srm institute of science and technology

15EE210L-ELECTRICAL MACHINES LAB-II

RECORD

ACADEMIC YEAR: ODD SEMESTER 2018-19

NAME :

REG.NO. :

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

FACULTY OF ENGINEERING & TECHNOLOGY

SRM Institute of Science and Technology (Deemed to be University)

S.R.M. NAGAR, KATTANKULATHUR – 603 203

KANCHEEPURAM DISTRICT

SRM Institute of Science and Technology (Deemed to be University)

S.R.M. NAGAR, KATTANKULATHUR -603 203

KANCHEEPURAM DISTRICT

BONAFIDE CERTIFICATE

Register No______________________________

Certified to be the bonafide record of work done by

________________________ of EEE department, B.Tech degree course in the

Practical 15EE210L Electrical machines Lab-II in SRM IST, Kattankulathur

during the academic year 2017-2018.

Lab in-charge

Date: Year Co-ordinator

Submitted for end semester examination held in

Electrical machines Lab, SRM IST, Kattankulathur.

Date: Examiner-1 Examiner-2

LIST OF EXPERIMENTS

1. Performance evaluation of single phase induction motor

2. a) Performance evaluation of three phase induction motor

b) Load test on three phase squirrel cage induction motor using open lab system

3. Speed control of rotating transformer

4. Synchronisation of alternator to infinite bus bar

5. Predetermination of voltage regulation

6. Determination of v and inverted v curves of synchronous motor

7. Determination of xd and xq for salient pole alternator using slip test

8. Characteristics of 3 phase induction generator

9. Single phasing in 3 phase induction motor

10. Armature reaction in synchronous generator

INDEX

Expe

rime

nt No

Date

of

Experi

ment

Title of Experiment

Viva

(10)

Executi

on

(10)

Calculation

/

Evaluation

(20)

Pre and

Post Lab

(10)

Total

(50)

Faculty

Signatu

re

1 Performance evaluation of

single phase induction motor

2 (a)

a) Performance evaluation

of three phase induction

motor

2(b)

b) Load test on three phase

squirrel cage induction

motor using open lab system

3 Speed control of rotating

transformer

4 Synchronisation of

alternator to infinite bus bar

5 Predetermination of voltage

regulation

6

Determination of v and

inverted v curves of

synchronous motor

7

Determination of xd and xq

for salient pole alternator

using slip test

8 Characteristics of 3 phase

induction generator

9 Single phasing in 3 phase

induction motor

10 Armature reaction in

synchronous generator

Average

PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION

MOTOR

PRE LAB QUESTIONS

1. What are the types of single phase induction motor?

2. Why single phase induction motors are not self-starting?

3. How the direction of a capacitor start Induction motor is be reversed?

4. In what respect does a 1-phase Induction motor differ from a 3-phase Induction

motor?

5. What is the rating of single phase machines? State its applications

Experiment No.

PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION

MOTOR

AIM

To conduct open circuit, short circuit and load test on the given single phase induction

motor and to plot its performance characteristics.

APPARATUS REQUIRED:

S.NO APPARATUS SPECIFICATIONS QUANTITY

1 VOLTMETER (0-300V) MI

(0-150V) MI

1

1

2 AMMETER (0-10A) MI

(0-5A) MI

1

1

3 WATTMETER (300V,10A,UPF)

(150V,10A, UPF)

(300V,5A,LPF)

1

1

1

4 TACHOMETER (0-10000 RPM) 1

5 Connecting wires As required

FORMULAE

Load test

1. Circumference of the brake drum = 2πR (m)

R = Radius of the brake drum

2. Input power =W (watts)

W = wattmeter readings

3. Torque (T) = 9.81x R x (S1 ~ S2) (N-m)

S1, S2 = spring balance readings (Kg)

4. Output power = 60

2 NT(watts)

N- Speed in rpm

5. % Efficiency (η) = 100xpowerinput

poweroutput

6. Power factor, cos Φ= VI

W

7. % Slip, s = 100

Ns

NNs

NS = synchronous speed = P

f120(rpm)

P = no. of poles

f=frequency of supply (Hz)

No load test

R1= 1.5x Rdc

cos Ф = Wo / Vo Io

VAB = Io xo

xo = VAB /Io

Blocked rotor test

cos Φsc =Wsc /Vsc Isc

Zeq = Vsc/ Isc

Req = Wsc /( Isc)2

Req = R1 + R2

R2 = Req - R1 = rotor resistance referred to stator

Xeq =√(Zeq 2 - Req

2)

X1 = X2

X2

Where W0 = no-load input power in watts (watts)

Wsc = short circuit input power in watts (watts)

V0 = line voltage on no-load

I0 = line current on no-load

CALCULATIONS TO DRAW THE EQUIVALENT CIRCUIT

Blocked rotor test

Zeq = Vsc/ Isc

Req = Wsc /( Isc)2

Xeq =√(Zeq 2 - Req

2)

R1= 1.5*Rdc

Req = R1 + R2

R2 = Req - R1

Xeq=X1 + X2

X1 = X2

x2 = X2 / 2

r2= R2 / 2

Where VSC= Short circuit voltage volts

ISC= Short circuit current in amps

WSC= Short circuit power in watts

No load test

VAB = Io xo

xo = | |




PRECAUTIONS

Load test

1. The auto transformer must kept at minimum voltage position.

2. The motor is started at no load condition.

3. The motor should not be stopped under loaded condition

No load test

1. Initially DPST Switch is kept open.

2. Auto transformer is kept at minimum potential position.

3. The machines must be started on no load.

Blocked rotor test

1. Initially the DPST Switch is kept open.

2. Auto transformer is kept at minimum potential position.

3. The machine must be started at full load (blocked rotor).

MODEL EQUIVALENT CIRCUIT

MODEL GRAPH

TABULAR COLUMN

No load test

V0

(volts)

I0

(amps)

W0

(watts)

MF OBS ACT

Load test

Voltage

V

(volts )

Current

I

Amps

Speed

N

(rpm)

Wattmeter

reading

(watts)

Spring balance

readings (Kg)

Torque

(T)

N-m

Output

Power

(watts)

Power

factor

(cos Φ)

% efficiency

(η)

%Slip(s)

S1 S2 S1~S2

OBS ACT

Blocked rotor test

VSC

(volts)

ISC

(amps)

WSC

(watts)

MF OBS ACT

D

P

S

T

S

W

I

T

C

H

230V,

50Hz 1

AC

Supply

Link

Fuse P

N

15A

Auto

Tra

nsf

orm

er

230/(

0-2

70)

V

M1

M2

(0-10)A

MI

(0-300)V

MI

300V, 10A, UPF

Brake Drum

S1 S2

Kg Kg

Rotor

S1 S2

FUSE RATING:

125% of rated current

125 x 9.5

---------------- = 15 A

100

NAME PLATE DETAILS:

Rated Voltage : 220V

Rated Current : 9.5A

Rated Power : 3HP

Rated Speed : 1470 RPM

C

S1, S2- AUXILLARY WINDING

M1, M2- MAIN WINDING

CIRCUIT DIAGRAM

A

M L

C V

V

PROCEDURE

Load test

1. Connections are given as per the circuit diagram

2. The DPST switch is closed and the single phase supply is given to the motor.

3. By adjusting the autotransformer, the rated voltage is applied and the corresponding

no load values of speed, spring balance and meter readings are noted down. If the

wattmeter readings show negative deflection on no load, switch of the supply &

interchange the terminals of current coils (M & L) of the wattmeter. Now, again start

the motor (follow above procedure for starting), take readings.

4. The procedure is repeated till rated current of the motor is reached.

5. The motor is unloaded, the auto transformer is brought to the minimum voltage

position, and the DPST switch is opened.

6. The radius of the brake drum is measured.

No load test

1. Connections are given as per the circuit diagram.

2. The motor is kept at no load condition.

3. The DPST switch is closed

4. By adjusting the 1Φ auto transformer the machine is brought to rated voltage.

5. The ammeter, voltmeter and wattmeter readings are noted down.

Blocked rotor test

1. Connections are given as per the circuit diagram.

2. The rotor is made standstill (held tight) by applying Load to the motor.

3. Close the DPST switch.

4. By adjusting the 1Φ auto transformer rated current is allowed to circulate.


RESULT

POST LAB QUESTIONS

1. What are the inherent characteristics of plain 1-Ø Induction motor?

2. Why single phase induction motor has low power factor?

3. State double field revolving theory.

4. How the direction of a capacitor start Induction motor is reversed?

5. Why is the starting torque of a capacitor start induction motor high, when compared

to that of a split phase induction motor?

PERFORMANCE EVALUATION OF THREE PHASE INDUCTION

MOTOR

PRELAB QUESTIONS

1. What is slip of an induction motor?

2. An induction motor is generally analogous to__________________

3. What are the operating modes of 3-φ induction motor?

4. State the advantages of skewing?

5. How can the direction of rotation of the 3-φ induction motor be reversed?

PERFORMANCE EVALUATION OF THREE PHASE INDUCTION

MOTOR

AIM

To conduct open circuit, short circuit and load test on the given three phase induction

motor squirrel cage induction motor and to plot its performance characteristics.

APPARATUS REQUIRED

SI.NO APPARATUS SPECIFICATIONS QUANTITY

1 VOLTMETER (0-600V) MI

(0-300V)MI

1

1

2 AMMETER (0-10A) MI

(0-5A) MI

1

1

3 WATTMETER (600V,10A,UPF)

(600V,5A,LPF)

2

2


FORMULAE

Load test

1. circumference of the brake drum = 2πR (m)

R = Radius of the brake drum

2. Input power W=W1+W2 (watts)

W1, W2 = wattmeter readings

3. Torque (T) = 9.81* R * (S1 ~ S2) (N-m)

S1, S2 = spring balance readings (Kg)

4. Output power = 60

2 NT(watts)

5. % Efficiency (η) = 100xpowerinput

poweroutput

6. Power factor, Cos Φ = VI

WW

3

21

Cos Φ= Power factor

7. %Slip, s = 100

Ns

NNs

NS = synchronous speed = P

f120 (rpm)

P = no. of poles

f=frequency of supply (Hz)

No load test

Cos Φ0 =

00

0

3 IV

W




Iw= Io Cos Φ0 Amps

Ro= w

ph

I

V )(0=

wI

V

3

0 Ω

Iµ= Io Sin Φ0 Amps

Xo= I

V ph)(0=

I

V

3

0 Ω

Blocked rotor test

ISN = SC

SCV

VI

WSN=

2

SC

SNsc

I

IW (watts)

Cos Φsc = IscVsc

WSC

3

X01= )(2

01

2

01 RZ

R2’ = R01/ 2 Ω

RL’ = R2

’

s

s1 Ω

Where

Wsc = short circuit input power in watts (watts)

Iw= Working current in amps

Iµ= Magnetizing current in amps

X0= No load reactance in Ω

VSC= Short circuit voltage volts

ISC= Short circuit current in amps

WSC= Short circuit power in watts

ISC=Line Current under blocked rotor condition for short circuit voltage

ISN=Line Current under blocked rotor condition for rated voltage

s= 5% (Assume

PRECAUTIONS

Load test

1. The auto transformer is kept at minimum voltage position.

2. The motor is started at no load condition.

3. The motor should not be stopped under loaded condition

PROCEDURE

Load test


2. The TPST switch is closed and the 3-phase supply is given

3. The motor is started with a Direct On-line (DOL) starter.

4. No load readings are noted down.

5. If any one of the wattmeter shows negative deflection, the connections of M and L in

the wattmeter are interchanged after switching off the supply.

6. Gradually the motor is loaded and in each case all the meter readings are noted down

and the procedure is repeated till the rated current is obtained.

7. The motor is unloaded. The DOL Starter is switched off and the TPST Switch is

opened.

8. The radius of the brake drum is measured.

No load test


2. Initially the motor is kept at no load condition.

3. The TPST switch is closed

4. By adjusting the 3Φ auto transformer the machine is brought to rated voltage.


Blocked rotor test


2. The rotor is made standstill (held tight) by applying Load to the motor.

3. Close the TPST switch.

4. By adjusting the 3Φ auto transformer rated current is allowed to circulate.


CIRCUIT DIAGRAM

FUSE CALCULATION:

1.25x4.5= 10A

300V, 10A, UPF

300V, 10A, UPF

TABULAR COLUMN

Load test

V

volts

I

Amps

Speed

N

(rpm)

Wattmeter reading

(Watts)

Spring balance

readings (Kg)

Torque

(T)

N-m

Output

power

(Watts)

Power

factor

(cos Φ)

%

efficien

cy

(η)

% Slip

(s) W1 W2

W1+W2

S1 S2 S1~S2

Obs Act Obs Act

No load test

V0

(volts)

I0

(amps)

W1

(watts)

W2

(watts)

W0

(watts)

Blocked rotor test

VSC

(volts)

ISC

(amps)

W1

(watts)

W2

(watts)

WSC

(watts)

MODEL GRAPH

EQUIVALENT CIRCUIT

Io

’

Ro Xo

N

X01 R01

V 1

I1’ P

RL’= 𝑅2(1/𝑠−1)

𝐾2

CIRCLE DIAGRAM

PROCEDURE FOR CONSTRUCTION OF CIRCLE DIAGRAM

By using the data obtained from the no load test and the blocked rotor test, the circle

diagram can be drawn using the following steps:

1. Take reference phasor V as vertical (Y-axis)

2. Select suitable current scale such that diameter of circle is 20-30cm.

3. From No load test, I0 and 0 are obtained. Draw vector I0, lagging V by angle 0.

This is line OA

4. Draw horizontal line through extremity of I0 i.e., A parallel to horizontal axis.

5. Draw the current ISN calculated from ISC with the same scale, lagging V by angle

SC, from origion O. This is phasor OB.

6. Join AB. The line AB is called output line.

7. Draw a perpendicular bisector to AB Extend it to meet line AD at point C. This

is the centre of the circle.

8. Draw the circle with C as a centre and radius equal to AC. This meets the

horizontal line drawn from A at B.

9. Draw the perpendicular from point B on the horizontal axis to meet AF line at D

and meet horizontal axis at E.

10. Torque line:

The torque line separates stator and rotor copper losses.

The vertical distance BD represents power input at short circuit i.e., WSN which

consist of core loss, stator and rotor copper losses.

FD = DE = fixed loss

AF sum of stator & rotor copper losses.

Pt ‘G’ is located as

losscopperStator

losscopperRotor

GD

BG

The line AG in called torque line

Power Scale: As AD represents WSN i.e., power input on short circuit at normal voltage, the

power scale can be obtained as

Power scale = cmWBE

WSN /)(

(BE) = Distance BE in cm

Location of point E (slip ring induction motor)

K = 2

1

I

I= transformation ratio

2

1

2

1

2

1

2

1

2

2

2

I

I

R

R

RI

RI

losscopperstator

losscopperRotor

EF

AE

2

21

2K

RR = Rotor resistance referred to stator.

1

1

2

R

R

GD

BG

Thus pt G can be obtained by dividing the line BD in the ratio 1

'

2 RR

Location of point D (squirrel cage induction motor)

In a squirrel cage motor, the stator resistance can be measured by conducting resistance test.

i.e., Stator copper loss = 1

23 RI SNwhere SNI is phase value.

Neglecting core loss, WSN = stator Cu loss + Rotor Cu loss

i.e., Rotor copper loss = 1

23 RIW SNSN

1

2

1

2

3

3

RI

RWSN

GD

BG

SN

SN

Dividing line BD in this ratio, the point G can be obtained and hence AG represents torque

line.

To get the torque line, join the points A and G.

11. To find the full load quantities, draw line BK (=Full load output/power scale).

Now, draw line PK parallel to output line meeting the circle at point P.

12. Draw line PT parallel to Y-axis meeting output line at Q, torque line at R, constant

loss line at S and X-axis at T.

RESULT

LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR USING

OPEN LAB SYSTEM

AIM

To conduct load test on three phase squirrel cage Induction motor, 2 pole, 24 V, ∆-

Connection.

APPARATUS REQUIRED

SL NO COMPONENT MODULE SPECIFICATION QUANTITY

1 3 phase cage rotor Open lab sys 24 V/5A AC (2pole) 1

2 Supply module DL 10281 Fixed 24 V/5A AC 1

Variable 42 V/5A 1

3 Measurement module DL 10282 AC voltmeter

(0-50)V

1

AC ammeter

(0-5)A

1

Wattmeter

75V/10A/300WUPF

2

Speed sensor 1

4 Electromagnetic brake DL 10300A G=3.5N,g=1.5N 1

PRECAUTIONS

1. In the supply module DL10281,select the selector switch‛I’ to position‛ b’

for fixed AC supply 42/10A and switch L1/L2/L3 to position ‛0’.

2. In the supply module DL10281,select the selector switch‛ IV’ to position ‛c’

for variable DC voltage and control knob to 0%.

3. In the measurement module 10282,ensure the ammeter and voltmeter for

AC measurements.

FORMULAE

INPUT POWER Pin = P1+P2 Watts

OUTPUT POWER Pout = 0.1047nM Watts

TORQUE M = G.b Nm

POWER FACTOR COS ɸ = Pin/√3 U I

EFFICIENCY % Ƞ = Pout/Pin × 100

Where,

U = supply voltage in volts

I = load current in Amps

n = speed of cage rotor in Rpm

M = torque in Nm

G = measuring weight

b = distance of the arm in m

TABULAR COLUMN

U(V) I

(A)

P1(W1) P2(W2) Pin

(W)

COSɸ G

(N)

b(m) M

(Nm)

n

(Rpm)

Pout(W) %Ƞ

act obs act obs

CIRCUIT DIAGRAM

MODEL GRAPH

PROCEDURE

1. Activate the supply modue by setting the switch L1/L2/L3 from position‛

0’ to‛ 1’.

2. Observe whether the motor runs in CW direction.

3. If not interchange any two phases.

4. Balance the brake by moving the balance weight ‛g’ until the water level

shows horizontal position and the speed measurement reads rated speed.

5. Now note down the No load measurements (U,I,P1,P2,n,G,b)

6. The motor is therefore loaded in steps by means of brake.

(The load is increased by moving the weight‛ g’ to a distance‛ b’ from the

No load initial position. Adjust the selector switch‛ IV’ to balance the

system again)

7. Perform the measurements as per previous step and repeat the procedure

until rated current.

8. Stop the system by setting the load voltage switch L1/L2/L3 to a position to

de-energize the brake.

RESULT

POST LAB QUESTIONS

1. What is the need for drawing a circle diagram?

2. How to calculate the power scale for drawing a circle diagram?

3. What are the advantages and disadvantages of circle diagram method of

predetermining the performance of 3 –phase IM?

4. What are the effects of increasing rotor resistance on starting current and starting

torque?

5. Draw the torque slip characteristics of 3 phase slip ring induction motor.

SPEED CONTROL OF ROTATING TRANSFORMER

PRELAB QUESTIONS

1. Why is an induction motor not capable of running at synchronous speed?

2. What are the different starters needed for three phase induction motors?

3. The rotor core loss of an induction motor under running condition is usually

neglected. Why?

4. Why are starters needed for induction motors?

4. What are the various methods of speed control of 3 phase induction motor?

5. What are the various methods of speed control of induction motor from the stator

side?

ROTOR RESISTANCE SPEED CONTROL METHOD OF 3ϕ SLIP

RING INDUCTION MOTOR

AIM

To vary the speed of the slip ring induction motor using rotor resistance speed control

method.

APPARATUS REQUIRED


1

2

3

Voltmeter

Ammeter

Tachometer

(0-600V) MI

(0-10A) MI

0-10000 (rpm)

1

1

1

TABULAR COLUMN

Voltage

(V)

Current (A) Resistance () Speed (rpm)

CIRCUIT DIAGRAM: ROTOR RHEOSTAT SPEED CONTROL OF 3ϕ SLIP RING INDUCTION MOTOR

MODEL GRAPH

PROCEDURE

1. The Connection are made as per circuit diagram

2. The TPST switch is closed and three phase supply is given.

3. The motor is started with rotor connected with rotor resistance.

4. The rotor resistance is varied and corresponding values of speed, voltage and

current are noted down.

RESULT

Speed vs resistance

1390

14301440

14501460

1470

13401360138014001420144014601480

Resi

stan

ce (W

)46

.632

.221

.8

12.12

5.88

resistance(ohm)

sp

eed

(rp

m)

Speed (rpm)

VARIBALE FREQUENCY AND VOLTAGE SPEED CONTROL

METHOD

AIM To control the speed of the 3 phase induction motor by changing the supply frequency and to

plot the speed Vs frequency curve.

APPARATUS


1

2

3

4

5

Voltmeter

Ammeter

Tachometer

Frequency meter Digital

. Rheostat Wire Wound

(0-600V) MI

(0-10A) MI

(0-2)A MC

0-10000 (rpm)

(0-60Hz)

300Ω, 1.2A

2

1

1

1

1

2

PRECAUTIONS

i) TPST in open position

ii) DPST1 and DPST2 in open position

iii) Motor field rheostat in minimum position

iv) Potential divider in minimum voltage position

v) Autotransformer at minimum voltage position

TABULATION

Induction motor on no load

Line voltage

In volts

Frequency

In Hz

Speed of IM

In rpm

NAME PLATE DETAILS:

Motor Alternator

Rated Voltage : 220V 415V

Rated Current : 19A 4.2A

Rated Power : 3HP 5KVA

Rated Speed : 1500 RPM 1500 RPM

CIRCUIT DIAGRAM

Fuse calculation:

125% of Rated current=1.25*19=30A

MODEL GRAPH

PROCEDURE

1. Make the connections as shown in diagram.

2. Switch on the DC supply to the DC motor by closing the switch DPST1. Start the DC

shunt motor using 3-point starter. Adjust the field rheostat of the alternator and bring

it to rated speed.(1500rpm).

3. Now, dc supply is given to the alternator field winding and adjust the potential divider

so that the generated voltage is rated value (410V).

4. Close the TPST switch. Increase the autotransformer. Induction motor starts running

on no load. Apply rated voltage by adjusting autotransformer. Note down the

frequency, voltage and speed of the induction motor. Now, decrease the frequency.

Decrease the voltage and frequency in proportion and note down the frequency,

voltage and speed of the induction motor each time. This procedure is continued till

frequency decreases to 48Hz.Switch off the supply after bringing the motor to no-

load.

RESULT

POSTLAB QUESTIONS

1. What does happen to the induction motor if supply frequency is reduced keeping the

supply voltage constant?

2. Write down the main feature of v/f control?

3. Name some applications of speed control of induction motor?

4. Why external resistance is added in slip ring induction motor?

5. When does the induction motor behave as induction generator?

6. What is single phasing in induction motor?

Experiment No.

SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR

AIM

To synchronize the 3Φ alternator to the infinite bus bar.

APPARATUS REQUIRED


1

2

3

VOLTMETER

AMMETERS

RHEOSTAT

SYNCHRONISING LAMPS

(0-600V) MI

(0-2A) MC

300Ω,1.2A

350Ω,2A

230V,15A

2

1

1

1

6

PROCEDURE

1) The DPST-1 is closed and the motor field rheostat is adjusted to make the

alternator run at rated speed.

2) The DPST-2 is closed and by keeping the TPST open, adjusts the alternator field

rheostat to supply the voltage equal to infinite bus bar.

3) The phase sequence of the alternator is made as same as that of the infinite bus bar

by observing the sequence of glowing of synchronizing lamps. If the phase

sequence is not same, any of the two phases are interchanged.

4) The field rheostat is adjusted to bring the frequency of the alternator to same

frequency of infinite bus bar. When the phase sequence of the two sides are same

all the lamps will begin to glow bright and dark simultaneously. In this condition,

when the frequencies are equal, the variation of lamps bright to dark is lowest.

5) At the dimmest point the TPST switch is closed thereby synchronizing the

alternator to the bus bar.

CIRCUIT DIAGRAM: SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR

RESULT

POSTLAB QUESTIONS

1. Three lights flashing rapidly in unison while paralleling alternators means

that ________________________

2. Advantage of paralleling of two machines?

3. How can the voltage and frequency be adjusted?

4. When the pointer of a synchroscope is stationary and points upward during the

paralleling operation, the __________________________

5. List the factors that affect the load sharing in parallel operating generators?

6. What is the possible effect of wrong synchronization?

PREDETERMINATION OF VOLTAGE REGULATION

PRELAB QUESTIONS

1. Define the term voltage regulation of alternator.

2. What is the necessity for predetermination of voltage regulation?

3. Name the various methods for predetermining the voltage regulation of 3-phase

Alternator.

4. What are the causes of changes in terminal voltage of Alternators when loaded?

5. What is meant by armature reaction?

PREDETERMINATION OF VOLTAGE REGULATION

AIM

To predetermine the regulation of alternator by EMF, MMF and ZPF methods

APPARATUS REQUIRED


1 VOLTMETER (0-600V) MI 2

2 AMMETER (0-5A) MI 1

3 RHEOSTAT 300Ω,1.2A 1


5 REACTIVE LOAD (1-15) amps 1

FORMULAE

EMF method

Synchronous impedance, Zs = phaseSCcurrent

phasevoltageOC

/

/(at constant If)

Synchronous reactance, Xs = )(22 RacZs

Where Rac = armature resistance

For rated conditions,

EMF, E0 = 22 )sin()cos( IXsVphIRaVph

+ corresponds to lagging power factor

- corresponds to leading power factor

% Regulation = 1000

xVph

VphE

MMF method

If1 = field current corresponding to Isc

E = Vph + IRa cosΦ

If2 = field current corresponding to E from graph

If0 = ))90(180cos(21221( 22 IfIfIfIf

E0 = open circuit voltage corresponding to If0 (from graph)

% Regulation = 1000

xVph

VphE

ZPF method

EMF, E1 = 22 )sin()cos( LIXVphIRaVph

+ corresponds to lagging power factor

- corresponds to leading power factor

IXL = RS (from graph)

If2 = PS (from graph)

If1 = field current corresponding to E1 (from graph)

If0 = ))90(180cos(21221( 22 IfIfIfIf

E0 = open circuit voltage corresponding to If0 (from graph)

% Regulation = 1000

xVph

VphE

PRECAUTION

1. The Motor field rheostat is kept at minimum resistance position.

2. The Generator field rheostat should be kept at maximum resistance position.

OC TEST

FIELD

CURRENT(If)

(amps)

LINE

VOLTAGE(VL)

(volts)

PHASE

VOLTAGE

(Vph)(volts)

CIRCUIT DIAGRAM

SC TEST

FIELD

CURRENT(If)

(amps)

S.C.CURRENT

(ISC)(amps)

ZPF TEST

If(amps) VZPF(VOLTS) ISC(amps)

VOLTAGE REGULATION

EMF method

COS Ø E0(volts) % regulation

LAG LEAD LAG LEAD

Unity

MMF method

cos Ø E0(volts) % regulation

0.8

LAG LEAD LAG LEAD

Unity

ZPF method

COS Ø E0(volts) % regulation

0.8

LAG LEAD LAG LEAD

Unity

MODEL GRAPH

MMF method

ZPF method

PROCEDURE

OC test


2. The TPST switch of the alternator is kept opened.

3. The DPST-1 switch is closed

4. The motor field rheostat is varied such that the alternator runs at rated speed.

5. The DPST-2 switch is closed.

6. The Generator field rheostat is varied in step and the readings of If and V are

noted, till 125% of the rated voltage is obtained.

SC test


2. The DPST-1 switch is closed

3. The motor field rheostat is varied such that the alternator runs at rated speed.

4. The TPST switch is closed.

5. The DPST-2 switch is closed.

6. The Generator field rheostat is varied to bring rated current of alternator and the

corresponding If is noted.

ZPF test (All the quantities are in per phase value)

1. Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field

Current)

2. Mark the point A at X-axis, which is obtained from short circuit test with full load

armature current.

3. From the ZPF test, mark the point P for the field current to the corresponding

rated armature current and the rated voltage.

4. Draw the ZPF curve which passing through the point A and P in such a way

parallel to the open circuit characteristics curve.

5. Draw the tangent for the OCC curve from the origin (i.e.) air gap line.

6. Draw the line PX from P towards Y-axis, which is parallel and equal to OA.

7. Draw the parallel line for the tangent from R to the OCC curve.

8. Join the points R and S also drop the perpendicular line PX, where the line RS

represents armature leakage reactance drop (IXL)

PS represents armature reaction excitation (Ifa).

RESULT

POST LAB QUESTIONS

1. Why it is called as zero power factor method?

2. Why ZPF is called most accurate method?

3. Why the field rheostat is adjusted such that the voltmeter reads 380V.

4. Why voltage regulation on alternator is negative for leading power factor?

5. What are the advantages and disadvantages of estimating the voltage regulation of an

Alternator by EMF method?

DETERMINATION OF V AND INVERTED V CURVES OF

SYNCHRONOUS MOTOR

PRELAB QUESTIONS

1. Why synchronous motor is not self starting?

2. Why a synchronous motor is a constant speed motor?

3. State the characteristic features of synchronous motor.

4. Name the methods of starting a synchronous motors

Experiment No.

DETERMINATION OF V AND INVERTED V CURVES OF

SYNCHRONOUS MOTOR

AIM

To determine the V and inverted V curve of synchronous motor

APPARATUS REQUIRED


1

2

3

4

VOLTMETER

AMMETERS

RHEOSTAT

WATTMETER

(0-600V) MI

(0-2A) MC

(0-10A)MI

300Ω,1.2A

600V,10A,UPF

1

1

1

1

2

FORMULAE

Φ =

21

211 3tancosWW

WW

Where W1 = wattmeter reading 1

W2 = wattmeter reading 1

PRECAUTION

1. The VARIAC is kept at minimum position.

2. The potentiometer should be kept at minimum voltage position.

TABULAR COLUMN

Ia If V W1(watts) W2(watts) W1+W2(watts) COSΦ

Amps Amps Volts OBS ACT OBS ACT

CIRCUIT DIAGRAM

MODEL GRAPH

PROCEDURE

1. Connections are as per the circuit diagram

2. The TPST switch is closed.

3. By varying auto synchronous motor starter the voltage is adjusted to 30-40% of rated

voltage.

4. Close the DPST switch.

5. Adjusted the rheostat and bring for rated current.

6. Now the Voltmeter is adjusted for rated voltage values.

7. The values of If1, W1 and W2 are noted down.

8. By adjusting the rheostat below rated current the corresponding reading are noted

down.

9. At some point the value of Ia will increase and the above procedure is repeated till the

rated value of current.

10. If any wattmeter shows negative deflection, change the current coil terminals of

wattmeter.

RESULT

POSTLAB QUESTIONS

1. How synchronous machine does behave in under excitation?

2. What is synchronous capacitor?

3. Distinguish between synchronous phase modifier and synchronous condenser.

4. Mention four applications of synchronous motor?

5. Define pull in torque in synchronous motor

.

.

DETERMINATION OF Xd AND Xq FOR SALIENT POLE

ALTERNATOR USING SLIP TEST

PRELAB QUESTIONS

1. What are the two types of alternators?

2. Compare salient pole and Non salient pole rotor.

SALIENT POLE ROTOR NON SALIENT POLE ROTOR

(Smooth cylindrical type )

3. What is meant by two reaction theory?

4. What is direct and quadrature axis reactance?

5. What are the normal values of Xq/Xd for the two types of syn. Machines.

Experiment No.

DETERMINATION OF Xd AND Xq FOR SALIENT POLE

ALTERNATOR USING SLIP TEST

AIM

To find the direct axis reactance Xd and quadrature axis reactance Xq by conducting

slip test.

APPARATUS REQUIRED


1

2

3

4

VOLTMETER

AMMETER

RHEOSTAT

TACHOMETER

(0-300V) MI

(0-5A) MI

300Ω,1.2A

(0-10000 RPM)

2

1

1

1

FORMULAE

Xd = Maximum armature voltage/phase

Minimum armature current/phase

Xq = Minimum armature voltage/phase

Maximum armature current/phase

PRECAUTION

1. The Motor field rheostat should be kept at minimum resistance position

PROCEDURE


2. The DPST switch is closed

3. The rheostat is varied from the minimum resistance position so as to bring the speed

to a value below or near to rated speed of the alternator

4. The TPST switch is closed keeping the variac in the minimum position.

5. The variac is varied to apply 15-20% of the rated voltage of alternator is observed.

6. Check the voltage in the field coil, if it reads high the phase sequence is changed so

that the voltmeter reads zero.

7. The maximum and minimum deflections of voltmeter and ammeter are noted.

8. The variac is brought to minimum position and TPST Switch is opened. The field

rheostat is brought to minimum position and DPST Switch is opened.

CIRCUIT DIAGRAM

TABULAR COLUMN

VMAX VMIN IMAX IMIN

MODEL CALCULATION

RESULT

POSTLAB QUESTIONS

1) Why does the pointer of ammeter and voltmeter oscillate at slip condition?

2) Which is higher Xd or Xq? Why?

3) Mention some application of synchronous motor

4) Can the slip condition achieved in non salient pole Synchronous machines? Why?

srm institute of science and technology

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