chapter 15 electrica motors

What are special considerations needed for hermetic compressors?

Cooling accomplished by fins, water in a coil, cool refrigerant from suction line or condenser. Requires leakproof electrical connections. wire insulation must be resistant to oil and chemicals in refrigerant

What does CSIR.

(Capacitor Start Induction Run) motor?

What are field poles?

Electromagnets whose polarity changes as current Flow alternates in the field windings.

What are the components in the motor circuit of CSCR motor and how does the motor work?

Induction motor that uses phase splitting to achieve initial rotation. Start capacitor adds more phase splitting which gives the motor extra torque at startup. At 75% of rated speed a switch opens disconnecting the start winding & capacitor. The run capacitor remains in the circuit to improve the power factor.

Why does the run winding have a lower ohm reading than the start winding?

Larger gauge wire, fewer turns than start winding

What is LRA?

Locked rotor amps - the current the motor draws as power is first applied to start turning the rotor. 2 to 6 times the full load amperage.

What is rated ambient temperature?

Maximum ambient temperature at which the motor can operate.

What is insulation class on a motor data plate?

Maximum temperature that the insulation on the wire of the motor windings can withstand before breaking down.

What happens if start winding is left in the circuit?

May overheat,

How do you ohm out a compressor to identify unmarked terminals and troubleshoot?

Measure ohms from C-S, C-R, R-S. Ohm out each terminal to case/ground of compressor. Use process of elimination to determine R,S and C terminals.

What form of energy does the rotor convert electrical into?

Mechanical energy

What is motor efficiency?

Mechanical energy produced by shaft divided by power input.

Why does the start winding have a higher inductance value than the run winding.

More coil turns

What can cause LRA besides motor startup?

Motor having to start under a heavy load or Mechanical Interference like fans with worn bearings, compressors pumping against excessively high head pressure etc...

Does CEMF have the same polarity as the stator?

No, polarity induced by rotor is opposite.

ECM motors are designed to

Operate very quietly.

What term describes windings out of phase?

Phase splitting.

What is ECM Motor?

Programmable de motor that has control module control voltage to the stator windings. Rotor made of permanent magnet, no induction, rotor is not energized.

What does run capacitor do?

Provides signal to start winding causing it to be out of phase with for added torque during motors entire operation

What is synchronous spced?

Refers to the speed of the rotating magnetic field in the stator.

How do you change 3 phase motors rotation?

Rotation can be changed by switching any two power leads.

What are the two main parts of a motor?

Rotor and stator

What are the components in the motor circuit of PSC motor?

Run capacitor only

Why are ohm readings different from terminal terminal?

Run- larger wire, fewer windings, less resistance Start- smaller wire, more windings, more resistance Common- Total both R ands.

What controls the speed of the compressor vs. motor driving it?

Size of pulley

What is the difference in synchronous and rated full load spced called?

Slip

What are the components in the motor starting circuit of CSIR.

Start capacitor and a start relay

What is the stationary part of a motor called?

Stator

What is a start winding?

Stator windings that are energized during motor starting only and to add additional torque.

What is run winding?

Stator windings that are energized during the entire operation of the motor.

What are important facts about a PSC motor?

T5-Can be multi-speed Sensitive to 5-10% voltage drops. Thermal overloads used low torgue applications 120-240v

Where are electrical connections made to control and power the motor?

Terminal box

What happens when a motor is slowed considerably by heavy load?

The current induced in the rotor inereases greatly. Current flow increases because the rotor Turns more slowly, which means counter em and resistance to current drops.

What is full-load amperage?

The current level at which the full-load torque and hp are reached.

What is a direct drive compressor?

The motor and compressor shaft are directly connected using coupling.

What is capacitive reactance?

The opposition to the flow of current that causes voltage to lag behind current and both to alternate out of phase.

What is service factor?

The overload capacity (or horsepower) at which a motor can operate without overheating or being damaged.

What is power factor?

The ratio of apparent power to true power under full load conditions.

What is frequency?

The sine wave cycles per second the electricity is generated at. 60 hz U.S. TI0-Power supply frequency must match frequency of motor.

What is rated full load specd?

The speed motors are rated at, which is the Operating specd of a motor under full load when both the rated voltage and frequency ure supplied

What is torque?

The work performed by twisting or turning action.

What are the two most common types of motor protection.

Thermally protected and impedance protected.

What are important facts about CSCR motors?

These are very efficient motors that have enough power to start heavy loads

How do run capacitors dissipate heat.

They are oil filled to dissipate heat compared to Q15- start capacitors that are dry electrolytic material that does not dissipate heat.

What is the purpose of phase splitting.

To create rotating magnetic field to start single phase motors.

What is rated voltage?

Voltage level where motor will perform best. Also called nameplate voltage

How do you wire a 3-phase motor for

Windings wired in series for high voltage high voltage?

How do you wire a 3-phase motor for Low voltage?

Wired in parallel for low voltage.

What are field windings?

Wires wrapped around the field poles of the stator. Current flowing through the field windings creates a magnetic field around the field poles.

Does the rotor create an electromagnetic tield?

Yes

Are single or 3-phase more efficient?

More efficient than single phase motors.

What is the stator attached to?

Motor Housing,

What is an induction motor?

AC motors that operate by using a magnetic field generated in the stator to induce current in the rotor.

What 3 properties help maintain the rotor af a constant speed.

Applicd voltage, CEMF, current

If an Air Conditioner runs for a hours, how long does the start capacitor run?

Approx. a second for motor only

How can rotor be slowed by a heavy load?

Bad bearings, belt too tight, high external static pressure

What parts hold the rotor in an exact position?

Bearings

What are terminals on a hermetic compressor?

C-common, R-Run, S- Start

What would be the result of that load to the motor.

CEMF drops causing amps to increase.

What causes capacitive reactance?

Capacitors

What causes a motor to bc less than 100% efficient? and load.

Clearance space, bearing friction, imperfect windings

Can 3-phase motor run on different voltages?

Commonly "dual voltage" motors, typically 240V or 460V motor duc to windings arranged in pairs.

How is the start winding in a compressor' wired?

Connected between the start terminal and common terminal of the compressor.

What can a VFD control on a motor?

Controls torque, acceleration and deceleration. Motors can be operated at specific speeds and improve system efficiency.

Describe basic motor operation?

Current from power source is applied to stator windings creating electromagnetic field. 2. Magnetic field induces current in the rotor. 3. Rotor creates an EMF that interacts with the electromagnetic field created by the stator. 4. The interaction between the rotor and stator magnetic fields cause the rotor to rotate.

What causes he run and start winding current to be out of phase with each other.

Different inductance values.

How does the CSIR motor work?

During start-up, current passes through both the start winding and the run winding. At about 75% of the motor's rated speed, centrifugal switch or a relay disconnects the start winding and start capacitor. The motor continues to run as an induction motor using only the run winding.

What does ECM stand for?

Electronically Commutated Motor

What are the caps/plates that close the openings at either end of the motor.

End bells

What 2 parts are found on the stator?

Field poles and field windings i.e. -stator windings.

How do 3 phase motor windings differ from a single phase windings? one phase of the power source?

Have sets of stator windings energized by a 3 phase power source. Lach set of windings connects

The speed of an AC motor is determined by

Hz, number of stator poles, 120 x 60HZ'# poles

How do you wire a start capacitor?

In series with the start winding

How do you wire a run capacitor?

In series with the start winding and in (*parallel with the run winding.) (*not clearly spelled out chapter.)

What information does "ohming out" a compressor give you. (Not in chapter)

Indicates if windings are shorted or grounded and identifies terminals.

What is split phase motor.

Induction motor that operates in the fractional horsepower range and uses phase splitting to achieve initial rotation. Found in capillary tube systems...

How does PSC motor work?

Induction motor that uses phase splitting to achieve initial rotation and a single run capacitor remains in the Induction motor that uses phase splitting to achieve initial rotation and a single run capacitor remains the circuit to improve the power factor. Current flows through both windings during the motors entire operation.

What is rated horsepower?

amount of mechanical work that a motor can perform based on both motor speed and torque.

What is the part of the motor called that rotates?

axle mounted part that rotates. Rotor or armature

What is a continuous duty motor?

motor that operates at an indefinitely long time.

how dose a shaded pole motor work?

single phase motor that uses shaded field poles instead of start winding to produce starting torque

Motors differ from each other by

the amount of starting torque and running torque that they generate.

How is an internal overload wired a single phase hermetic compressor? (Not in chapter)

the run and start winding connect to thermal overload which in turn connects to the common terminal. you get OL from S-C and R-C but ohms S R

What is possible in regard to programming ECM motors?

when powering fans motor may be set to maintain a constant airflow that will adjust the speed of the motor to account for closed dampers obstructions or high external static pressure. both speed torque can be set for specific applications

how is torque generated with 3 phase?

within one cycle the three separate currents signals reach peak voltage at separate times. as a result a threephase motor generates the necessary torque from its rotating magnetic field in the stator

what are important facts about this motor? psc motor

have low torque than any other motor. 1/100th to 1/6th hp

At what percent of full-load speed is the start winding opened.

60% to 75%.

What is an open-drive compressor motor?

A compressor driven by an external motor. The compressor can be directly connected to the motor or connected by belt.

What is a variable frequency drive?

A device that uses a rectifier circuit to convert ac to dc voltage and an inverter convert it back an sine wave whose frequency can now be changed to alter the speed of motor.

What is a hermetic compressor?

A motor and compressor sealed inside dome.

What is an intermittent duty motor?

A motor that operates at alternate intervals on/off.

What is a squirrel cage rotor

A rotor made of metal bars instead of wires.

What is a single phase motor?

A single-phase motor is an ac motor that runs on a single phase of alternating current.