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Home Electrical and Electronics Electrical Machines 2 To determine the efficiency of 3- ɸ induction motor by performing load test. To obtain the performance curves for the same.
Electrical Machines 2 Lab Experiments

To determine the efficiency of 3- ɸ induction motor by performing load test. To obtain the performance curves for the same.



Aim

To determine the efficiency of 3- ɸ induction motor by performing load test. To obtain the performance curves for the same.

Apparatus Required:

S.no Equipment Type Range Quantity
1 Voltmeter MI (0-600)V 1nos
2 Ammeter MI (0-10)A 1nos
3 Wattmeter Electro dynamo meter type 10A/600V UPF/10A/600V LPF 1no
4 Techometer Digital (0-9999)RPM 1nos
5 Connecting Wires -- ---- Required

Name plate details:-

Power rating : 5Hp

Voltage : 400V

Current : 6.8A

Speed (RPM) : 1450

Frequency : 50Hz

PF : Lagging

3- ɸ Auto transformer Details:

Input Voltage: _____415_____________ (Volt)

Output Voltage: ___0-470_____________ (Volt)

Current:__________________ (Amp)

Freq.:_____________50Hz______________(Hz)

Circuit Diagram:

circuit-diagram

Procedure:-

  1. Connections are made as per the circuit diagram
  2. Ensure that the 3- ɸ variac is kept at minimum output voltage position and belt is freely suspended.
  3. Switch ON the supply. Increase the variac output voltage gradually until rated voltage is observed in voltmeter. Note that the induction motor takes large current initially, so, keep an eye on the ammeter such that the starting current current should not exceed 7 Amp.
  4. By the time speed gains rated value, note down the readings of voltmeter, ammeter, and wattmeter at no-load.
  5. Note down the various meters readings at different values of load till the ammeter shows the rated current.
  6. Reduce the load on the motor finally, and switch OFF the supply.

Tabular column:

S.no Voltage(V) NO.Volt age( V) Curre nt(A) Wattmeter reading/W1+/W2 I/P Poqwe /W1+ /W2(W) Spring Balance kg/S1/S1-S2 Speed (N) rpm % Slip Power factor cosΦ= w1+w2 /√3vi Torque (Nm) Pout(W)
1 400 1.2 240/240 280 0/0/0 1498 0.13 0.57 0 0 0
2 400 2.2 880/240 1160 1.5/6.5/5 1485 1 0.76 5.49 853.74 76.31
3 400 3 1120/480 1600 2.5/10/7.5 1454 3.6 0.76 8.24 1254.64 78.41
4 400 3.6 1440/640 2080 3.5/14/10.5 1424 5.06 0.83 11.53 1720.85 827.3
5 400 4 1600/720 2320 4.5/16.5/12 1398 6.8 0.83 13.18 1929.52 83.16
6 400 5 1960/880 2840 5.5/19/13.5 1382 7.8 0.81 14.83 2146.23 75.57
7 400 6 2000/960 2960 6.0/50/14 1268 7.54 0.7 15.38 2093.76 70.23

Model Calculation:

Input power drawn by the motor W = (W1 ± W2) watts

Shaft Torque, T sh= 9.81 (S1~ S2) R→N-m R → Radius of drum in meters

Output power in watts =2πNTsh/60 watts

1. efficiency = output power in watts /Input power in watts x 100

Calculations:

% Slip = (Ns-N)/Ns*100

=120f/P

Power factor of the induction motor cosϴ=W/√3 VLIL

Model Graphs:

  1. Speed or slip Vs output power
  2. Torque Vs output power
  3. % efficiency Vs output power
graph
graph-1
graph-2
graph-3

Precautions:

  1. Connections must be made tight
  2. Before making or breaking the circuit, supply must be switched off

Result:The load test on 3-Φ squirrel cage induction motor conducted and the characteristics of torque, speed, efficiency versus output power were drawn.

Via Questions:

  1. Why starter is used? What are different types of starters?
  2. Compare a slip ring induction motor with cage induction motor?
  3. Why the starting torque is zero for a Single Phase induction motor and non-zero of 3phase induction motor?
  4. What are the disadvantages of this method?
  5. Can we use rotor resistance method for starting?











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