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© 2017 WEG Electric Corporation. All rights reserved.
WEG Variable Frequency Drives Training
Dave Mintzlaff – Product Line Manager, LV Drives and Soft Starters
July 2017
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© 2017 WEG Electric Corporation. All rights reserved.
Agenda
1. VFD Terminology
2. VFD System Architecture
3. Typical VFD Features
4. Induction Motors
5. Speed Range
6. VFD System Installation Considerations
7. VFD and Motor Cabling and Grounding
8. Summary of Major Points
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© 2017 WEG Electric Corporation. All rights reserved.
Terms and Definitions
Variable Frequency Drive – “An electronic device used for controlling
the rotational speed of an alternating current (AC) electric motor by
controlling the frequency and voltage of the electrical power supplied
to the motor.”
Other names you may have heard:
• Variable Frequency Drive (VFD)
• Variable Speed Drive (VSD)
• Adjustable Frequency Drive (AFD)
• Adjustable Speed Drive (ASD)
• Freq. Drive (Frequency Drive)
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© 2017 WEG Electric Corporation. All rights reserved.
Terms and Definitions
A Variable Frequency Drive consists of:
• Converter or Rectifier: Changes the AC Supply Power to DC Voltage
• DC Bus or DC Link: Capacitors that Filter and Store the DC Voltage
• Inverter: A Group of Transistors that Change the DC Bus Voltage to a
Variable AC Voltage and Frequency to Control the AC Motor
• Controller: Typically a Microprocessor and Circuitry that Manages
the Operation of the System
Utility
AC Power
DC Bus Rectifier Inverter
Controller
Logic I/O
Communication
Analog I/O
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© 2017 WEG Electric Corporation. All rights reserved.
4 Basic Parts of a VFD
Rectifier, Capacitors, Inverter, and CPU
Inverts
DC to AC
Capacitors Rectifier Inverter
Converts
AC to DC
Filters
DC Power
Controller
Utility
(AC Power)
Motor
(VFD Power)
Logic I/O
Communication
Analog I/O
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© 2017 WEG Electric Corporation. All rights reserved.
Rectifier and Capacitors • At the supply to a typical VFD is a full wave diode
bridge rectifier module.
• The purpose of this module is to convert AC voltage
into DC voltage (to rectify).
Example of 480 Vac Converted to DC by a Six-Pulse Rectifier
480 Vac
3-phase 60Hz
Supply
D1 D3 D5
D6 D4 D2
L1
L2
L3
DC –
DC +
+/– 650 Vdc
(DC Bus)
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© 2017 WEG Electric Corporation. All rights reserved.
Inverter
• By utilizing six transistors, this inverter example is able to convert DC
voltage into a simulated sinusoidal output waveform. This method of
power conversion is called Pulse Width Modulation (PWM). There are 2
transistors per phase, one for the positive switching and one for the
negative.
• The frequency of these pulses is significantly higher than the frequency
of the simulated sinusoidal output, and is known as the carrier
frequency.
Pulse Width Modulation Output Basic IGBT configuration in an Inverter
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© 2017 WEG Electric Corporation. All rights reserved.
Basic Power Sections
Reactors
(design specific)
Input
• Fixed Voltage
• Fixed Frequency
Output
• Variable Voltage
• Variable Frequency
Diode Rectifier Inverter DC Bus Induction Motor
Reactors
(design specific)
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© 2017 WEG Electric Corporation. All rights reserved.
AC Induction Motors
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© 2017 WEG Electric Corporation. All rights reserved.
Conduit Box (F3 Position)
Fan Shroud
End Bell (Drive End)
Lubrication Point
Stator Windings
Stator Laminations
Rotor Bars & Laminations
Bearing (Drive End)
Motor Frame
Motor Shaft
Drive End Non-Drive End
(Opposite Drive End)
Motor Mounting Feet
Air Gap
Bearing
(Non-Drive End)
AC Motor Nomenclature
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© 2017 WEG Electric Corporation. All rights reserved.
Motor Operating Speed • Variable frequency drives operate on the principle that the
synchronous speed of an AC motor is determined by the frequency
of the AC supply and the number of poles in the motor.
𝑅𝑃𝑀 = 120 × (𝐻𝑧)
# 𝑃𝑜𝑙𝑒𝑠 𝑖𝑛 𝑀𝑜𝑡𝑜𝑟
• Synchronous RPM = The speed of the rotating magnetic field
produced in the motor stator windings.
• Full Load RPM of rotor is slower due to SLIP
• Through a process called induction, the
rotor bars (conductors) become energized
and create a magnetic field of their own.
• The motor speed is determined by number
of magnetic poles which is typically fixed by
the motor design and can be calculated from
the motor nameplate data.
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© 2017 WEG Electric Corporation. All rights reserved.
Motor Speeds: 60 Hz • Below are typical speeds vs. number of poles for
60Hz rated motors:
Full Load
Speed
Synchronous
Speed
Number
of Poles
3555 3600 2
1771 1800 4
1179 1200 6
886 900 8
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© 2017 WEG Electric Corporation. All rights reserved.
Motor Speeds: 50 Hz • Below are typical speeds vs. number of poles for
50Hz rated motors:
Full Load
Speed
Synchronous
Speed
Number
of Poles
2962 3000 2
1476 1500 4
983 1000 6
738 800 8
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© 2017 WEG Electric Corporation. All rights reserved.
VFD Environmental Considerations
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© 2017 WEG Electric Corporation. All rights reserved.
• Consideration must be given to the environmental conditions where the VFD will
be installed.
• Ambient temperature range and moisture levels are most often identified as
potential problems, but high altitude may also be an issue.
• VFD’s should be located in clean, dry, well ventilated areas.
• Heat is the enemy for electrical equipment. Be sure the installation site has
sufficient cooling air available.
• Most drives installed inside buildings may only need a NEMA Type 1 enclosure
for protection. There may be situations where more protection is needed.
• Be sure to identify any airborne contaminants and vapors that may damage
the VFD electrical components. These can be present wherever solvents or
other chemicals are in use such as with water treatment systems.
• Combustion systems can emit corrosive vapors as well as particulate matter.
• WEG includes a conformal coating for all VFD circuit boards to help protect
against these contaminants.
Environments and Enclosures
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© 2017 WEG Electric Corporation. All rights reserved.
Environment: Temperature • WEG VFD’s are rated for a range of ambient temperature and altitude.
• Common temperature ranges are between -10°C (14°F) to 50°C (122°F).
• In some applications higher temperatures may be allowed provided the VFD can
be de-rated per the guidelines in the user manual.
Example of a temperature de-rating scenario:
• A common derating formula for temperatures above the VFDs rated ambient
temperature is 2% decrease in current per degree C.
• For example, a 480V VFD rated 55 kW (75 HP) has a current rating of 88 Amps at
50°C (122°F).
• In a 60°C (140°F) environment the VFD would require a decreased maximum
current per the following:
60°C (140°F) - 50°C (122°F) = 10°C (18°F)
10°C (18°F) x 2% per degree C = 20% i.e.{(60-50) x 2% = 20%}
Or: Derate 88 Amps by 20% = 70.4 Amps maximum
NOTE: Always consult with WEG Drives Application Engineers when derating a VFD
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© 2017 WEG Electric Corporation. All rights reserved.
Environment: Temperature (cont’d.)
The graph below shows that as the temperature increases (horizontal axis) the
available drive current is reduced.
At 50°C the current rating is at 100% of the drive’s rating but at 60°C as described
in the prior slide, the drive’s rating has to be reduced to 80% (derated by 20%).
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© 2017 WEG Electric Corporation. All rights reserved.
Environment: Altitude • WEG VFDs are rated for operation at altitudes up to 1000 meters (3300 feet)
without de-rating.
• In some applications the installation site may be at a higher altitude.
• Higher altitudes may be allowed provided the VFD can be de-rated per the
manufacturer’s recommendations.
Example of a high altitude de-rating scenario:
• A common derating formula for altitude above the VFDs rating is 1% decrease in
current per 100 meters (330 feet) additional altitude.
• For example, a 480V VFD rated 110 kW (150 HP) has a current rating of 180 Amps
at 1000 meters (3300 feet).
• At 3000 meters (9900 feet) altitude, the VFD has a current de-rating of 1% per
100 meters which means 20% decrease in maximum current
i.e. {(3000-1000)/100 = 20%}.
Or: 180 Amps – 20% derating (36 Amps) = 144 Amps maximum
NOTE: Always consult with WEG Drives Application Engineers when derating a VFD
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© 2017 WEG Electric Corporation. All rights reserved.
Environment: Altitude (cont’d.) The graph below shows that as the altitude increases (horizontal axis) the available
drive current is reduced.
At 1000 meters the current rating is at 100% of the drive’s rating but at 3000
meters described in the prior slide, the drive’s rating has to be reduced to 80%
(derated by 20%).
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© 2017 WEG Electric Corporation. All rights reserved.
Installation Considerations
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© 2017 WEG Electric Corporation. All rights reserved.
Drive Installation: Grounding
Improper grounding is a common VFD installation issue
• VFDs must be properly grounded before they can function as designed.
• Follow recommended grounding practice as in the example below:
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© 2017 WEG Electric Corporation. All rights reserved.
Improper grounding is a common VFD installation issue
• VFDs must be properly grounded before they can function as designed.
• Follow recommended grounding practice as in the example below:
NO! Enclosure
backpanel
Yes Enclosure
backpanel
Drive Installation: Grounding
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© 2017 WEG Electric Corporation. All rights reserved.
PVC - Inner &
Outer Sheath
Armor Cable Example
Filler
Cable
Armor
B
G
C
A
G
G
Three
Ground
Conductors
Typical VFD Grounding Scheme
Example of Wiring for VFD and Armor Cable
Drive Installation: Motor Cables
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© 2017 WEG Electric Corporation. All rights reserved.
Drive Installation: LV Cables
• Proper low voltage cable routing practices should be followed to ensure
optimal performance for the VFD and connected system devices.
• Electromagnetic interference (EMI) can be a very important issue with
high power devices such as VFDs.
• Most VFD manufacturers offer an RFI filter built into the VFD to help
mitigate electrical interference problems.
Variable Frequency Drive
+
AI-AO+AO– DI1 DI2 DI3 DI4+24vGND
Basic VFD Low Voltage Wiring Example
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© 2017 WEG Electric Corporation. All rights reserved.
Drive Installation: LV Cables
Some common wiring recommendations:
• Control wiring should never be run in the same conduit that
contains power wiring of any kind.
• For 120 Vac signals, a standard 600 volt stranded wire or single
conductor can be used.
• For 24 Vdc signals, it is best to use multi-conductor twisted pair
control cable. An overall shield is recommended but not required.
• For analog signals such as 0-10 Vdc, 0-20mA or 4-20mA, a twisted
pair cable with a shield should be used.
• A recommended separation of 200 mm (8 inches) should be
maintained between power and control wiring when run along side
each other.
• If power and control cables need to cross each other, it should be
done at a 90 degree angle.
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© 2017 WEG Electric Corporation. All rights reserved.
Summary and Key Points
• Variable Frequency Drives are widely used today to vary the speed of the AC motors in pumping applications
• Care must be taken in selection and installation of the drive and motor to ensure trouble free operation and long service life.
• Ensure the Variable Frequency Drive and AC motor are suited for the environment and load characteristics.
• Know the ‘worst case’ operating environment and evaluate enclosure designs.
• Understand the potential issues of cable length between VFD and motor and don’t exceed the manufactures recommendations.
• Make sure that motors used with VFD’s are VFD suitable. VFD operation can impact cooling, insulation and bearings.
• Be sure to consult the VFD and motor manufacturer(s) for additional guidelines and recommendations for long service life.
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© 2017 WEG Electric Corporation. All rights reserved.
It’s HERE!
The new 2017 Automation Catalog:
• Focused on Low Voltage Drives,
Soft Starters & Engineered Panels
• New layout, easier to follow
• Updated Quick Selection Guides
with current products
• Updated pricing
• Available in hard copy, or download
the PDF at: http://www.weg.net/us
• The online version will be
maintained regularly
• Just updated January 2017!
Low Voltage Drives and Soft Starters
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© 2017 WEG Electric Corporation. All rights reserved.
WEG Variable Frequency Drives Training
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© 2017 WEG Electric Corporation. All rights reserved.
Thank you!