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electrical machines lab manual

### Transcript of Electrical Machines Lab-II Manual

BRAKE TEST ON D

ELECTRICAL MACHINES LAB-II

3- INDUCTION MOTORLOAD TEST ON 3- INDUCTION MOTORAim:

To conduct load test on the given 3- induction motor and to plot its performance characteristics.

Apparatus:

S. No.Name of the EquipmentRangeTypeQuantity

13- Variac415V/(0-470)V-1

2Ammeter(0-10)AMI1

3Voltmeter(0-600)VMI1

4Wattmeter600V/10AUPF2

5Tachometer(0-9999)rpmDigital1

6Connecting Wires--Required Some

Circuit Diagram:

Precautions:

1. 3- Variac should be in minimum position.Procedure:

1. Connect the circuit as shown in circuit diagram.

2. Observing the precautions close the TPST Switch and switch ON 440V A.C supply.3. Apply the rated voltage to the stator windings of 3- Induction Motor with the help of 3- Auto-transformer.

4. Note down the readings of wattmeter, ammeter and voltmeter on no-load.

5. Load the Induction Motor in steps using the brake-drum arrangement. At each step note down the readings of all meters, speed and spring balance readings till full load current.

7. Observing the precautions switch OFF the supply.

Tabular Column:S. No.VL(V)IL

(A)Wattmeter

FactorTorque

(N-m)Output

(W)

(%)

W1 (W)W2 (W)S1S2S1~S2

1

2

3

4

Formulae:Torque, Tsh = 9.81 (S1 ~ S2) R N-mInput Power, Winp = W1 + W2 W

Output Power, Wout = (2 NTsh)/60 W%Slip = Ns N X 100

Ns

cos = Wout 3 VL ILEfficiency = % = (Output/Input) X 100Model Graph:

Result:O.C & S.C TESTS ON 1- TRANSFORMER

O.C & S.C TESTS ON 1- TRANSFORMER

Aim:a) To determine the efficiency and regulation of 1- transformer by conducting no-load and S.C Test.

b) To draw the equivalent circuit of 1- transformer referred to L.V side as well as H.V side.Apparatus:

S. No.Name of the EquipmentRangeTypeQuantity

11- Variac230V/(0-230)V, 10A-1

21- Transformer115V/230V, 2kVACore1

3Ammeter(0-10)AMI1

(0-2)AMI1

4Voltmeter(0-150)VMI1

(0-30)VMI1

5Wattmeter150V/2ALPF1

75V/10AUPF1

6Connecting Wires--Required Some

Circuit Diagram:O.C Test:

S.C Test:

Precautions:

1. Connections should be made tight.

2. 1- Variac should be in minimum position.Procedure:

1. Connect the circuit as shown in circuit diagram for O.C test.

2. Observing the precautions switch ON 1- A.C supply and by using the 1- variac apply the rated voltage of the primary of the transformer.

3. Note down all the meter readings. Here wattmeter reading gives iron loss.

4. Observing the precautions switch OFF the supply.

5. Connect the circuit as shown in circuit diagram for S.C test.

6. Observing the precautions switch ON 1- A.C supply and by using the 1- variac apply the rated current to the transformer. (Rated power of the transformer/Voltage of primary of transformer)

7. Note down all the meter readings, here wattmeter reading gives full-load copper loss.8. Observing the precautions switch OFF the supply.Tabular Columns:O.C Test:

S.C Test:Vo (V)Io (A)Wo = W X M.F (W)VSC (V)ISC (A)WSC = W X M.F (W)

Efficiencies at different loads and power factor:

cos = 0.6cos = 0.8

Cu Loss

(W)Output

(W)Input

(W)Efficiency

(%)Cu Loss

(W)Output

(W)Input

(W)Efficiency

(%)

Power Factor% RegulationPower Factor% Regulation

Model Calculations:

Let the transformer be the step-down transformer (O.C Test)

Primary is H.V side and secondary is L.V side

Ro=V1/Iw () where Iw=Iocoso

Xo=V1/I () where Iw=Iocoso

Ro1=WSC/ISC2 ()

ZO1=VSC/ISC

Xo1=( ZO12 - Ro12)

Ro2=K2 Ro1

Xo2=K2 Xo1

where,

K=V2/V1=Transformation Ratio

Calculations to find efficiency:

For example, at 1/4th full load,

Copper Losses=WSC x (1/4)2 (w)

Constant Losses=Wo (W)

Output=(1/4) X VA X cos (cos may be assumed)

Input=Output + Copper Loss + Constant Loss

Efficiency (%) = (Output/Input) X 100

Efficiency at different loads and power factor can be calculated.

Model Graph:

Result:NO-LOAD & BLOCKED ROTOR TESTS ON 3- INDUCTION MOTOR

NO-LOAD & BLOCKED ROTOR TESTS ON 3- INDUCTION MOTOR

Aim:

To draw the equivalent circuit of a 3- Induction Motor and construct the circle diagram by conducting No-Load & Blocked Rotor Tests.Apparatus:S. No.Name of the EquipmentRangeTypeQuantity

13- Variac415V/(0-470)V-1

2Ammeter(0-10)AMI1

(0-5)AMC1

3Voltmeter(0-600)VMI1

(0-150)VMI1

(0-30)VMC1

4Wattmeter600V/10ALPF2

300V/10AUPF2

5Rheostat100/5AWW1

6Connecting Wires--Required Some

Circuit Diagram:

Blocked Rotor Test:

To find stator resistance per phase:

Precautions:

1. 3- Variac should be in minimum position.Procedure:No-Load Test:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the TPST Switch and switch ON 440V A.C Supply.

3. Apply the rated voltage to the stator windings of 3- Induction Motor with the help of 3- Auto-Transformer.4. Note down the no-load readings of wattmeter, ammeter and voltmeter.

5. Bring back the auto-transformer to its minimum position and switch OFF the supply.

Blocked Rotor Test:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the TPST Switch and switch ON 440V A.C Supply.

3. By varying the variac, apply small voltage until the full load current flows in the stator windings with the rotor unmoved.4. Note down the readings and switch OFF the supply after bringing back the auto-transformer output to minimum position.Measurement of Stator Resistance:1. Connect the circuit as per the circuit diagram.

2. Keeping rheostat in maximum resistance position switch ON 220V D.C supply.3. Using Volt-Ammeter method measure the resistance of the stator winding.

4. After finding the stator resistance Rdc must be multiplied with 1.6 so as to account for skin effect i.e., Rac = 1.6RdcTabular Column:Blocked Rotor Test:

Current, ISC (A)Voltage, VSC (V)W1 (W)W2 (W)

Io (A)V (V)W1 (W)W2 (W)

Stator Resistance per phase = Formulae:

Go = Wo ; Yo = Io ; Bo = (Yo2 Go2) 3V2 V

Z01 = VSC ; R01 = WSC ; X01 = (Z012 R012) ISC 3ISC2For Circle Diagram:

cos o = Wo 3 Vo Iocos SC = WSC 3 VSC ISCISN = ISC [Vo / Vsc]Model Graph:

Result:PARALLEL OPERATION OF

1- TRANSFORMERPARALLEL OPERATION OF 1- TRANSFORMERAim:

To connect two 1- transformers of equal ratings in parallel and to supply study how they share a common load.Apparatus:

S. No.Name of the EquipmentRangeTypeQuantity

1Voltmeter(0-300)VMI1

(0-150)VMI1

21- Transformer115V/230V, 2kVACore2

3Ammeter(0-20)AMI1

(0-10)AMI2

5SPST Switch-Knife1

6DPST Switch-Knife1

7Wattmeters300V/10AUPF2

150V/20AUPF1

8Connecting Wires--Required Some

Circuit Diagram:

Precautions:

1. Load should be in OFF position.

2. SPST Switch is in open position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions switch ON the supply.

3. Two readings of the voltmeter connected across switch K is observed. If it reads zero which means that the two secondary emfs are opposing each other, then switch K is closed. If it reads twice the secondary rated voltage the secondary terminals of any of the transformer are interchanged and then the switch K is closed to make it read zero reading.4. The load switch is closed and total load on the transformer is increased in steps. At each step, the readings of the various meters are noted down. The total load is increased till the current supplied reaches the maximum load current of both the transformers when connected parallely.5. Observing the precautions switch OFF the supply.

Tabular Columns:From S.C Test:

From O.C Test:

S.No.ISC (A)Vsc (V)WSC (W)Core Loss, Wo (W) =

1

2

3

S.No.IA(A)IB(A)IL(A)VL(V)WA(W)WB

(W)WL

(W)IA|

(A)IB|

(A)WA|

(W)WB|

(W)(%)% Reg

1

2

3

Formulae:

IA| = IL X ZB ; IB| = IL X ZA ZA+ZB

ZA+ZBWA| = WL X ZB ; WB| = WL X ZA ZA+ZB

ZA+ZBWSC = Isc2R ; WCu = I2R (Since I=IA|+IB|)ZSC = ZA = ZB = VSC / ISC

%Reg = VNL VFL X 100 VFLVNL = No Load VoltageVFL = Load Voltage at different loads

Output, Wout = VL IL

;

Input,Win = Wout + WCu + Wo

Efficiency, % = Wout X 100

WinModel Graph:

Result:

SEPARATION OF CORE LOSSES OF 1-