KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 1 AIM: To perform open and short circuit tests on 1-phase transformer and to calculate efficiency. Apparatus required:
Theory: Transformer is a static device which transfers electrical power from one circuit to another circuit either by step up or step down the voltage with corresponding decrease increase in the current, with out changing the frequency. OC Test The main aim of this test is to determine the Iron losses & No- load current of the T/F which are helpful in finding Ro & Xo.In this test generally supply will be given to primary and secondary kept open. Since secondary is opened a small current(magnetizing current will flow and it will be 5 to 10% of full load current. The wattmeter connected in primary will give directly the Iron losses (core losses). SC Test: The main aim of this test is to determine the full load copper losses which is helpful in finding the R01, X01, Z01, efficiency and regulation of the T/F. Generally low voltage side will be short circuited and supply will be given to high voltage side & it will be of 5-10% of the rated voltage. The wattmeter connected in primary will give directly the full load copper losses of the T/F. Circuit Diagram: Open Circuit: Fig- 1.
Short Circuit: Procedure: OC Test: 1.Give connections as per the circuit diagram. 2.Switch-ON the supply and apply rated voltage to the primary of the winding by using the auto transformer. 3.Note the readings of Ammeter, Voltmeter & Wattmeter SC Test: 1.Give connections as per the circuit diagram. 2.Switch-ON the supply and vary the Dimmerstat till rated full load current flows through transformer. 3) Note the readings of Ammeter, Voltmeter & Wattmeter. Graph: A graph is drawn between P.F and % regulation by taking P.F on X- axis and % regulation on Y-axis.
Observations: Calculations:
PRECAITIONS: 1) The Dimmer stat should be kept at minimum O/P position initially. 2) In OC test, rated voltage should be applied to the Primary of the Transformer. 3) In SC test, the Dimmer stat should be varied up to the rated load current only. 4) The Dimmer stat should be varied slowly & uniformly. Result: We perform open and short circuit tests on 1-phase transformer and calculate efficiency. PREPARED BY: APPROVED BY: CHECKED BY:
KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 2 AIM: To perform Sumpner s back to back test on-1 phase transformer. Apparatus required: Theory: Sumpner's test is also known as back-to-back test. This test requires two identical transformers and is connected as shown in circuit diagram. By this test,the equivalent Circuit parameters, efficiency, regulation & heating of both the T/F can be determined. Each T/F is loaded on the other and both are connected to same supply. The primaries of Two T/Fs are connected in parallel across same supply and the Wattmeter connected in Primaries reads the core losses (Iron losses) of both transformers. The secondaries are so connected such that their potentials are in opposite to each other.by connecting so there would be no secondary current flowing around the loop formed by the two secondaries.
Circuit diagram: Procedure: OC Test: 1) Give connections as per the circuit diagram. 2) Switch-ON the supply keeping the polarity switch open and apply rated voltage to the primary of the winding by using the auto transformer. 3) Note the readings of Ammeter, Voltmeter & Wattmeter. SC Test: 1) Keeping the primary supply as it, Switch-ON the supply and close the polarity switch. 2) Vary the Dimmerstat till rated full load current flows through transformers. 3) Note the readings of Ammeter, Voltmeter & Wattmeter. Graph: 1) A graph is drawn between P.F and % regulation by taking P.F on X-axis and % reg on Y-axis 2) A graph is drawn between efficiency & O/P power by taking efficiency on X- axis and O/P power on Y-axis.
Observations: Calculations: Precautions: 1) The Dimmerstat should be kept at minimum O/P position initially. 2) In OC test, rated voltage should be applied to the primary of the Transformer. 3) In SC test, the Dimmerstat should be varied upto the rated load current only. 4) For sc test, close the polarity switch only when both secondaries are at same potential 5) If the polarity voltmeter indicates some voltage, change secondary winding connections. Result: We perform Sumpner s back to back test on-1 phase transformer. PREPARED BY: APPROVED BY: CHECKED BY:
KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 3 AIM: Parallel Operation Of Two Single Phase Transformers APPRATERS:- Circuit Diagram:-
Theory:- It is required to connect a second transformer in parallel with the first transformer if the load exceeds the rating of the transformer shown in Figure 1.46. The primary windings are connected to the supply bus bars while the secondary windings are connected to the load bus bars. During paralleling of the transformer, similar polarities of the transformers should be connected to the same bus bars shown in Figure 1.46. Otherwise, the two emfs induced in the secondary windings with incorrect polarities will produce the equivalent of a dead short circuit shown in Figure 1.47. The following conditions are important for parallel opera-tion of transformers: The voltage ratings of both the primary and the secondary of the transformers should be identical. Small differences are permissible if the resultant circulating currents can be tolerated. The connections of the transformers should be proper with respect to their polarities. The percentage impedances should be equal in magnitude and the X/R ratio must be the same to avoid circulating current and operation at different power factors. The equivalent impedances must be inversely proportional to the respective kva ratings. The above conditions must be satisfied by paralleling transformers of identical ratings of the same make/model. With different kva ratings of even the same make/model, the effects in steps 1, 2 and 3 may appear in undesirable amounts. Step 2 must be carried out satisfactorily even if steps 1, 3 and 4 are slightly modified. Figure 1.46 Parallel Operation of Transformers Figure 1.47 Parallel Operation of Transformers with Incorrect Polarities
PROCEDURE :- a) Make connections as for circuit diagram, keep the load switch and switch S open. b) Switch on the mains, see the volt meter reading of V1, if this reading is 460V(double the secondary voltage of both the machines) then switch of and inter change the connections of secondary of any transformer. if reads zero then the switch S can be closed, this way the polarities can be checked since wrong polarity will short circuit the transformers if operated in parallel. c) Close switch S and then close the load switch. d) For various values of load current, record terminal voltage,current in two secondary s,power supply by the two transformers and the total power,(do not exceed 10 A for total current) e) Switch of load and switch of main. f) Determine the equivalent reactance s and resistance s of both transformers referred to HV winding by SC test. Observation Table:- CAULATIONS :- RESULTS:- a) With the help of phasor diagram verify if IA = IB= I. b) Check if the load shared is proportional to the KVA capacities of the respective transformers c) From the results state if RA /XA =RB /XB PREPARED BY: APPROVED BY: CHECKED BY:
KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 4 AIM: To study scott connection of transformer. Apparatus required: Circuit Diagram:- Theory: In some cases, we may require 2 power instead of 3 or 1 power. For that it is necessary to convert 3 to2 power (since 3 power is available at every nook corner). Scott connection is one by which 3-phase to 2-phase transformation is accomplished with the help of two identical 1 T/Fs having same current rating. One T/F has a center tap on primary side and it is known as Main transformer. It forms the horizontal member of the connection. Another T/F has 0.866tap on primary side and known as Teaser transformer. The 50% tap point on primary side of the main T/F is joined to 86.6% tap on primary of the teaser T/F. Obviously full rating of the T/Fs is not at all used. Refer to the fig. The main T/F primary winding center tap point D is connected to one end of the primary of the teaser T/F on secondary side, both the main & teaser T/F turns are used (not only 86.6%).Hence
the voltage per turn will be equal for both T/Fs. Since point D is located midway on AB, VCD leads VAB by 900 i.e, voltages across primary are 900 apart also. Position of Neutral point N on primary side: Remember point D is not the neutral on primary, since its voltages w.r.t R, Y, B are not equal to V1/3 i.e, the neutral point is that one which gives equal voltage with R, Y, B. The neutral point is one third the waydown the teaser T/F winding from C to D Or point N divides the teaser primary winding in the ratio of 1:2. Hence the neutral must be At 86.6/3=28.8% from D Current in Teaser T/F: w.r.t For 2:1 T/F, Current in Main T/F: N2 /0.866N1 = IR/IX IR = InK(1.15) IR = 0.57xIX N2/N1 = (IR/2 - IY/2) For balanced load, since IX & IY are at 900 IR = 1200; IB = -1200 Like wise, IR, IY & IB are equal in magnitude and are 1200 apart from each other. Procedure: 1) Give all connections as per the circuit diagram. 2) Switch-ON the supply and apply rated voltage to the primaries. 3) Note the voltmeters readings of both sec. Sides of both T/Fs. 4) Now join the sec. in series aiding as shown in fig.and note he resultant voltage. 5) Load both the T/Fs equally with out exceeding the rating And note the ammeter readings on primary side. Observations: V4 (across sec. of teaser T/F) = V5 (across sec. of main T/F) = Resultant voltage, VT =V21+V22 = PRECAITIONS: 1) The Dimmerstat should be kept at minimum O/P position initially. 2) The Dimmerstat should be varied slowly & uniformly. 3) Rated voltage should be applied to the primary of the Transformer. Result: We study scott connection of transformer. PREPARED BY: APPROVED BY: CHECKED BY:
KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 5 AIM :- TO PLOT V CURVE OF SYNCHRONOUS MOTOR. APPARATUS REQUIRED :- SYNCHRONOUS MOTOR,AMMETER, VOLT METER AND WATTMETER. THEORY:- With constant mechanical load on the synchronous motor, the variation of field current changes the armature current drawn by the motor and also its operating power factor. As such the operation of synchronous motor is described below under three modes of excitation. Normal excitation :- the armature current is minimum at a particular value of field current. The operating power factor is unity and thus the motor is like a resistive load. Under excitation :- when the field current is decreased the armature current increases and the power factor is lagging and the motor is like an inductive load. Over excitation :- when field current is increased the armature current also increases, the power factor is leading and the motor is like a capacitive motor. CIRCUIT DIAGRAM :- GRAPH:-
PROCEDURE :- 1.Connect the circuitt. as per fig. 2. Switch on supply and start the motor. 3. Set the rheostat of field to the position of normal excitation.and note down the readings of all meters. 4. Reduce the excitation insteps and note down the armature current and readings of both wattmeters 5. Adjust the generator voltage by varying the field rheostat. 6. Load the generator to half the full load and maintain it. 7. Repeat steps 3,4,5 under this condition of loading. 8. Remove the load from the generator slowly. 9. Switch off the power to stop the motor. 10. Plot the curve between armature current and field current. OBSERVATION TABLE:- PRECAUTIONS :- 1. All connections should be tight. 2. Take the readings carefully. 3. Increase and decrease the excitation voltage slowly. 4. Increase and decrease the load on generator slowly. Result:-The V-curve of synchronous motor is drawn successfully.
PREPARED BY: APPROVED BY: CHECKED BY:
KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF ------- SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 6 AIM: Light running & block rotor test of 3-phase I.M. with starting. Apparatus required: Circuit Diagram:-
Theory: With the help of circle diagram, the behavior of the Induction motor under various load conditions i.e, the characteristics can be studied. Apart from that the max torque and max O/P that can be developed by the motor can be predetermined. Efficiency, slip, p.f, rotor cu losses, stator cu losses, no-load losses, full load O/P, stable region of operation etc. can also be predetermined. To draw a circle diagram, it is necessary to conduct two tests on the motor. a) No-load test and b) blocked rotor test. Construction of circle diagram: 1) Obtain the values of VL, IO, WO & Cos from the OC test. 2) Obtain the vales of VS.C, IS.C, WS.C & CosS.C from the SC test. 3) Represent the voltage vector on Y-axis to to some convenient scale. 4) Take a suitable current scale. 5) Represent the vector IO lag behind VL byo as per the current scale. 6) Name the vector as OA. 7) Join O1A & Draw a le line to the X-axis through O1 and name as O1X1. 8) Draw a perpendicular bisector to O1A so that it meets the line O1X1 at C as center. 9) Draw a semicircle on the line O1X1 taken O1C as radius and C as center. 10) Draw a perpendicular bisector to O1A so that it meets the line O1R1 at C. 11) Draw a perpendicular from A to X-axis so that it meets X-axis at C. O1Z = IO CosO similarly: AB = I1S.C CosO Procedure: No-load test: 1) Give all connections as per the circuit diagram. 2) Switch-ON the supply & apply the rated voltage to motor with out any load. 3) Note the readings of voltmeter, ammeter & wattmeter. Blocked rotor test: 1) Give all connections as per the circuit diagram. 2) Apply a low voltage to motor with auto transformer
Model Graph Precautions: 1)The Dimmerstat should be kept at minimum O/P position initially. 2) In the rotor-blocked test, the rotor should be blocked firmly. 3) In SC test, the Dimmerstat should be varied slowly such that current should not exceed the rated value. 4) If the wattmeter shows negative deflection, then reverse either pressure coil or current coil & take that reading as negative. Result:- We have studied the Light running & block rotor test of 3-phase I.M. with starting. PREPARED BY: APPROVED BY: CHECKED BY: