no load and blocked rotor test on singlephase induction motor

Adam’s Engineering College, PalonchaEEE Department – EM-II LAB

Experiment No: 7 III/IV EEE (I Semester) of 5

NO LOAD & BLOCKED ROTOR TEST ON1-Φ INDUCTION MOTOR.

Aim : - To obtain the parameters of single-phase induction motor and draw its equivalent circuit diagram.

Apparatus: -

S.No. Meter Range Type Quantity

1. Voltmeter 0-300V MI 1

2. Ammeter 0-10A MI 1

3. Wattmeter

75/150/300V, 5/10 A, UPF

Dynamometer 1

4. Variac 1- Φ, 260V/15A 1

Name Plate Details: -Single-Phase Induction Motor

Volts : 230 KW : 0.75Amps : 7 Phase : 1Rpm : 1400 Hz : 50

Circuit Diagram: -

Theory: -

Lab In Charge HOD, EEE



The equivalent circuit of a single-phase induction motor can be developed on the bases of two revolving field theory. To develop the equivalent circuit it is first necessary to consider standstill or blocked rotor conditions. The motor with a blocked rotor merely acts like a transformer with its secondary short circuited in the equivalent circuit ‘Em’ being emf induced in the stator the motor may now be viewed from the point of view of the two revolving field theory. The two flux components induce in the stator winding respectively Emf & Emb. The phasor sum of Emf & Emb equals the applied voltage V. Since at standstill the two oppositely rotating fields are of the same strength, the magnetizing and rotor impedances are divided into two equal halves connected in series. Thus the equivalent circuit of single phase induction motor at standstill, on the basis of two revolving field theory is shown in figure.

When the rotor is running at speed N with respect to forward field, the slip is s with respect to forward field and (2-s) with respect to the backward rotating field and the equivalent circuit is shown in figure.

At standstill, s is unity and the equivalent circuit takes the form shown in equivalent circuit diagram. The parameters of the equivalent circuit can be calculated from the data obtained from the following three tests.1. No-load test (Running –light test): With the motor running light from a rated voltage, rated frequency source, the input current I and the input power P0 are recorded. The auxiliary winding must not in circuit while recording the observations.2. Blocked-rotor test: With rotor blocked and a reduced voltage applied to the main winding, the input current Ise, the input powers Psc

and the voltage applied Vse are recorded. The auxiliary winding should not in circuit during this test as well. 3. Measurement of DC resistance of main winding: This may be measured by the voltmeter-ammeter method, immediately after the blocked rotor test, to get the value at actual winding temperature. Alternatively, the resistance may be measured with the winding at room temperature and hot resistance computed there from. This hot resistance of the main winding is hereafter denoted by R14.

Procedure: -




1. Connect the circuit as per the circuit diagram.2. To conduct no load test apply rated voltage to the motor using 1-

Φ variac. 3. Note the readings of Voltmeter, Ammeter & Wattmeter.4. Now block the rotor to conduct blocked rotor test.5. Apply voltage to the motor slowly using variac such that rated

current flows in the stator.6. Note down the readings of Voltmeter, Ammeter & Wattmeter.7. Calculate the motor parameters and draw the equivalent circuit.

Tabular forms: - No Load Test Blocked Rotor Test

V0

(Volts)

I0

(Amp)W0

(Watt)VS

(Volts)IS

(Amp)WS

(Watt)

Calculations: -Let R1 = Resistance of stator main winding. X1 = Leakage reactance of stator main winding.

Xm = Magnetizing reactance of stator main winding.R2’ = Rotor resistance at standstill.X2’ = Rotor reactance at standstill.Rm = Core loss equivalent resistance.Emf = emf induced because of forward revolving flux.Emb = emf induced because of backward revolving flux.

From blocked rotor test

Zs = VS / IS =

Assuming R1 = R2’ = RS / 2 and X1 =X2

’ = XS / 2. R1 = R2

’

X1 =X2’




From no load testZ0 = V0 / I0 =

X0 =

Xm / 2 =[X0 –X1 –(X’2/2)] =

Equivalent Circuit Diagram: -




Precautions: - 1. Take care such that stator current does not exceed the rated

current.2. The pulley must be water cooled during blocked rotor test.3. LPF wattmeter must be used during no load test and UPF

wattmeter during blocked rotor test.

Result: -No load and blocked rotor tests are performed on 1- Φ induction

motor and calculated the circuit parameters and equivalent circuit diagrams are drawn for the same.


no load and blocked rotor test on singlephase induction motor

Engineering

Transcript of no load and blocked rotor test on singlephase induction motor