Then switch the polarity on one phase and see the difference in the waveforms.) (To see this for yourself - plot the three phases and their sum on a single graph. If one phase has the polarity changed, then the magnetic field distribution within the motor winding becomes uneven, and the output torque will "pulse". NOTE: THIS IS NOT THE SAME AS CHANGING THE POLARITY OF A SINGLE PHASE. If two phases are connected incorrectly (L1 to M2 and L2 to M1, for example) - the motor will rotate opposite to the desired direction. This type of motor has low starting torque and is suitable to be used in small fan motors such as the fan coil unit of a split air conditioning system.For correct rotation, the phase sequence has to be correct (L1 to M1, L2 to M2, and 元 to M3 - where L refers to LINE and M to MOTOR phase). This motor does not have any switch and the START winding, RUN winding and the RUN capacitor are active whenever the motor is ON. This motor has similar design to the phase-split motor except that there is a RUN capacitor connected to the START and RUN windings. Permanent Split Capacitor(PSC) Air Conditioner Motor The capacity of this type of motor can go up to 10 horsepower and is one of the most efficient motors used in the HVAC industry.
The RUN capacitor helps to correct the power factor of the circuit making it more efficient. The START winding remains in the circuit. This provides a higher starting torque and can be used to drive the compressor as well as in belt-driven motors.Īs the rotor speed reaches 75% of the rated speed, the switch will be automatically open to disconnect the START capacitor from the circuit. During starting, the effective capacitance is the combination of both capacitors causing a greater phase angle shift between the windings. Usually the capacitance of the RUN capacitor is lower than the START capacitor. When this happens, the phase difference between the two windings is 90° electrically hence a true two-phase starting is achieved. The current in the RUN winding lags the voltage. This capacitor will cause the current in the START winding to lead the voltage.
#Motor winding system series#
This motor is similar to the split-phase motor except that there is an external capacitor that is connected in series with the START winding. These days, electronic relay is also being widely used to disconnect the START winding. When the motor is powered off, the switch will close the circuit to get ready for the next starting of the motor. This is to protect the START winding from overheating.
Once the switch opened, the START winding in circuit is disconnected. This mechanical switch will open when the motor speed reaches 75% of the rated speed typically within 2 seconds. There is a switch known as centrifugal switch which is connected in series with the START winding.
Speed(rpm) = (Frequency of AC power X 120)/number of polesįor example, if your supply is 60 Hz and the motor is using two-pole, the synchronous speed = (60X120)/2 The no-load speed of the motor is given by: When the load is connected, the speed can go down to 1725 rpm and 3450 rpm respectively. Typically the speed of the motor is 1800 rpm or 3600 rpm when running without any load. This out-of-phase effect on the stator produces a starting torque and causes the rotor to start rotating. When power is connected to the motor, both the windings will be energized with the current in the RUN winding lags the current in the START winding by about 30° electrically.
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