Synchronousity
The Speed at which the magnetic field rotates in a 3-PHASE motor
Synchronous Speed
The direction of 3-phase motor rotation can be changed by
Reversing (swapping) two of its stator leads, Industry standard is to change Leads 1 & 3
Three basic types of 3-Phase motors
1. Squirrel Cage Induction Motor
2. Wound Rotor Induction Motor
3. Synchronous Motor
Most motors are marked with a Max. Temperature of 40 C. What does this equate to in Fahrenheit
104 degrees Fahrenheit
this motor is very popular for it's High Starting torque and Low Starting Current
Wound Rotor Motor
Three factors that cause the magnetic field to rotate
1. Voltages in a 3-phase system are 120 degrees out of phase with each other.
2. The 3 Voltages change polarity at regular intervals.
3. The arrangement of Stator windings around the inside of the motor.
Direction of motor rotation can be determined without test meters by ___________.
Momentarily applying power, known as a (bump test) prior to coupling a motor to equipment
The Code letter on the Nameplate of Squirrel Cage motors refers to the KVA per Horsepower with Locked Rotor. The actual amount of starting current is determined by 3 things
1. The type of Rotor bars
2. The Horsepower rating of the motor
3. The Applied Voltage
When Calculating for motor overload protection two areas on the nameplate are used
1. FLA according to the voltage being utilized
2. Service Factor determined by NEC 430.32(A)(1)
This motor requires DC Excitation to operate
Synchronous Motor
Synchronous speed of a 6-pole motor connected to 80 hertz
S = (120 x 80Hz)/6
S = 1600 RPM
When it is not practical or very inconvenient to apply power to the motor before it's connected to the load a ______________ could be used for checking rotation.
Phase Rotation Meter
The squirrel-cage rotor is constructed of _____ and end _____ embedded in steel laminations.
Bars, End Rings
Locked Rotor Current for a 480 volt 3-Phase 20 Horsepower Squirrel Cage motor with a Code letter L can be determined by
228.54 amps
I Locked Rtr=(HPxKVA)/(Vx1.732)
This speed of this motor can be controlled by permitting the resistance to remain in the rotor circuit during operation
Wound Rotor Motor
Two factors that determine the synchronous speed of the rotating magnetic field
1. The number of stator poles (per phase)
2. The frequency of the applied voltage
A Phase Rotation Meter has _____ leads
SIX
When wiring a 3-Phase motor for a WYE configuration how are the nine leads connected for High Voltage
T1-T2-T3 are connected to the Line Voltage
T4 & T7 are Tapped together
T5 & T8 are Tapped together
T6 & T9 are Tapped together
What relationship does Service Factor have with the Horsepower of the motor
By multiplying the Horsepower times the Service factor we find the range that the motor may work in regarding Horsepower for short periods of time without damage
This motor has the ability to correct it's own power factor as well as other devices power factor connected to the same line
Synchronous Motor
What frequency should applied to a 4 pole motor to produce a synchronous speed of 900 RPM
30 Hz
f = (PS)/120
When connecting a Phase Rotation Meter, three of the leads are labeled ________ and the other three leads are labeled _________.
MOTOR & LINE
When wiring a 3-Phase motor for a WYE configuration how are the nine leads connected for Low Voltage
T1 & T7 are tapped & connected to Line Voltage
T2 & T8are tapped & connected to Line Voltage
T3 & T9 are tapped & connected to Line Voltage
T4 & T5 & T6 are Tapped together
When determining the length of time a motor may run for a given application the __________ should be checked on the nameplate
Duty Cycle
Sometimes a Synchronous Motor can be operated at no load simply for power factor correction. When this is done the motor is referred to as a __________
Synchronous Condenser