VFDS and Soft Starting Flashcards
What does VFD stand for?
Variable Frequency Drive
What are four advantages of using a VFD to run a motor?
Less wear on the motor
Fault capabilities
Easy to Program
More Functions
What is the most popular method used by VFDs to control motor speed?
Pulse Width Modulation
What are the considerations for methods of starting motors?
Motor H.P
Motor Torque
Power Line Capabilities (current)
What is across the line starting?
Apply full voltage at start
What is the result of across the line starting?
Full inrush
Full Torque
Where is across the line starting typically used?
Small Horse Power motors
Why is reduced voltage start used?
To avoid overloading the power lines
To limit wear and tear on machines by lowering torque
What is auto transformer start?
It applies lower voltage by tapping off
of the XFMR in stages of 50%, 65%, 85%, 100% feeding Line 1, Line 2, and Line 3 to starter
What does auto transformer starting do to the torque?
It reduces torque proportionally
What is resistive starting?
Lowers current by connecting resistors in series with Line 1, Line 2, Line 3
What happens to the resistors once the inrush current is gone?
They are typically timed out of the circuit
What is reactor starting?
Uses coils in series with motor leads instead of resistors
What is the reactor starting method typically used for?
Large Horse Power Motors
What does the coils inductive reactance time curve limit?
The current to the motor at start
