Chapter 14 AC Motors

what motor is a 1 phase AC motor that uses a shaded stator pole for starting?

shaded-pole motor

Some ___ motors include a thermal switch that automatically turns the motor off when it overheats.

split-phase

What AC motors use fractional horspower, usually 1/20HP to 1/3HP?

split-phase motor

What single phase AC motor includes a running winding (main winding) and a starting winding (auxiliary winding).

split-phase motor

To develop a rotating magnetic field in a 3Φ motor, the ___ must be connected to the proper voltage level.

stator windings

What are the three types of Capacitor Motors?

1. Capacitor Start 2. Capacitor Run 3. Capacitor Start and Run

A motor with a service factor of 1.0 is derated when it operates at altitudes above ___'.

3300

Which capacitor motor operates much the same as a split phase motor in that it uses a centrifugal switch that opens at approximately 60-80%?

A capacitor start motor

A ________ motor has the starting winding and capacitor connected in series at all times

Capacitor run

How many circuits does a wye connected dual voltage motor have and what are they?

Four circuits 1. T1 - T4 2. T2 - T5 3. T3 - T6 4. T7 - T8 - T9

When starting a split-phase motor, both the running windings and the starting windings are ___.

connected in parallel

What motors are the best choice for applications that include overcyclying?

Open, dripproof motors rated for continuous duty

In a dual voltage wye AC motor, how are the windings wired for high voltage?

Series

___ motors that fail are usually replaced.

Shaded-pole

___ the stator pole is the simplest method used to start a 1Φ motor.

Shading

What benefit does a capacitor motor have over a split-phase motor?

The capacitor in series with the starting winding provides more torque than a split-phase motor.

How many circuit does a delta connected dual voltage motor have and what are they?

Three Circuit 1. T1 - T4 - T9 2. T2 - T5 - T7 3. T3 - T6 - T8

________ is the process of turning a motor on and off repeatedly.

overcycling

When does the centrifugal switch open, disconnecting the starting winding from the circuit?

approximately 75% of full speed

When oiling a motor, oil should be applied to the ___ only.

bearings

Why are Three phase motors used in most applications?

because they are simple in construction, require little maintenance, and cost less to operate than single phase or DC motors

How is a split-phase motor wired when it is initially started?

both the running windings and the starting windings are connected in parallel

How does an induction motor induce current?

by the rotating magnetic field of the stator

A ___ motor has the starting winding and capacitor connected in series at all times.

capacitor-run

The capacitor used in the starting winding gives a ___ motor high starting torque.

capacitor-start

In a dual voltage wye AC motor, how are the windings wired for low voltage?

coils are wired in parallel to distribute the voltage to the individual coil ratings.

How do you wired a dual voltage motor in a wye connection for High voltage?

1. L1 to T1 2. L2 to T2 3. L3 to T3 4. T4 is tied to T7 5. T5 is tied to T8 6. T6 is tied to T9

Split-phase motors have an internal centrifugal switch that is used to disconnect the starting winding at what percentage of the full-load speed?

60 - 80%

When a split-phase motor reaches approximately ___% of full speed, the centrifugal switch opens, disconnecting the starting winding from the circuit.

75

What is the most common three phase motor?

Induction motor

When a motor is first connected to power, the ___ of the starting winding is lower and the resistance is higher than the running winding.

reactance

What is the difference between the construction of a Capacitor Motor and a Split-phase motor?

a capacitor motor has a capacitor connected in series with the starting winding.

Which capacitor motor has the highest running torque?

a capacitor start and run motor

How do you wire a dual voltage motor in a wye connection for Low voltage?

1. L1 to T1 and T7 2. L2 to T2 and T8 3. L3 to T3 and T9 4. T4 is tied to T5 and T6

What are the steps for troubleshooting split-phase motors?

1. Visually inspect the motor after turning the power to the motor off 2. Check to determine if the motor is controlled by a thermal switch 3. Check for voltage at the motor terminals using a DMM set to measure voltage if the motor does not start 4. Turn off and lock out and tag out the starting mechanism per company policy 5. With power turned off, connect a DMM set to measure reistance to the same motor terminals from which the incoming power leads were disconnected 6. Check the centrifugal switch for signs of burning or broken springs

What are the steps for troubleshooting capacitor motors?

1. turn the handle of the saftey switch or combination starter to the OFF position 2. Use a DMM set to measure voltage at the motor terminals to esnure the power is OFF 3. Remove the cover of the capacitor 4. Visually inspect the capacitor for leakage, cracks, or bulges 5. Remove the capacitor from the circuit and discharge it. 6. After a capacitor is discharged, connect the leads of a DMM set to measure resistance to the capacitor terminals

What is the range of a capacitor motor?

1/8 HP to 10 HP

What is the simplest method used to start a single phase motor?

Shading the stator pole

In a 3Φ motor, the leads that are brought out externally are labeled with a(n) ___.

T

What are the leads that come out of a Single voltage three phase motors labeled as?

T1, T2, T3

What is an induction motor?

a motor that has no physical electrical connection to the rotor. they have no brushes that wear or require maintenance.

A(n) ___ may be used to determine the winding circuits on an unmarked motor by connecting one test lead to any motor lead and temporarily connecting the other test lead to each remaining motor lead.

continuity tester

A dual-voltage, wye-connected motor has ___ separate circuits.

four

The ___ of a motor should be grounded, especially if the motor is used in a damp location.

frame

The maximum recommended acceleration time depends on the motor ___ size.

frame

What should be checked before putting a motor into operation?

motor nameplate

An electrician can observe the even blackening of all motor windings that occurs when a motor has failed due to ___.

overloading

The ___ is the stationary part of an AC motor.

stator

What are most of the problems involved with Single phase AC motors?

the centrifugal switch, thermal switch, or capacitors

What should you do if you go to start a motor and and the rotor shaft does not rotate?

the motor should be immediately unplugged to prevent the windings from becoming seriously overheated.

What causes the phase shift difference between the running and starting windings in a split-phase motor?

the reactance/resistance difference between the running and the starting windings. Running lags behind the starting.

What is the difference in wiring between the running windings and the starting windings?

the running windings are made of heavy insulated copper wire, and the starting windings are made of fine insulated copper wire

What are the steps for troubleshooting shaded-pole motors?

1. visually inspect the motor after turning power to motor off. 2. Check the stator windings

The normal dual-voltage rating of industrial motors is ___ V.

230/460

What is another name for a capacitor start and run motor?

Dual capacitor motor

When does the centrifugal switch reclose?

When the motor is turned off, the switch will close at approximately 40% of full-load speed.

Which capacitor motor uses two capacitors?

a capacitor start and run motor

All capacitors are made with two conducting surfaces separated by ___.

dielectric material

What are the steps for Re-marking Dual-Voltage, Wye-connected motors?

1. Determine the windings circuits using a DMM or continuity tester. 2. Mark the leads of the one three lead circuit T7, T8, and T9 in any order. 3. While wearing prper PPE, connect the motor to the correct supply voltage. (Connect T7 to L1, T8 to L2, and T9 to L3). 4. Turn on the supply voltage and let the motor run. 5. While wearing proper PPE, measure the voltage across each of the three open circuits while the motor is running, using a DMM set on at least the 440 VAC measuring scale. 6. connect one lead of any two-wire circuit to T7 and connect the other lead of the circuit to one side of a DMM. 7. Connect the other lead of the DMM to T8 and then to T9. Mark T1 and T4 permanently if the two voltages are the same and are approximately 335v 8. Perform the same procedure on another two-wire circuit if the voltages are unequal. 9. Connect one lead of the two remaining unmarked two wire circuit to T8 and the other lead to one side of the DMM 10. Connect the other side of the DMM to T7 and T9 and measure the voltage. 11. Check the third circuit in the same way until a position is found at which both voltages are the same and approximately 335v. 12. AFter each motor lead is found and marked, turn off the motor and connect L1 to T1 and T7, L2 to T2 and T8, and L3 to T3 and T9. Connect T4, T5, and T6 together. 13. Start the motor and let it run. 14. Take voltage readins between each line. The voltage should be equal between each line.

What are the steps for toubleshooting Three phase motors

1. Measure the voltage at the motor terminals using a DMM set to measure voltage 2. Check the current draw on each motor lead using a clamp-on ammeter and compare the current to the motor nameplate current rating 3. Turn the handle of teh safety swtich or combination starter to the OFF position if voltage is present but the motor is not operating 4. Disconnect the motor from the load to verify the load is not the problem 5. Turn power on and repeat steps 1 and 2. 6. Turn power off and lock out the power 7. Check the motor windings with a DMM set to measure resistance for any opens or shorts.

How big of a phase difference is required to produce maximum starting torque?

90 degrees

What are the steps for Re-marking Dual-Voltage, Delta-Connected Motors?

1. Determine the winding circuits using a DMM or continuity tester. 2. Measure the resistance of each circuit to find the center terminal. Resistance will be half that of the others in the circuit. 3. Connect the group marked T1, T4, and T9 to L1, L2, and L3. 4. Turn the motor on and let it run with the power applied to T1, T4, and T9. 5. Connect T4 (which is also connected to L2) to T7 and measure the voltage between T1 and T2. - the lead markings of T4 and T9, and T7 and T5, are correct if the measure voltage is approximately 440v. -Interchange T5 and T7 or T4 and T9 fi the enw emasured voltage is approximately 380v. -Interchange both T5 with T7, and T4 with T9 if the new measured voltage is approximately 220v. - T4, T9, T7, and T5 may be permanently marked if the voltage is approximately 440v.