SINGLE PHASE MOTORS WEEK 2 Flashcards
What is Duty?
How long the motor can operate
What is the service factor?
% of rated work the motor can perform 24 hours/day
What is HP?
Rate @ which the motor can work; the output of the motor
What is the Speed (rpm) formula?
(120 X frequency)/ Poles
Run winding?
Remains connected to the source whenever the motor is running. Uses larger wire and few coils.
Stator winding?
The ends of the stator winding can be connected together for various different voltages and speeds. if the voltage source is connected to the winding terminals; a magnetic field is created in the current in the rotor bars, into the rotor, causing the shaft to spin.
End Bells/plates
connected to each end of the frame, with through bolts, protrude through holes through the entire frame and connect the end bells together. End plates also house the bearings, the end or centrifugal switch and also protect the inside of the motor depending on the type of enclosure.
What is the rotor?
part of the motor that rotates. Consists of a steel core with slots on the outside. Copper or aluminum bars inserted into the slots. These rotor bars are then connected together with two rings @ each end of the rotor, end rings. Squirrel cage rotor.
What is in the stator?
Consists of a laminated iron core of silica steel with slots to contain the motor winding. Each of these windings is wound to create a different number of magnetic poles. The # of poles determines the speed of the motor.
What does a single phase motor consist of?
Frame, stator, rotor, endbells
What motor is not considered a split phase motor?
Shaded pole motor
What are the 5 types of single phase motors?
Resistance start induction run
capacitor start induction run
capacitor start capacitor run
permanent split capacitor
shaded pole
Motors convert electrical energy into?
mechanical energy & it is rated in HP in North America and KW in other parts
What do you need to get the rotor to start? RSIR
Auxiliary contacts or start winding
how many turns less does the start winding have than the run winding? RSIR
20-30% less turns
Where is the run winding mounted?
RSIR
Closer to the bottom, closest to the stator core
The start winding is more ___ and the run winding is more ____/ RSIR
resistive, inductive
Once the motor has reached about 75% of its rated speed the ___ will open and remove the ___ from the circuit/ RSIR
the centrifugal switch will open and remove the start winding
What is a centrifugal switch? in an RSIR
set of contacts mounted on a spring steel. The amount of centrifugal force will cause these contacts to open.
does the run winding stay in the circuit the whole time? RSIR
true
What are starting capacitors usually rated for in a CSIR?
50-90 uf
Why do split phase motors have bad starting torque? RSIR
due to the phase angle between the current and the voltage.
What HP is the CSIR rated for?
1/6 HP to 10 HP
What are start capacitors rated in?
voltage and microfarads
When the motor has reached 75-80% in a CSCR the ____ opens and removes the ___ and ___ from the circuit?
centrifugal switch will open and remove the start capacitor and start winding
Can CSIR be dual voltage?
yes. With the same terminal designations as the resistance or split phase dual voltage motors
What are CSCR rated for?
1/2 Hp to 10 HP
The CSCR run capacitor is wired?
permanently in series with the start winding
The CSCR start capacitor is wired?
in series with the centrifugal switch
How are the start cap and centrifugal switch wired in a CSCR?
in parallel with the run capacitor
If the run winding, start winding and run capacitor remain in the CSCR circuit; what is removed once the motor reaches 75% of its speed?
Start capacitor
What does the run capacitor improve?
power factor
What is the most common motor in commercial HVAC?
PSC motor (permanent split capacitor)
Does a PSC have a centrifugal switch?
no
what is the PSC rated for?
1/20 Hp to 1/2 HP
PSC are used typically on?
Direct drive equipment
hermetic compressor thermal protection can be ?
externally mounted or internally mounted
Hermetic compressor thermal protection is?
built in or mounted in contact with the compressor motor. Senses the unusual temperature rise or excess current draw. Bimetallic strip interrupts current flow.
An externally mounted hermetic compressor thermal protection?
senses just temperature and current draw
An internally mounted hermetic compressor thermal protection?
above plus loss of charge
not repair or replaceable
cannot be bypassed
how many watts does 1 HP have?
745.7 Watts (746Watts)
