Download VFD

AC Motor Speed:
• The speed of an AC Inductions motor depends on two factors:
AC Motor Speed:
• The speed of an AC Inductions motor depends on two factors:
• Number of motor poles.
• Frequency of the applied voltage source.
AC Motor Speed:
• The speed of an AC Inductions motor depends on two factors:
• Number of motor poles.
• Frequency of the applied voltage source.
• RPM = (120 x f)/# Poles
• Example:
•
•
•
•
A six pole motor operating at a frequency of 60hz will run at
1200 RPMs.
The same motor in Europe will run at 1000 RPMs
Two pole motors have the highest RPM speed of 3600 RPMs.
Note the above calculated speed are the synchronize speed of
the magnetic field not the rotation of the motor shaft.
VFD:
• A variable frequency drive is used to control a three phase
induction motor.
VFD:
• A variable frequency drive is used to control a three phase
induction motor.
• A VFD unit will control the voltage and frequency to a motor.
VFD:
• A variable frequency drive is used to control a three phase
induction motor.
• A VFD unit will control the voltage and frequency to a motor.
• A VFD units is also called an Inverter.
VFD:
• A variable frequency drive is used to control a three phase
induction motor.
• A VFD unit will control the voltage and frequency to a motor.
• A VFD units is also called an Inverter.
• An inverter is used to change DC voltage to AC voltage.
• A full wave rectifier is used to change AC voltage to DC
voltage.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
 This helps eliminate shock on mechanical components:
 Couplings
 Gearboxes
 Pumping systems.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
 This helps eliminate shock on mechanical components:
 Couplings
 Gearboxes
 Pumping systems.
 Filter out natural frequency of a mechanical system on startup.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
 This helps eliminate shock on mechanical components:
 Couplings
 Gearboxes
 Pumping systems.
 Filter out natural frequency of a mechanical system on startup.
 Provide overload protections.
 Provide single phasing protection.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
 This helps eliminate shock on mechanical components:
 Couplings
 Gearboxes
 Pumping systems.
 Filter out natural frequency of a mechanical system on startup.
 Provide overload protections.
 Provide single phasing protection.
 Helps reduce energy consumption.
 Will provide voltage, current, and power readings.
Benefits of a VFD over a Motor Starter:

A VFD provides a smooth start by ramping up motor speed.
 This helps eliminate shock on mechanical components:
 Couplings
 Gearboxes
 Pumping systems.
 Filter out natural frequency of a mechanical system on startup.
 Provide overload protections.
 Provide single phasing protection.
 Helps reduce energy consumption.
 Will provide voltage, current, and power readings.
 Interfaces with PLCs
 Interfaces with different types of industrial networks
 DH+, Remote I/O, Device Net, etc.
VFD Speed Control:
• The speed of an induction motor is controlled by varying the
voltage and frequency output from the VFD.
VFD Speed Control:
• The speed of an induction motor is controlled by varying the
voltage and frequency output from the VFD.
• The reduction of frequency and voltage has a linear
relationship.
VFD Speed Control:
• The speed of an induction motor is controlled by varying the
voltage and frequency output from the VFD.
• The reduction of frequency and voltage has a linear
relationship.
•Example: A 460 volt – 60 Hz system has a relationship of 7.6 volts/Hz.
• The inductive reactance of a motor in an AC circuit is directly proportional to
the frequency. XL = 2πfL
• HP = T x w
• T = HP/w
VFD Speed Control:
• The speed of an induction motor is controlled by varying the
voltage and frequency output from the VFD.
• The reduction of frequency and voltage has a linear
relationship.
•Example: A 460 volt – 60 Hz system has a relationship of 7.6 volts/Hz.
• The inductive reactance of a motor in an AC circuit is directly proportional to
the frequency. XL = 2πfL = wL
• HP = T x w
• T = HP/w
vL = L x di/dt
Irms = Vrms/XL
Theory of Operation of a VFD:
• When three phase voltage enters a VFD unit it is converted to
DC voltage.
Theory of Operation of a VFD:
• When three phase voltage enters a VFD unit it is converted to
DC voltage.
• The VFD has an internal DC bus voltage of 650 volts.
Theory of Operation of a VFD:
• When three phase voltage enters a VFD unit it is converted to
DC voltage.
• The VFD has an internal DC bus voltage of 650 volts.
•V
•
= VRMS x 1.414
A capacitor is placed across the DC bus to smooth out the ripple.
P
Theory of Operation of a VFD:
• When three phase voltage enters a VFD unit it is converted to
DC voltage.
• The VFD has an internal DC bus voltage of 650 volts.
•V
= VRMS x 1.414
A capacitor is placed across the DC bus to smooth out the ripple.
P
•
• The VFD taps off the DC bus to create an AC sinusoidal
wave.
• The VFD can control voltage magnitude and frequency of the
new created sine wave.
Theory of Operation of a VFD:
• When three phase voltage enters a VFD unit it is converted to
DC voltage.
• The VFD has an internal DC bus voltage of 650 volts.
•V
= VRMS x 1.414
A capacitor is placed across the DC bus to smooth out the ripple.
P
•
• The VFD taps off the DC bus to create an AC sinusoidal
wave.
• The VFD can control voltage magnitude and frequency of the
new created sine wave.
• This output sine wave from the VFD unit is called a:
•Pulse Width Modulated PWM sine wave.
Theory of Operation of a VFD:
Theory of Operation of a VFD:
• The PWM waveform is created by transistors that are acting like
electronic switches.
Theory of Operation of a VFD:
• The PWM waveform is created by transistors that are acting like
•
electronic switches.
Example:
• On the picture shown below the red arrows indicate how voltage is applied across one
•
phase of the motor.
180° electrical degrees later the green arrow indicate how the voltage has been
reversed across the coil.
Theory of Operation of a VFD:
Theory of Operation of a VFD:
• The PWM waveform is made up of squares that vary in width.
• The height of the square is always the same.
• The magnitude of the voltage is determined by the width of the
pulse.
Theory of Operation of a VFD:
• From AC circuits we learned that the effective value of a
oscillating wave is calculated by the following formula:
•
Theory of Operation of a VFD:
Installation considerations of a VFD:

VFD units can create harmonics on a power distribution system.
Installation considerations of a VFD:


VFD units can create harmonics on a power distribution system.
VFD units should be used with motors that have good winding insulations.
Type F and H winding insulations are the best.
Installation considerations of a VFD:


VFD units can create harmonics on a power distribution system.
VFD units should be used with motors that have good winding insulations.
Type F and H winding insulations are the best.
 VFD drives can damage a motor if distance between motor and VFD unit is
over 150 feet.
 A line reactor will help protect motor.
Installation considerations of a VFD:


VFD units can create harmonics on a power distribution system.
VFD units should be used with motors that have good winding insulations.
Type F and H winding insulations are the best.
 VFD drives can damage a motor if distance between motor and VFD unit is
over 150 feet.
 A line reactor will help protect motor.
 Motor leads on a VFD unit can cause noise in adjacent wiring.
 Consider using special VFD wiring on new installations.
Installation considerations of a VFD:


VFD units can create harmonics on a power distribution system.
VFD units should be used with motors that have good winding insulations.
Type F and H winding insulations are the best.
 VFD drives can damage a motor if distance between motor and VFD unit is
over 150 feet.
 A line reactor will help protect motor.
 Motor leads on a VFD unit can cause noise in adjacent wiring.
 Consider using special VFD wiring on new installations.
 Some VFD installations may require air circulation around the drive unit if
installed in an outdoor enclosure or in a hot environment.