BRAK E TEST ON A THREE PHASE SLIP RING INDUCTION MOTOR

Circuit Diagram:

BRAKE TEST ON A THREE PHASE SLIP RING INDUCTION MOT OR Aim : To conduct the load test on a three phase slip ring Induction motor and to draw

the performance and mechanical characteristics. Name plate details: Apparatus: Theory: Procedure: 1. The name plate details of the motor are noted down. 2. The cir4cuit is connected as per the connections in the circuit diagram. 3. The TPST’s is closed and the motor is started using rotor resistance starter where

the rotor resistance starter is turned from maximum resistance to minimum resistance position to run at rated speed.

4. The speed, current, voltage and power are noted down at no load. 5. The varies values of current, speed, voltage and power are recorded by applying

the load. 6. The load is later released and the motor is switched off. The rotor resistance

starter is brought to the original position before switching off the motor, the load is later released and the motor is switched off and the graph is drawn.

Graph: Precautions: 1. The rotor should lbe started without any load. 2. The rotor resistance starter should be in the maximum resistance position without

starting. Results: . The brake test on a three phase slip ring Induction motor is performed and its found that the maximum efficiency of 68.64 % occurs at a load of 3.65 A. Conclusions: By performing the Break test on a slip ring Induction motor, we conclude that the starting torque of the motor is increased by improving the pf. Due to its high starting torque, this motor is used to drive heavy loads. From the performance characteristics drawn, we conclude that the torque/ current curve is fairly a straight line since the speed is nearly constant. As the current increases from no load, the pf rises to a maximum near full load. The pf will fall again to S.C value if load is increased and motor will stall. The efficiency is zero at a load. But rises to maximum where I2R losses equal the no-load losses. Thereafter, the efficiency falls because the losses will increase more rapidly than the output.

LOAD TEST ON A 3 PHASE ALTERNATOR

Circuit Diagram:

LOAD TEST ON A 3 PHASE ALTERNATOR Aim : To conduct the load test on a three phase alternator and to draw its performance

characteristic curves. . NAME PLATE DETAILS: Apparatus: Theory: Procedure: 1. The connections are made as per the circuit diagram. 2. The supply is given as per the circuit diagram. 3. The motor is started using the 3-point starter and is made to run at synchronous

speed, Ns, by using the field rheostat of the motor. 4. The generator voltage is built up to the rated voltage by varying the field exciter. 5. The TPST switch is closed. 6. The speed and excitation current are kept constant throughout the process, the

load is applied and the values of load current and load voltage for various values of the loads and different types of loads.

7. The speed and load voltage are kept constant through out the process, the load is applied and the values of load current and excitation current for various values and different types of load.

8. The load is later released and the motor is switched off and the graphs are drawn. Graph: Precautions: 1. The motor field rheostat should be kept in minimum position. 2. The speed should be kept constant through out the experiment. 3. The alternator field potential devider should be in the minimum voltage position. Results: . The performance characteristics of the 3-phase alternator were drawn after conducting the load test and they are in agreement with expected curves. Conclusions: From the graphs plotted, it can be concluded that for a resistive load, as the load current increases, the voltage decreases. Similarly for an inductive load (lagging load) the load voltage versus load current characteristics are more dropping than those for a resistive load. For unity and lagging power factors, there is always a voltage drop with increase in load, hence, the regulation is dependent on the power factor of the load. Also, all the unity and lagging pfs load require an increase of excitation with increase in load current.

LOAD TEST ON SINGLE PHASE TRANSFORMER

LOAD TEST ON SINGLE PHASE TRANSFORMER AIM To perform load test on a 1 - φ transformer and determine efficiency at different loads, voltage regulations of the transformer and draw the efficiency Vs load curve. NAME PLATE DETAILS: Apparatus: Theory: Procedure: 1. Make the connections as per the circuit diagram. 2. Apply 230V, 1 - φ , 50 Hz supply by closing the DPST switch. 3. Vary the position of 1 -φ varioc until the voltmeter reads 230 V. 4. Note down the readings of all the meters. 5. The transformer is loaded in regular steps and meter readings are noted 6. Remove the load in the same regular steps and open the DPST switch.

Precautions: 1. The varioc must be placed initially in the minimum position. 2. The load should be applied and removed in regular steps. Graphs: Results:

NO LOAD AND BLOCKED ROTOR TEST ON A 3 PHASE SLIP RING

INDUCTION MOTOR

Circuit Diagram:

NO LOAD AND BLOCKED ROTOR TEST ON A 3 PHASE SLIP RI NG INDUCTION MOTOR

Aim : To conduct the no load and blocked rotor test on a three phase slip ring induction

motor and to predetermine the performance using circle diagram. NAME PLATE DETAILS: Apparatus: Theory: Procedure: 1. The name plate details of the motor are noted down. 2. For the no-load test, the rated voltage is applied by adjusting the auto transformer

and the ammeter and wattmeter readings are noted down. Here the rotor is free to rotate.

3. For the blocked-rotor test, the rated current is applied by adjusting the autotransformer, and the voltmeter and wattmeter readings are noted down. Here, the rotor is blocked.

4. Connections are made as per the circuit diagram to measure the rotor and stator resistances.

5. By adding the load through the loading rheostat, note down the ammeter and voltmeter readings for various values of load.

Procedure to draw the circle diagram: 1. The lines are drawn by taking current on x-axis and voltage on y-axis. 2. From the no-load test, the no-load current I0 is drawn from the origin by a

suitable current scale, which laps the voltage V by an angle φ 0 = Cos-1 (Woc / √3 V0 I0)

3. From the current ISC , the current ISN (short – circuit current corresponding to the normal voltage) through the formula, ISN = ISC. V rated / VSC is found and is drawn as the vector OA. By the same current scale, which lags the voltage by an angle, SCφ = Cos-1 (WSC / √3 VSCISC).

4. The points O1 and A are joined to get the output line. 5. Draw a line parallel to x-axis from O1 and a line parallel to y-axis from pt. A onto

the x-axis (F) and let these lines intersect at G. 6. The bisector for the output line is drawn and is extended to the line O1G, let the

point of intersection be C. 7. With C as center and O1C as radius, a semicircle is drawn. 8. Let AF be the line of total loss [FG (const.losses) + GA (variable loss)] 9. The point E is located on the line AG to separate the stator and rotor Cu losses by

using

the formula ssStatorculo

sRotorculos =

RsI

RsIW

SC

SCSC

2

2

3

3− This formula is valid for

squirrel cages IM where Rs denotes the stator resistance per phase.

For a slip-ring motor, RsI

RrI

ssStatorculo

sRotorculos2

1

22=

10. The points O1 & E are joined to obtain the torque line to find out the maximum quantities.

11. The tangent to the semi circle is drawn in such a way that it should be parallel to the output line. Let the point of tangent be M.

12. The points M & C are joined which is tr to the output line, then draw a parallel line to the y-axis from M to the output line. The pt. Where this parallel line meets the output line is named R. Thus MR gives the maximum output power.

13. A tangent to the semi circle is drawn in such a way that its parallel to the torque line. Let the point of tangent be N. Join N & C which is tr to torque line. Drop N onto the torque line and let the point of intersection be φ . Thus Nφ gives the maximum torque.

14. A tangent to the semi circle is drawn in such a way that it should be parallel to x-axis and let the point of intersection be J1. Thus, JJ1 gives maximum input power.

15. From the circle diagram, the maximum input power, maximum torque, maximum output power, rotor Cu loss, Stator Cu loss and slip.

To find out full-load quantities: 16. Extent the line AF from A to S such that AS = Output power (from the name plate of machine) Power scale 17. Draw a parallel line to output line O1A which cuts the semicircle at point P. 18. Draw a parallel line to y=axis from P onto x-axis (point k) then join O and P. Fixed losses = FG × Power scale = LK × Power scale (watts) Full-load stator Cu loss = DL × Power scale (watts) Full-load Rotor Cu loss = MD × Power scale (watts) Full-load current = OP × current scale (amps) Full-load p.f = Cos (angle b/w OP & y-axis)

Full-load torque = PD × powerscale × ( )MNN S

−π2

60

Full-load output power = PH × power scale (Watts) Full-load input power = PK × power scale (Watts) Full-load efficiency = Full load o/p power Full load i/p power Full-load rotor i/p = PD × power scale (watts)

Full-load slip, s = PD

HD

Full-load speed = NS × (I – S)

Starting torque = AE × power scale × Nsπ2

60 (N-M)

Precautions: 1. The autotransformer should be kept at minimum voltage position before starting. 2. The circle diagram is drawn with care. 3. Make sure that there exists no-load on the machine that is the hold of the belts on

the brake drum is very loose during the no-load test. Results: The quantities found out from the circle diagram 1. Fixed losses = 286.378 Watts 2. Stator Cu losses = 1431.89 Watts 3. Rotor Cu losses = 3579.725 watts 4. Maximum torque = 28.94 Watts 5. Maximum Output power = 2.992 KW. 6. Maximum Input power = 5.727 KW. 7. Full-load current = 5.6 A 8. Full-load power factor = 0.743 9. Full-load torque = 16.407 N-m 10. Full-load output power = 2.255 KW

11. Full-load input power = 2.971 KW 12. Full-load efficiency = 75.9 % 13. Full-load stator Cu loss = 143.189 Watts 14. Full-load rotor Cu loss = 322.175 Watts 15. Full-load rotor input = 2.577 KW 16. Full-load slip = 12.5% 17. Full-load speed = 1312.5 rpm 18. Starting torque = 22.789 N-m Conclusions: The no-load and blocked rotor tests data help in the construction of the circle diagram through which the performance of the machine can be predetermined without actually applying the load on the machine.

O.C AND S.C TESTS ON A SINGLE PHASE TRANSFORMER

Circuit Diagram:

O.C AND S.C TESTS ON A SINGLE PHASE TRANSFORMER Aim : To conduct OC and SC tests on a given angle phase transformer to predetermine

the efficiency and regulation and draw the equivalent circuit diagram of the transformer.

NAME PLATE DETAILS: Apparatus: Theory: Procedure: For Open-circuit test: 1. Connections are made as per the circuit diagram given. 2. After applying the supply, the input voltage is adjusted on the L.V. side of the

transformer to the rated value by using an auto transformer. 3. The corresponding readings of V0, O0 and W0 are noted. 4. The branch parameters of the equivalent circuit are thus calculated. For Short-circuit test:

1. The connections are made as per the circuit diagram. 2. After applying the supply to G.V. side, the voltage is adjusted by using auto

transformer until the ammeter shows rated current. 3. The corresponding readings of the voltmeter, ammeter and wattmeter are noted. 4. From these readings, efficiency, regulation and equivalent circuit parameters are

determined. Graph: Precautions: 1. Readings must be taken without parallax error. 2. While the S.C test is in progress, full load current should not exceed the rated

current.. Results: . From the graphs plotted, it has been determined that (i) a maximum efficiency of 95% occurs at a load current of 11A (ii) Maximum regulation occurs at 0.8 lagging Pf. (iii) Zero regulation occurs at 0.37 leading pf. The shunt branch parameters are : Core-loss resistance, R0 = 367.611 Ω Magnetizing reactance, X0 = 110.153 Ω Equivalent primary resistance, R01 = 1.189 Ω Equivalent primary reactance, X01 = 0.7428 Ω Conclusions: On performing OC and SC tests on a given transformer, its efficiency and percentage voltage regulation can be predetermined for any load.

REGULATION OF 3 PHASE

ALTERNATOR BY EMF AND MMF METHODS

Circuit Diagram:

REGULATION OF 3 PHASE ALTERNATOR BY EMF AND MMF

METHODS Aim : To predetermine the regulation of three phase alternator by EMF and MMF

methods and also to draw the vector diagrams. NAME PLATE DETAILS: Apparatus: Theory: Procedure: 1. The name plate details of the motor and alternator are noted down. 2. The circuit is connected as per the connections made in the circuit diagram. 3. The supply is given by closing the DPST switch. 4. Using the three point starter, the motor is started and is run at the synchronous

speed by varying the motor field rheostat. 5. The O.C test is conducted by varying the potential divider for various values of

field current and the corresponding open-circuit voltages are tabulated.

6. The S.C test is conducted by closing the TPST switch, the potential divider is adjusted so as to set the rated armature current and the corresponding field current is tabulated.

7. The stator resistance test is conducted by giving connections as per the circuit diagram and the voltage and current reading for various resistive loads are tabulated.

Graph: Precautions: 1. The motor field rheostat should be kept in the minimum resistance position. 2. The alternators’ field rheostat should be in the maximum voltage position. 3. Initially, all the switches are in open position. Results: 1. The voltage regulation obtained by emf methods is 55.95% 2. The voltage regulation obtained by mmf method is 15.66 % Conclusions: The value of the voltage regulation obtained by emf method is more than that obtained by mmf method. Moreover, the voltage regulation computed by emf method is much higher than the actual value and hence is also called a pessimistic method. And therefore, mmf method is more accurate and reliable than emf method.

SCOTT CONNECTION VERIFICATION OF 3-PHASE TO 2-

PHASE CONVERSION

Circuit Diagram:

SCOTT CONNECTION VERIFICATION OF 3-PHASE TO 2-PHASE CONVERSION

Aim : To convert three phase supply into two phases using Scott connected

transformers. NAME PLATE DETAILS: Apparatus: Theory: Procedure: 1. The connections are made as per the circuit diagram. 2. The variac must be placed initially in the minimum position. 3. The three phase, 415 v, 50Hz supply is applied by closing the TPST switch. 4. The position of the variac is varied and the corresponding voltmeter readings are taken.

5. It is verified whether if the voltage V3 = 22

21 VV + .

6. The variac is varied until the voltmeter V1 shows rated value. 7. The variac is brought to the minimum position and the supply is switched OFF.

Precautions: 1. Loose connections are avoided and parallax error too. 2. The variac is to be placed in minimum position before starting the experiment. Results: . The three phase to two phase conversion was observed by using Scott connection and the necessary conditions were verified. Conclusions: A three phase supply can be converted into a two phase supply as well as a two phase supply can be converted into a three phase supply.

SEPERATION OF LOSSES OF A 1-φ TRANSFORMER

Circuit Diagram:

SEPERATION OF LOSSES OF A 1-φ TRANSFORMER

AIM To separate the hysterysis and eddy current losses. Apparatus: NAME PLATE DETAILS: Theory: Procedure: The low tension winding is excited by a variable frequency alternating current, frequency may be varied from a very low value to the 50 Hz. To make the transformer induction constant the voltage should be proportional to variable frequency. This can be achieved from variable speed alternator.

Graphs: Precautions: 1. Connections should be tight.. 2. 1 - φ variac should be in minimum position at time of switching ‘ON’ the 1 - φ

supply. Results:

SLIP TEST ON A 3 PHASE SALIENT POLE ALTERNATOR

Circuit Diagram:

SLIP TEST ON A 3 PHASE SALIENT POLE ALTERNATOR Aim : To determine the values of xd and xq , the direct and quadrature reactances

respectively. . Name plate details: Apparatus: Theory: Procedure: 1. The circuit is connected as per the circuit diagram. 2. The motors’ field rheostat is put in minimum position. 3. The DC supply to the motor is switched ON and is started with the help of a 3-

point started. 4. The speed of the motor is adjusted to near the rated value with the help of the

field rheostat of the motor. 5. A reduced 3-φ voltage with the help of the 3 -φ variac is applied to the armature

winding of the alternator. If the field winding voltmeter reads a zero value, then the 3-φ variac is varied till ammeter and voltmeter pointers vibrates from minimum to maximum values.

6. The maximum and minimum values of armature current are noted down. 7. The 3 φ variac is brought down to zero position, the 3φ supply is switched off

and also, the D.C supply is switched off by making all devices to their starting position.

8. Conduct the O.C and S.C tests on the salient pole alternator and note down the O.C and S.C test data.

.Graph: Results: . 1. The direct axis synchronous reactance is, xd = 19.647 Ω . 2. The quadrature exis synchronous reactiance is, xq = 17.277 Ω Conclusions: The direct axis reactance is always greater than the quadrature axis reactance and these reactance are due to the non-uniform air-gap on the periphery of the rotor.

SUMPNERS’ TEST ON A PAIR OF SINGLE PHASE TRANSFORMER

Circuit Diagram:

SUMPNERS’ TEST ON A PAIR OF SINGLE PHASE TRANSFORMER Aim : To obtain the equivalent circuit and to predict the efficiency and voltage

regulation of a transformer by conducting Sumpners’ test on two identical transformers.

Name plate details: Apparatus: Theory: Procedure: 1. Connections are made as per the circuit diagram and initially DPST 2 and3 must

be opened. 2. The DPST 1 switch is closed and input voltage is adjusted until the voltmeter

indicates the rated value of LV winding of transformer by means of variac 1 3. The secondary voltmeter (V2) reading is observed. If it’s greater than zero volts,

the secondary terminals of one of the transformers must be reversed, such that V2 reads zero.

4. After noting down the readings of ammeter A1, voltmeter V1 and Wattmeter W1, the DPST switches 2 & 3 are closed.

5. The readings of ammeter A2, Voltmeter V2 and Wattmeter W2 are noted after adjusting the voltage which circulates the rated current in secondaries of two transformers by means of variac 2.

6. The variacs are adjusted to their initial positions and finally all the DPST switches are opened.

Graph: Precautions: 1. Readings should be taken without parallax error. 2. Before switching on the supply, the two auto-transformers are set to zero

position. 3. While taking the readings of the two wattmeter, to get more accurate values, the

ammeters should be short circuited. 4. Loose connections are to avoided before starting the experiment. Results: . From the graphs plotted, its determined that (i) a maximum efficiency occurs a load current of 5.7A and the maximum efficiency obtained is 94.5%. (ii) A maximum regulation occurs at 4.9 % occurs at 0.8 lagging pf. (iii) Zero regulation occurs at 0.39 leading pf. The shunt branch parameters are : Core-loss resistance, R0 = 315.457 Ω Magnetising reactance, X0 = 105.485 Ω Equivalent primary resistance, R2e = 1.255 Ω Equivalent primary reactance, X2e = 0.5135 Ω Conclusions: On performing the Sumpners’ test on a pair of identical transformers, its efficiency and percentage regulation can be predetermined for any load.