Electric Motors
- Motor Principle
- Magnetism
- Direction of the flow of electrons
- Left –hand conduction rule
- Motor Rotation
- Two interacting magnetic fields
- Attraction repulsion used to start motor rotation
- Right hand motor rule.
- Types of motors
- DC Motors
- Permanent-Magnet
- Series: Since the series field winding will carry the same amount of current as the armature it is wound with heavy-gauge wire that is large enough to carry the full motor load current. They will have a lower resistance.
- Shunt
- Compound
- Motor Counter Electromotive Force (CEMF)
Counter EMF is a form of resistance that opposes and limits the flow of motor armature current.
Problem: The armature of a 250 VDC Motor draws 15 Amps when operating at full load and has a resistance of 2 Ohm. Determine the Counter EMF Produced by the armature when operating at full load.
Solultion: IA = VMTR - CEMF / RA
CEMF = VMTR - (IA X RA)
= 250V -( 15A X 2 Ohms)
= 250 - 30
= 230 V
- Type Of Three Phase Electric Motors
- Induction
- Squirrel Cage
Percent Slip = (Synchronous speed -Actual Speed/
Synchronous speed) X100
(1800-1750)/1800 X 100 = 2.9 %
- Wound –Rotor Induction
- Synchronous
- Single-Phase AC Motors
- Split-Phase
- Split-Phase Capacitor
- Shaded-Pole
- Universal
- Motor Selection
HP = (Torque X Speed)/Constant
The constant = 5,252
LR Current (Single-Phase Motor)
=Code Letter Valve X HP X 1000/Rated Voltage
LR Current (Three Phase Motor)
= Code Letter Valve X HP X 577/Rated Voltage
- Troubleshooting
- Voltage Imbalance: Measure Voltage and Calculate Valve
No more that 1 to 2 percent Allowed
Average Voltage Deviation = L1 + L2 +L3 / 3
Max Voltage Deviation From the Average Voltage /Average Voltage X 100 = Percent of Voltage Imbalance
- Go over Troubleshooting Charts for both AC and DC Motors