the torque is negative, and thus, the machine operates as a generator developing a negative torque, which opposes the motion.

The kinetic energy of the rotating parts is available as electrical energy which may be supplied back to the mains. In dynamic braking, the energy is dissipated in the resistance. The III (third) quadrant operation is known as the reverse motoring. The motor works, in the reverse direction. Both the speed and the torque have negative values while the power is positive.

In the IV (fourth) quadrant, the torque is positive, and the speed is negative. This quadrant corresponds to the braking in the reverse motoring mode.

Applications of Four Quadrant Operation

• Compressor, pump and fan type load requires operation in the I quadrant only. As their operation is unidirectional, they are called one quadrant drive systems.
• Transportation drives require operation in both directions.
• If regeneration is necessary, application in all four quadrants may be required. If not, then the operation is restricted to quadrants I and III, and thus dynamic braking or mechanical braking may be required.
• In hoist drives, a four-quadrant operation is needed.

The four-quadrant operation and its relationship to speed, torque and power output are summarized below in the table:

Function	Quadrant	Speed	Torque	Power Output
Forward Motoring	I	+	+	+
Forward Braking	II	+	-	-
Reverse Motoring	III	-	-	+
Reverse Braking	IV	-	+	-

This is all about Four-Quadrant operation of DC Motor.

The post Four Quadrant Operation of DC Motor appeared first on Circuit Globe.

Contents:

• Circuit Diagram of the Hopkinson’s Test
• Calculation of the Efficiency of the Machine by Hopkinson’s Test
• Advantages of Hopkinson’s Test
• Disadvantages of Hopkinson’s Test

The mechanical output of the motor drives the generator, and the electrical output of the generator is used in supplying the input to the motor. Thus, the output of each machine acts as an input to the other machine.

When both the machines are running on the full load, the supply input is equal to the total losses of the machines. Hence, the power input from the supply is very small.

The circuit diagram of the Hopkinson’s Test is shown in the figure below:

Supply is given and with the help of a starter, the machine M starts and work as a motor. The switch S is kept open. The field current of M is adjusted with the help of rheostat field R_M, which enables the motor to run at rated speed. Machine G acts as a generator.

Since the generator is mechanically coupled to the motor, it runs at the rated speed of the motor.

The excitation of the generator G is so adjusted with the help of its field rheostat R_G that the voltage across the armature of the generator is slightly higher than the supply voltage. In actual, the terminal voltage of the generator is kept 1 or 2 volts higher than the supply voltage.

When the voltage of the generator is equal and of the same polarity as that of the busbar supply voltage, the main switch S is closed, and the generator is connected to the busbars. Thus, both the machines are now in parallel across the supply.

Under this condition, when the machines are running parallel, the generator is said to float. This means that the generator is neither taking any current nor giving any current to the supply.

Now with the help of a field rheostat, any required load can be thrown on the machines by adjusting the excitation of the machines with the help of field rheostats.

Let,

• V be the supply voltage
• I_L is the line current
• I_m is the input current to the motor
• I_g is the input current to the generator
• I_am is the motor armature current
• I_shm is the motor shunt field current
• I_shg is the generator shunt field current
• R_a is the armature resistance of each machine
• R_shm is the motor shunt field resistance
• R_shg is the generator shunt field resistance
• E_g is the generator induced voltage
• E_m is the motor induced voltage or back emf

We know,

Since the field flux is directly proportional to the field current.

Thus, the excitation of the generator shall always be greater than that of the motor.

Calculation of the Efficiency of the Machine by Hopkinson’s Test

• Power input from the supply = VI_L = total losses of both the machines
• Armature copper loss of the motor = I²_am R_a
• Field copper loss of the motor = I²_shm R_shm
• Armature copper loss of the generator = I²_ag R_a
• Field copper loss of the generator = = I²_shg R_shg

The constant losses Pc like iron, friction and windage losses are assumed to be equal and is written as given below.

Constant losses of both the machines = Power drawn from the supply – Armature and shunt copper losses of both the machines

Assuming that the constant losses known as stray losses are divided equally between the two machines.

Total stray loss per machine = ½ P_C

Efficiency of the Generator

• Output = VI_ag
• Constant losses for the generator is given as P_C/2
• Armature copper loss = I²_ag R_a
• Field copper loss = I²_shg R_shg

The efficiency of the generator is given by the equation shown below:

Efficiency of the Motor

• Constant losses of the motor are given as P_C/2
• Armature copper loss = I²_am R_a
• Field copper loss = I²_shm R_shm

The Efficiency of the motor is given by the equation shown below:

Advantages of Hopkinson’s Test

The main advantages of using Hopkinson’s test are as follows:

• This method is very economical.
• The temperature rise and the commutation conditions can be checked under rated load conditions.
• Stray losses are considered, as both the machines are operated under rated load conditions.
• Large machines can be tested at rated load without consuming much power from the supply.
• Efficiency at different loads can be determined.

Disadvantage of Hopkinson’s Test

The main disadvantage of this method is the necessity of two practically identical machines for performing the Hopkinson’s test. Hence, this test is suitable for large DC machines.

The post Hopkinson’s Test appeared first on Circuit Globe.

Electrical Braking allows smooth stops without any inconvenience to passengers.

When a loaded hoist is lowered, electric braking keeps the speed within safe limits. Otherwise, the machine or drive speed will reach dangerous values.

When a train goes down a steep gradient, electric braking is employed to hold the train speed within the prescribed safe limits. Electrical Braking is more commonly used where active loads are applicable. In spite of electric braking, the braking force can also be obtained by using mechanical brakes.

Disadvantages of Mechanical Braking

The main disadvantages of Mechanical Braking are as follows:

• It requires frequent maintenance and replacement of brake shoes.
• Braking power is wasted in the form of heat.

In spite of having some disadvantages of mechanical braking, it is also used along with the electric braking to ensure reliable operation of the drive. It is also used to hold the drive at the standstill because many braking methods do not produce torque at standstill condition.

Types of Electrical Braking

There are three types of Electric Braking in a DC motor. They are Regenerative Braking, Dynamic or Rheostatic Braking and Plugging or Reverse Current Braking.

For a detailed study of regenerative braking click on the link given below:

Also See: Regenerative Braking

Detail description of Dynamic Braking in given in the article Dynamic Braking or Rheostatic Braking.

Also See: Dynamic Braking or Rheostatic Braking of DC Motor

For more information on the topic Plugging or Reverse, Current Braking click on the link given below:

Also See: Plugging or Reverse Current Braking

The post Electrical Braking of DC Motor appeared first on Circuit Globe.

Thus, during plugging the effective voltage across the armature will be (V + E_b) which is almost twice the supply voltage. The armature current is reversed, and high braking torque is produced. An external current limiting resistor is connected in series with the armature to limit the armature current to a safe value.

The connection diagram of DC separately excited motor and its characteristics is shown in the figure below:

Where,

• V is the supply voltage
• R_b is the external resistance
• I_a is the armature current
• I_f is the field current.

Similarly, the connection diagram and the characteristic of the series motor in plugging mode is shown in the figure below:

For braking, a series motor either the armature terminals or field terminals are reversed. But both armature and field terminals are not reversed together. Reversing of both the terminals will give only normal working operation.

At the zero speed, the braking torque is not zero. The motor must be disconnected from the supply at or near zero speed when the motor is used for stopping a load. If the motor is not disconnected from the supply mains, the motor will speed up in the reverse direction. For disconnecting the supply, centrifugal switches are used.

The method of braking, known as Plugging or Reverse Current Braking is a highly insufficient method because, in addition to the power supplied by the load, power supplied by the source is also wasted in resistance.

Applications of Plugging

The Plugging is commonly used for the following purposes listed below:

• In controlling elevators
• Rolling Mills
• Printing Presses
• Machine tools, etc.

This is all about plugging or reverse current braking.

The post Plugging or Reverse Current Braking appeared first on Circuit Globe.

For the braking operation in Dynamic Braking, the motor is connected in two ways.

Firstly the separately excited or shunt motor can be connected either as a separately excited generator, where the flux is kept constant. The second way is that it can be connected to a self-excited shunt generator, with the field winding in parallel with the armature. The connection diagram of Dynamic Braking of separately excited DC motor is shown below:

When the machine works in the motoring mode.

The connection diagram is shown below when braking with separate excitation is done.

The connection diagram is shown below when braking with self-excitation is performed.

This method is also known as Rheostatic Braking because an external braking resistance R_b is connected across the armature terminals for electric braking. During electric braking, the kinetic energy stored in the rotating parts of the machine and the connected load is converted into electric energy, when the motor is working as a generator. The energy is dissipated as heat in the braking resistance R_b and armature circuit resistance R_a.

The connection diagram of the Dynamic Braking of DC Shunt Motor is shown below:

When the machine is working in the motoring mode.

The connection diagram of shunt motor braking with self and separate excitation is shown in the figure below:

For Dynamic Braking, the series motor is disconnected from the supply. A variable resistance R_b as shown in the figure below is connected in series, and the connections of the field windings are reversed.

Also,

The field connections are reversed so that the current through the field winding flows in the same direction as before i.e. from S₁ to S₂ so that the back EMF produces the residual flux. The machine now starts working as a self-excited series generator.

In self-excitation, the braking operation is slow. Hence, when quick braking is required, the machine is connected in self-excitation mode. A suitable resistance is connected in series with the field to limit the current to a safe value.

The Dynamic or Rheostatic Braking is an insufficient method of braking because all the energy which is generated is dissipated in the form of heat in the resistance.

The post Dynamic Braking or Rheostatic Braking of DC Motor appeared first on Circuit Globe.

The concept of speed regulation is different from the speed control. In speed regulation, the speed of the motor changes naturally whereas in dc motor the speed of the motor changes manually by the operator or by some automatic control device. The speed of DC Motor is given by the relation shown below:

Here equation (1) shows the speed is dependent upon the supply voltage V, the armature circuit resistance R_a and the field flux ϕ, which is produced by the field current.

Contents:

• • Armature Resistance Control of DC Motor
  • Disadvantages of Armature Resistance Control Method
  • Field Flux Control Method of DC Motor
  • By Using a Diverter
  • Tapped Field Control
  • Advantages of Field Flux Control
  • Armature Voltage Control of DC Motor

For controlling the speed of DC Motor, the variation in voltage, armature resistance and field flux is taken into consideration. There are three general methods of speed control of a DC Motor.

They are as follows.

• • • Variation of resistance in the armature circuit.
      This method is called Armature Resistance or Rheostatic control.
    • Variation in field flux
      This method is known as Field Flux Control.
    • Variation in applied voltage
      This method is also known as Armature Voltage Control.

The detailed discussion of the various method of controlling the speed is given below.

Armature Resistance Control of DC Motor

Shunt Motor

The connection diagram of a shunt motor of the armature resistance control method is shown below. In this method, a variable resistor R_e is put in the armature circuit. The variation in the variable resistance does not affect the flux as the field is directly connected to the supply mains.

The speed current characteristic of the shunt motor is shown below.

Series Motor

Now, let us consider a connection diagram of speed control of the DC Series motor by the armature resistance control method.

By varying the armature circuit resistance, the current and flux both are affected. The voltage drop in the variable resistance reduces the applied voltage to the armature, and as a result, the speed of the motor is reduced.

The speed–current characteristic of a series motor is shown in the figure below.

When the value of variable resistance Re is increased, the motor runs at a lower speed. Since the variable resistance carries full armature current, it must be designed to carry continuously the full armature current.

Disadvantages of Armature Resistance Control Method

• • • A large amount of power is wasted in the external resistance Re.
    • Armature resistance control is restricted to keep the speed below the normal speed of the motor and increase in the speed above normal level is not possible by this method.
    • For a given value of variable resistance, the speed reduction is not constant but varies with the motor load.
    • This speed control method is used only for small motors.

Field Flux Control Method of DC Motor

Flux is produced by the field current. Thus, the speed control by this method is achieved by control of the field current.

Shunt Motor

In a Shunt Motor, the variable resistor R_C is connected in series with the shunt field windings as shown in the figure below. This resistor R_C is known as a Shunt Field Regulator.

The shunt field current is given by the equation shown below:

The connection of RC in the field reduces the field current, and hence the flux is also reduced. This reduction in flux increases the speed, and thus, the motor runs at a speed higher than the normal speed.

Therefore, this method is used to give motor speed above normal or to correct the fall of speed because of the load.

The speed-torque curve for shunt motor is shown below:

Series Motor

In a series motor, the variation in field current is done by anyone method, i.e. either by a diverter or by a tapped field control.

By Using a Diverter

A variable resistance R_d is connected in parallel with the series field windings as shown in the figure below:

The parallel resistor is called a Diverter. A portion of the main current is diverted through a variable resistance R_d. Thus, the function of a diverter is to reduce the current flowing through the field winding. The reduction in field current reduces the amount of flux and as a result the speed of the motor increases.

Tapped Field Control

The second method used in a series motor for the variation in field current is by tapped field control. The connection diagram is shown below:

Here the ampere-turns are varied by varying the number of field turns. This type of arrangement is used in an electric traction system. The speed of the motor is controlled by the variation of the field flux.

The speed-torque characteristic of a series motor is shown below.

Advantages of Field Flux Control

The following are the advantages of the field flux control method.

• • • This method is easy and convenient.
    • As the shunt field is very small, the power loss in the shunt field is also small.

The flux cannot usually be increased beyond its normal values because of the saturation of the iron. Therefore, speed control by flux is limited to the weakening of the field, which gives an increase in speed.

This method is applicable over only to a limited range because if the field is weakened too much, there is a loss of stability.

Armature Voltage Control of DC Motor

In armature voltage control method the speed control is achieved by varying the applied voltage in the armature winding of the motor. This speed control method is also known as Ward Leonard Method, which is discussed in detail under the topic Ward Leonard Method or Armature Voltage Control. The link is provided below.

Also See: Ward Leonard Method of Speed Control of DC motor or Armature Voltage Control

The post Speed Control of DC Motor: Armature Resistance Control and Field Flux Control appeared first on Circuit Globe.

For small machines direct loading test is performed. For large shunt machines, indirect methods are used like Swinburne’s or Hopkinson’s test.

Contents:

• Efficiency when the machine is running as a Motor
• Efficiency when the machine is running as a Generator
• Advantages of Swinburne’s Test
• Disadvantages of Swinburne’s Test
• Limitations of Swinburne’s Test

The machine is running as a motor at rated voltage and speed. The connection diagram for DC shunt machine is shown in the figure below:

Let V be the supply voltage,

I₀ is the no-load current,

I_sh is the shunt field current,

Therefore, no load armature current is given by the equation shown below:

No-load input = VI₀

The no-load power input to the machine supplies the following, as given below:

• Iron loss in the core
• Friction losses in the bearings and commutators.
• Windage loss
• Armature copper loss at no load.

When the machine is loaded, the temperature of the armature winding and the field winding increases due to I²R losses.

For calculating I²R losses, hot resistances should be used. A stationary measurement of resistances at room temperature of t degree Celsius is made by passing a current through the armature and then field from a low voltage DC supply. Then the heated resistance, allowing a temperature rise of 50⁰C is found.

The equations are as follows:

Where, α₀ is the temperature coefficient of resistance at 0⁰C

Therefore,

Stray loss = iron loss + friction loss + windage loss = input at no load – field copper loss – no load armature copper loss

Also, constant losses,

If the constant losses of the machine are known, its efficiency at any other load can be determined as follows.

Let I be the load current at which efficiency is required.

Efficiency when the machine is running as a Motor.

Therefore, the total loss is given as:

The efficiency of the motor is given below.

Efficiency when the machine is running as a Generator.

Therefore, the total loss is given as:

The efficiency of the generator is given below:

Advantages of Swinburne’s Test

The main advantages of Swinburne’s test are as follows:

• The power required to test a large machine is small. Thus, this method is an economical and convenient method of testing of DC machines.
• As the constant loss is known the efficiency can be predetermined at any load.

Disadvantages of Swinburne’s Test

• Change in iron loss is not considered at full load from no load. Due to armature reaction flux is distorted at full load and, as a result, the iron loss is increased.
• As the Swinburne’s test is performed at no load. Commutation on full load cannot be determined whether it is satisfactory or not and whether the temperature rise is within the specified limits or not.

Limitations of Swinburne’s Test

• Machines having a constant flux are only eligible for Swinburne’s test. For examples – shunt machines and level compound generators.
• Series machines cannot run on light loads, and the value of speed and flux varies greatly. Thus, the Swinburne’s Test is not applicable for series machines.

This is all about Swinburne’s Test.

The post Swinburne’s Test appeared first on Circuit Globe.