Cycle 2 EE6512 Electrical Machines II Lab...

Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy.

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Cycle 2 EE6512 Electrical Machines II Lab Manual

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CIRCUIT DIAGRAM FOR SLIP TEST

NAME PLATE DETAILS:

3Ф alternator DC shunt motor FUSE RATING: 125% of rated current (full load current) For DC shunt motor : ……………. For Alternator : …………….

Volts: Amps: kVA: RPM:

Volts: Amps: kW: RPM:

3 Point Starter L F A

350Ω, 2 A

180V DC SUPPLY



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REGULATION OF THREE PHASE SALIENT POLE ALTERNATOR BY SLIP TEST AIM: The aim of the experiment is to predetermine the regulation of three phase salient pole alternator by conducting the slip test. APPARATUS REQUIRED: S.NO NAME OF THE

APPARATUS RANGE TYPE QUANTITY

1. 2. 3. 4. 5. 6. 7. 8.

Ammeter Ammeter Voltmeter Voltmeter Rheostat

3 Ф Auto transformer Tachometer

Connecting wires

(0-5) A (0-5) A

(0-150) V (0-150)V

300Ω,1.5A

MI MC MI MC

Wire wound

1 1 1 1 1 1 1

As required FORMULAE USED:

1. Armature Resistance, Ra =1.6 X Rdc

2. Direct impedance per phase (Zd) = max

min

IV in Ω

3. Quadrature axis impedance per phase (Zq) = min

max

IV in Ω

4. Direct axis reactance per phase (Xd) = 22ad RZ in Ω

5. Quadrature axis reactance per phase (Xq) = 22aq RZ in Ω

6. Percentage Regulation = 1000 u

rated

rated

VVE

7. ddaqt XIRIVE Gcos0 (for Motoring)

8. ddaqt XIRIVE Gcos0 (for Generating)

9. I\G (for Generator) 10. \IG (for Motor)

11. ¸¹

·¨©

§rr

aat

qat

RIVXIV

II

\cossin

tan 1 + For generating mode; -- For Motoring mode

THEORY: In non salient pole alternators air gap length is constant and reactance is also constant. Due to this the MMFs of armature and field act upon the same magnetic circuit all the time hence can be added vectorically. But in salient pole alternators the length of the air gap varies and reluctance also varies. Hence the armature flux and field flux cannot vary sinusoid ally in the air gap. So the reluctance of the magnetic circuit on which mmf act is different in case of salient pole alternators. This can be explained by two reaction theory.



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PRECAUTIONS: 1. The motor field rheostat should be kept in minimum resistance position. 2. The alternator field should be kept open throughout the experiment. 3. The direction of rotation due to prime mover and due to the alternator run as the

motor should be same. 4. Initially all the switches are kept open.

PROCEDURE: 1. Connections are given as per the circuit diagram and confirm that the alternator filed

is in open condition. 2. Give the supply by closing the DPST switch. 3. Using the three point starter start the motor to run at the synchronous speed by

varying the motor field rheostat. 4. Apply 20% to 30% of the rated voltage to the armature of the alternator by adjusting

the autotransformer. 5. To obtain the slip and maximum oscillations of pointers, the speed is reduced slightly

lesser than the synchronous speed. 6. Note down the maximum current, minimum current, maximum voltage and minimum

voltage. Find out the direct and quadrature axis impedance (Zd,Zq). TABULATIONS: a. To find Zd and Zq :

S.No Vmax Vmin Imax Imin

b. To predetermine % Regulation:

S.No Powerfactor % Regulation

Lagging Leading Unity

1 0.2

2 0..4

3 0.6

4 0.8

GRAPH: i. Powerfactor Vs Percentage Regulation

RESULT: Thus the percentage regulation of the given three phase alternator is predetermined using

slip test.



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Circuit Diagrams for Negative Sequence and Zero Sequence Impedances of Salient Pole Alternator

Name Plate Details:

D.C Shunt Motor 3 Phase Alternator kW : …………………………..

Speed: …………………………RPM

Voltage: ……………………….V

Current : ……………………….A

Field Voltage: ………………….V

Field Current : ………………….A

kVA : …………………………..

Speed: …………………………RPM

Voltage: ……………………….V

Current : ……………………….A

Field Voltage: ………………….V

Field Current : ………………….A

220V, DC

350Ω

, 2A

3 POINT STARTER

R

Y B

F1 F2

415/(0-470)V, 3ϕ VARIAC

+

-

V

(0-10)A,MI

(0-3

00)V

,MI

415V, 50Hz

415V, 50Hz

R

Y

B

A

T

P

S

T

S

N

A

(0-2)A,MI

M

L F A

F1

F2

A1

A2

D

P

S

T

S

N

NEGATIVE SEQUENCE IMPEDANCE



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TABULATION: Negative Sequence Zero Sequence

S.No V I Z2=V/I S.No V I Z0=3V/I

220V, DC

350Ω

, 2A

3 POINT STARTER

R

Y B

F1 F2

415/(0-470)V, 3ϕ VARIAC

+

-

V

(0-10)A,MI

(0-3

00)V

,MI

415V, 50Hz

415V, 50Hz

R

Y

B

A

T

P

S

T

S

N

A

(0-2)A,MI

M

L F A

F1

F2

A1

A2

D

P

S

T

S

N

ZERO SEQUENCE IMPEDANCE



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MEASUREMENTS OF NEGATIVE SEQUENCE AND ZERO SEQUENCE IMPEDANCE OF ALTERNATORS.

AIM: To measure the negative and zero sequence impedances of the given salient pole

alternator. APPARATUS REQUIRED: S.NO NAME OF THE


1. 2. 3. 4. 5. 6. 7.

Ammeter Ammeter Voltmeter Rheostat 3 Ф Auto transformer Tachometer Connecting wires

(0-5) A (0-2) A

(0-300) V 300Ω,1.5A

-- -- --

MI MC MI

Wire wound --

Digital --

1 1 1 1 1 1

As required THEORY:

When a synchronous generator is carrying an unbalanced load its operation may be

analyzed by symmetrical components. In a synchronous machine the sequence current produce

an armature reaction which is stationary with respect to reactance and is stationary with respect

to field poles. The component currents therefore encounter exactly same as that by a balanced

load as discussed. The negative sequence is produced and armature reaction which rotates around

armature at synchronous speed in direction to that of field poles and therefore rotates part the

field poles at synchronous speed. Inducing current in the field damper winding and rotor iron.

The impendence encountered by the negative sequence is called the – ve sequence impedance of

the generator. The zero sequence current produce flux in each phase but their combined armature

reaction at the air gap is zero. The impedance encountered by their currents is therefore different

from that encountered by + ve and –ve sequence components and is called zero sequence

impedance of generator. Negative sequence:

The –ve sequence impedance may be found by applying balanced –ve sequence voltage to the armature terminals. While the machine is drive by the prime mover at its rated synchronous speed with the field winding short circuited. The ratio of v/ph and Ia/ph gives –ve sequence Z/ph. The reading of the wattmeter gives I2 R losses. This loss /ph divided by Iph required gives the –ve sequence R/ph from the impedance and reactance/ph. –ve sequence can be

calculated. Another method of measuring –ve sequence reactance is found to be connect the arm



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terminals. The machine is driven at synchronous speed and field current adjusted until rated current flows in the phases shorted through armature and current coil of wattmeter respectively

Zero sequence:

The sequence impedance may be determined by the connecting the armature windings of the three phase in series and then connecting them to the single phase source of power. If the

machine is driven at synchronous speed with field winding shorted, then ZO=V/3I practically the

same results will be obtained with rotor stationary. If windings are connected in parallel, then

PROCEDURE: For Negative Sequence : i. Make connection as shown in circuit diagram. ii. Run DC motor with synchronous speed. iii. Keeping the speed constant, vary the excitation and measure the voltmeter, ammeter and

wattmeter reading. iv. Take 3-4 readings for different excitation. v. The excitation should not be increased beyond the rated capacity of synchronous machine i.e.

6.9 A For Zero Sequence: i. Make connection as shown in circuit diagram. ii. Set the autotransformer output to zero volts and switch on the supply. iii. Gradually increase input voltage and note the ammeter reading for the voltage applied. iv. Repeat reading upto the rated current rating of the machine (i.e, 6.9A). RESULT: Thus the negative and zero sequence impedances of the salient pole alternator is measured.



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SEPARATION OF NO LOAD LOSSES OF THREE PHASE INDUCTION MOTOR AIM:

To separate the no load losses of a 3 phase squirrel cage induction motor as iron losses

and mechanical losses.

NAME PLATE DETAILS: 3Ø Induction motor: HP: ……………… HP Speed: : ………………… RPM Voltage : ………………..V Current : ………………..A

FUSE RATING: No load : 10% of rated current (full load current).

APPARATUS REQUIRED: S.NO NAME OF THE


1. 2. 3. 4. 5. 6.

Ammeter Voltmeter Wattmeter 3 Ф Auto transformer Tachometer Connecting wires

(0-5) A (0-600) V 600Ω,5A

415/(0-470)V -- --

MI MI

LPF --

Digital --

1 1 2 1 1

As required

PRECAUTIONS: i. The autotransformer should be kept in minimum voltage position. ii. The motor should not be loaded throughout the experiment.

PROCEDURE: i. Connections should be made as per the circuit diagram. ii. Start the motor by giving three phase supply. iii. Vary the autotransformer till rated speed is attained and note the input power, voltage and

current. iv. Repeat the same procedure for and tabulate the reading.



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v. Find the stator copper loss and constant loss by respective formulas. vi. Draw the suitable graph to find the mechanical losses. vii. Obtain the core los by separating the mechanical loss from constant losses.

GRAPH: x The graph drawn between constant losses (watts) and input voltage(volts).

MODEL CALCULATIONS: 1. Input power (W) =(W1+W2)in watts 2. Stator copper loss =3I2Rs in watts

3. Constant loss/phase (Wc)= (W-3I2Rs)/3 in watts

4 Core loss/phase (Wi)= (constant loss/phase)-mechanical loss

TABULTAION:

S.No V I W1 W2 W Stator Cu Loss

Constant Loss per

Phase (Wc)

Core Loss per

Phase (Wi)

RESULT: Thus the no load losses of 3-phase squirrel cage induction motor was separated as core

losses and mechanical losses.



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NO LOAD TEST



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NO LOAD AND BLOCKED ROTOR TEST ON SINGLE PHASE INDUCTION MOTOR AIM:

To draw the performance characteristics of a single phase induction motor by conducting the no-load and blocked rotor test. APPARATUS REQUIRED:

S.No Name of Apparatus Range Type Qty. 1 Voltmeter (0-300)V MI 1 2 Voltmeter (0-150)V MI 1 3 Ammeter (0-10)A MI 1 4 Ammeter (0-2)A MI 1 5 Wattmeter (330V,10A) UPF 1 6 Wattmeter (300V,5A) LPF 1 7 Connecting wires -- -- As reqd.

FUSE RATING: 125% of ……..A= ………..A THEORY:

A 1-Ф induction motor consists of stator,rotor and other associated parts.In the rotor of a single phase winding is provided.The windings of a 1- Ф winding(provided) are displaced in space by 120º.A single phase current is fed to the windings so that a resultant rotating magnetic flux is generated.The rotor starts rotating due to the induction effect produced due to the relative velocity between the rotor winding and the rotating flux. PRECAUTIONS: No load test:

x Initially TPST Switch is kept open. x Autotransformer is kept at minimum potential position. x The machines must be started on no load.

BLOCKED ROTOR TEST:

x Initially the TPST Switch is kept open. x Autotransformer is kept at minimum potential position. x The machine must be started at full load (blocked rotor).

PROCEDURE: NO LOAD TEST:

1. Connections are given as per the circuit diagram. 2. Precautions are observed and the motor is started at no load. 3. Autotransformer is varied to have a rated voltage applied.

BLOCKED ROTOR TEST:



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1. Connections are given as per the circuit diagram. 2. Precautions are observed and motor is started on full load or blocked rotor position. 3. Autotransformer is varied to have rated current flowing in motor. 4. Meter readings are the noted.

FORMULAE USED:

Re = 1.6XRdc 1. No Load Test:

x cos Ф = W0/V0I0 x Iw = I0 cosФ x Im = I0sin Ф x R0 = V0/Iw x X0 = V0/Im

2. Blocked Rotor Test: o Zsc = Vsc/Isc Ω o Rsc = Wsc/Isc

2 Ω o Xsc = √(Zsc

2 – Rsc2) Ω

TABULATION NO LOAD TEST

S.No. Vo(volts) Io(amps) Wo(watts) m.f Observed Acual

BLOCKED ROTOR TEST

S.No. Vsc(volts) Isc(amps) Wsc(watts) m.f Observed Actual

RESULT:

Thus the no load and blocked rotor test on the single phase induction motor has been conducted and the equivalent circuit has been drawn.


Cycle 2 EE6512 Electrical Machines II Lab...

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