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SUMPNERS TEST

AIM :To predetermine the efficiency and regulation of a given single phase

Transformer by conducting back-to-back test and also to find the parametersof the equivalent circuit.

APPARATUS REQUIRED:

S.

No.

Name of the Apparatus Range Type Quantity

1 Auto Transformer (0-270) V - 2

2 Wattmeter 300 V, 10A

75 V, 5 A

LPF

UPF

1

1

3 Ammeter (0-2) A

(0-20) A

MI

MI

1

1

4 Voltmeter (0-75) V

(0-150) V

MI

MI

1

1

5 Connecting Wires 2.5sq.mm Copper Few

PRECAUTIONS:1. Auto Transformer whose variac should be in zero position, before

switching on the ac supply.2. Transformer should be operated under rated values.

PROCEDURE:

1. Connections are made as shown in the circuit diagram.2. Rated voltage of 110V is adjusted to get in voltmeter by adjusting the

variac of the Auto Transformer which would be in zero beforeswitching on the supply at the primary side.

3. The readings of voltmeter, ammeter and wattmeter are noted on theprimary side.

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4. A voltmeter is connected across the secondary and with the secondarysupply off i.e switch S is kept open. The voltmeter reading is noted.

5. If the reading of voltmeter reads higher voltage, the terminals of anyone of secondary coil is interchanged in order that voltmeter readszero.

6. The secondary is now switched on and SPST switch is closed withvariac of auto transformer is zero.

7. After switching on the secondary the variac of transformer (Auto) isadjusted so that full load rated secondary current flows.

8. Then the readings of wattmeter, Ammeter and voltmeter are noted.9. The Percentage Efficiency and percentage regulation are calculated

and equivalent circuit is drawn.
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FORMULAE:W1

Core loss of each transformer W o = ----- Watts2

W2Full load copper loss of each transformer W c = ------ Watts.

2

Wo IoWo = V1I1 Cos o o = Cos -1 --------- I 1 = ---- A

V1 I1 2

Iw = I 1 Cos o I = I 1 Cos V2 = Vs/2 x A

Ro = V 1 / Iw Xo = V 1 / I R o2 = Wc /I22 Zo2 = V2 / I2

Xo 2 = Zo 22 Ro 22

Copper loss at various loads = I 22 Ro 2

PERCENTAGE REGULATION:

1. Upf : I 2 / V (Ro 2 Cos o) X 100

2. Lagging pf : I 2 / V (Ro 2 Cos o + Xo 2Sin o) X 100

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3. Leading pf : I 2 / V (Ro 2 Cos o - Xo 2Sin o) X 100

Output Power (1) Upf : 3Kw(2) Pf : 3Kw Cos o

Input Power = Output Power + Core loss + Cu loss

Output power Efficiency % = -------------------------- X 100%

Input Power

EQUIVALENT CIRCUIT:
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MODEL GRAPHS:

RESULT:Thus the efficiency and regulation of a given single phase

Transformer is carried out by conducting back-to-back test and theequivalent circuit parameters are found out.
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HOPKINSONS TEST

AIM:To conduct Hopkinsons test on a pair of identical DC machines

to pre-determine the efficiency of the machine as generator and asmotor.

APPARATUS REQUIRED:

S.No. Apparatus Range Type Quantity

1 Ammeter (0-1)A

(0-20) A

MC

MC

1

2

2 Voltmeter (0-300) V

(0-600)V

MC

MC

1

1

3 Rheostats 1250 , 0.8AWire

Wound2

4 Tachometer (0-3000) rpm Digital 1

5 Resistive Load 5KW,230V - 1

6 Connecting Wires 2.5sq.mm. Copper Few

PRECATUIONS:1. The field rheostat of the motor should be in the minimum position at

the time of starting and stopping the machine.2. The field rheostat of the generator should be in the maximum positionat the time of starting and stopping the machine.

3. SPST switch should be kept open at the time of starting and stoppingthe machine.

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PROCEDURE:1. Connections are made as per the circuit diagram.2. After checking the minimum position of field rheostat of motor,

maximum position of field rheostat of generator, opening of SPSTswitch, DPST switch is closed and starting resistance is graduallyremoved.

3. The motor is brought to its rated speed by adjusting the field rheostatof the motor.

4. The voltmeter V 1 is made to read zero by adjusting field rheostat of generator and SPST switch is closed.

5. By adjusting field rheostats of motor and generator, various Ammeter readings, voltmeter readings are noted.

6. The rheostats and SPST switch are brought to their original positionsand DPST switch is opened.
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TABULAR COLUMN:

S.No.

Supply

Voltage

V(Volts)

I1(Amps)

I2(Amps)

I3(Amps)

I4(Amps)

I1 + I2(Amps)

Mot

Armat

Cu Lo

W (wa

AS MOTOR:

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S.No.V

(Volts)

I1

(Amps)

I2

(Amps)

I3

(Amps)

Motor

Armature

Cu LossW (Watts)

Field Loss

(Watts)

str

AS GENERATOR:

S.No.V

(Volts)

I1(Amps)

I2(Amps)

Motor

Armature

Cu LossW (Watts)

Field Loss

(Watts)

Stray

losses

/2(Watts)

T

L

(W
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PROCEDURE:1. Connections are made as per the circuit diagram.

2. Supply is given by closing the DPST switch.3. Readings of Ammeter and Voltmeter are noted.4. Armature resistance in Ohms is calculated as R a = (Vx1.5) /I

TABULAR COLUMN:

S.No. Voltage

V (Volts)

Current

I (Amps)

Armature Resistance

R a (Ohms)

FORMULAE:

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Input Power = VI 1 wattsMotor armature cu loss = (I 1+ I2)2 Ra watts

Generator armature cu loss = I 22 Ra watts

Total Stray losses W = V I 1 - (I1+I2)2 Ra + I 22 Ra watts.Stray loss per machine = W/2 watts.

AS MOTOR:Input Power = Armature input + Shunt field input

= (I1+ I2) V + I 3V = (I 1+I2+I3) VTotal Losses = Armature Cu loss + Field loss +stray loss

= (I1 + I2)2 Ra + VI 3 + W/2 wattsInput power Total Losses

Efficiency % = -------------------------------------x 100%

Input Power AS GENERATOR:

Output Power = VI 2 wattsTotal Losses = Armature Cu loss+ Field Loss +

Stray loss= I22 Ra + VI 4 + W/2 watts

Output power Efficiency % = -------------------------------------- x

100%Output Power+ Total Losses

MODEL GRAPH:

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RESULT:
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Thus Hopkinsons test is conducted on a pair of identical DC machines

the efficiency of the machine as generator and as motor are pre-

determinedOPEN CIRCUIT CHARACTERISTICS OF SEPARATELY EXCITED

DC SHUNT GENERATOR

AIM:To obtain open circuit characteristics of separately excited DC

shunt generator.

APPARATUS REQUIRED:

S.No. Apparatus Range Type Quantity1 Ammeter (0-1)A MC 1

2 Voltmeter (0-300)V MC 1

3 Rheostats 1250 , 0.8A Wire Wound 2

4 Tachometer (0-1500)rpm Digital 1


PRECAUTIONS:

1. The field rheostat of motor should be in minimum resistance positionat the time of starting and stopping the machine.

2. The field rheostat of generator should be in maximum resistanceposition at the time of starting and stopping the machine.


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2. After checking minimum position of motor field rheostat, maximumposition of generator field rheostat, DPST switch is closed and startingresistance is gradually removed.

3. By adjusting the field rheostat, the motor is brought to rated speed.4. By varying the generator field rheostat, voltmeter and ammeter

readings are taken.5. After bringing the generator rheostat to maximum position, field

rheostat of motor to minimum position, DPST switch is opened.

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TABULAR COLUMN:

S.No.Field Current

If (Amps)

Armature Voltage

E o (Volts)

MODEL GRAPH:

If (Amps)

RESULT:Thus open circuit characteristics of separately excited DC shunt

generator is obtained.

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AIM:To obtain open circuit characteristics of separately excited DC

shunt generator.

APPARATUS REQUIRED:


1 Ammeter (0-1)A MC 1





PRECAUTIONS:1. The field rheostat of motor should be in minimum resistance position

at the time of starting and stopping the machine.2. The field rheostat of generator should be in maximum resistance

position at the time of starting and stopping the machine.

PROCEDURE:

1. Connections are made as per the circuit diagram.2. After checking minimum position of motor field rheostat, maximum

position of generator field rheostat, DPST switch is closed and startingresistance is gradually removed.

3. By adjusting the field rheostat, the motor is brought to rated speed.

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4. By varying the generator field rheostat, voltmeter and ammeter readings are taken.

5. After bringing the generator rheostat to maximum position, fieldrheostat of motor to minimum position, DPST switch is opened.
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TABULAR COLUMN:

S.No.Field Current

If (Amps)

Armature Voltage

E o (Volts)

MODEL GRAPH:

If (Amps)

RESULT:Thus open circuit characteristics of separately excited DC shunt

generator is obtained.

LOAD CHARACTERISTICS OF SELF EXCITED

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DC SHUNT GENERATOR

AIM:To obtain internal and external characteristics of DC shunt

generator.

APPARATUS REQUIRED:


1 Ammeter (0-2)A

(0-20) A

MC

MC

1

1


3 Rheostats 1200

, 0.8A Wire Wound 24 Loading Rheostat 5KW, 230V - 1



PRECAUTIONS:1. The field rheostat of motor should be at minimum position.

2. The field rheostat of generator should be at maximum position.

3. No load should be connected to generator at the time of startingand stopping.


2. After checking minimum position of DC shunt motor fieldrheostat and maximum position of DC shunt generator field

rheostat, DPST switch is closed and starting resistance isgradually removed.

3. Under no load condition, Ammeter and Voltmeter readings arenoted, after bringing the voltage to rated voltage by adjusting thefield rheostat of generator.

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4. Load is varied gradually and for each load, voltmeter andammeter readings are noted.

5. Then the generator is unloaded and the field rheostat of DCshunt generator is brought to maximum position and the fieldrheostat of DC shunt motor to minimum position, DPST switch isopened.

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DETERMINATION OF ARMATURE RESISTANCE:

PROCEDURE:1. Connections are made as per the circuit diagram.2. Supply is given by closing the DPST switch.3. Readings of Ammeter and Voltmeter are noted.4. Armature resistance in Ohms is calculated as R a = (Vx1.5) /I

TABULAR COLUMN:
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S.No. Voltage

V (Volts)

Current

I (Amps)

Armature Resistance

R a (Ohms)

TABULAR COLUMN:

FORMULAE:Eg = V + I a R a (Volts)

Ia = IL + If (Amps)Eg : Generated emf in Volts

S.No.Field Current

If (Amps)Load Current

IL (Amps)Terminal Voltage

(V) VoltsIa = IL + If (Amps)

E g =V Ia R a(Vol

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V : Terminal Voltage in VoltsIa : Armature Current in AmpsIL : Line Current in AmpsIf : Field Current in AmpsR a : Armature Resistance in Ohms

MODEL GRAPH:

RESULT:Thus the load characteristics of self excited DC shunt generator

is obtained.

OPEN CIRCUIT CHARACTERISTICS OF SELF EXCITED
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DC SHUNT GENERATOR

AIM:To obtain open circuit characteristics of self excited DC shunt

generator and to find its critical resistance.

APPARATUS REQUIRED:


1 Ammeter (0-1)A MC 1



4 SPST Switch - - 15 Tachometer (0-1500)rpm Digital 1


PRECAUTIONS:1. The field rheostat of motor should be in minimum resistance


2. The field rheostat of generator should be in maximum resistance


3. SPST switch is kept open during starting and stopping.


2. After checking minimum position of motor field rheostat,maximum position of generator field rheostat, DPST switch isclosed and starting resistance is gradually removed.

3. By adjusting the field rheostat, the motor is brought to ratedspeed.

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4. Voltmeter and ammeter readings are taken when the SPSTswitch is kept open.

5. After closing the SPST switch, by varying the generator fieldrheostat, voltmeter and ammeter readings are taken.

6. After bringing the generator rheostat to maximum position, fieldrheostat of motor to minimum position, SPST switch is openedand DPST switch is opened.

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TABULAR COLUMN:

S.No.Field Current

If (Amps)

Armature Voltage

E o (Volts)

MODEL GRAPH:

RESULT:Thus open circuit characteristics of self excited DC shunt

generator are obtained and its critical resistance is determined.
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Documents

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