S J P N Trust's

Hirasugar Institute of Technology, Nidasoshi.

Inculcating Values, Promoting Prosperity
Approved by AICTE New Delhi, Recognized by Govt. of Karnataka and
Affiliated to VTU Belagavi.

Tq: Hukkeri Dist: Belagavi

DEPARTMENT OF ELECTRICAL & ELECTRONICS

ENGG.

LABORATORY MANUAL

Name of the Lab: Electrical Machine Laboratory-I

Semester: III
Subject Code: 17EEL37
Staff Incharge: Prof. A. U. Neshti

Prof P M Murari
 Hirasugar Institute of Technology,Nidasohi
Sl. NO Experiments
1 Open Circuit and Short circuit tests on single phase step up or step
down transformer and predetermination of (i) Efficiency and
regulation (ii) Calculation of parameters of equivalent circuit.
2 Sumpner’s test on similar transformers and determination of
combined and individual transformer efficiency.
3 Parallel operation of two dissimilar single-phase transformers of
different kVA and determination of load sharing and analytical
verification given the Short circuit test data.
4 Polarity test and connection of 3 single-phase transformers in star –
delta and determination of efficiency and regulation under balanced
resistive load.
5 Comparison of performance of 3 single-phase transformers in delta –
delta and V – V (open delta) connection under load.
6 Scott connection with balanced and unbalanced loads.
7 Separation of hysteresis and eddy current losses in single phase
transformer.
8 Voltage regulation of an alternator by EMF and MMF methods.
9 Voltage regulation of an alternator by ZPF method.
10 Slip test – Measurement of direct and quadrature axis reactance and
predetermination of regulation of salient pole synchronous machines.
11 Performance of synchronous generator connected to infinite bus,
under constant power and variable excitation & vice - versa.
12 Power angle curve of synchronous generator

Dept. of Electrical and Electronics Engg. 2

 (I) CIRCUIT DIAGRAM:(Open Circuit test)

OBSERVATION:

1. KVA rating of transformer = KVA

2. Primary voltage = _V
3. Secondary voltage = _V
Voltage range × Curre
Wattmeter constant = nt Range
Full Scale Division of Wattmeter
TABULATION(OCC):

Sl.No Open Circuit Voltage No Load Current No Load Power (W0)

in Volts (V0) in Amps (I0) In Watts
1

CIRCUIT DIAGRAM:(Short circuit test)

TABULATION(SCC):

Sl.No Short Circuit Voltage No Load Current No Load Power

VSC (in Volts) ISC(in Amps) WSC (In Watts)
1
EXPT.NO.1 DATE:
OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE STEP UP
OR STEP DOWN TRANSFORMER AND PREDETERMINATION OF
(I) EFFICIENCY AND REGULATION
(II) CALCULATION OF PARAMETERS OF EQUIVALENT CIRCUIT.

AIM: Predetermination of efficiency and regulation by open circuit and short circuit test on single
phase transformer, also calculate equivalent circuit parameters from short circuit and open
circuit test .
APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Ammeter MI 0-2A 1No
2 Ammeter MI 0-5A 1No
3 Voltmeter MI 0-300V 1 No
4 Voltmeter MI 0-75V 1 No
5 Wattmeter 0-75V/0-5A UPF 1 No
6 Wattmeter 0-300V/0-2A LPF 1 No
7 Auto transformer 230V/0-260V 1-Phase, 1 No
8 Transformer 1KVA, 230V/115V,50Hz 1 No
9 Connecting wires -- Few
THEORY:
The OC and SC test are used to calculate the efficiency and regulation of a transformer.
Also, we find equivalent circuit parameters of transformer.
Open Circuit Test (OC Test):
The transformer primary is connected to AC supply through variac, ammeter and
Wattmeter. The secondary of the transformer is kept open. Usually low voltage side is used as
primary and high voltage side is used as secondary to conduct OC test.
The primary is excited by rated voltage which is adjusted precisely with the help of a variac. The
Wattmeter measures input power. The ammeter measures input current. The voltmeter gives the
value of rated primary voltage applied at rated frequency.
Sometimes a voltmeter may be connected across the secondary to measure secondary
voltage which is V2=E2. As the voltmeter resistance is very high secondary current is negligible.
Short circuit Test (SC Test):
The secondary of the transformer is short circuited with the help of thick copper wire or
solid links. As high voltage side is always low current side to supply and low current flows
through meters.As the secondary is short circuited its resistance is very small and on rated voltage
it will draw very large current such large current can cause overheating and burning of the
transformer. To limit this short circuit current primary is supplied with low voltage which is
enough to cause rated current to flow through primary. This can be observed on an ammeter. The
low voltage can be adjusted with the help of variac. Hence this test is also called Low voltage Test
or Reduced voltage Test.
PROCEDURE:a) Procedure for OC Test:

1. Connections are made as per the circuit diagram.

2. Ensure that the HV side of transformer winding is kept open and the knob of the
auto transformer at its zero position.
3. Switch ‘ON’ the power supply.
4. Slowly, go on varying the auto transformer knob until the voltmeter shows the rated
voltage of the transformer.
5. Note down the readings of the voltmeter, ammeter and wattmeter then bring the
auto transformer to its zero position.
6. Switch ‘OFF’ the supply.
b) Procedure for SC Test:
1. Connections are made as per the circuit diagram.
2. Ensure that the LV side of transformer winding is kept short circuited by thick
copper wire and the knob of the auto transformer at its zero position.
3. Switch ‘ON’ the power supply.
4. Slowly, go on varying the auto transformer knob until the ammeter connected on
HV side shows the rated current of the transformer.
5. Note down the readings of the voltmeter, ammeter and wattmeter then bring the
auto transformer to its zero position.
6. Switch ‘OFF’ the supply.

NATURE OF GRAPH:

CALCULATIONS:
I) PREDETERMINATION OF EFFICIENCY AND REGULATION
From Open Circuit Test:

Core loss �0 = �0�0𝑐𝑜𝑠∅0 Watts.

∴ No-load power factor = 𝑐𝑜𝑠∅0 = �0 =

�0 �0
Ic= �0𝑐𝑜𝑠∅0 =
Im = �0𝑠𝑖𝑛∅0 =
Once Ic and Im are known we can determine exciting circuit parameters as-
= Ω
�0 = 0�
�𝑐
= Ω
�0 �0
= ��
From Short Circuit Test:

Full load current of Transformer

𝐾�� ×1000
= �𝑎𝑡𝑒𝑑 𝑝𝑟𝑖�𝑎𝑟𝑦 �𝑜𝑙𝑡𝑎𝑔𝑒 = Amps

�𝑠𝑐 = �𝑠𝑐 �𝑠𝑐 𝑐𝑜𝑠∅𝑠𝑐 Watts.

∴ 𝑐𝑜𝑠∅ 𝑠𝑐 �
=�𝑠𝑐𝑠𝑐�𝑠𝑐 =

Also, �𝑠𝑐 = �2 �
𝑠𝑐
= 1𝑒 Ω
∴ �1𝑒 = 2𝑠𝑐
�
�𝑠𝑐

Vsc
Z = = R2 + X2 = Ω
1e 1e 1e
Isc
∴ X1e = Z2 − R2 = Ω
1e 1e

Practically:
𝑥 × 𝐾�� × 103 𝑐𝑜𝑠� × 100
%𝜂=
𝑥 × 𝐾�� × 103 × 𝑐𝑜𝑠� +0 � +
𝑥2�𝑠𝑐

Where, x= Load factor,

x =3/4 for 3/4th of load,

x = ½ for half load.

�1 �1𝑒 𝑐𝑜𝑠𝜑 ± �1 𝑥1𝑒 𝑠𝑖𝑛𝜑 × 100 +ve sign for lagging power factor
% Regulation = �1

–ve sign for leading power factor.

EFFICIENCY TABULATION:

LOAD 100%(x=1) 75%(x=3/4) 50%(x=1/2)

P.F 0.7 0.7 0.7
%η
REGULATION TABULATION:

Power %R %R
factor (Leading) (Lagging)
0.1
0.2
0.3
0.4
CONCLUSION:
VIVA VOCE
CIRCUIT DIAGRAM:

OBSERVATION:
1. KVA rating of transformer T1= KVA
2. Primary voltage = _V
3. Secondary voltage = _V
4. KVA rating of transformer T2= KVA
5. Primary voltage = V
6. Secondary voltage = V
7. Full load current = Amps.

Voltage range × Current Range

Wattmeter constant =
Full Scale Division of Wattmeter
for UPF Wattmeter

NATURE OF GRAPH:
EXPT.NO.2 DATE:
SUMPNER’S TEST ON SIMILAR TRANSFORMERS AND DETERMINATION
OF COMBINED AND INDIVIDUAL TRANSFORMER EFFICIENCY.

AIM: To conduct sumpner’-s test on similar transformers and determination of combined and
individual transformer efficiency.
APPARATUS REQUIRED:
S.no Particulars Range Quantity
1 Voltmeter MI 0-300V 1 Nos
2 Voltmeter MI 0-75V 2 Nos
3 Ammeter MI 0-2A 1 No
4 Ammeter MI 0-5A 1 No
5 Wattmeter MI 300V / 5A LPF 1 No
6 Wattmeter MI 75V/5A UPF 1 No
7 1-phase auto-transformer 230V/0-260V 2 Nos
1KVA, 230V/115V
8 Transformers 2 Nos
Single phase, 50Hz
9 Connecting wires -- Few
THEORY:
The Sumpner’s test is conducted simultaneously on two identical transformers and
provides data for finding the efficiency, regulation and the effect of temperature rise.

Operation: The secondary’s of the transformer are in phase opposition with switch S 1 closed and
switch S2 open, there will be no circulating current in the loop circuit. It is because the induced
emf’s in the secondaries are equal and in opposition. The reading of the wattmeter W 1 will be
equal to the core losses of two transformers.

W1= core loss of two transformers.

Now switch S2 is also closed and output voltage of the regulating transformer is adjusted
to fill full load current I2 flows in the secondary circuit. The full load secondary current will cause
full load current I1 in the primary circuit. Note that, full load current are flowing through the
primary and secondary windings. The reading of wattmeter W 2 will be equal to the full load
copper losses of the two transformers.
W2= Full load copper losses of two transformer.
Advantages:
1. The power required to carry out the test is small.
2. The transformers are tested under full load conditions.
3. The iron losses and copper losses are measured simultaneously.
PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Ensure that the position of the auto transformer knob at its zero position.
3. Switch ‘ON’ the power supply.
4. Slowly, go on varying the auto-transformer knob until the voltmeter shows the
rated voltage of the transformer. If the polarities are correct then voltmeter across
SPST switch shows zero, otherwise change the polarity of any one of the
transformer on secondary side.
5. When voltmeter across SPST switch shows zero reading.
6. Then note down the readings of wattmeter, Voltmeter, ammeter on the primary
side of transformer.
7. Then close SPST switch, Then vary the auto transformer knob, connected in
secondary side of transformer until ammeter shows its full load current.

Dept. of Electrical and Electronics Engg. 9

 Hirasugar Institute of Technology,Nidasohi
8. Then note down the readings of wattmeter, Voltmeter and ammeter on secondary
side of transformer.
9. Open the SPST switch and bring the auto transformer to its zero position.
10.Switch OFF the supply.
TABULATION:

I0 V0 W0 ISC VSC in WSC

S.no
In Amps in Volts In Watts in Amps Volts in Watts

Determination of combined and individual transformer efficiency.

Load 100% 80% 60% 40% 20%

P.F 0.8 0.8 0.8 0.8 0.8

Individual
transformer%
η
Combined
transformer %
η
CALCULATIONS:

i) Individual Transformer Efficiency:

Core loss of each transformer:

W0
 W= = Watts.
1
2

Copper loss of each transformer:

 W2 WSC
= 2
= Watts.

Full Load Current of Transformer:

 IL = KVA × 103 = Amps.

230

x × KVA × 103 ×cosφ

% η= × 100
(x ×KVA ×10 × cosφ) + W1 + x W2
3 2

Where x- Load factor

ii) Combined Transformer Efficiency:

Total core loss = W0 =W1 Watts.

Total Copper Loss=Wsc =W2 Watts.

Full Load Current of Transformer:
KVA
 IL = × 103 = Amps.
230

x × KVA × 103 ×cosφ

 % η= × 100
(x ×KVA ×103 × cosφ) + W1 + x2 W2
Where,

Where x- Load factor

CALCULATIONS:

CONCLUSION:

Dept. of Electrical and Electronics Engg. 11

 Hirasugar Institute of Technology,Nidasohi
VIVA VOCE
CIRCUIT DIAGRAM:

OBSERVATION:

1. KVA rating of the Transformer T1 = KVA

2. Primary voltage of Transformer T1 = V
3. Secondary voltage of Transformer T1= V
4. KVA rating of the Transformer T2 = KVA
5. Primary voltage of Transformer T2 = V
6. Secondary voltage of Transformer T2 = V
TABULATION:

ANALYTICAL VERIFICATION GIVEN THE SHORT CIRCUIT TEST DATA.

Za= Impedance of transformer 1= Vsc/Isc, Ω
Zb= Impedance of transformer 2= Vsc/Isc Ω

DETERMINATION OF LOAD SHARING

EXPT.NO.3 DATE:
PARALLEL OPERATION OF TWO DISSIMILAR SINGLE-PHASE
TRANSFORMERS OF DIFFERENT KVA AND DETERMINATION OF LOAD
SHARING AND ANALYTICAL VERIFICATION GIVEN THE SHORT CIRCUIT
TEST DATA.

AIM: Conduct an experiment to understand load sharing by two single phase transformer
connected in parallel.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter MI 0-300V 2No
2 Voltmeter MI 0-600V 1 No
3 Ammeter MI 0-5/10A 3 No
4 Auto transformer 1- 230V/0-260V 1 No
5 Transformer 1KVA, 230V/115V Single phase, 50Hz 1 No
6 Transformer 2KVA, 230V/115V Single phase, 50Hz 1 No
7 Connecting wires -- Few

THEORY:
The secondary emf of the two transformers are equal because they have the same turns ratio and
have their primary connected to the same supply.
The transformers are connected in parallel when the load on them is more than the rating
of individual transformer, generally smaller units are operated in parallel which share a common
load. The parallel operation is advantageous as they can be interchangeable in some conditions for
satisfactory. Hence polarity should be carried out for proper operation. The voltage ratio of
primary and secondary must be same. The % impedance should be same in magnitude and hence
same transformer ratio in order to avoid the circulating current and operating at different power
factor.
PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Ensure that the position of the auto transformer knob at its zero position, and SPST
switch in open position.
3. Switch ‘ON’ the power supply.
4. Give a small voltage using auto transformer and check with some positive voltage.
If the polarities are correct then voltmeter across SPST switch shows zero
otherwise change the polarities of any one of the transformer on the secondary
side.
5. When voltmeter across SPST switch shows zero reading then close SPST switch,
apply rated voltage of the transformer.
6. Then go ON varying the load in the steps and at each step note down all meter
readings.
7. Repeat this procedure until rated current of the transformer.
8. Bring load on the transformer to zero position, open the SPST switch and auto
transformer to its zero position.
9. Switch OFF the supply.
10.Conduct the short circuit test on the two transformers used for the parallel
operations & find transformer impedances (Za &Zb).
CALCULATIONS:

CONCLUSION:
VIVA VOCE
 CIRCUIT DIAGRAM:

I. POLARITY TEST:

a) SUBTRACTIVE:

- -

+ +

b) ADDITIVE:
EXPT.NO.4 DATE:
POLARITY TEST AND CONNECTION OF 3 SINGLE-PHASE TRANSFORMERS IN
STAR – DELTA AND DETERMINATION OF EFFICIENCY AND REGULATION
UNDER BALANCED RESISTIVE LOAD.

AIM: Conduct polarity test on single phase transformer and connection of 3- single phase
transformers in star-Delta and determination of efficiency and regulation under balanced
resistive loads.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter MI 0-600V 2Nos
2 Ammeter MI 0-10A 2 Nos
3 3-φ Auto-transformer 415V/0-440V,50Hz 1 No
4 1-φ Auto-transformer 230V/0-260V, 50Hz 1 No
5 1- φ transformer 1KVA, 230V/230V, Single phase, 50Hz. 3 Nos
6 Connecting wires -- Few

THEORY:
A Star-delta connection of transformer is mainly used in the substation and in
transmission line. The main use connection is to step down the voltage. The neutral available on
primary side is grounded. It can be seen that there is a phase difference of 30º between primary
and secondary line voltages. In this type of connection, primary is connected in star fashion and
the secondary is connected in delta fashion.

PROCEDURE:
I. Polarity Test:

1. Connections are made as per the circuit diagram.

2. With Auto-transformer knob at zero position, Switch ON the supply.
3. Slowly vary the Auto-transformer knob and apply rated voltage (230V) on primary
side of the Transformer.
4. If Voltmeter reads E1-E2 , Then it is subtractive polarity or if voltmeter reads E 1+E2
, then it is additive polarity.
5. Then mark the respective polarity as A1, A2, a1, and a2.
6. Bring the Auto-transformer knob to zero position and switch OFF the supply.
II. Star-Delta Connection:

1. Connections are made as per the circuit diagram.

2. Ensure load on the transformer is in OFF position and position of the auto
transformer knob at its zero position.
3. Then switch ON the supply.
4. Slowly go on varying the auto transformer knob until the voltmeter shows the rated
voltage on the transformer.
5. Then gradually apply load on the transformer and at each step note down the
readings.
6. Bring load on the transformers to zero position.
7. Switch OFF the supply.
STAR-DELTA CONNECTION:

OBSERVATIONS:

1. KVA= KVA
2. Primary Voltage = V
3. Secondary Voltage = V
4. Current = Amps.
5. Phases = Phase.

TABULATION:
Primary side Secondary side
S.no %η %R
V1 in volts I1 in Amps V2 in Volts I2 in Amps
1

CONCLUSION:
VIVA VOCE
EXPT 5 DATE
COMPARISON OF PERFORMANCE OF 3 SINGLE-PHASE TRANSFORMERS IN
DELTA – DELTA AND V – V (OPEN DELTA) CONNECTION UNDER LOAD.

AIM: comparison of performance of 3 single-phase transformers in delta – delta and v – v (open

delta) connection under load.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter MI 0-600V 2Nos
2 Ammeter MI 0-10A 2 Nos
3 3-φ Auto-transformer 415V/0-440V,50Hz 1 No
4 1-φ Auto-transformer 230V/0-260V, 50Hz 1 No
5 1- φ transformer 1KVA, 230V/230V, Single phase, 50Hz. 3 Nos
6 Connecting wires -- Few

THEORY:
As seen previously in connection of three single phase transformers that if one of
the transformers is unable to operate then the supply to the load can be continued with the
remaining tow transformers at the cost of reduced efficiency. The connection that
obtained is called V-V connection or open delta connection.
If one of the transformers fails in ∆ - ∆ bank and if it is required to continue the supply
eventhough at reduced capacity until the transformer which is removed from the bank is
repaired or a new one is installed then this type of connection is most suitable.
When it is anticipated that in future the load increase, then it requires closing of open
delta. In such cases open delta connection is preferred.
Key point : It can be noted here that the removal of one of the transformers will not give
the total load carried by V - V bank as tow third of the capacity of ∆ - ∆ bank.
The load that can be carried by V - V bank is only 57.7% of it. it can be proved as
follows.
It can be seen from the Fig. 2(a)
∆ - ∆ capacity = √3 VL IL = √3 VL (√3 Iph )
∆ - ∆ capacity = 3 VL Iph.................................................(i)
It can also be noted from the Fig. 2(b) that the secondary line current I L is equal to the
phase current Iph.
V- V capacity = √3 VL IL = √3 VL Iph....................................(ii)
Dividing equation (ii) by equation (i)
CIRCUIT DIAGRAM:

DELTA- DELTA CONNECTION:

OPEN- DELTA CONNECTION:

THEORY:
TABULATION:(DELTA –DELTA CONNECTION)

Primary side Secondary side

S.no %η %R
V1 in volts I1 in Amps V2 in Volts I2 in Amps
1

PROCEDURE:

I. Delta-Delta Connection:

1. Connections are made as per the circuit diagram.

2. Ensure load on the transformer is in OFF position and position of the auto
transformer knob at its zero position.
3. Then switch ON the supply.
4. Slowly go on varying the auto transformer knob until the voltmeter shows the rated
voltage on the transformer.
5. Then gradually apply load on the transformer and at each step note down the
readings.
6. Bring load on the transformers to zero position.
7. Switch OFF the supply.

CALCULATION:

Output power
V2 I2 × 100 =
%η= Input power =
V1 I1

V02 - V2 × 100 =
% Regulation =
V02

PROCEDURE:

II. Open-Delta Connection:

1. Connections are made as per the circuit diagram.

2. Ensure load on the transformer is in OFF position and position of the auto
transformer knob at its zero position.
3. Then switch ON the supply.
4. Slowly go on varying the auto transformer knob until the voltmeter shows the rated
voltage on the transformer.
5. Then gradually apply load on the transformer and at each step note down the
readings.
6. Bring load on the transformers to zero position.
7. Switch OFF the supply.
TABULATION:(OPEN–DELTA CONNECTION)

Primary side Secondary side

S.no %η %R
V1 in volts I1 in Amps V2 in Volts I2 in Amps
1

CALCULATION:

Output power
V2 I2 × 100 =
%η= Input power =
V1 I1

% Regulation= V02 - V2 * 100 =

V02

CONCLUSION:
VIVA VOCE
CIRCUIT DIAGRAM:
EXPT.NO.6 DATE:
SCOTT CONNECTION WITH BALANCED AND UNBALANCED LOADS

AIM: To determine the load shared by two transformers when they are connected in scott .

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter MI 0-300/600V 3 Nos
2 Ammeter MI 0-10 3 Nos
3 3- Auto transformer 415V/0-440V 1 Nos
4 Single phase transformers 1KVA, 230V/230V, Single phase, 50Hz 2 Nos
5 Connecting wires -- Few

THEORY:
The Scott connection is the most common method of connecting two single phase transformers to
perform the 3- to 2- conversion and vice-versa. The two transformers are connected electrically
but not magnetically, one transformer is called main transformer and other is auxiliary or teaser
transformer. The main transformer is having 50% tapping and auxiliary transformer is having
86.6% tapping.
One end of primary winding of the auxiliary transformer is connected to the centre
tapping provided on the primary winding of the main transformer with equal number of turns on.
The voltage per turn is same in primary of both main & teaser transformer with equal
number of turn on secondary on both the transformer. The secondary voltage will be equal in
magnitude which results in symmetrical & phase system.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Ensure load on the transformer is in OFF position & position of the auto
transformer knob at its zero.
3. Switch ON the single phase AC supply.
4. Slowly go on varying the autotransformer until the voltmeter shows on primary
the rated (86.6%) voltage of the transformer.
5. Then close the load switch & gradually apply the balanced load on the transformer
& at each step note all the meter readings.
6. Repeat the above by applying the unbalanced load on the transformer & note
down the meter readings.
7. Bring load on the transformers to zero position & auto transformer knob to zero
position.
8. Switch OFF the supply.

TABULATION:
FOR BALANCED LOAD:
S.no Current Current Current Voltage Voltage Lamp load
I1 Amps IL1 Amps IL2 Amps V1 Volts V2 Volts In Watts
1.

2.

3.

4.
FOR UNBALANCED LOAD:

S.no Current Current Current Voltage Voltage Lamp load

I1 Amps IL1 Amps IL2 Amps V1 Volts V2 Volts In Watts
1.

2.

3.

4.

CALCULATION:

CONCLUSION:
VIVA VOCE
NATURE OF GRAPH:
EXPT.NO.7 DATE:
SEPARATION OF HYSTERESIS AND EDDY CURRENT LOSSES IN SINGLE
PHASE TRANSFORMER.

AIM: To separate the eddy current loss and hysteresis loss from the iron loss of single phase
transformer.
APPARATUS REQUIRED:
S.no Particulars Range Quantity
1 Rheostat 1250Ω , 0.8A
2 Wattmeter 300 V, 5A
3 Ammeter (0-2) A
5 Voltmeter (0-300) V
7 Connecting Wires -- --
1KVA, 230V/115V
8 Transformers 1 Nos
Single phase, 50Hz
DC Motor coupled with
9 --
alternator
10 Connecting wires -- Few
THEORY: *Refer: 1) Theory and performance of Electrical Machines, by J.B. Gupta.
2) A Text book of Electrical Technology, by B.L. Theraja & A.K. Theraja.

PROCEDURE:

1. Connections are given as per the circuit diagram.

2. Supply is given by closing the DPST switch.
3. The DC motor is started by using the 3 point starter and brought to rated speed by
adjusting its field rheostat.
4. By varying the alternator field rheostat gradually the rated primary voltage
is applied to the transformer.
5. The frequency is varied by varying the motor field rheostat and the readings of
frequency are noted and the speed is also measured by using the tachometer.
6. The above procedure is repeated for different frequencies and the readings are
tabulated.
7. The motor is switched off by opening the DPST switch after bringing all the
rheostats to the initial position
TABULATION:

Wattmeter
Speed in Frequency Voltage Iron loss Wi/f
S.no reading
RPM in HZ V (volts) Wi(watts) Joules
(Watts)
1
2
3
4
5
6
7
8
FORMULAE USED:
1. Frequency, f =(P*Ns) / 120 in Hz P = No.of Poles & Ns = Synchronous speed in rpm.
2. Hysteresis Loss Wh = A * f in Watts A = Constant (obtained from graph)
3. Eddy Current Loss We = B * f2 in Watts B = Constant (slope of the tangent drawn to
the curve)
4. Iron Loss Wi = Wh + We in Watts Wi / f = A + (B * f)
Here the Constant A is distance from the origin to the point where the line cuts the Y-
axis in the graph between Wi / f and frequency f. The Constant B is Δ(Wi / f ) / Δf

CALCULATIONS:

CONCLUSION:
VIVA VOCE
CIRCUIT DIAGRAM:

a) For OC Test:

OBSERVATION:

For Motor For Alternator

Voltage : V Voltage : V
Current : Amps. Current : Amps.
Power : KW/HP Power : KVA/KW
Speed : rpm Speed : rpm
TABULATION:

a) For OC Test :

Sl.no If in Amps VOC in Volts

1
2
3
4
5
6
7
8
 CIRCUIT DIAGRAM:

b) For SC Test:

TABULATION:

b) For SC Test :

Sl.no ISC in Amps If in Amps

1
EXPT.NO.8 DATE:
VOLTAGE REGULATION OF AN ALTERNATOR BY EMF AND MMF
METHODS.
AIM: Determination of regulation of an alternator by EMF method or synchronous impedance
method and MMF method or ampere turn method.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter 0-300V MC 1 No
2 Voltmeter 0-600V MI 1 No
3 Ammeter 0-2A MC 2 No
4 Ammeter 0-10A MI 1 No
5 Rheostat 200Ω/2.8A 1 No
6 Rheostat 1200Ω/0.6A 1 No
7 Tachometer -- 1 No
8 Connecting wires -- Few

THEORY:
The KVA ratings of commercial alternators are very high (ex: 500MVA). So, it’s not
convenient to determine voltage regulation by direct loading. Therefore we have to determine
voltage regulation by indirect methods. These methods require very small power as compared to
direct loading method. The EMF and MMF methods are indirect methods.
In EMF method, we are determining the armature resistance Ra and synchronous
impedance

Zs= Open circuit voltage

short circuit current

For some selected value of field current If. Then we are finding synchronous reactance
Xs= X 𝑠− R2 .aOnce know about Ra and Xs draw the phasor diagram for any load and any power
2

factor.
Taking Ia as reference phasor, then IaRa drop is in phase with Ia while Ia Xs leads Ia by 90º.
The phaser sum of V, IaRa and IaXs gives the no load emf E0.

E0= 𝑂� 2 + �� 2

Where OB= Vcos + IaRa

BC= Vsin + IaXs

∴ �0 = Vcos + IaRa 2 + (Vsin + IaXs) 2

�0 − �
∴ % �𝑜𝑙𝑡𝑎𝑔𝑒 𝑟𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = × 100
�

The main drawback of this method is its approximate method. The reason is the combined
effect of XL (armature reactance) and XAR (reactance of armature reaction) is measured on short
circuit. Since current in this condition is almost lagging 90º, the armature reaction will produce its
worst demagnetizing effect. This method gives value higher than the value obtained from the
actual load test for this reason it is called pessimistic method.
In MMF method it is assumed that the armature leakage reactance to be additional armature
reaction neglecting armature resistance, this method assumes that change in terminal pd on load is
due to entirely armature reaction. Same tests (OCC and SC) required for this test also, but
interpretation of result only is different.
i) Suppose the alternator is supplying full load current at normal voltage V and ZPF lagging. Then
dc field amp-turn required will be those needed to produce normal voltage ‘V’ Let OA= field
AT required to produce the normal voltage ‘V’ at no load OB 1= field AT required to neutralize
the armature reaction, then total field AT required are phasor sum of OA and OB, The OA can
be found from OCC and OB1 can be determined from SCC.
ii) At full load current of ZPF lead the armature AT are unchanged, since they aid the main
field, less field AT is required to produce the given emf
Total field AT, AB2=A0-B2O
B2O=field AT required to neutralize armature reaction. Here A 0 is determined from
OCC and B2O from SCC.
iii)Between zero lagging and zero leading power factors, the armature mmf rotates through 180º
At UPF armature reaction is cross magnetizing only. Therefore OB 3 is drawn perpendicular to
AO No AB3 shows the required AT in magnitude and direction.

This method gives a regulation lower than actual performance of machine. For this reason it is
known as optimistic method.

NATURE OF GRAPH b) For MMF method

a) For EMF method Voc(Phase)

Voc(line) Isc Eph Isc

Eoc Vph

Ia(Rated) Isc

If If2 If1 If
PROCEDURE:

A) Open Circuit Test:

1. Connections are made as per the circuit diagram.

2. Keep the field rheostat of alternator in cut in position 1200 Ω /0.6A and field
Rheostat of motor 200 Ω /2.8A in cut out position.
3. Switch ‘ON’ the supply by closing the DPST switch.
4. Start the motor with the help of 3-point starter and gradually cut in the field
rheostat step-by step to bring motor to the rated speed of alternator.
5. Excite the field of alternator by closing the DPST switch.
6. Go on varying the 1200Ω rheostat and build up the rated voltage across the
armature terminals of alternator in steps and at each step note down the reading of
voltage across armature and corresponding field current.
7. Reduce current to Zero. And open the DPST switch.
8. Bring all rheostats to original position and switch ‘OFF’ the supply.
B) Short Circuit Test:
1. Connections are made as per the circuit diagram.
2. Keep the field rheostat of alternator in cut in position 1200 Ω /0.6A and field
Rheostat of motor (200 Ω /2.8A) in cut out position.
3. Switch ‘ON’ the supply by closing the DPST switch.
4. Start the motor with the help of 3-point starter and gradually cut in the field
rheostat step-by step to bring motor to the rated speed of alternator.
5. Excite the field of alternator by closing the DPST switch.
6. Go on varying the 1200Ω rheostat and build up the rated voltage across the
armature terminals of alternator in steps and at each step note down the reading of
voltage across armature and corresponding field current.
7. Then note down the reading of field current and also short circuit current.
8. Bring all rheostats to original position and switch ‘OFF’ the supply.

CALCULATATION:

For EMF method:

Armature resistance between R & B = Ω

= Ω

From the graph: �𝑂�

= �𝑆�
=
Synchronous impedance Zs
= Ω

Synchronous reactance per phase Xs = �𝑆 2 − �𝑎2

Xs = _ 2 − 2
Xs = Ω

Regulation of an alternator at different power factor can be calculated as follows.

2 2
E0 = �𝑝� 𝑐𝑜𝑠𝜑 + �𝑎 �𝑎 + �𝑝� 𝑠𝑖𝑛𝜑 ± �𝑎 �𝑠

Where Vph �𝐿
= = = V
3

Case I: At 0.8 power factor Lagging:

2 2
Ea = �𝑝� 𝑐𝑜𝑠𝜑 + �𝑎 �𝑎 + � 𝑠𝑖𝑛𝜑 + �𝑎 �𝑠

=
=
0 −�𝑝 �
Voltage Regulation= � × 100
�𝑝 �

= X 100

Case II: At 0.8 power factor Leading:

2 2
Ea = �𝑝� 𝑐𝑜𝑠𝜑 + �𝑎 �𝑎 + � 𝑠𝑖𝑛𝜑 − �𝑎 �𝑠

=
=

0 −�𝑝 �
Voltage Regulation= � × 100
�𝑝 �

= X 100

Case III: At Unity power

2
factor: Ea = �𝑝� + �𝑎 �𝑎 +
2
�𝑎 �𝑠

=
=
0 −�𝑝 �
Voltage Regulation= � × 100
�𝑝 �

= X 100
=
For MMF Method:

Armature resistance = Ra = Ω

Voc
/phase = � =
3

Eoc = Vo c / phase + Isc Ra cosφ

=
�𝑓2=
From graph �𝑓1 =

If 2=( If1+ If2sinφ)2+( I f2cosφ)2------- lagging p.f for I ffind E ph(lag)from graph I
2
=( sinφ) 2+( I f2
f I -f1 I f2 cosφ)2------- leading p.f for I ffind E ph(lead) from graph I
2 2 2
=(
f I )f1+( I ) -------
f2 Unity p.f for I findf E fromph(upf)
graph

For If from graph calculate Eph

Voltage Regulation=(Eph-Vph)/ Vph *100

Regulation of an alternator at different power factor can be determined as follows.

CALCULATIONS:
CONCLUSION
VIVA VOCE:
 CIRCUIT DIAGRAM:

b) For OC Test:

OBSERVATION:

For Motor For Alternator

Voltage : V Voltage : V
Current : Amps. Current : Amps.
Power : KW/HP Power : KVA/KW
Speed : rpm Speed : rpm
TABULATION:

a) For OC Test : Sl.no If in Amps VOC in Volts

1
2
3
4
5
6
7
8
EXPT.NO.9 DATE:
REGULATION OF ALTERNATOR BY ZPF METHOD
AIM: To determine the regulation of an alternator by potier triangle ZPF method.
APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter 0-300V (MC) 01 No
2 Voltmeter 0-600V (MI) 01 No
3 Ammeter 0-2A (MC) 01 No
4 Ammeter 0-10A (MI) 01 No
5 Rheostat 200Ω/2.8A 01 No
6 Rheostat 1200Ω/0.6A 01 No
7 Connecting wires -- Few

THEORY:
The regulation obtained by MMF and EMF methods is based on the total synchronous
reactance (The sum of reactance due to armature leakage flux and due to armature reaction effect)
This method is based on the separation of reactance due to leakage flux and that due to armature
reaction flux. Therefore, it is more accurate method.

Regulation by this method, the data required are i) Effective resistance of armature
winding ii) Open circuit characteristic iii) Field current to circulate full load current in the stator
iv) Zero power factor full load voltage characteristics- a curve between terminal voltage and
excitation while machine is being run on synchronous speed and delivering full load current at
zero power factor.A machine is run at synchronous speed by prime mover. A purely inductive load
is connected across the armature terminals and the excitation is raised so as to cause flow of full
load armature current. The value of reactance is increased in such a way that the excitation current
is adjusted to a value that causes full load rated armature current. The armature terminal voltages
are varied from 125% to 25% of rated voltage in steps, maintaining speed and rated armature
current constant throughout the test. The curve is drawn between terminal voltage and excitation
current, gives the zero power factor lagging characteristics. There is a definite relationship
between zero power factor lagging characteristics and an open circuit characteristics of an
alternator. The ZPF characteristic curve is of exactly of same shape as the OCC but it is shifted
vertically downward by leakage reactance drop IX L and horizontally by the armature reaction
MMF.

NATURE OF GRAPH

Eph P

E1ph
R
Q S

Voltage in volts

If1 If If
 CIRCUIT DIAGRAM:

b) For SC Test:

TABULATION:

b) For SC Test :

Sl.no ISC in Amps If in Amps

1

PROCEDURE:

A) Open Circuit Test:

1. Connections are made as per the circuit diagram.

2. Keep the field rheostat of alternator in cut in position 1200 Ω /0.6A and field
Rheostat of motor 200 Ω /2.8A in cut out position.
3. Switch ‘ON’ the supply by closing the DPST switch.
4. Start the motor with the help of 3-point starter and gradually cut in the field
rheostat step-by step to bring motor to the rated speed of alternator.
5. Excite the field of alternator by closing the DPST switch.
6. Go on varying the 1200Ω rheostat and build up the rated voltage across the
armature terminals of alternator in steps and at each step note down the reading of
voltage across armature and corresponding field current.
7. Reduce current to Zero. And open the DPST switch.
8. Bring all rheostats to original position and switch ‘OFF’ the supply.
 B) Short Circuit Test:
1. Connections are made as per the circuit diagram.
2. Keep the field rheostat of alternator in cut in position 1200 Ω /0.6A and field
Rheostat of motor (200 Ω /2.8A) in cut out position.
3. Switch ‘ON’ the supply by closing the DPST switch.
4. Start the motor with the help of 3-point starter and gradually cut in the field
rheostat step-by step to bring motor to the rated speed of alternator.
5. Excite the field of alternator by closing the DPST switch.
6. Go on varying the 1200Ω rheostat and build up the rated voltage across the
armature terminals of alternator in steps and at each step note down the reading of
voltage across armature and corresponding field current.
7. Then note down the reading of field current and also short circuit current.
8. Bring all rheostats to original position and switch ‘OFF’ the supply.
CIRCUIT DIAGRAM:

C) For ZPF Test:

TABULATION:
a) For ZPF Test:

Terminal
Sl.no If in Amps
Voltage V
1

C) Zero Power Factor Method:

1. Connections are made as per the circuit diagram.

2. Keep the field rheostat of an alternator in cut-in position (1200Ω/0.6A).and rheostat
(200Ω/2.8A) of motor in cut out position.
3. Switch ON the power supply, by closing the DPST switch.
4. Start the motor with the help of 3 point starter and gradually cut in the field rheostat
step by step to bring the motor to rated speed.
5. Excite the field of alternator by closing the DPST switch.
6. With the zero reactance load vary the excitation current of the alternator until the
generated voltage reaches rated value.
7. Slowly vary the reactance load in steps until the rated armature current and note
down the values of excitation.
8. Bring all rheostats to their original position and switch OFF the supply.

CALCULATIONS:

From potier triangle PQR, the armature leakage reactance drop is L(RS)
Iph*XLph= L(RS)*scale

Case 1)
Find (E1ph)2=(VphcosФ)2+( VphsinФ+ Iph*XLph)2 From
OCC corresponding If1 is calculated
From potier triangle ,field current balancing armature reaction is L(PS)
If2=L(PS)*Scale
Add If1 & If2 to get If
Find -------
I 2=( I + I sinφ)2+( I cosφ)2 lagging p.f
f2 f1 f2 2 f2 2--------
I =( I - I sinφ) +( I cosφ) leading p.f
f f1 f2 f2
I 2=( I )2+( I )2------- Unity p.f
f f1 f2
For If from graph calculate Eph
Voltage Regulation=(Eph-Vph)/ Vph *100

CALCULATIONS:
CONCLUSION:
VIVA VOCE:
CIRCUIT DIAGRAM:

OBSERVATION:

For Motor For Alternator

Voltage : V Voltage : V
Current : Amps. Current : Amps.
Power : KW/HP Power : KVA/KW
Speed : rpm Speed : rpm
EXPT.NO.10 DATE:
SLIP TEST – MEASUREMENT OF DIRECT AND QUADRATURE AXIS
REACTANCE AND PREDETERMINATION OF REGULATION OF SALIENT
POLE SYNCHRONOUS MACHINES.
AIM: Determination of component of direct axis reactance (X d) and quadrature component of
reactance (Xq) of salient pole generator & Regulation.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter 0-300V (MI) 2 Nos
2 Voltmeter 0-300V (MC) 1 No
3 Voltmeter 0-600V (MI) 1 No
4 Ammeter 0-2A (MC) 1 No
5 Ammeter 0-10A (MI) 1 No
6 Rheostat 200Ω,2.8A 1 No
7 3- auto transformer 415V/0-440V,10A 1 No
6 Tachometer -- 1 No
7 Connecting wires -- Few
THEORY:

A salient pole synchronous machine has non uniform air gap, due to which its reactance
varies with rotor position. Thus salient pole machine possesses two axis of geometric symmetry i)
field pole axis, or d-axis or direct axis ii) Axis passing through the centers of interpolar space
called the quadrature axis or q-axis. Where as in cylindrical rotor machine only one axis of
symmetry (Pole axis or d-axis) in salient pole machines X q= 0.6 to 0.7 times Xd. Where as in
cylindrical rotor machine Xd= Xq.
The value of Xd and Xq are determined by applying balanced reduced voltage say V volts
to an excited machine at a speed little less than synchronous speed (The slip is less than 1%).

TABULATION:

%Regulation
Vmax in Vmin in Imax in Imin in Xd Xq
Sl.No Volts Volts Amps Amps 0.8(lag) 0.8(Lead)
CALCULATIONS:

Determination of Stator Resistance (Ra)

a. Connections are made as shown in the circuit diagram (9.b).
b. By keeping rheostat in cut-in position the supply switch (S1) is closed.
Rheostat is adjusted to any value of current (say 1A)
c. All the meter readings are noted down.
d. The supply switch (S1) is opened.

NOTE: Field of the alternator is kept opened.

Calculation
V = Rated phase Voltage, Volt
I = Rated current, Ampere.
Xd = Vmax / Imin =..............Ω
Xq = Vmin / Imax =..............Ω

For 0.8 p.f lagging

CosФ = 0.8
SinФ = 0.6
Therefore Ф = 36.86
tanθ = ( V sin Ф ± I Xq ) / ( V cos Ф + I Ra) ( Note: + → lag , - → lead)
θ = tan-1 ((V sin Ф ± I Xq ) / ( V cos Ф + I Ra))
Therefore α = θ - Ф
Therefore
Eo/phase = (V cos α ± Id .Xd + Iq. Ra) Volt
Where Iq = I cos θ
Id = I sin θ
Therefore
Regulation %R=(E0-V/V)*100
The applied voltage to armature, armature current and voltage induced in the field winding are
measured by oscillographs. Due to voltage V applied to the stator terminals a current I will flow
causing a stator mmf. This stator mmf moves slowly, relative to the poles and induces an emf in
the field circuit in the similar fashion to that of rotor in an Induction motor at slip frequency. The
effect will be that the stator mmf will move slowly relative to the poles. The physical poles and
the armature reaction mmf are alternately in phase and out, the change occurring at slip frequency.
When the axis of pole and axis of armature reaction mmf wave coincide the armature mmf acts
through the field magnetic circuit. The voltage applied to the armature is then equal to drop
caused by direct component of armature reaction and leakage reactance. When the armature
reaction mmf is in quadrature with the field poles the applied voltage is equal to the leakage
reaction drop plus the equivalent voltage drop of cross magnetizing field component. From the
oscillograph record:

Maximum voltage
Xd=
Minimum current
Minimum voltage
Xq=
Maximum current
PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Keep the field rheostat (200Ω, 2.8A) in Cut-out position and auto transformer at
zero value. Keep the field of an alternator as open circuited.
3. Switch ON the power supply to DC motor by closing DPST switch.
4. Start the motor with the help of 3-point starter and gradually cut in the field
rheostat step by step to bring the motor to its speed less than synchronous.
5. Switch ON the 3-phase power supply to auto transformer, gradually increase the
voltage to the armature winding of an alternator up to about 25% of the rated value.
6. Note down the max and min value of voltage in rotor and armature current.
7. Bring all the rheostats to their original position and switch OFF the supply.

CONCLUSION:
Viva Voce:
 Hirasugar Institute of Technology,Nidasohi
CIRCUIT DIAGRAM:

OBSERVATION:

For Motor For Alternator

Voltage : V Voltage : V
Current : Amps. Current : Amps.
Power : KW/HP Power : KVA/KW
Speed : rpm Speed : rpm
EXPT NO 11 DATE:
SYNCHRONIZATION & PERFORMANCE OF SYNCHRONOUS GENERATOR
CONNECTED TO INFINITE BUS, UNDER CONSTANT POWER AND
VARIABLE EXCITATION & VICE - VERSA.

AIM: To operate the Alternator on

 Infinite Bus.
 Constant Power and Variable Excitation.
 Variable Excitation and Constant Power.

APPARATUS REQUIRED:

S.no Particulars Range Quantity

1 Voltmeter 0 – 500 V (MI) 2 Nos
Ammeters
5 Ammeter 0-1/2A MC 1 No
0-5/10A MI
0-750Ω,1.2A(2)
6 Rheostat 2+1 No
0-38Ω,8.5A(1)
10/20A,0 – 600 V
7 Wattmeter 2 No
LPF
6 Tachometer -- 1 No
7 Connecting wires -- Few

PROCEDURE
a. Operation on Infinite Bus Bar
1. Connections are made as shown in the circuit diagram (4.a)
2. Keeping the rheostat R1 in the field circuit of motor in cut-out position, the rheostat
R2 in the armature circuit of motor and the rheostat R3 in the field circuit of
alternator in cut-in positions, the bus bar switch (S2) and synchronizing switch (S3) in
open positions, the supply switch (S1) is closed.
3. The motor is brought to the synchronous speed of the alternator by gradually
cutting out the rheostat R2 and cutting in the rheostat R1, if necessary. By gradually
cutting out the rheostat R3, the alternator voltage is built-up to the bus
bar voltage.
4. Now, bus bar switch (S2) is closed, and the phase sequence is verified. For correct
phase sequence, all the lamps will flicker simultaneously. Otherwise, they flicker
alternately. If they flicker alternatively, the bus bar voltage switch is opened and any
two terminals of the bus bar supply are interchanged.
5. Repeat step number 2, 3 and 4.
6. By varying the rheostats R1, R2 and R3 the dark period of the lamps are obtained.
7. When all the lamps are in dark condition, the synchronization switch S3 is closed
and now the alternator is connected in parallel with the bus bar.
8. Switches (S3) and (S2) are opened; all the rheostats are brought back to their
respective initial positions, and supply switch (S1) is opened.
b. Constant Power - Variable Excitation Operation
1. Connections are made as shown in the circuit diagram (4.b)
2. Follow the procedure steps 2, 3.
3. By gradually cutting out the rheostat R3, the alternator voltage is built-up to its rated
voltage.
4. Apply load gradually.
5. Vary generator excitation (R3) to keep wattmeter readings constant (Total Power).
6. Tabulate the readings.
7. Bring back the load to zero, reduce the excitation to a normal value and all rheostats
are brought back to respective initial positions & supply switch (S1) is opened.

c. Constant Excitation - Variable Power Operation

1. Connections are made as shown in the circuit diagram (4.b)
2. Follow the procedure steps 2, 3.
3. By gradually cutting out the rheostat R3, the alternator voltage is built-up to its
rated voltage.
4. Apply load in steps & note down all meter readings (Excitation should be constant
By adjusting the speed of the Motor).
5. Bring back the load to zero, reduce the excitation to a normal value and all
Rheostats are brought back to respective initial positions & supply switch (S 1) is
opened.
TABULAR COLUMN
1. Constant Power - Variable Excitation Operation
Sl. No. If(A) Power(W1+W2) Speed Voltage IL
(RPM) (V) (A)

2. Constant Excitation - Variable Power Operation

Sl. No. If(A) Power(W1+W2) Speed Voltage IL

(RPM) (V) (A)

CALCULATIONS:

CONCLUSION:
 P.A. COLLEGE OF ENGINEERING
VIVA VOCE:
EXPT NO 12 DATE:
POWER ANGLE CURVE OF SYNCHRONOUS GENERATOR

AIM: TO STUDY THE POWER ANGLE CURVE OF SYNCHRONOUS GENERATOR

APPARATUS REQUIRED:

SN Particulars Range Type Quantity

1 Voltmeters 0-30V MC 01

0-500V MI 01

2 Ammeters 0-10/20A MI 01

0-1/2A MC 01

3 Rheostats 0-750 ohm, 1.2A - 02

0-38 ohm, 8.5A 01

4 Tachometer - - 01

PROCEDURE

a. Open circuit test

1. Connections are made as shown in the circuit diagram 13.a

2. Keeping the rheostat R1 in the field circuit of motor in cut-out position, the rheostat
R2 in the armature circuit of the motor and the rheostat R3 in the field of the
alternator in cut-in positions and TPST (S2) in open position, the supply switch (S1)
is closed

3. The motor is brought to synchronous speed by cutting out the rheostat R2 and then
by cutting in the rheostat R1, if necessary.

4. By gradually cutting out the rheostat R3, the readings of ammeter (A1, 0-2A) and
voltmeter (V) are noted down.

5. The above step is continued until voltmeter reads about 1.25 times the rated
voltage of the alternator.

b. Short circuit test

1. The rheostat R3 is brought to its initial position (cut-in) and TPST (S2) is closed.

2. By gradually cutting out the rheostat R3, reading of the ammeter (A2, 0-10/20A) is
adjusted to the rated current of the alternator and the corresponding field current (A1)
is noted down.
3. All the rheostats are brought back to their respective initial positions, TPST switch(S2)
and supply switch (S1) are opened.

Fig. Determination of armature resistance

Determination of Stator Resistance of Alternator (Ra)

V I Resistance Resistance
Sl.No
(Volts) (Ampere) RDC = V/I Ω RAC =1.5*RDC
 Determination of Armature Resistance (Ra) by V-I Method
1. Connections are made as shown in the circuit diagram(13.b)
2. Keeping the rheostat in cut-in position, the supply switch (S1) is
closed, Rheostat is adjusted to any value of current (say 1A) and the
readings of ammeter and voltmeter are noted down.
3. The supply switch (S1) is opened.

Power angle curve

1. Connections are made as shown in the circuit diagram (13.c)
2. Follow the procedure steps 2, 3 of procedure (a).
3. By gradually cutting out the rheostat R3, the alternator voltage is built-up to its rated
voltage.
4. Apply load in steps & note down all meter readings (Excitation should be constant by
adjusting the speed of the Motor).
5. Bring back the load to zero, reduce the excitation to a normal value and all rheostats are
brought back to respective initial positions & supply switch (S1) is opened.

CALCULATION

EMF Method
1. Draw OCC and SCC for suitable scales as shown in model graph no (1).
2. Mark a point A on the OCC corresponding to the rated voltage and draw a Perpendicular
so that it cuts SCC line at a point B and X-axis at point C.
3. Corresponding to point A, E1 is the open circuit voltage per phase, and BC is the Short
circuit current.
4. Therefore Synchronous impedance per phase Zs = E1/I1Ω (If Constant) Synchronous
reactance per phase Xs = √ Zs2- Ra2 Ω s a

Model Graph
 Sl. If Ia W1 x K1 W2 x K2 |V| |E| P = W1 + W2 δ
N (rpm)
No. (Amps) (Amps) (Watt) (Watt) (Volts) (Volts) (Watt) Degree

Model Graph

CONCLUSION:
VIVA VOCE: