Electrical Engineering Principle (EET 211)Laboratory Module

EXPERIMENT 8

PRINCIPLE OF A SINGLE PHASE INDUCTION MOTOR

Objectives:

  • To constructsingle phase induction motor using split – phase motor.
  • To study the starting of split – phase motor, the condenser starting methods as the ways of driving the single – phase induction motor.
  • To evaluate the parameters of single phase induction motor

Introduction:

One of the most widely used types of single – phase motors is the split – phase induction motor. Split – phase induction motors are designed to used inductance, capacitance or resistance to develop a starting torque.

The essential parts of the split – phase motor are shown in Figure 1(a). It shows the auxiliary winding, also called the starting winding, in space quadrature (i.e., 90electrical degrees displacement) with the main stator winding. The rotor is normally a normal squirrel – cage type. The two stator windings are connected in parallel to the ac supply voltage. A phase displacement between the winding currents are obtained by adjusting the winding impedances, either by inserting a resistor in series with the starting winding or as generally the practice, by using a smaller – gauge wire for the starting winding. A phase displacement between the currents of can be achieved at the instant of starting. A typical phasor diagram for this motor at startup is shown in Figure 1(b).

(a)(b)

Figure 1 Split – phase motor: (a) schematic representation: (b) phasor diagram at instant of starting.

When the motor revolves to about 70% to 75% of synchronous speed, the starting winding may be opened by a centrifugal switch and the motor will continue to operate as a single – phase motor. At the point where the starting winding is disconnected, the motor develops nearly as much torque with the main winding alone as with both windings connected, as can be observed from the typical torque – speed characteristic for this type of motor as shown in Figure 2.

Figure 2 Typical torque – speed characteristic of a general purpose split – phase motor

There are 2 types of split – phase induction motor. The first type of split – phase induction motor is the capacitor – start type. Figure 3 shows a simplified schematic of a typical capacitor – start motor.

Figure 3 Capacitor – start of induction motor

Another type of split – phase induction motor is the resistance – start motor as shown in Figure 4.

Figure 4 Resistance – start of induction motor

Unlike the three – phase induction motor, which may start in either direction (depends on the phase sequence connection), the split – phase induction motor is factory assembled in such that its direction of rotation is fixed (counterclockwise when viewed from the opposite end of the shaft extension). To reverse the direction of rotation it is necessary to reverse the connection to the starting winding. Again in contrast to its three – phase counterpart, this reversal (plugging) cannot be done under running conditions, since the split – phase motor torque will be much less than the torque developed by the single main winding, and rotation will not reverse.

Equipment and parts:

  1. Power supply (NO-5306)…………………………………………………………1 set
  2. AC Voltage / Ammeter (NO-5307)……………...……………………………….1 set
  3. Machine field frame (NO-5310)………………………………………………….1 set
  4. Split – phase motor graphic board (NO-5319)…………………………………1set
  5. Cage rotor (A06)…………………………………………………………………..1set
  6. Wide pole piece for field winding (A10)…………………………………………2set
  7. Narrow pole piece for field winding (A11)………………………………………2 set
  8. Field winding / 300 turns (A13)…………………………………………………..2 set
  9. Field winding / 1700 turns (A15)…………………………………………………2set
  10. Rotor fixture (A20)………………………………………………………………….1 set
  11. Magnetic pole fixture (A21)……………………………………………………….4 set
  12. Fixing bolt (A22)……………………………………………………………………4 set
  13. 8mm spanner (A24)……………………………………………………………….1 set

Procedure:

  1. Design and construct the circuit based on single-diagramas shown in Figure 5 and Figure 6.

Figure 5 Circuit diagram of split – phase induction motor

Figure 6 Assembling diagram for split – phase induction motor

  1. Turn ON the power supply. (Since the starting torque of split – phase induction motor is too small; there is possibility that the rotor is not getting started, so turn the rotor manually with your hand and wait for about 2 minute until the spinning is stable). Measure and record the starting current, starting voltage and the rotor speed. Which direction the rotor spin?
  1. Then, eliminate the connection of T5 and T6. Wait for about 2 minute until the rotor stable. Observe and record the speed of rotor. Does the rotor keep spinning? Briefly explain why.
  1. After that, connect T5 and T6 to C1 (). Observe and record the speed. Is the rotor started well compared with the experiment in procedure no 2? Explain it.
  1. Replace C1 with C2 .Observe and record the speed. Does it start well than procedure no 4? Explain it.
  1. Turn OFF the power supply. Reassemble and set up your connection again as shown in Figure 7.

Figure 7 Connection diagram for control the rotary direction of split – phase induction motor.

  1. Turn ON the power supply. Wait for about 2 minute until the spinning stable. Observe and record the speed and current value. Is the direction of rotor is different from the previous experiment? Explain it.
  1. A 208 V, 10hp, 4-pole, 60 Hz, Y-connected induction motor has a full-load slip of 5%. What is the synchronous speed of this motor, what is the rotor speed of this motor at the rated load and what is the rotor frequency of this motor at rated load.
  1. Turn OFF the power supply and disconnect the connecting code after complete the experiment. Disassemble the equipments, parts and store it in the designated places.

EXPERIMENT 8

PRINCIPLE OF SINGLE PHASE INDUCTION MOTOR

Name: ______Matric No: ______

Group: ______Date: ______

Results:

1.

Starting voltage, V = ______V

Starting current, I =______A

Speed, Nr = ______rpm

Q2:

2. After eliminate T5 and T6

Speed, Nr=______rpm

Q3:

3. When T5 and T6 connect with C1

Speed, Nr =______rpm

Q4:

4. When T5 and T6 connect with C2

Speed, Nr= ______rpm

Q5:

5. After reconnect again based on Figure 8.

Current, I=______A

Speed, Nr=______rpm

Q7:

Calculation:

  1. When T5 and T6 are connected with C2 and the motor operate in 60 Hz;
  2. How many are the poles and calculate the synchronous speed, Ns
  3. Calculate the slip and the rotor frequency.

Q8:A 208 V, 10hp, 4-pole, 60 Hz, Y-connected induction motor has a full-load slip of 5%. What is the synchronous speed of this motor, what is the rotor speed of this motor at the rated load and what is the rotor frequency of this motor at rated load?

Q9:Design the equivalent circuit of single phase induction motor with rotor in motion

Conclusion:

1

UNIVERSITI MALAYSIA PERLIS (UniMAP) – Exp.8 (Revision 2)