Richard Class Flashcards
LINE VA formula
3 phase
E line x I line x 1.73
Line WATTS formula
3 phase
E line x I line x 1.73 x power factor
Power factor formula (2)
Cos angle or watts/va
Other names for VA and Watts
Power theoretical and power actual
Maximum voltage imbalance BETWEEN PHASES
2%
Why are brass bars skewed on squirrel rotor
To provide more uniform motor torque (less jitters)
Maximum POWER SUPPLY. Variations
+/- 10%
NEMA design with most efficiency
NEMA A
TQ question
How to increase starting torque on VFD
Reduce frequency output….. but not really
NEMA A
Current / starting torque
600%/ 150%
NEMA B
Starting current / torque
500%/ 150%
NEMA C
Starting current / torque
500%/ 225%
NEMA D
Starting current / torque
400%/ 275%
HIGH INERTIA LOADS (punch press)
Best method of joining conductors
Solder
What is a class 2 circuit
Less than 150V at 100 VA
The larger the capacitor the _____ it will charge and discharge
Slower
Capacitors oppose the change in….
Voltage
1 TC is equal to…
63.2% of difference
(0->100v = 63.2v)
(100->200v = 163.2v)
E leads I. I leads E
By how many degrees
90
Electrolytic start capacitors designed for maximum number of starts…
20 per hour at 3 second starts
Current carrying conductors are affected by 4 factors
MALT Material Area (cross sectional) Length Temperature
Analog Megaohmmeter (merger) when turned off reads…
Near infinite or over scale
L and M terminals on OFC
Overload trip
Timer settings on OFC heater
30/60/90 second time out
OFC pressure connections
Crank case pressure
—————-
Oil pump discharge
Purpose of resistor in OFC cct
Voltage drop resistor (120v)
1mA will cause
Fuck all, no harm
Damper actuator is fully open at ____ V
24, no voltage to actuator means fully closed
Most common substation transformer configuration
4 wire Y
VFD NETURAL carries _____ current
Excessive
Counter torque causes motor to…
Slow down
VFD construction
Thinner steel laminations in rotor
Better winding insulation
Shaft bonding rings
Insulated bearings
TQ question
3 main parts of VFD
Rectifier
dc link filter
Inverter
Voltage imbalance formula
Greatest difference
—————————
Average voltage
Arc flash temp
35000F
How many contactors does a wye delta starter need
3
Reduced voltage starting method that is adjustable the entire way
Solid state
Multi winding motors, can you apply more voltage across each winding?
No. Each winding is rated for a maximum set voltage
Eg.
240 volts is 2 windings in series (120 per winding)
120 is 2 windings in parallel (120 per winding still)
Part winding is reduced voltage on one winding (120 per winding)
