Download Electromagnetic compatibility consideration and

Electromagnetic Compatibility
Consideration and Recommendation
with Variables Speed Drives
Eduardo Gie
Pacific Engineering Manager at Danfoss
Electromagnetic Compatibility (EMC)
• It describes the ability of a device
to resist electrical interference
and not to emit electrical
interference to other devices
• Natural electrical interference
– Lightning
– Magnetic field that surround the
globe
• Unnatural electrical interference
– Interferences occur when
electrical energy is used. This
interference can disperse through
air or electrical wiring
– i.e light switch may cause flicker on
old TVs or radios
Interference diffusion paths
Radiated
Emission
Conducted
Emission
50Hz 2.5Hz
Harmonic
2.5KHz –
150KHz
150Khz –
30Mhz
Cond. RFI
Transmitted through mains and
earth cables
30MHz 400GHz
Rad. RFI
Emitted from the VSD housing
and motor cables
Harmonic cause and effect
•
Power Electronics equipment with input
rectifiers have the drawback of increasing the
non-sinousoidal currents into the power
network
•
Pulse input current which does not follow
voltage waveform causes Current Distortion
THiD
•
THiD causes:
–
–
–
Transformer and/or cable overheating
Nuisance switchgear trips
Stress on Power Factor correction banks, etc.
•
When multiplying THiD by the impedance of the
system, it causes Voltage Distortion THvD
•
THvD causes:
–
–
•
Malfunction and/or breakdown of electronic
equipment
Increased losses with motor running in DOL, etc.
NB! Harmonic distortions are repetitive and
continuously deform the voltage or current
waveforms.
Harmonics Limits
System Level (THvD limits)
AS 61000.3.6.2001 (TR IEC 61000.3.6.2012)
System Level (THvD Limits)
AS 61000.2.2.2003 (Domestic)
AS61000.2.4.2009 (Industry)
Product Level (THiD Limits)
AS61000.3.2.2007
<=16A (VSD <1kw)
AS61000.3.12.2006
16 to 75A
AS61000.3.4.2007
> 75A
IEEE 519.2014 Utility
limit THvD @ PCC
IEEE 519.2014 customer
limit TDD @ PCC
Mitigation Techniques
Passive:
Active:
DC-Inductors
AC-Inductors
Active filter (AAF)
Low Harmonic Drive (LHD)
12-pulse
d
18-pulse
+20%
D
D
y
///
///
0%
-20%
Advanced Harmonic Filters
(AHF)
Active Front End with PWM-rectifier (AFE)
///
Harmonic Considerations
•
Identify the applicable THiD/THvD harmonic limit to meet the relevant standards, electricity code
and installation rules of the electrical distributor.
•
VSD supplier shall provide details of all harmonic currents up to and including the 49th when
operating at full load and provide an estimation of the total harmonic voltage distortion resulting at
the point(s) of common coupling due to the installation of all the VSDs on the project.
•
Details such as
–
–
–
–
–
–
–
•
Single Line Diagram (SLD),
Supply transformer size, type, voltages and impedance
short-circuit power or short-circuit current at the primary side of transformer ( SCR has a decisive impact on
the filter performance)
Linear and non-linear loads schedule with their diversity factor
Standby, duty and assist loads
Power factor correction banks
and other relevant supply network data will be supplied to enable this calculation to be made
If this simulation concludes the total harmonic voltage and/or current distortion is expected to be
above the value prescribed by relevant standards or electricity distributor, the VSD manufacturer
shall propose additional passive or active advanced harmonic filters to reduce the harmonic
distortion to within limits.
High frequency conducted noise
•
Use of Active Power Techniques such as
Active Front Ends, Low Harmonic Drive, and
Active Harmonic Filters make it possible to
reduce the harmonic currents, however it
may cause High Frequency conducted
disturbances & Harmonic Resonances >2Khz
•
2-150kHz frequency range is currently not
covered by international standards. Mainly
due to the lack of reported cases and
complexity to simulate them
•
Factors causing significant impact on
Harmonic Resonances are:
–
–
–
–
•
Switching frequency
EMI filter design
Supply Network Impedance
Supply Network Short circuit Ratio
Possible solution adding HF Passive Filters to
reduce both the discrete frequency and the
band of frequencies levels.
How can HF-disturbances be
minimised?
• Whenever possible, limit the number of devices using power electronics with
switching technologies in the same part of the grid.
• Consider adding HF-harmonics filters.
• Avoid switching frequencies of the power electronic equipment in the frequency
band allocated for communications, or if these switching frequencies are close to
possible network resonance points.
• Always consider harmonic resonance, even when applying small power rated
equipment with power electronics. High harmonic order resonances can be
especially troublesome, because of significant heat and interference which could
created.
• EN61000-2-4 recommendations for compatibility levels in the frequency range 29kHz are not considered in any EMC susceptibility tests for electrical equipment.
As a result, applying these recommendations does not guarantee safe operation
for all consumers at the power network.
The nature of the RFI
• VSDs typically uses PWM for the
generation of the 3 phase
voltages by switching the
transistors ON and OFF at a very
fast rate
• The high frequency switching of
relatively high currents by a VSDs
output transistors and the very
short rise times of each pulse can
result in high levels of RFI noise
radiated and/or conducted onto
the mains supply, control wiring
and devices
Why it’s important to follow
manufacturer's instructions
•
•
AS 61800.3-2005 (IEC61800-3:2004) standard specify the EMC requirements and
the recommended engineering practice for power drive systems, NOT only VSDs.
The Power Drive System consists of a Complete Drive Module (VSD), the motor
and its interconnection such as motor cables, control cables, supply cables,
junction box, contactors, etc. except for the driven load
Power Drive System
RFI Mitigation Techniques
Radiated
Emission
Conducted
Emission
•
•
•
Install RFI Filter, a low pass filter
to reduce the HF common-mode
current to acceptable levels.
The RFI Filters designed is based
on the input current to the VSD
and maximum. allowable motor
cable length.
Install Screened Motor Cable
bonded at both ends to ensure a
low impedance path for HF
common-mode current to go
back to the VSD
30MHz 400GHz
RFI
150Khz –
30Mhz
RFI
•
•
•
•
•
Install Screened Motor Cable to avoid capacitive
coupling, inductive coupling and Electromagnetic
coupling.
Follow Cable Segregation and Routing as per
manufacturer.
It is essential that motor screened cables are “properly”
glanded and terminated at both ends. This means
ensuring that the screen makes contact through 360 of
the gland.
Do not break the screen at any point between the VSD
and the motor.
No Pigtail at cable screen!!
Bearing Motor Currents - EDM
• Fast switching pulse width modulation (PWM) causes high frequency
voltage pulses with respect to motor ground. High Frequency capacitively
coupled currents between the motor stator windings & rotor; and
between the motor stator windings & motor frame, can flow causing
premature bearing failures.
Bearing and Shaft current categorised
• Low Frequency nature,
– These currents which can be localised in
the bearing or are driven through the
bearing are due to asymmetries in the
motor material properties or
construction; and even occurrin DOL
motors.
• High Frequency nature,
– Fast switching pulse width modulation
(PWM) causes high frequency voltage
pulses with respect to motor ground.
High Frequency capacitive coupled
currents between the motor stator
windings & rotor; and between the
motor stator windings & motor frame
can flow.
EDM Mitigation Techniques
Low Frequency Currents
High Frequency Currents
•
•
Follow strict EMC installation practice state by VSD’
manufacturer documentation
•
It is essential that screened cables are “properly” glanded
and terminated.
Protective Conductor Earth (PE) shall be inside the cable
screen and terminated by very short connection at the
same place as screen at both ends
Do not break the screen at any point between the VSD and
the motor. If there is a local isolator between the VSD and
motor for safety purposes, connect the screen continuously
with the help of a metal back plate. Connect the screen to
the back plate using proper metal cable clamps.
Proper HF grounding of the motor
Proper HF ground connection between motor chassis &
driven load
Shaft grounding brush & isolating couplings can be used as
additional mitigation
HF Common Mode Filter cores can also be used as a
preventative measure
Reduce Switching frequency
•
Motor design optimised for
symmetry
Insulate one bearing
•
•
•
•
•
•
•
Care must be taken when specifying, selecting and
installing VSD and options
• “Prevention is better than
cure”
• The best time to consider all
aspect of EMC is during the
preliminary design.
• Specify relevant limits
• Select the correct product and
options
• Plan EMC Plan for PDS
• Validate the performance with
instruments
Avoid the need to call the
Electromagnetic Compatibility Crime
Scene Investigator (EMC-CSI)
Thank You