The voltage induced in secondary winding of transformer either in phase arrangement or a position comparison with primary voltages how the output terminal are consider when the terminal have been (DO).For high voltages and (c,d,a) for low voltage when the voltage induced between d and q in phase with voltage induced between d and q in phase with voltage induced the polarity is said to be subtractive otherwise polarity is addition.
When two corresponding terminals (Dand q) have been interconnected a suitable voltage is connected to one of the winding DO and the voltage assured between other two terminal.Q and q if the voltage connected between the terminals DO. The polarity is subtractive otherwise it is additive.
The short circuit test consists in measuring the input characteristics (quantities) of the transformer when the secondary side is shorted and the primary side is supplied with a suitable decreased voltage so that the current in the winding are equal to related current.The purpose of the test is to determined:
(1)The value of copper loss in the winding
(2)The value of short circuit voltage (Vsc) ,resistance (Ro1) and reactance (Xo1).
The instruments are arranged as for the circuit diagram and small voltage about 10% of the rotted value is supplied to primary side keeping the secondary side short circuited.Voltage is gradually increased till rotted current flow in winding which is recorded by ammeter.This value of voltage whose cause to flow rotted current in short circuited condition is called short circuited voltage (Vsc).
Watt meter reading gives the value of 'Cu' loss.Iron in this case is very much negligible (But value is same as in no-load) then Cu loss.Copper loss depend on current similarly iron loss depend on voltage therefore copper loss is negligible in no-load and iron loss is neglible in short circuit condition.
(1)The value of copper loss in the winding
(2)The value of short circuit voltage (Vsc) ,resistance (Ro1) and reactance (Xo1).
The instruments are arranged as for the circuit diagram and small voltage about 10% of the rotted value is supplied to primary side keeping the secondary side short circuited.Voltage is gradually increased till rotted current flow in winding which is recorded by ammeter.This value of voltage whose cause to flow rotted current in short circuited condition is called short circuited voltage (Vsc).
Watt meter reading gives the value of 'Cu' loss.Iron in this case is very much negligible (But value is same as in no-load) then Cu loss.Copper loss depend on current similarly iron loss depend on voltage therefore copper loss is negligible in no-load and iron loss is neglible in short circuit condition.
When a test is performed by leaving one winding open and giving supply to the another side,the test on the transformer is performed to ensure the working condition to the transformer.The main of the open circuit test are as follows:
(a)To find no-load current (Io)
(b)To obtain no-load parameters i.e,IuIwRo1Xo
(c)To find core loss (V1Iocos)
Supply is given to low voltage side of the transformer because it is either to use lower rating equipment for the measurement.Supply is given through auto transformer to get variable voltage and also for matching winding voltage capacity.Supply voltage V1 is indicated by voltmeter,no load current.Io is measured by ammeter and core loss is given by watt meter.Secondary side was no current hence there is no copper (Cu) loss and primary side has small amount of no load current hence small copper loss is there which can be ignored.In this way,open circuit test is carried out in the transformer.
(a)To find no-load current (Io)
(b)To obtain no-load parameters i.e,IuIwRo1Xo
(c)To find core loss (V1Iocos)
Supply is given to low voltage side of the transformer because it is either to use lower rating equipment for the measurement.Supply is given through auto transformer to get variable voltage and also for matching winding voltage capacity.Supply voltage V1 is indicated by voltmeter,no load current.Io is measured by ammeter and core loss is given by watt meter.Secondary side was no current hence there is no copper (Cu) loss and primary side has small amount of no load current hence small copper loss is there which can be ignored.In this way,open circuit test is carried out in the transformer.
TRANSFORMER ON NO-LOAD
When there is no load connected in secondary side operation of transformer is called no load operation in the case of transformer draw a small amount of current which is called no-load current (Io). No-load current is 5% to 10% of full load current.No load current is utilized for magnetizing to core and eddy current loss the hysteresis loss.It means Io has two component one is magnetizing component (Iu) and another is working component (Iw).Now from phasor diagram
Io=..
Iw=Iocos..
where cos is power factor in no load case and.. is phase angle between V1 and Io.Now power consumed on no-load operation
P=V1Iocos..
TRANSFORMER ON LOAD
When certain load is connected to transformer load current I2 start to flow in secondary coil.This current will set up () flux in the core in opposite direction to no-load flux ().() will link to primary winding and induced some voltage in the primary coil decreases.Now potential difference between supply and winding voltage will be increased.Hence additional current I2 will start to flow in addition to Io in primary side. Amount of I2 depends on amount of I2.Now I2 in primary side sets up into its own flux ().Hence () and () get conduced each other resulting only () in the core.Therefore in this transformer flux remains constant in the core.
N2I2=N1I2
N2/N1=I2/I2
Transformer
Transformer is that electrical machine which transfer electrical energy from one part to another part (i.e primary winding to secondary winding) without changing the frequency of the supply by the use of transformer voltage level can be increased or decreased.
Principle or operation
The winding where input is given is called primary winding and from where output is taken out that winding is called secondary winding.There is no electrical connection to common core.
Voltage available in primary winding is called primary voltage (V1).Similarly voltage in secondary side is called secondary voltage (V2).N1 is the no. of turns in primary and N2 is the no. of turns in secondary.When supply is given to primary side small amount of current circulated in primary winding which produced flux and flux flow towards secondary winding through a core made of silicon steel. The flux in the core made of silicon steel. The flux in the core made of silicon steel.The flux in-the core comes in contact with secondary winding and voltage is induced according to Faraday's law of electro magnetic induced. Voltage level can be increased or decreased by increasing or decreasing no. of turn in secondary side.
If voltage level of secondary side greater than primary side then the transformer is called step up transformer. If the voltage level of secondary side is lower than the primary side than the primary side then the transformer is called step down transformer.
Transformer is that electrical machine which transfer electrical energy from one part to another part (i.e primary winding to secondary winding) without changing the frequency of the supply by the use of transformer voltage level can be increased or decreased.
Principle or operation
The winding where input is given is called primary winding and from where output is taken out that winding is called secondary winding.There is no electrical connection to common core.
Voltage available in primary winding is called primary voltage (V1).Similarly voltage in secondary side is called secondary voltage (V2).N1 is the no. of turns in primary and N2 is the no. of turns in secondary.When supply is given to primary side small amount of current circulated in primary winding which produced flux and flux flow towards secondary winding through a core made of silicon steel. The flux in the core made of silicon steel. The flux in the core made of silicon steel.The flux in-the core comes in contact with secondary winding and voltage is induced according to Faraday's law of electro magnetic induced. Voltage level can be increased or decreased by increasing or decreasing no. of turn in secondary side.
If voltage level of secondary side greater than primary side then the transformer is called step up transformer. If the voltage level of secondary side is lower than the primary side than the primary side then the transformer is called step down transformer.
(1) It protects armature conductor from short circuit.At starting position of motor.It cannot rotates immediately due to inertia at that time N=0, and Eb=a. Thus maximum current is flow from the armature.
(2) It helps to produce required amount of torque.When motor is over loaded it's speed decreases and then Eb also decreases but Ia increase Eb=Z
So the motor develops more torque to over come additional load.Similarly when the motor is under loaded,it is speed increases and Eb also increases but Ia decrease so the motor develop less torque to compensates the respective load.In every energy conversion their must be an opposing agent in this case Eb.Opposes the source voltage V.d So that the source V has to supply current against the Eb and the cause to rotate the armature and hence electrical energy is converts in mechanical energy.
(2) It helps to produce required amount of torque.When motor is over loaded it's speed decreases and then Eb also decreases but Ia increase Eb=Z
So the motor develops more torque to over come additional load.Similarly when the motor is under loaded,it is speed increases and Eb also increases but Ia decrease so the motor develop less torque to compensates the respective load.In every energy conversion their must be an opposing agent in this case Eb.Opposes the source voltage V.d So that the source V has to supply current against the Eb and the cause to rotate the armature and hence electrical energy is converts in mechanical energy.
Characteristics of DC motor
The characteristics curve of a motor are those curves which show relation ships between the following quantities.
(1) Torque and armature current (Ta/Ia) characteristics
(2) Speed and armature current (N/Ia) characteristics
(3) Speed and torque (N/Ta)
Characteristics of series motor:
(1) Ta/Ia characteristics:
In series motor field winding also carry the armature current.Therefore Ia is proportional to flux upto the point of magnetic saturation.
At the decreasing load Ia and flux is small.But as Ia is increase.Ta decrease as the square of the current.Hence Ta/Ia curve is a parabola. After saturation flux is almost independ of Ia.Hence Ta is directly proportional to Ia only so tje characteristics becomes straight lines.The shaft torque (Tsh) is less than armature torque due to stray loss.After saturation flux is constant over the Ia is increases.
(2) N/Ia characteristics
When load is heavy Ia is large.Hence speed is low this decrease Eb.Hence increasing Ia decrease Eb.But small Ia speed varies inversely as armature current.DC series motor has higher starting torque and low speed so it is useful for traction purpose like trolly bus, electirc train, roapway, machine.
(3) N/Ta characteristics
When torque is increased,armature has the supply more,current and Ia=If and hence flux increases but Eb decrease resulting low value of speed.When the torque is decrease or no load or light load condition the armature or field draws very low value of current and flux will be very low.So the speed is dangerously high.Therefore it is said that dc series motor should never be start on without load.
The characteristics curve of a motor are those curves which show relation ships between the following quantities.
(1) Torque and armature current (Ta/Ia) characteristics
(2) Speed and armature current (N/Ia) characteristics
(3) Speed and torque (N/Ta)
Characteristics of series motor:
(1) Ta/Ia characteristics:
In series motor field winding also carry the armature current.Therefore Ia is proportional to flux upto the point of magnetic saturation.
At the decreasing load Ia and flux is small.But as Ia is increase.Ta decrease as the square of the current.Hence Ta/Ia curve is a parabola. After saturation flux is almost independ of Ia.Hence Ta is directly proportional to Ia only so tje characteristics becomes straight lines.The shaft torque (Tsh) is less than armature torque due to stray loss.After saturation flux is constant over the Ia is increases.
(2) N/Ia characteristics
When load is heavy Ia is large.Hence speed is low this decrease Eb.Hence increasing Ia decrease Eb.But small Ia speed varies inversely as armature current.DC series motor has higher starting torque and low speed so it is useful for traction purpose like trolly bus, electirc train, roapway, machine.
(3) N/Ta characteristics
When torque is increased,armature has the supply more,current and Ia=If and hence flux increases but Eb decrease resulting low value of speed.When the torque is decrease or no load or light load condition the armature or field draws very low value of current and flux will be very low.So the speed is dangerously high.Therefore it is said that dc series motor should never be start on without load.
Types of DC motor
There are three types of DC motor.They are:
(1) Series motor
(2) Shunt motor
(3) Compound motor
(1) Series motor
In series motor the winding is joined in series with the armature
conductors.As they carry full load current, field winding consists of a few turns of thick wire.
In series motor supply current I is equal to field current (If) and armature current (Ia) if (Ra) be armature winding resistance and (Rf) be field winding resistance.
I=Ia=If-(1)
V=Eb+(+,-)If Rf+Ia Ra-(2)
=Eb+I (Rf+Ra)-(3)
I=(V-Eb/Rf+Ra)-(4)
(2) Shunt motor:
In shunt motor field winding are connected across or in parallel with the armature conductor.Shunt field winding have maximum resistance.It is wounded many turns with thin wire.The same applied volt
age is available in both armature and field winding.
In this type of motor
I= Ia+If-(1)
If= V/Rf-(2)
V= (Eb+Ia Ra)-(3)
Ia= (V-Eb/Ra)-(4)
(3) Compound motor:
In compound motor both shunt and series field is stronger than series field.When the series field flux aids the shunt field flux then motor is said to be commutativity compound motor in which fluxes and series are added.
On the other hand if series field opposes the motor is said to be differentially compound in which the fluxes series are subtracted.
There are three types of DC motor.They are:
(1) Series motor
(2) Shunt motor
(3) Compound motor
(1) Series motor
In series motor the winding is joined in series with the armature
conductors.As they carry full load current, field winding consists of a few turns of thick wire.In series motor supply current I is equal to field current (If) and armature current (Ia) if (Ra) be armature winding resistance and (Rf) be field winding resistance.
I=Ia=If-(1)
V=Eb+(+,-)If Rf+Ia Ra-(2)
=Eb+I (Rf+Ra)-(3)
I=(V-Eb/Rf+Ra)-(4)
(2) Shunt motor:
In shunt motor field winding are connected across or in parallel with the armature conductor.Shunt field winding have maximum resistance.It is wounded many turns with thin wire.The same applied volt
age is available in both armature and field winding.In this type of motor
I= Ia+If-(1)
If= V/Rf-(2)
V= (Eb+Ia Ra)-(3)
Ia= (V-Eb/Ra)-(4)
(3) Compound motor:
In compound motor both shunt and series field is stronger than series field.When the series field flux aids the shunt field flux then motor is said to be commutativity compound motor in which fluxes and series are added.
On the other hand if series field opposes the motor is said to be differentially compound in which the fluxes series are subtracted.
Motor is an electrical machine which converts the electrical energy into the mechanical energy.
It's action is based on the principle that when a current carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Flemming's left hand rule.Constructionally there is no difference between DC motor and DC generator.
When the DC supply is provided to field pole through field winding so that it produces uniform magnetic field in between the field poles where armature is placed.Again the DC supply is feed to armature winding through carbon brush and commutator segments, the current enters through C1X1B and comes out through A1Y1C2.Then by principle when current carrying armature winding placed in magnetic field ,the armature experiences a force and hence it rotates in clock wise direction (due to Flemming's left hand rule).
After 180 degree rotation the commutator segments change it's position therefore the direction of current is same and hence the motor rotates in same direction i.e,clockwise direction.
It's action is based on the principle that when a current carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Flemming's left hand rule.Constructionally there is no difference between DC motor and DC generator.
When the DC supply is provided to field pole through field winding so that it produces uniform magnetic field in between the field poles where armature is placed.Again the DC supply is feed to armature winding through carbon brush and commutator segments, the current enters through C1X1B and comes out through A1Y1C2.Then by principle when current carrying armature winding placed in magnetic field ,the armature experiences a force and hence it rotates in clock wise direction (due to Flemming's left hand rule).
After 180 degree rotation the commutator segments change it's position therefore the direction of current is same and hence the motor rotates in same direction i.e,clockwise direction.
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