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HVACR318 – Core for Refrigeration. Three Phase Power Three Phase Motors. Single Phase Power. Up until now we have been talking about single phase power. Single sign wave that modulates 60 times per second between positive.
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HVACR318 – Core for Refrigeration Three Phase Power Three Phase Motors
Single Phase Power • Up until now we have been talking about single phase power. • Single sign wave that modulates 60 times per second between positive. • Motors (other than shaded pole) have a start winding and a run winding. • L1 and Neutral or L1 and L2 are standard sources.
Single Phase Power • Single phase power also has a few problems. Mainly that the power pulsates and modulates through 0 volts three times each cycle.
Three Phase Power • Three phase power contains three sign waves that run 120 degrees out of phase with each other.
Three Phase Power • There are three reasons why three phase power is superior to single phase power • The horsepower rating of three phase motors and the amperage ratings of three phase transformers are about 150% greater than single-phase transformers and motors of similar frame sizes.
Three Phase Power • The power delivered by three phase supplies is more constant. While it also moves through zero three times every cycle not all three legs move through zero at one time. • In a balanced three phase system conductors need only be about 75% the size of a conductor for a single-phase two wire system.
Three Phase Power • Three phase power is supplied mainly to larger commercial and manufacturing customers. • Three phase power requires a third line from the power company as well as three phase breakers.
Generating Single Phase • Remember a single phase generator spins a magnet inside a coil of wires. The magnet has a north and south pole which generates an alternating current in the wires. • Example of this on the next slide
Generating Three Phase • To generate three phase power there are three coils of wire set inside the generator, exactly 120 degrees apart from each other electrically. • As the magnet moves through each of the tree windings the current produced is 120 degrees out of phase with the other two windings.
Generating Three Phase • This out of 120 degree difference produces three sign waves that are 120 degrees out of phase with each other.
Generating Three Phase • If you notice on the sign wave that there are no more than a single sign wave going through zero at any one time. • In a single phase system this same effect can be produced by a capacitor on the start winding of the motor.
Disconnect Switches • Single Phase systems will use a disconnect switch with two fuses. • This disconnects Line 1 and Line 2
Disconnect Switches • Three phase disconnect switches will use three fuses or disconnects. • Three phase disconnects will use L1, L2, and L3 as there are three live legs required.
Residential / Single Phase Panels • A Residential or a Single Phase breaker panel has two hot legs (L1 and L2) and a neutral bar (N) running through the center.
Three Phase Breaker Panel • A three phase commercial breaker panel has an L1, L2, and L3 running through the panel.
Three Phase Breaker Panel • It is important to know the phase of the system you are reaching into. As there is no neutral all the legs in a commercial breaker panel are live (or hot). • Make sure you use your meter to verify the panel. • HVAC technicians may not do ANY work inside a panel other than verifying voltage.
Any questions? • At this time ASK any questions you have on three phase power supplies. We are now going to move on to three phase motors.
Three phase motors. • Three phase motors are: • More rugged • More Reliable • More Dependable Than single phase motors.
Three Phase Motors • The most common type of three phase motor used in the HVAC industry is the squirrel cage induction type.
Three phase motors • Three phase motors are considerably stronger than the single phase motors. • Three phase motors do not require any starting components. • Three phase motors are much more able to start heavy loads.
Three phase motors • Have three sets of windings, all the windings have close to the same resistance. • The windings are 120 degrees out of phase with the other windings. • Remember the Rotor is the moving part of the motor and contains the magnet.
Three phase motors • The stator is the stationary part of the motor and contains the windings.
Three Phase Motors • There are two main windings found on three phase motors. • The Delta winding • The Start or Wye (Y) windings. • Both of these windings allow you to have both High and Low voltage hookups.
Dual Voltages • Most (if not all) three phase motors will come with the directions on what windings or leads to tie together to give you the proper configuration for voltage. • Make sure you carefully follow these directions as three phase motors are pretty unforgiving.
Troubleshooting • A three phase motor can first be checked by disconnecting from the circuit and reading the resistance of all the windings with an ohm-meter. • If the reading is 0, the motor is shorted. • If the reading is OL (or infinite) the motor has an open winding. • There is normally a 1 to 50 ohm resistance based on motor size.
Troubleshooting • The smaller the motor most often the higher the resistance of the windings. • The larger the motor most often the lower the resistance of the windings. • Correct Rotation • Proper rotation of the three phase motor must be confirmed any time equipment is started up or repaired.
Troubleshooting • When three phase motors are running in reverse take and change two of the lines. • An example of this would be to exchange L1 and L2 if needed. • If that does not correct the rotation swap L2 and L3 • Three phase motors can be made to run in reverse based on the phase of the power coming into them.
