Ct337installationconsiderationswhenapplyingvariablefrequencydrives-raotmlancasterpa2015.pdf

CT337 Installation Considerations When Applying Variable Frequency Drives

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Rev 5058-CO900E

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Agenda

Today You Will Learn: • How to correctly size your VFD • How to properly install to minimize problems. • How to mitigate Reflective Wave voltage spikes • How to dampen the effects of Common Mode Current

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2

Collect the Motor Data Select Your VFD Based on Motor Nameplate Amps Record: Volts Amps RPM Hz

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Read the Nameplate Confirm the Input Voltage Confirm the Output Current Current needs to be greater than or equal to the motor nameplate value Always Select the VFD Based on Motor Nameplate Current! Horsepower is a nominal rating

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Plan the Installation UVW ASD Output Conduit / Armor bond to cabinet

Cabinet Back Plane

RST

A

PE

ASD - 1

PE

ASD - 2

A

B PLC or Electronics

ASD Input Conduit / Armor Bond to cabinet

Transient Common Mode Current on Armor PE

PE

ASD - 3

ASD - 4

PE

PE

PE Copper Bus

B

Transient Common Mode Current on PE Wire

Optional PE to Building Structure

B

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Pay Attention to Clearances

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Pay Attention to Clearances?

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Heat Is Your Enemy! Just because it fits in the box, doesn’t make the enclosure the correct size!

5.98”

Think of it as a 100 watt light bulb! Don’t bake your VFD in an Easy Bake Oven! 3.15”

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Heat Is Your Enemy! Heat rises, give it a path to flow.

Install the unit vertically to allow airflow through the heatsink cooling fins. Don’t block the cooling fan! PUBLIC INFORMATION

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Pay Attention to Clearances?

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Power to Power Motor to Motor

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Pay Attention to the Control Voltage

Don’t let the Magic Smoke out! PUBLIC INFORMATION

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Proper Grounding is a Must!

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Is Your Input Power Grounded or Floating?

L1 L2 L3

Ungrounded Power Systems may require the removal of the Input MOV jumper

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AC Drive and Motor Installation Practices Line Transients

ACME INCORPORATED

A little protection and good technique go a long way to insure a good drive installation

Common Mode & Capacitive Coupling Tell me again why I’m using drives?

?

Harmonics

Reflected Wave

Grounding & Bonding

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Why Should I use a DRIVE ? • To improve process control though speed and torque control • To improve system efficiencies • To extend life of equipment by reducing mechanical stress • Reduce power demand –Save Energy

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Why Develop the Variable Frequency Drive? • The Promise: • To be able to electronically vary the speed and torque of any constant speed AC Motor. • Torque is proportional to applied Voltage. • Speed is proportional to applied Frequency.

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A Little Motor Fodder?

• Most Common Enclosure is “TEFC” • • • • •

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Totally Enclosed, Fan Cooled Fan attached to motor shaft rotates at same speed as motor shaft Blows air over outside of motor frame to dissipate internal heat Designed to provide sufficient cooling on line power to keep motor from overheating Remember: HEAT KILLS

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What Do We Know About Fans?

• Governed by the “Laws of Affinity” • It’s a LAW, which means it applies under all circumstances • Law # 1 •

The volume of air moved by a fan is directly proportional to its speed. • •

Faster = More Air Slower = Less Air

• If That Fan is Being Used to Cool an AC Motor, and the AC Motor is Operating at Less than Nameplate Speed, the Fan is Moving Less Air and Providing Less Cooling!

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A Little History Lesson About AC Motors

• Late 1980’s/Early 1990’s • No general supplier of “Inverter Rated” motors • VFDs applied to motors caused failures due to overheating! • A few niche suppliers modified general purpose motors to keep them cool when operating at reduced speeds. •

De-rated Higher Horsepower Motors •

•

Larger metal mass = better heat transfer

Added Constant Speed Blowers •

Constant cooling regardless of motor speed

• Addressed Only the Motor Thermal Issues • IGBT Start to be Used By VFD Manufacturers •

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Motor Service Centers Started Seeing Increased Volume of Motor Winding Failures

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What is an IGBT? • Insulated Gate Bipolar Transistor •

Hybrid cross between a MosFET and a Darlington Power Transistor

An Insulated Gated Bipolar Transistor is a power switching device capable of interfacing with low signal level logic control. RMOD

C1

POWER OUTPUT

Power Bipolar

SIGNAL INPUT

G1 RBE

Power MOSFET

E1

Conventional model of IGBT PUBLIC INFORMATION

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IGBT Advantages in AC drives

• Higher Switching (Carrier) Frequencies than Bipolar Transistors – Lower Motor Noise – Higher Switching Frequency – 4kHz Typical

– Lower Motor Heating – Motor Friendly Current Waveform Due to Higher Switching Frequency producing Less Waveform Ripple

– Better Field Oriented Control – Higher Switching Frequency Allowing for Faster Response Time

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IGBT vs. Bipolar Transistor Current

7.5HP MOTOR

Bi-Polar

IGBT

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1336 @ 60HZ NO LOAD SWITCHING FREQUENCY 1.26KHZ

1336 PLUS @ 60HZ NO LOAD SWITCHING FREQUENCY 8KHZ

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IGBT Advantages in AC drives • Drive Size Reduction – High Input Impedance – IGBT – Voltage “Gated (Switch on/off)” Device – Reduces Base Driver Power Consumption – Reduces Base Driver Board Size

5Hp 1333 Darlington Pwr

5Hp PowerFlex40 IGBT

4” x 8.4” x 5.4” 10.2” x 13.6” x 7”

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IGBT’s in VFDs • IGBT Associated Phenomenom •

Reflective Wave or dv/dt

Long Wires Runs to Motor Input Power

AC DRIVE

Energy stored in distribution system between drive and motor is released during switching and produces voltage spikes.

Output Power

[PWM] typical

Hotter motors

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Distribution network

IGBTs can stress motor insulation because of faster rise times Copyright © 2013 Rockwell Automation, Inc. All Rights Reserved.

The Physics of it All • Rapid voltage rise times • The cable surge impedance does not match the motor surge impedance---– Voltage reflection WILL occur !!

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Physics! Agh! Just tell me what I need to do!

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Reflected Wave Investigation • FACT: Reflected wave voltage at motor is a function of : • Cable Length • Cable distance between VFD and Motor

• Output Voltage Risetime • When you turn on the switch (IGBT), how long does it take the voltage being sent to the motor to go from 0 to Max (DC Bus Voltage). • Typically in Micro/Nano seconds.

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Reflected Wave

VLL @ Drive

Drive

Motor VLL @ Motor

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Effect: Peak voltage levels that search and find insulation voids

Breakdown, Corona or Partial Discharge of motor windings Eventual motor turn-to-turn, winding-to-winding or winding-tomotor frame shorts

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Reflected Wave Result

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Motor Manufacturers Step to the Plate

• Most Manufacurers Now Provide a “Inverter Duty” Product Offering • Motors are built with “Spike Resistant” Wire • Special Coating on Wire to Resist Voids Caused by Their Manufacturing Process, Handling for Forming Prior to Stator Insertion

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Protect the Motor • Output Reactor between drive & motor – – – –

Slopes off the waveform (lengthens rise time) Reduces destructive force for same amplitude Allows longer lead lengths Does create Voltage drop

• Output Filters – dV/dt • 1204-RWR2, 1204-RWC-17A • 1204-TFA1, TFB2 “terminator” • Third party devices

– Sine Wave Filter – Distances Beyond 1000’ – Expensive Solution

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GENERATION OF COMMON MODE or LINE-GROUND ELECTRICAL NOISE

Common Mode Issues

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What is Common Mode Current & How is it Generated? DRIVE FRAME C

MOTOR FRAME

MODULE

MOTOR WINDINGS

LOGIC

C MODULE

CONDUIT

DRIVE FRAME C MODULE

MOTOR FRAME

PE X INCIDENTAL CONTACT OF X CONDUIT TO BUILDING STEEL LOGIC

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C MODULE

MOTOR WINDINGS

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IGBT Switching Creating Common Mode Current

Occurs at every IGBT switching

Top Vl-l output voltage vs. I line-ground stray cable & motor current

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How to Measure Common Mode Current

Current to motor = current from motor. Resultant should be zero! Current seen is real current going somewhere? Common Mode to Ground grid.

Oscilloscope PUBLIC INFORMATION

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The Paths of Common Mode Current and it’s affect on Sensitive Electronic Equipment AC Drive

Input Transformer A

R B

XO

Ilg

C

(+) Vdc bus (-)

S

Ilg PE

U

T

Ilg

EARTH GROUND

V

Motor Tach

W

C lg-m

Logic

Ilg Common Mode Current Path

Motor Frame

Ilg

PE

C lg-c I lg

Vng

Potential #1

Potential #2

Potential #3

Interface Electronics 0-10V, communication, 4-20 ma,sensor interface,etc

Potential # 4

True Earth Ground (TE)

Common Mode Noise Current Path causing ground EMI Interference PUBLIC INFORMATION

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Containing Common Mode Current Input Transformer A

R B

XO

Ilg Ilg

PE

C

Ilg

S

V Vdc bus

T

(-)

Ilg

Ilg

W

s t r a p

PE

Potential #1

Motor

C lg-m Motor PE GND wire

PE

Ilg

Motor Frame

U

(+)

Common Mode Current Path

EARTH GROUND Potential 4

Conduit

AC Drive

Accidental Contact of conduit

Ilg

Potential #2

Potential #3

CONDUIT PROVIDES GOOD WIRING NOISE CONTROL BUT ACCIDENTAL CONDUIT CONTACT TO GROUND MAY ALLOW Ilg NOISE PATH BACK TO GROUND

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Additional Containment Shielded Cable / Armor AC Drive with PVC Jacket Motor Frame

Input Transformer A

R B

XO

Ilg Ilg

PE

C

Ilg

S

V

Motor

Vdc bus

T

(-)

Ilg

PVC

W

C lg-m

PE

Ilg

PE

Common Mode Current Path

EARTH GROUND Potential 4

U

(+)

Ilg

Potential #1

Additional Motor PE GND wire

Potential #2

Potential #3

Shielded output cable/armor with PVC jacket PROVIDES BETTER WIRING & NOISE CONTROL WITH NO ACCIDENTAL ARMOR CONTACT TO GROUND. BUT IF NOT USED ON INPUT MAY ALLOW Ilg NOISE PATH BACK TO GROUND PUBLIC INFORMATION

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Additional Containment Transformer Cabinet Frame

Cable / Armor & PVC JacketAC Drive

A

Cable / Armor & PVC Jacket Motor Frame

R U

Ilg X

B

O

Ilg C

PE

S V PVC

PVC

EARTH GROUND Potential 4

C lg-m

T W PE

PE HRG or SOLID GND

Motor

Ilg

Ilg Common Mode Current Path

Potential #1

Additional Motor PE GND wire

Potential #2

Potential #3

Shielded input & output cable/armor with PVC jacket PROVIDES BETTER WIRING & NOISE CONTROL WITH NO ACCIDENTAL ARMOR CONTACT TO GROUND. Prevents Ilg NOISE inteference PATH BACK TO GROUND.

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Common mode cores and common mode capacitors as a solution A

AC Drive

R B

XO

Vdc bus (+)

S

Motor Frame

U

Ilg

V

Motor

W

T PE

Common Mode Choke

C lg-m

(-) C

Common Mode Bus Capacitors

PE

PE

Ilg

IlgCommon Mode Current Path EARTH GROUND Potential 4

Potential #1

Motor PE GND wire

C lg-c Ilg

Potential #2

Potential #3

Implementation of CM core in drive output, CM cores are smaller than output line reactors.

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Common mode core solution Inverter output Voltage Vu-v

70 nS

Ipeak Common Mode Ilg Current Ilg Current With Common Mode Chokes

6 MHz Oscillation

Slower 1.5 us to 5 us risetime Lower 200 kHz to 63 kHz Oscillation Lower 1/3 Ipeak

CM ferrite cores attenuate the high frequency noise peak amplitude and more importantly the ILG noise current rise time that develops CM noise ground voltage

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CE or RFI filter solution Main Plant Xfmr.LISN

Drive EMI Filter

A

XO

B

R

U

S

V

T

W PE

Lf C

HRG Unit

Cf

PE

Potential #1

Ilg

Motor

C lg-m Motor PE GND wire

C lg-c

Ilg EARTH GROUND Potential 4

Motor Frame

AC Drive

Potential #2

Ilg

Potential #3

* EMI filters re-direct noise current back to drive input leads and out of ground , must be used with shielded output cables. * (+) and (-) DC Bus capacitors to Ground also perform the same function PUBLIC INFORMATION

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Isolation transformer solution Main Plant Xfmr.

Drive Isolation Xfmr. A

A

XO

B

XO

Ilg Ilg

C

HRG Unit

EARTH GROUND Potential 4

C

to other plant loads

Ilg

Motor Frame

AC Drive

B

R

U

S

V

T

W PE

Ilg

C lg-m

PE

Motor PE GND wire

C lg-c

Ilg

Potential #1

Motor

Potential #2

Ilg

Potential #3

* solidly ground drive isolation XFMR re-directs noise current back to drive input leads and out of ground. Mount close to drive. Must be used with shielded output cables. * NO Ground noise in upstream ground from XFMR PUBLIC INFORMATION

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Using common mode (ferrite) cores on signal wires

SEND

RECEIVE

Hi Load

Isignal Isignal

Lo Z Common Mode Choke on Interface Leads

Ground Potential #1

Shield

Ground Potential #2

Implementation of CM core in signal lines between noisy grounds works PUBLIC INFORMATION

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Panel layout is important U VW

B

RST

A

PE

A

ASD Output Conduit / Armor bond to cabinet

PE

ASD Input Conduit / Armor Bond to cabinet

Cabinet Back Plane ASD - 1

ASD - 2

AB PLC or Electronics

A

Transient Common Mode Current on Armor PE

PE

ASD - 3

ASD - 4

AB PE

B

Transient Common Mode Current on PE Wire

PE

PE Copper Bus

B Wire To System PE of Building Structure PUBLIC INFORMATION

B

Poor panel layout allows Ilg noise on output armor to flow back to ground behind the PLC ground , causing possible interference Copyright © 2013 Rockwell Automation, Inc. All Rights Reserved.

Better panel layout UVW ASD Output Conduit / Armor bond to cabinet

Cabinet Back Plane

RST

A

PE

ASD - 1

PE

ASD - 2

A

B PLC or Electronics

ASD Input Conduit / Armor Bond to cabinet

Transient Common Mode Current on Armor PE

PE

ASD - 3

ASD - 4

PE

PE

PE Copper Bus

B

Transient Common Mode Current on PE Wire

Optional PE to Building Structure

B Better panel layout allows Ilg noise on output armor to flow back to input armor and out of PLC ground PUBLIC INFORMATION

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Strategy to Reduce or Eliminate CM Noise Issues •Follow grounding recommendations to the letter •Use recommended panel layout •Keep motor cables short •Use shielded cable whenever possible •Route wires intelligently •Use drives with CM internal cores or •Use external CM cores •Set drives for the lowest carrier frequency PUBLIC INFORMATION

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QUESTIONS and ANSWERS

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