Adjustable Speed Drive Issues and
Changes to IEEE519
Presented by:
Tom Farr, Senior Member IEEE
Engineering Manager
MV Drives
Eaton Corporation
Asheville NC
Past Chair of WNC IEEE PES/IAS
Member IEEE PSRC
Member NEMA 1IS SC7 IEC TC22
Adjustable Speed Drive Issues and
Changes to IEEE519
TODAY’S AGENDA
• Why Use Drives?
• IEEE C37.96-2012 AC Motor Protection Guide
• IEEE 519-2014
• Drive Output Issues
• Questions
Why Use Adjustable Speed Drives?
• The ability to vary the speed of a motor is beneficial
• A pump run at 50% speed uses only 12.5%KW
$$$$$$$$$
Adjustable Speed Drives and Motor Systems:
Other Benefits
• Ultimate Soft Start Capability
• Short Circuit Current Reduction
• Reduced Maintenance over other Process Control Technologies
Reduced Voltage Autotransformer Start:
Motor Inrush
Motor Current 4X FLA
Adjustable Speed Drives
Reduce Motor Inrush
Motor Current less than FLA
IEEE C37.96-2012 AC Motor
Protection Guide Section 4.4
• The guide is by the IEEE Power System Relaying Committee,
section 4.4 discusses the use of Adjustable Speed Drives
• Describes 3 zones of protection within ASD’s
ASD and Motor System
Basic Blocks of an ASD
Input: Zone 1
Input
section
Input filter
Input
Drive: Zone 2
Rectifier
DC - link
Inverter
Filter/Motor: Zone 3
Output filter
Motor
transformer
M
Basic Blocks of an ASD
Input : Zone 1
• Disconnect from the main supply
• Contains last level of motor protection
• Input filter can be used to limit harmonic currents
• Input filter can also improve displacement power factor
• Input transformer can be used to isolate the motor from the power system
• Can be used to step the system voltage up or down
• May have multiple secondary's for rectifiers with pulse numbers > than 6
Input
section
Input filter
Input
transformer
Basic Blocks of an ASD
Drive : Zone 2 Converter
•
•
•
•
Rectifier, converts AC to DC.
Voltage Source usually use Diodes, 6 (12,18,24, etc.)
Current Source may use SCR’s
AFE may use IGBT’s or other Active Devices
• DC Link stores energy and filters power flow
• Voltage source use capacitors
• Current source use inductors
Rectifier
DC-link
Inverter
Common Rectifier Types
• 6 pulse connected directly to the main supply
• Active Front End
• 18 Pulse, with Auto transformer
• 12, 24, 36 pulse with phase shifting transformer
What is IEEE 519?
IEEE Recommended Practice and
Requirements for Harmonic Control in
Electric Power Systems
What is wrong with
Harmonics?
• Cause excess heat in transformers
• Cause over currents in capacitors due to resonance
• May cause nuisance operation of breakers or fuses
• May interfere with metering or other electronics
• Makes your Utility and Neighbor unhappy
What in a Drive can cause
Harmonics?
• Converting AC to DC creates harmonics on the line
side of the rectifier
• The impacted harmonic orders are on either side of
the pulse number, 6 pulse sees 5th and 7th, 12 pulse
11th and 13th etc.
• Harmonic Filters can be used on lower order
rectifiers to reduce the specific offending frequency
• Phase shifting isolation transformers are used on
higher order rectifiers to cancel harmonics
Six Pulse Harmonics
12, 18 and 24 Pulse Harmonics
Typical Input Current Waveform: 12-pulse
Typical Input Current Waveform: 18-pulse
Typical Input Current Waveform: 24-pulse
What is new for IEEE 519-2014?
IEEE 519-2014 Point of Common Coupling
Changes
IEEE 519-2014 TDD Changes
TDD vs THD
IEEE 519-2014 Harmonic Measurement
Methods
IEEE 519-2014 Voltage Distortion Limits
IEEE 519-2014 Maximum Harmonic Current
Distortion
IEEE 519-2014 Increases Harmonic Current
Limits
Basic Blocks of an ASD
Zone 3: Output filter
• Output filter can be used to smooth the output waveform
• With VSI to reduce dv/dt which can lead to standing wave
• With CSI to reduce torque pulsations caused by current
waveform
Output filter
Motor
M
Fundamental Contributors to
Motor Voltage Rise From
NEMA
AC Drives Application Guide
• Pulse Rise Time (dv/dt)
• Cable Distance
• Minimum pulse duration and time between pulses
dv/dt is the change in voltage over
time
2 level inverter output
LV vs MV ASD output
• LV ASD’s switch at high frequency, smaller devices require less time to turn on/off
• Up to ~20KHz
• MV ASD’s switch at lower frequency, larger devices require more time
• Less than ~2KHz
• LV ASD’s usually have higher dv/dt than MV ASD’s
• LV ASD’s may require an output filter with cable run of 50 feet
• Check with vendor
• MV ASD’s may not require output filters with cable runs of 500 feet
• Check with vendor
• Larger motors have less impedance than small motors, therefore
less issue with standing wave
3 level inverter output
Sine Filtered Inverter Output
Motor Converts Electricity into Motion
Basic Blocks of an ASD
Zone 3: Motor
• The Motor converts electrical energy into mechanical energy
• The Motor can be induction or synchronous
• The Motor may be standard or inverter duty
Output filter
Motor
M
Things to consider when a
motor is run on a drive
• Motor duty, constant or variable torque?
• Cable type
• Inverter type and method of addressing dv/dt
• Distance of the motor from the drive
Motor Duty: Reduced Frequency Operation
Effects
• The applied frequency dictates the motor speed
• At lower speeds the rotor mounted fan does not cool as effectively
• Low speed CT applications usually require auxiliary motor cooling
• Actual motor FLA is a function of the frequency applied
• Lower FLA is drawn at lower frequency
• Nameplate FLA must is used for overload protection
• Can difficult for the protective device to measure current at off frequencies
High Frequency Harmonic Impact
• Harmonics in the applied voltage can cause additional motor heating
• up to 15% added thermal heating at near rated load
• Harmonics can cause circulating currents which can result in bearing current
• Ground brushes or insulated bearings may be recommended
• Harmonic currents and voltages can trick meters and protection relays
• Power factor correction or surge capacitors should not be used at the motor
Ground Faults Conditions
• ASD’s with input transformers have galvanic isolation
• A ground fault on the motor will not activate the ground fault protection on the feeder
• ASD’s without an input transformer have no galvanic isolation
• A ground fault on the motor may trigger ground fault protection on the feeder
• Check with the ASD vendor to ensure ground fault protection can be coordinated
Conclusions
• ASD’s reduce peak demand and save energy
• IEEE 519-2014 has a few important changes
• PCC defined as connection to Utility
• Voltage limits redefined
• Current limits ignore >50th
• TDD is expressed in % of maximum demand
• The type of control, motor and installation determine
if a filter is required