variable frequency drives: applications and power quality

Variable Frequency Drive and

Power Quality Workshop

Robin Priestley

Power Control Manager

Rockwell Automation

52ND ANNUAL RURAL

ENERGY

CONFERENCE &

WORKSHOP

FEBRUARY 12-14, 2014

Ask the question

We can go deeper into any subject

We can go “up bubble” too

Ask the question!

RULES OF

ENGAGEMENT

Be BRUTALLY Honest!

The goal is to make MREC seminars & Robin BETTER!

Please fill out each section while we’re there

CRITIQUE SHEET

COPY WRITE © 2013 ROBIN PRIESTLEY ROCKWELL AUTOMATION ALL RIGHT S RESERVED

ROBIN’S DISCLAIMER

• Based on today…

• 100% Accurate?

• Compiled by “Drives Guy”

• Balanced with Resources

• List of Web Sites

• Discussion is technical

• Not brand specific

• Not “correct”, “sensitive” or “inclusive”


RESOURCES

• http://www.ab.com/drives/energy_savings/index.html

• http://www.angelfire.com/pa/baconbacon/page2.html

• http://www.pupman.com/listarchives/2001/June/msg00679.html

• http://www.energysafe.com.au/products.html

• http://www.iserv.net/~alexx/lib/general.htm

• http://www.myronzuckerinc.com/docs/Specification%20-

%20Trap%20Filter.pdf

• http://www.transcoil.com/

• http://www.et-sales.com/K_Factor.html

• http://www.ab.com/drives/energy_savings/index.html

http://www.ab.com/drives/energy_savings/index.html

http://www.angelfire.com/pa/baconbacon/page2.html

http://www.pupman.com/listarchives/2001/June/msg00679.html

http://www.energysafe.com.au/products.html

http://www.iserv.net/~alexx/lib/general.htm

http://www.myronzuckerinc.com/docs/Specification - Trap Filter.pdf



http://www.transcoil.com/

http://www.et-sales.com/K_Factor.html




TOOLS

• Engineering Assistant

• Break/Regeneration Calculator

• Harmonics Estimator

• Energy Savings Calculator

• Allen-Bradley Team

• Seminars

• Harmonics/Power Quality, Etc.

• Application Expertise

How many can you think of?

DRIVES IN

RURAL

APPLICATIONS


• Irrigation

• Hammer, flow, energy, aquifer management, saves

piping

• Dairy

• Agitation, vacuum pumps

• Three Phase Conversion

• Animal Health

• Air Quality, Temperature control

HMMMMM?

AC Input Rectified to DC Waveform Smoothed Chopped into AC

1. Alternating Current is brought into the drive.

2. The AC voltage is rectified to DC using bridge rectifiers or an

SCR circuit.

3. The DC voltage has it’s ripple removed by a capacitor bank.

4. Transistors “switch” the DC voltage on and off.

Using Pulse Width Modulation, AC is seen by the motor.

1 2 3 4

How Do AC Drives Work?


WHAT IS PWM?

Pulse Width Modulation

Pulse Width Modulation is a technique that involves turning an output ON for a period of time, and then OFF

for the balance of the time. This is done without varying the voltage.

When all Pulses have same Width, the output is a square wave.


WHAT IS PWM?

Short ON times with

Long OFF times result in

lower average voltage.

Long ON times with

Short OFF times result

in Higher average

Voltage.

WHAT IS PWM?

Changing the Pulse Width in a dynamic way will result in a simulated

AC sine wave.


PARAMETERS AND

PROGRAMMING

Local Control (HIM)

Remote Potentiometer (0-10V)

Analog (0-10V, 4-20ma)

Preset Speeds MOPs

Network Control EtherNet and 30 others

Speed Control


PROGRAMMABLE

INPUTS

Control Wiring


CONTROL WIRING

Control Wiring


CONTROL WIRING

Stop Modes

Ramp to Stop

Coast To Stop

Ramp to Hold

DC Brake

MOTOR CONTROL- WHAT IS

IMPORTANT?

• What dynamics does the application require?

• Ultimately, A motor shaft should:

• 1) Start to spin when commanded, i.e..; suitable “Breakaway Torque”

• 2) Accelerate as quickly as the application demands: “Speed Response”

• 3) Maintain operating speed without drift in motor speed

(not frequency): “Speed Regulation”

• 4) Produce torque quickly enough satisfy the speed regulator

needs “Dynamic Response”

• 5) Provide the Greatest Efficiency as a combined motor/VFD system,

• i.e.: what is the wire to shaft efficiency ! !

• VFD should not be susceptible to, or create problems with other electrical

equipment operated on the same power distribution circuit.

2

4

BASIC CONTROL TYPES

Volts/Hertz Control

(V/Hz)

Sensorless Vector Control

(SVC)

Flux Vector Control

(FVC)

Field Oriented Control

2

5

BASIC CONTROL CLASSES

Volts/Hertz

Control

(V/Hz)

Sensorless Vector

Control

Encoderless

Field Oriented

Control

Field Oriented

Control

w/ Encoder Fdbk

Basic Volts/Hertz Enhanced V/Hz Vector Control

V/Hz with current

limiting

V/Hz with slip

comp.

2

7

VOLTS / HERTZ CONTROL

Voltage

Control

Inverter

V/Hz Control

V/Hz

M Ref V mag

Slip Frequency

Slip

Estimator

Current

Limit

Current Fdbk


• Ratio exists between voltage and frequency “volts per hertz” (V/HZ)

• 460/60 = 7.7 V/HZ (Voltage at 10hz =77v, voltage at 30hz=230v)

VOLTS/HERTZ CURVE

0 Frequency

Voltage

Base Voltage

Base Frequency 460

60

COPY WRITE © 2013 ROBIN PRIESTLEY ROCKWELL AUTOMATION ALL RIGHT S RESERVED 2

9

• Allows complete motor/drive optimization to produce maximum performance with minimum

current.

• Used on applications with tougher starting, acceleration or running torque requirements.

AC Drive Functionality

CUSTOM VOLTS-PER-HERTZ

Break Voltage

Break Frequency Start

Boost

Base Voltage

Base Frequency

Maximum Voltage

Maximum Frequency Voltage

Frequency 0


0

• Allows drive and motor to adapt to various starting conditions.

• Provides optimum motor performance while controlling current.

AC Drive Functionality

AUTO DC BOOST IN

VOLTS/HZ

0 Frequency

Voltage

Base Voltage

Base Frequency

Automatic Selection


1

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

450.0

500.0

0 5 914

19

23

28

33

38

42

47

52

56

61

66

70

75

Output Voltage

Output Frequency

Allen Bradley Speed Torque Curve1336S PLUS Drive w/ Custom Volt/Hertz Curve

Volts/Hertz Ratio

0.0

10.0

20.0

30.0

40.0

1.4

4.2

7.0

9.8

12

.7

15

.5

18

.3

21

.1

23

.9

26

.7

29

.5

32

.3

35

.2

38

.0

40

.8

43

.6

46

.4

49

.2

52

.0

54

.8

57

.7

60

.5

63

.3

66

.1

68

.9

71

.7

74

.5

77

.3

80

.2

83

.0

85

.8

88

.6

FrequencyVo

lta

ge

VOLTS / HERTZ MOTOR CONTROL

3

2

VOLTS/HERTZ CONTROL-

TORQUE VS SPEED

Per Unit

Torque

Speed in Hertz

3.0

2.5

2.0

1.5

1.0

.5

0 16.7 33.3 50 66.7 83.3

3

3

SENSORLESS VECTOR

CONTROL

“V Angle” controls the amount of total motor

current that goes into motor flux

Current

Limit

Voltage

Control

Inverter

V/Hz Control

Volt

Vector

M Ref

V mag

Current Fdbk

Slip Frequency

Slip

Estimator

V ang

Autotune Parameters

Torque Cur

Estimator

Torque Cur

Estimator


4

WHAT IS THE DIFFERENCE BETWEEN “OUT OF THE BOX”,

WIZARD STARTUP & A STARTUP WITH TUNING?

Constant Torque Speed Range

0%

50%

100%

150%

200%

250%

0

1

2

3

4

5

6

7

8

9

10

Output Hertz

Torq

ue

Optimum (Detailed StartUp) = 120:1

MotorNameplate DataEntered = 40 :1

Out of the box = 20 :1

3

5

FLUX VECTOR CONTROL -

TORQUE VS SPEED

2

1

Torq

ue

Speed (Hz)

1 2 5 10 20 30 40 50 60


6

STARTING TORQUE

• Out of the Box = 150%

• W/ Motor NP Values = 200%

• Optimum Tuning = 250%


7

SPEED TORQUE CURVES

Per Unit

Torque

Speed in Hertz

3.0

2.5

2.0

1.5

1.0

.5

0 10 20 30 40 50 60 70 80 90 100

3

8

DC DRIVE CONTROL WITH

FEEDBACK

Field

Cur. Reg. Speed

Reg.

SCR

Control

Field

Bridge

High Bandwidth Current regulator

Armature

Cur. Reg.

Arm

Bridge

M

PG

Ref

Voltage Fdbk

Current Fdbk

Current Fdbk

Speed Fdbk

3

9

FIELD ORIENTED CONTROL

W/ FEEDBACK

Torque

Ref

Flux

Reg. Speed

Reg.

Voltage

Control

High Bandwidth Current regulator

Current

Reg.

M

PG

Ref

Inverter

V mag

V ang

Autotune Para

Adaptive

Controller

Slip Frequency

Current Fdbk

Voltage Fdbk

Speed Fdbk

4

0

TORQUE VS SPEED

Per Unit

Torque

2.5

2.0

1.0

0.0 1 3 10 20 30 40 50 60 70 80 90

Flux Vector Drive, 1000:1 motor, Tuned


CONSTANT TORQUE LOADS

Heat generated is same at all speeds

Cooling system deteriorates at reduced speed

unless equipped with blower

Example: Conveyer

Winch

Auger


CONSTANT TORQUE 4:1

0

10

20

30

40

50

60

70

80

90

100

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90

Torque

Torque

Acceptable Region

for Continuous Operation)

HZ


CONSTANT TORQUE TO ZERO

SPEED

Torque Horsepower

Constant Torque Range Constant Horsepower Range

100% Percent of Base Speed

Torque &

Horsepower

0

100%

200%

CONSTANT TORQUE LOADS

Typical of conveyors and machine tools

Torque demand remains constant

throughout speed range

Operation at low speed may need

consideration

Motor enclosure a possible issue

VARIABLE TORQUE LOADS

Typical of Centrifugal Pumps and Fans

Torque drops as square of speed reduction

Operation at low speed not a problem due

to low torque requirement

Motor enclosure not an issue

Variable Torque Loads


WHAT’S MY LINE VOLTAGE?

• Some common ratings are:

• 120v, 1phase

• 200-230v, 1 phase

• 200-230v, 3 phase

• 380-480v, 3 phase

• 500-600v, 3 phase

• Medium Voltage (2300, 4160, 6600, 13800)


WHAT IS THE MOTOR VOLTAGE?

• Some common motor voltages are:

• 200-230v, 3 phase

• 380-480v, 3 phase

• 500-600v, 3 phase

• (Even if the incoming line voltage is single phase, the drive output will always be 3 phase. Single phase motors and Variable Frequency Drives are not designed to work together.)


WHAT HORSEPOWER?

• Three phase ¼ hp to 80,000 hp

• Single phase conversion to 40,000 HP


WHAT IS THE FULL LOAD AMP RATING

OF THE MOTOR?

• Even though motor and drive sizes

are commonly referred to in Horse

Power, it is best to make certain that

the drive can supply the current that

the motor requires.


WHAT VOLTAGE DO THE DIGITAL

INPUTS NEED TO CONFORM TO?

• Will there be external controls such

as Start, Stop, or Jog pushbuttons?

And if so how will they be wired. Some

drives have Contact Closure Only

inputs while other drives have options

of 120v,or 24v


ARE SPECIFIC ANALOG INPUTS

AND OUTPUTS NEEDED?

• Will there be remote speed control and if so what type? Is there a need for analog outputs and how many?

• Some common options are:

• Ohms, 10K potentiometer

• Voltage, 0-10v or -10v/+10v

• Current, 4-20ma or 0-20ma

Drives usually come standard with all of the analog inputs above. 0-10v is usually a standard analog output. Sometimes additional analog option boards are required when multiple analog inputs and outputs are required, or when a current outputs are required.


ENCLOSURE RATING • Panel Mount IP 20(NEMA Type 1)

• Flange Mount IP 20(NEMA Type 1)

• NEMA 4

• NEMA 12


ARE COMMUNICATIONS OPTIONS

NEEDED?

Some communication networks are:

• DeviceNet

• ControlNet

• EtherNetIP

• Modbus, Profibus, P1, Metasys…

Additional options may be needed when drives are

communicating on a network.


WILL DYNAMIC BRAKING BE

REQUIRED?

• If the motor needs to be

stopped abruptly and/or

moves a high inertia load,

dynamic braking options may

be required.

• Full Text LCD with Multiple

language support

• Multiple control options

(or no control)

HUMAN INTERFACE MODULE


HOW FAR APART WILL THE DRIVE

AND MOTOR BE MOUNTED?

• Long motor leads can create conditions such as

Reflected Wave Phenomena and Capacitive

Coupling.

• A good “rule of thumb” is to check the lead length

recommendations in the drive user manual any

time the lead lengths approach 50ft or more.

• There are many different corrective measures and

devices to correct long lead conditions.

TROUBLESHOOTING


HELPFUL MANUALS:

• User Manuals

• Troubleshooting Guides

• Installation Instructions

• Spare Parts Lists

• Manufacturer’s Website


TROUBLESHOOTING TIPS

• Is the problem with the Motor or with the Drive??

• Before assuming the drive is defective, try

disconnecting the motor leads from the drive.

Then run the drive as you normally would, you

should see the drive status on the HIM (Drive

Running, Stopped) If the drive still faults without

the motor connected there is most-likely a

problem with the drive.



• Is the problem with the Motor or with the Drive??

• In the case of reoccurring phase faults, sometimes it is helpful to rotate all three of the motor leads. (i.e. U to V, V to W, and W to U) If the re-occurring fault was a UV short, a bad drive component would have the same fault. If the UV short changes to a VW short, it would appear that the motor has bad windings.



• Is there a problem with the Control Wiring or

with the Drive??

• Before assuming that drive inputs are bad, try

using Jumper wires to manually connect the

appropriate connections on the drive terminal

block. This will ensure that the correct

connections are made in the correct sequence.



• Is there a problem with Parameter Settings??

• In some cases the drive parameter settings can

prevent a drive from running as expected. If incorrect

parameters are suspected, sometimes the easiest solution

is to reset the drive to Factory Defaults and go through the

Drive Startup routine. During the procedure you will run

start the drive from the HIM and ensure that the drive runs

appropriately.



Overvolt Faults

• Overvolt faults occur when the Drive’s DC bus

exceeds safe limits. There are a number of reasons this

can happen including:

• Voltage spikes on the incoming line.

• Excess regenerative braking.

• Reciprocating loads that cause regeneration.

• The first step in determining the cause of an Overvoltage

fault is to determine when the fault is occurring.



Overvolt Faults caused by Voltage spikes on the

incoming line

• If the Overvoltage fault occurs when the drive is not

running and the motor is not spinning.

• If the Overvoltage faults occur at random times

• Check incoming line voltage and verify it is not too high

• 5 to 6 in the morning?



Overvolt Faults caused by Excess Regenerative Braking

• The fault only occurs when the drive is decelerating.

• As the drive decelerates the motor becomes a “generator” and the

power is absorbed by the DC bus. If the load is decelerated too

quickly, it may create too much voltage for the DC bus.

• Try increasing the Decel time and see if the fault still occurs. If

the Decel time must be increased to an unacceptable level, then

Dynamic Braking must be used to achieve the required

deceleration time.



Overvolt Faults caused by

Reciprocating Loads

• If you are turning a load with uneven weight.

• Sometimes the load regenerates on every “downward” swing of the rotation.

• If your load moves back and forth repetitiously.

• Sometimes these loads reach a resonant frequency that causes

line regeneration.

These are both cases where Dynamic Braking may be required.

Why are we using Drives?

• Process Improvement

• Increased Reliability

• Energy Savings

• Extending Service Life of Existing

Systems

30 Second Answers for

the Most Frequently

Asked Questions

• Multiple Motors on Single Drives?

– Independent Overload Protection

– Oversize Drive + 20%

• Over Speeding Motors?

• Minimum Speeds on Pumps?

• Are Energy Savings Real?

• Reactors?

– Up Stream? Downstream?

Biggest “Missed”

Opportunities

• Process Trim

• Flying Start

• Velocity Profiling

Radiate, Emitted & Conducted

Noise

• Ideal Variable Torque Load Phenomenon

Potential

Energy

Savings

Frequency Control

• Cycle Converter 1950s

• Six Step SCR / Drive 1960s

• PWM GTO Drive 1970s

• PWM Bipolar Transistor 1980s

• PWM IGBT Drive 1990s

• PWM 4th Generation IGBT 2000

The Reflected Wave

Phenomenon

• First identified in 1900 with power distribution

lines.

• Also known as Standing Wave or

Transmission Line Effect.

• Well documented in digital communications.

• Coming to the forefront in IGBT based drives.

• Can cause voltage peaks at the motor.

• Presents the possibility for insulation

breakdown.

0

-1

+1

+2

Typical PWM VLL Output

Pulse at the Motor Terminal

IGBT vs. Bipolar

Transistor Current

1336 @ 60HZ NO LOAD

SWITCHING FREQUENCY

1.26KHZ

1336 PLUS @ 60HZ

NO LOAD SWITCHING

FREQUENCY 9KHZ

7.5HP MOTOR

Bi-Polar

IGBT

• The cable between the drive and motor represents a substantial impedance to the

PWM voltage pulses of the drive

• Cable impedance is proportional to length

Inductance / unit length

Capacitance / unit length

• If the cable surge impedance does not match

the motor surge impedance----

– Voltage reflection WILL occur !!

Z 0 =

The Physics of it All

1

1.2

1.4

1.6

1.8

2

2.2

Mo

tor

Over

vo

ltag

e /

V

dc

1 10 100 1000 10000

Cable Distance [ft]

4 us

2 us

1 us

600 ns

400 ns

200 ns

100 ns

50 ns

Semiconductor Risetime

IGBT

BJT

GTO

Predicted Motor Overvoltage

for IGBT’s, BJT’s & GTO’s

• NEMA MG1 Part 31 1600V Motor is Inadequate

• Reduction of 1000 Vpk Motor Insulation Life Accelerated

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Time ( m s)

Pea

k L

ine-

Lin

e M

oto

r V

olt

ag

e (V

PK

)

480 Volt System V LL /V DC = 3 Per Unit

Corona Susceptible Areas 1600 Volts

1000 Volts

480v Reflected Wave Stress - Long

Cable

• Begin Corona

• Not Harmful

• Extreme Corona

• Damaging > 5 - 10pc

Corona Testing

• White Residue

• Phase to Phase W/O Separator

• Turn to Turn

• Drive Typically OL Trip

Effect of Corona

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

• May cause reduction in torque

• Output Filters

– 1204-RWR2

• LR filter

– KLC filters

The Terminator

• Highly Cost Effective

• Smaller

• No Voltage Drop

• Works @ any cable distance

• Maintains current waveform

• 2 - 3 choices fit all applications

• Most effective solution

• Solves multi-motor installations concerns

• Works on all A-B IGBT & BJT drives

Solutions AC Drive

Allen-Bradley 1329 Inverter Duty

Motor AC

Motor

AC Drive

1204-RWR2 Reactor

KLC filter @drive or

AC Motor

Terminator 1204-TFA1 1204-TFB2

@Motor

Non Inverter Duty Motor

After addition of

1204-RWR2

720Vpk @ Motor

660Vpk @ Inverter

Before addition of

1204-RWR2

1180Vpk @ Motor

660Vpk @ Inverter

Plot 2

Before and after the addition of a 1204-RWR2 & 3.0mhy output reactor

1305 3HP 460V 60HZ No-load

300ft shielded cable

After addition of

1321 output reactor

1140Vpk @ Motor

14ms/rise time

Custom Eliminator

• PVC Cable failures on IGBT drives, the conditions were: 12 awg

- wet , steam, Water based lubricant used,

- PVC cold flow problem

• Noise problems are reduced when shielded cable used.

QUESTIONS:

• What insulation type is the best for IGBT drives ?

• What insulation thickness withstands reflected wave

voltage spikes for 20 year cable life?

CABLE OBSERVATIONS

Scale Comparison of Single #12 AWG Conductors

0.045”

0.030”

0.019”

XLPE,

RHW-2

Focus Cable

XLPE,

XHHW-2

Standard Wire

Thickness

PVC 15 mil -

Nylon 4 mil,

THHN

Measured CIV vs. Insulation Thickness

for 600 V Un - Aged PVC & XLPE Insulation

20 00

30 00

40 00

50 00

60 00

70 00

80 00

Pea

k S

inew

ave V

olt

ag

e [

Vpk

]

10 10 0

XLPE & PVC Insulation Thickness [mils]

y = 902 x0.408

y = 2526 x0.290

y = 1255 x0.403

XLPE Extreme Corona

XLPE Begin Corona

PVC Begin Corona

PVC

BEGIN CIV

XLPE EXTREME CIV

XLPE

BEGIN CIV

BEGIN CIV ~ 10 % failures

EXTREME CIV ~ 90 % failures

XLPE is 1.4x better than PVC

Degradation of PVC & XLPE 600V

Insulation under Hi pot and BIL Testing

.0.1 1 100 10

5,000

4,000

3,000

2,000

1,000

0

Measured BEGIN Corona,new & un-aged

Insulation Service Life [Years]

20 mil

XLPE 15 mil PVC

• Hypot Testing: [ 2 * VRATED( eg. 600V) + 1,000 VRMS ] ~ 3,110 VPK

•Basic Impulse Level Testing: [ 1.25 *VPK ] ~ 1.25 * (600V * 1.414) ~ 3,889 VPK

•UL 1569 Recommended test value

• 30 mil XLPE XHHW 3 kVRMS ( 4,240 VPK)

• 15 mil PVC THHN 2 kVRMS ( 2,820 VPK)

Hipot Testing @ 600V

BIL Testing @ 600V

UL 1569 XLPE

UL 1569 PVC

Other Cable Issues Require

Attention.

• Capacitive Coupling.

• Cable charging current.

Problems Identified With

Common Mode Noise

• Non operational

– Control Interface(4-20ma, 0-10V)

• PLC communication errors

• Radiated noise

• Conducted Noise

– Ultra Sonic Sensors

– Temperature Sensors

– Bar Code

– Vision System

– Metal Detectors

L LINK

PHASE A

MOTOR C MOD

Cable Without Shield

Triangular 3 Phase

Power Cable

I SG1 SG C

I SG2

I SG

CHASSIS GND

C MOD

GROUND

WIRE ALL CURRENTS I MUST

RETURN HERE OR HERE G

I G RETURN

Problem: Customer Ground Noise

* Return Path in Ground Through Stray Capacitive Divider (i.e.. Unknown Paths)

* I GND Can Find Its Way Into CNC, PLC, And Computer Grounds

* Conducted Ground Current Customer EMI Noise Problem

Existing Condition: dv/dt

“Noise” Current

70 ns

V LL

Inverter output voltage

6 MHz

I PEAK

Common Mode

Current

I Cdv

dt

Fundamental Problem

MOTOR

CHASSIS

ATTENUATES NOISE WITH

COMMON MODE CHOKE

LEM

LEM

SHIELD CAPTURES NOISE

RETURNING TO DRIVE L LINK

L LINK

+

+

+

GND

COMMON MODE CAPS

Capture and Return Noise

to Source

70 ns

V LL Inverter output voltage

6 MHz

I PEAK

Common Mode

Current

1.5 to 50 us

I PEAK 1/3

200 kHz to 63 kHz SPECTRUM Current With

Common Mode

Chokes

V Ldi

dt Vground Lground

di

dt

What Do Common Mode Chokes Do?

Common Mode Chokes

• Common Mode Chokes Reduce High

Frequency Current To Ground.

• Reducing High Frequency Ground

Potential Difference.

• Reducing PLC Errors & Other

Problems.

i.e.. 20 amps Peak Current with 100 nano

second Rise Time is reduced to typically less

than 5 amps with 5 micro second Rise Time.

Cable Impact on

Conducted & Radiated Emissions

AC Drive

Common Mode

Current Path

PE

EARTH

GROUND

Potential #3 Potential #1

Motor

Potential #2

X O

R U

V

W

S

T

PE

I lg

Motor Frame

I lg

I lg

I lg

I lg

I lg

C lg-c

C lg-m

A

B

C

Vdc

bus

(-)

(+)

Logic

True Earth Ground (TE)

Interface Electronics

0-10V, communication,

4-20ma,sensor, interface, etc

Potential # 4

Tach

Input Transformer

Non - Recommended VFD Wiring Practice

AC Drive

Common Mode Current Path

PE

EARTH GROUND

Potential 4


Motor

Motor PE

GND wire

Potential #2

X O

R U

V

W

S

T

PE

PE

I lg

Motor Frame

I lg

I lg I

lg

I lg

I lg

I lg

C lg-m

A

B

C

Vdc

bus

(-)

(+)

Accidental

Contact of

conduit

Conduit

s

t

r

a

p

Input Transformer

GOOD VFD Wiring Practice

AC Drive

Common Mode Current Path

PE

EARTH GROUND

Potential 4


Motor

Additional

Motor PE

GND wire

Potential #2

X O

R U

V

W

S

T

PE

PE

Motor Frame

I lg

I lg

I lg

I lg

I lg

I lg

C lg-m

A

B

C

Vdc

bus

(-)

(+)

Shielded Cable / Armor

with PVC Jacket

PVC

Input Transformer

BETTER VFD Wiring Practice

AC Drive

Common Mode

Current Path

PE

EARTH GROUND

Potential 4


Motor

Additional

Motor PE

GND wire

Potential #2

X O

R U

V

W

S

T PE

PE

Motor Frame

I lg

I lg

I lg

I lg C

lg-m

A

B

C

Cable / Armor

& PVC Jacket

PVC PVC

Cable / Armor

& PVC Jacket

Transformer

Cabinet Frame

HRG or

SOLID GND

BEST VFD Wiring Practice

• Shielded Input & output keep noise out of ground grid.

6 Apk CM current of 3 output phases

3.6 Apk Current in Braided Shield & Foil

1.6 Apk Current in Insulated PE wire

0.8 Apk Net Ground Current outside of Cable

All traces: 2 Amps / Div 10 microseconds / Div

Measured VFD Currents Showing Cable Effectiveness

in Substantially Reducing Ground Grid Noise.

System Grounding

PE - Power Earth Ground

TE - True Earth Ground

1305 1305

Logic

PE Logic

PE TE

PE Bus PE Bus

TE Bus

1336 Plus

Logic

PE

1336 Plus

Logic

PE TE

1336 Impact 1336 Force

ao

Ground Potential #1 Ground Potential #2

Common Mode Current I ao I

Common Mode Voltage V 1-2

Logic

PE

Logic

PE

PE Bus

System Grounding Scheme

PE Copper Bus

PLC

PE

Drive 4

PE

Drive 3

PE

Drive 1

PE

Drive 2

Cab

inet

Ba

ck P

lan

e

Output Conduit / Armor

M1, M2, M3, PE

W V U

Conduit or

Armor Bond

To System Ground

Noise Current

Return Path

PE

Output Conduit / Armor

L1, L2, L3

Conduit or

Armor Bond

S R T

Improper Cabinet Grounding w/Drives &

Susceptible Equipment.

PE Copper Bus

PLC

PE

Drive 4

PE

Drive 3

PE

Drive 1

PE

Drive 2

Cab

inet

Back

Pla

ne

SR TU V W

PE PE

Common Mode

Current on Armor

Co

mm

on

Mo

de

Cu

rren

t o

n G

reen

Wir

e

Optional PE to Structure

Steel if Required

Output Conduit or Armor

Bond to Cabinet

All Drives

Input Conduit / Armor

L1, L2, L3, GND

Proper Cabinet Grounding w/Drives &

Susceptible Equipment.

STRANDED

NEUTRAL

Cable Construction Can Affect Current Balance In V/Hz Drives

Greater Than 125HP

A

B C

A

B C

CONTINUOS WELDED

ALUMINUM ARMOR

A

B C A

B C

INTERLOCKED

ARMORED

STANDARD

TRAY CABLE EUROPEAN

UTILITY

PVC PVC ARMOR

PVC

A B C A B C

TRAY TRAY ARMOR

Effect of Cable Construction

What is Capactive Coupling?

• In any given motor cable there will be a

certain amount of distributed stray

capacitance.

• Every time the drives’ DC bus voltage

switches at the carrier (or PWM)

frequency it causes current to conduct

through this capacitance.

• These capacitive current spikes then get

reflected back to the drive and measured

by it’s current feedback circuitry.

• THIS IS ALSO REFERRED TO AS

“CABLE CHARGING CURRENT”.

MOTOR WINDINGS

MOTOR FRAME

MOTOR WINDINGS

MOTOR FRAME

CONDUIT

INCIDENTAL CONTACT OF CONDUIT TOBUILDING STEEL

X

X

CMODULE

DRIVE FRAME

LOGIC CMODULE

LOGIC

CMODULE

CMODULE

PE

DRIVE FRAME

Cable Charging Current

Cable Charging Current

• This phenomenon exists for all drives

• 460 volt drives will exhibit this phenomenon to a

greater degree then will 230 volt drives.

• One of the ways to mitigate this effect is by

reducing the carrier (or PWM) frequency to 2

KHz.

• Another mitigation technique is adding a 3 phase

inductor on the output.

• 6 Pulse

• 12 Pulse

• 18 Pulse

• 24 Pulse

• Active Front End

• Liquid Cooled

• Air Cooled

DRIVE TOPOLOGIES


WHAT’S HAPPENING

IN DRIVE DESIGN

• Better

• Faster

• Cheaper

Past

Motor

MARKET ISSUES

& DRIVERS

DC/AC AC/DC

SMPS

dc/dc

EMI

FILTER

Gate drive

PowerFlex 700

Cm

core

• Motor Insulation Failure

Issue

• Motor Bearing Failure Issue

• Common Mode Noise Makes

System User Unfriendly

• Customer Sensor

Misoperation

Line

Reactor Line

Reactor

AB

1204 Insulation Type

• 1000 Vpk

• 1200 Vpk

RWR

1-5

hp

• Noise Issue reduced

• Reflected Wave Issue

addressed With Various

solutions in the Drive.

EMI

Filter

Lower $

DC/AC

AC/DC

new pre

charge

Lower $

SMPS

dc/dc

EMI

FILTER

Gate drive Dynamic

Brake

Insulation Type

• 1000 Vpk

• 1200 Vpk

• 1600Vpk

• 1850 Vpk

Motor RWR

1-5 hp

(Maxima)

Dynamic

Brake

Today’s Hardware is Being Replaced by Software & Improved Packaging

Size Reductions With Increased

Packaging

CE Filter Built In Added Noise Reduction

Built in 7th IGBT Internal Brake Resistor (option)

SIZE REDUCTION - CONTROL

BOARD DENSITY

Smaller Packages with More Functionality

Transistors &

2nd Gen IGBT’s

Duals

3rd Gen IGBT’s

6 Pack

7th IGBT

3rd Gen IGBT’s

6 diodes

6 Pack

7th IGBT

Integrated drivers

4th Gen IGBT’s

6 diodes

6 Pack

7th IGBT

Integrated drivers

Inverter Control

SIZE REDUCTION - POWER

MODULE INTEGRATION

1992 1995 1998 2000+

• Conclusion: Integrated module substantial reduction in radiated noise

Radiated emission reduction [ in dBuV/Mhz ] is a LOG [ Anew / Aold ]

Anew

Aold

Rectifier Diodes,

IGBT’s, brake IGBT

Reducing Radiated Emissions

Radiated emission reduction [ in dBuV/Mhz ] is a LOG [ Anew / Aold ]

Anew

Aold

•Conclusion: smaller board substantial reduction in radiated emissions

lower SMPS frequency and slower FET risetime also helps, no heatsink

Reducing Radiated Emissions

122

Now that they’re saving money,

Can I still sleep at night?

RETROFIT

CONSIDERATIONS

123

RETROFIT SEQUENCE

• Analysis of Existing and Future Customer

Needs

• Analysis of Existing System

• Decision on Existing Hardware

• Obtaining all Parts to Complete System;

Hardware, Software, Communication

Scheme, Service and Training

124

ANALYSIS OF CURRENT

AND FUTURE NEEDS

• Speed and or Torque Regulation Levels

• Speed Range

• Environment

• Communication (Now and Tomorrow)

• Support (Parts, Expertise, Training)

125

ANALYSIS OF FUTURE

NEEDS

• Desired Communications Capability

• General Life Cycle Considerations

• Parts

• Training

• Service

• Obsolescence

126

ANALYSIS OF CURRENT

SYSTEM TYPE

• Mechanical

• Hydraulic

• Eddy Current

• Rotating DC / MG Sets

• DC

• AC

127

REASONS FOR CHANGING

FROM A MECHANICAL DRIVE • Increasing Efficiency(approximately 40%)

• Enhanced Speed Control

• Better Flexibility

• Better Regulation

• Reduced Space Requirements

128

CHARACTERISTICS OF

TYPICAL MECHANICAL DRIVE

• Constant Torque from Low Speed to Midpoint

Speed

• Constant HP from Midpoint Speed to Full

Speed

• Internal Gearbox is the Norm

• Typical AC / DC drive is 1-5 times the HP of a

typical Mechanical Drive

129

HYDRAULIC SYSTEM

• Must Define Speed / Torque Needs

• Hydraulic can and usually does

regulate Torque DC torque regulation

standard but AC requires use of Force

Technology

• Need to Define Physical Constraints

• Potential Energy Savings

130

EDDY CURRENT SYSTEM

• Must Define Speed / Torque Needs

• Eddy Current Torque is outstanding

• Duty Cycle can be critical since Eddy

Current is basically a mechanical not

an electrical system

• Energy Savings must be considered

131

REASONS FOR

CHANGING A MG SET • Inability to Get Spare Parts Economically

• Reduced Operating Cost under Load

• MG Efficiency (Less DC Motor) 72-81%

• DC Drive Efficiency is 98.6%

• Reduced costs at No Load

• MG Losses 10-12%

• DC Losses .6-.7 %

• AC Losses 2.5%

132

MOTOR CONCERNS

• Obtain Nameplate Data

• Frame Size, HP, Armature

Voltage Armature Current, Field

Voltage / Amps, Base Speed /

Max. Speed, Tach Volts /

1000RPM & Blower HP / FLA

• Determine if Regeneration is

Needed

133

DRIVE CONCERNS

• Torque that is really required

• Older Motors could accept greater overload

conditions for longer periods of time

• System may be over powered for Application

• Is Field Voltage Adequate

• Is Speed above Base Speed Required

• Will Motor Commutate Properly

• Is a Generator Involved

134

OPERATOR CONCERNS

•Sequencing

•Reference

135

DC BENEFITS AND

LIMITATIONS

136

Speed - RPM

300

250

200

150

100

50

0

BREAKDOWN TORQUE

FULL VOLTAGE

PULLUP TORQUE

FULL LOAD

TORQUE

1800

1740

rpm

P

E

R

C

E

N

T

T

O

R

Q

U

E

STARTING TORQUE

0

DC ASSESSMENT OF

CURRENT HARDWARE

137

PLS® Bearing

Lubrication System

Cast Iron

Construction

Stator & Rotor Epoxy

Coating

Stainless Steel

T-Drains

Neoprene Lead

Separator

Cast Iron

Conduit Box

V-Ring Slinger

Anti-static

Polypropylene

Corrosion

Resistant Fan

AC BENEFITS AND

LIMITATIONS

A Practical Discussion for the Real

World

Capacitors & Drives

Power Factor Improvements

The Pros & Cons of:

–Power Factor Correction Capacitors

–Variable Speed Drives

You Pay for Power Factor

• Power Factor

–Charge or credits (depending on the power factor)

•Charged if power factor is below 85%

•Credited if power factor is above 95%

Power Factor

• What is Power Factor?

–Power factor is the ratio between active power (KW) and total power (KVA)

•Active power does work

•Reactive power produces an electro-magnetic field for inductive loads.

PF(%) = KW ÷ KVA x 100

Power Factor as a Cost

(In phase with line voltage)

Your Total True Cost

Real Work Power Factor

-.5

-.6

-.7

-.8

-.95

Unity

Total PF = PF (Displacement) * PF (Distortion)

• Displacement power factor

– PF (displacement) = Ireal / I fundamental

– involves only the fundamental quantities

– includes the real and reactive currents

• Distortion power factor

– PF(distortion) = I fundamental / I total

– includes the fundamental and harmonic currents

Displacement Power Factor


Fundamental Current

Real Current

Reactive Current

Distortion Power Factor


Total Current

Fundamental Currents

Harmonic Currents

What are the benefits of Power Factor Improvement?

• Less KVA (apparent) same KW (real work)

• More KW same KVA demand

• Better Voltage Regulation

• (K Factor)

–Reduction in size of transformers, cables and switchgear in new installations

• Reduced Losses in Distribution System

K Factor

• An IEEE method of Rating I2R losses and Survivability

– >K=> I2R

– Nonlinear loads increase Eddy Current (Apparent) losses in Transformers

• Magnetic Structure is Enhanced

• De-Rating Transformers

– Increases Available Fault Currents

– Decrease Effective Load

– High Cost

What can change our Power Factor?

• Capacitance

• Load Characteristics

• LRC Tank Circuits

– Inductive, Reactive (resistance), Capacitive Circuit

•Tuned Filter Traps

•Harmonic Filters

•Active or Passive Filters

Remember “Reactive” Power

• Electro-magnetic field for inductive loads –Capacitors, rated in (KVAR)

•Reduces the amount of Reactive Power the Utility must supply for Inductive Loads

– Inductive/Capacitive Relationship

Changing Your Power Factor

• Capacitance

–Flexible Configuration

–Proven & Simple

–Automatic “Switching” Banks

•Can create disturbances

–Location

•Capacitors effect the Upstream…

Capacitor Location?

Utility

Distribution

Infrastructure

Metering Service

Entrance

MCC


• Load Characteristics

– Lightly Loaded Inductive Loads

• Transformers

–Remember K Factor Concerns

•Motors

–Increase % Load

–Decrease Inductive Value

–Use a Variable Speed Drive


• Hybrid Tank Circuits

–Location Sensitive

•Typically Service Entrance

–Power Factor Correction is Side Effect

•Generally Applied for Multiple Symptoms

–New, Advanced Technology

•Dynamic Marketplace

Variable Speed Drives

• Located at Motor

–The VFD is a Capacitor

VFD as the Big Payoff

• Exponential Reduction in Consumed kW

–Variable Torque

•Fans & Pumps

–“Variable Torque” Characteristics

•Systems that Cycle

–Throttled Loads

•Restricted Flows

POWER QUALITY

CONSIDERATIONS

Harmonics and Noise for

those on a “low geek” diet

A Functional Understanding


REMOVING THE

MYSTERY

• Harmonics

• Defining the common terms

• The biggest hazard

• Financially prudent mitigation

• Displaced Neutral Voltage*

• AKA….

• Easy ways to stop the damage

• Common Mode Noise*

• The “real” harmonic issue

• Creation, Symptoms and Mitigation

• Grounding

• The copper connection rule..


HARMONICS: DEFINITIONS

• IEEE 519

• This guide applies to all types of static power converters used in industrial and commercial power systems. The

problems involved in the harmonic control and reactive compensation of such converters are addressed, and an

application guide is provided. Limits of disturbances to the ac power distribution system that affect other

equipment and communications are recommended. This guide is not intended to cover the effect of radio

frequency interference.

• Date of Publication : April 9 1993 Status : Active Page(s): 1 - 112 E-ISBN : 978-0-7381-0915-2 Sponsored by :

IEEE Industry Applications Society INSPEC Accession Number: 4441390 Digital Object Identifier :

10.1109/IEEESTD.1993.114370 Persistent Link: http://ieeexplore.ieee.org/servlet/opac?punumber=2227

More »

Year : 1993 Date of Current Version : 06 August 2002 Issue Date : April 9 1993 Related Information : An Errata is

available

Revision of ANSI/IEEE Std 519-1981

http://www.ewh.ieee.org/soc/ias/pub-dept/options.html

http://dx.doi.org/10.1109/IEEESTD.1993.114370

http://ieeexplore.ieee.org/xpl/opac.jsp

http://standards.ieee.org/reading/ieee/updates/errata/519-1992_errata.pdf

http://standards.ieee.org/reading/ieee/updates/errata/519-1992_errata.pdf

http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=2541



Harmonic Estimator Report - One Line

Project Name WTF Consolidation Project Prepared by Robin Priestley

End User City of Iowa City Date prepared 1/22/2014

Customer ESCO email of preparer [email protected]

notes Stanley Consulting SP1 w DG1

version 050519P Notes:

PCC is a Point of Common Coupling

A "buffered drive" is one that has a DC Link Choke

A "xfmr" is a transformer

All of the values are recalculated when cell data is entered

Source

60 Hz Linear Load 1 on utility xfmr (hp+kW+A) 0 set Ifund load

0 total hp motor loads on utility xfmr to

PCC1 PCC2 PCC3 + 0 total kW resistive loads this % of Irated 1

PCC at utility xfmr PCC at user xfmr PCC at distribution panel + 0 additional Amp loads

Linear Load 2 on user xfmr (hp+kW+A) 0 set Ifund load

100 feet 1 50 feet 2 51.75 total hp motor loads on user xfmr to

Utility feet between User feet between Distribution + 0 total kW resistive loads this % of Irated 2

Transformer utility xfmr Transformer user xfmr and Panel + 90 additional Amp loads

or Generator and user xfmr distribution panel 6 pulse unbuffered drive without line reactor

750 kVA 1 300 kVA 2 total hp

3.00 %Z 1 5.75 %Z 2 50 feet to panel 100.0 % load

12470 Vsec 1 480 Vsec 2 480 Vsec 3 6 pulse buffered drive without line reactor

- OR - 0 Isc 1 - OR - 0 Isc 2 0 total hp

at PCC1 at PCC2 at PCC3 100 feet to panel 100.0 % load

750 kVA 1 300 kVA 2 6 pulse buffered drive with 3% line reactor

35 Irated 1 361 Irated 2 49.5 total hp

1158 Isc 1 6276 Isc 2 6002 Isc 3 100 feet to panel 100.0 % load

16499.2 L, uH 1 117.1 L, uH 2 5.3 L, uH 3 6 pulse buffered drive with 5% line reactor

1.3 K-factor 1.3 K-factor 0 total hp

22.2 % Irms total to Irated 55.5 % Irms total to Irated 100 feet to panel 100.0 % load

22.3 % thermal rating 55.8 % thermal rating 6 pulse buffered drive with basic harmonic filter

0.6 Irms harmonics 15.7 Irms harmonics 15.7 Irms harmonics 0 total hp

7.7 Irms fundamental 199.5 Irms fundamental 199.5 Irms fundamental 100 feet to panel 100.0 % load

7.7 Irms total 200.1 Irms total 200.1 Irms total 12 pulse buffered drive with auto xfmr

0 total hp

150.7 Isc/Iload 31.5 Isc/Iload 30.1 Isc/Iload 0 feet to panel 100.0 % load

0.3 % V(THD) Limit 2.0 % V(THD) Limit 2.1 % V(THD) Limit 12 pulse buffered drive with iso xfmr

7.9 % I(TDD) 15.0 7.9 % I(TDD) 8.0 7.9 % I(TDD) 8.0 0 total hp

YES IEEE special (3% Vthd) YES IEEE special (3% Vthd) YES IEEE special (3% Vthd) 0 feet to panel 100.0 % load

YES IEEE general (5%Vthd) YES IEEE general (5%Vthd) YES IEEE general (5%Vthd) 18 pulse buffered drive with auto xfmr

YES IEEE dedicated (10% Vthd) YES IEEE dedicated (10% Vthd) YES IEEE dedicated (10% Vthd) 0 total hp

0 feet to panel 100.0 % load

18 pulse buffered drive with iso xfmr

Design Checks: (blank if no issues) Cell Key: 0 total hp

data entry 0 feet to panel 100.0 % load

intermediate calc Custom Ifund at FL

100.0 % load

harmonic results

Before using this for the first time, go to the worksheet tab labeled "Tutorial"

For help and additional information, go to the worksheet tab labeled "Notes & Tools"

M

M

M

M

Mfilter

MIso

MAuto

MIso

MAuto

M

M

No

n-L

inear

Dri

ve L

oad

Please note that the information shown here is typical and does not constitute any guarantee of performance or measurement. Several outside factors can influence the harmonics measured on a power system, including other equipment within the plant and other equipment in neighboring plants. This can include, but is not limited to, drives, varying loads and/or other factory equipment.

The calculated current and voltage harmonics shown in this report are for estimation purposes only.

IEEE 519 INTENTIONS



• Fundamental Frequency

• Native frequency, cycles per second (CPS), Hertz (Hz)

• 60 Hz in America, 50Hz in Europe

Rfund.V =...

0

0

40.00m

40.00m

10.00m

10.00m

20.00m

20.00m

30.00m

30.00m

-150.0 -150.0

150.0

0 0

-100.0 -100.0

-50.0 -50.0

50.0 50.0

100.0 100.0



• Harmonics are multiples of the Fundamental Frequency

• 5th Harmonic is 5 x 60Hz = 300Hz

• 7th Harmonic is 7 x 60Hz = 420Hz

• Full spectrum to 127th harmonic

• Discontinuous Loads

• Solid State “switching” power supplies

• Lighting ballasts, computers, variable speed drives

• Greatest disturbance: One up/One down

• 6 Pulse drive

• 5th, 7th primary disturbance then 11th, 13th followed by 17th, 19th

• 12 Pulse drive

• 11th, 13th; then 23rd, 25th


HARMONICS: POP QUIZ

• An 18 Pulse drive’s greatest impact

can be measured at which

harmonics?

• _____th and _____th


SO? WHAT ARE WE REALLY

TALKING ABOUT?

Rfund.V =...

0

0

40.00m

40.00m

10.00m

10.00m

20.00m

20.00m

30.00m

30.00m

-150.0 -150.0

150.0

0 0

-100.0 -100.0

-50.0 -50.0

50.0 50.0

100.0 100.0


START OFF CLEAN, ADD THE HARMONICS AND

PRESTO!

YOU NOW HAVE THE “CAMEL’S HUMP”

Rfund.V =...

0

0

40.00m

40.00m

10.00m

10.00m

20.00m

20.00m

30.00m

30.00m

-150.0 -150.0

150.0

0 0

-100.0 -100.0

-50.0 -50.0

50.0 50.0

100.0 100.0


OK, BIG HARMONICS =

CAMEL’S HUMP

• Heat is the big hazard

• 100 amp load (fundamental current 100 amps)

• 5% current (THD) total harmonic Distortion (5 amps)

• Current you didn’t pay for or use for work

• Current you didn’t measure

• Added heat and losses to your distribution system

• How much do you spend to eliminate the camel’s hump?

• When should you be really concerned?


MOST “HARMONIC”

PROBLEMS ARE NOT

HARMONICS!

• Displaced Neutral Voltage

• AKA “Shaft Bearing Currents” , “Common Mode Noise (CMN)

• Fluted Bearings

• “drifty” transducers

• “flakey” sensors

• “everything is fine until the drive is turned on”

Before you take any measurements,

troubleshoot anything or spend any

money, (Except for PowerFlex Drives):

Understand your ground system!

There are many like it but

this one is yours!

Installation Considerations for AC Drives

Line Transients/Sags

Grounding

&

Bonding

Common Mode &

Capacitive Coupling

Reflected Wave

The 99% of issues you

thought were harmonics

GROUNDING

CONSIDERATIONS

TODAY’S RESEARCH

• What would an internet search reveal?

• “There is only one choice”

• High Resistance Ground

• Transients

• Locating Faults

• Fault Damage

• Personnel Safety

• Coordination

• First Fault

ROBIN’S REBUTTAL

• Why is the information so consistent?

• If HRG increases safety exponentially, why

isn’t it mandated?

• Why do so many organizations still use:

• Ungrounded

• Solidly Grounded (Effectively Grounded)

• Why is low voltage safer in your home now?

FAULT STATISTICS

• 98% of faults are phase to ground

• Detection and response is far more important than available current

• Phase to phase 1.5%, 3 phase 0.5%

• Arcing faults are discontinuous

• Strike, extinguish and strike again

• Provides time for protection to work

THIS IS AN OPEN DISCUSSION

ZIGZAG (WYE-DELTA) AKA

INTERCONNECTED STAR OR STAR

DELTA

• Unusual

• Requires short term transformers

• 10 to 60 second ratings

• Better suited to generator sets and

prehistoric MV systems

UNGROUNDED

• Significant advantages do exist

• Safety, production, Limits damage

• Requires

• Discipline

• Consistency

• Modification for VFD and some other systems

UNGROUNDED

• Principle Benefits

• Low value of current flow and reliability during a fault (<5 amps is industry expectation)

• Ensures production through first fault

• Low probability of line-to-ground arcing fault escalating to phase-to-phase or 3 phase fault

UNGROUNDED

• Claims I can not substantiate

• Substantial Over Voltages

• Sputtering Faults

• “Produced in Laboratory Tests”

• Drives see no difference between Ungrounded and HRG. Modifications are required.

HIGH RESISTANCE

GROUND

• Lowers incident energy levels

• Not enough in most cases

• Coordination still required and more effective

• Personnel injury will still occur unless PPE and other measures are in place and used.

• Reduces ground fault current

• Modification for VFD and some other systems

HIGH RESISTANCE

GROUND

Clamps ground fault current at lower

level and may change time base

• May eliminate the ability for

Variable Frequency Drives to

detect ground faults.

• This can allow greater damage

to infrastructure. (example)

HIGH RESISTANCE

GROUND


• Eliminates or marginalizes protective

systems

• Lightning arrestors

• TVSS

• Distribution

• VFD

HIGH RESISTANCE

GROUND


• Eliminates low impedance path for noise

• Encoders

• VFD signal common and VCC

• Communication networks

• Displaced neutral voltage

• High frequency

sources that can

cause Nuisance

tripping and

alarms:

• VFD

• Servo

• Encoders

• Ultrasonic

Measurement

• SCR

• DC Drives

• Heating

• Electron Beams

HRG & HIGH FREQUENCIES

SOLIDLY (EFFECTIVELY)

GROUNDED

• Still preferred by utilities

• Eliminates transient voltages that cause intermittent ground faults

• Stabilizes the neutral voltage

• Prevents elevation of phase to ground voltage

• Faults are easily located

• Can supply line to neutral loads


GROUNDED

• Arc and stray path current

• Limited only by the impedances

which are small

• Result is a short term fault

• Current level is high enough to

permit ground fault protection to

function


GROUNDED

• Arc flash

• All shorts cause an arc

• All arcs release energy as heat and light

• Mitigation is mandated

• Coordination

• PPE

Questions and discussion

WE HAVE ONLY SCRATCHED THE

SURFACE

UTILITY POWER, THE BEST KEPT

SECRET CAUSING

MANUFACTURING DOWNTIME

John McWeeney Regional BDM

19

4

DEFINITION OF A “POWER GRID”

Merriam-Webster

A network of electrical transmission lines connecting a

multiplicity of generating stations to loads over a wide area


GRID OVERVIEW

Source: Department of Energy

19

5


POWER QUALITY VS.

POWER RELIABILITY

Power Quality: Related to fluctuations in electricity, such as momentary

interruptions, voltage sags or swells, flickering lights, transients, harmonic

distortion and electrical noise

Fewer such incidents indicate greater power quality

Events go mostly untracked by Utilities

Power Reliability: Continuity of electric delivery measured by the number and

duration of power outages (Zero voltage)

Outages are tracked by Utilities

Power can be as high as 99.999% reliable

Remaining 0.001% can take out a process as many as 20-30 times per year

19

6

The Grid is designed for Reliability, not Quality…


EPRI (ELECTRICAL POWER RESEARCH INSTITUTE)

Monitored 300 sites for 2+ years.

• 1993 Data Showed 92% of all events were voltage sags

under 2 seconds in duration

• Second study in 1995 verified initial study, but showed

that almost 96% of all events were power sags less than 2

seconds

• A typical site experienced 20-30 significant voltage sags

per year

• Today PQ monitoring shows that now 98% of all events are

sags of less than 2 seconds

How Often is it Only a Sag?

IMPORTANCE OF POWER

QUALITY

Power quality events are mostly random

Utility side: Weather, animal / trees hitting

power lines, car accidents, construction,

equipment failure

Facility-side: Starting of large loads – motors,

poor electrical connections, Customer

equipment (arc welders)

Impact on production

Shut down equipment: voltage sags with as

little as 80% remaining can impact production

(lights may not blink)

Immediate or long-term damage to sensitive

electrical equipment

Consumer is responsible for power quality

Utility is responsible for power reliability Consumer is responsible for protecting their sensitive equipment

19

8


VOLTAGE SAG (DIP)

CHARACTERIZATION

• Sag - RMS voltage reduction between 1/2 cycle - 60 sec

• Magnitude and Duration

19

9

-1

-0.5

0

0.5

1

0 1 2 3 4 5 6 7 8

Duration: 4 Cycles

Magnitude: 60% Remaining

-35%

-70% -25%

The depth of your sag is proportional

to the distance you are from the event

What is the result of fault?

1. When a short occurs, voltage sags until the re-closer trips

2. Voltage sag severity depends on user distance from fault and location of fault on grid

3. Control equipment does not like voltage sags!

Sag = Variation below nominal RMS voltage

of 10-90% with a duration ½ cycle to 1

minute


THE MOST COMMON

EVENT: VOLTAGE SAG

Sag - RMS voltage reduction between 1/2 cycle - 3 sec

Magnitude - % Remaining

20

1

*Source: EPRI

20

2

Magnitude Duration

Power Quality Report Summary

Variable Frequency

Drives Review

Safety

• Don’t sue or call Human Resources

– Lock out tag out

• Never work on energized circuits

– Verify condition with Test Instrumentation

• Test the instrument prior to and after measurement

– Observe all applicable Safety Regulations

Including yet not limited to State, Federal,

Local guidelines

Basic Drive Components

• Draw A Basic AC Drive

• Describe what the components are

responsible for

PWM Drive Theory

Drive Rectifies the

Incoming AC voltage.

Section known as:

CONVERTER

RECTIFIER

“FRONT END”

Drive STORES

The DC Voltage.

Section known as:

STORAGE

BUS CAPACITORS

DC BUS

Drive INVERTS The DC

Voltage into a wave

The motor interprets to be a

sine Wave. Section known as:

INVERTER

Output Section

AC Drive’s Output? Voltage is a DC Square Wave made up of

pulses of various widths

Motor INDUCTANCE causes the current

wave shape to be sinusoidal

What does PWM Stand for?

DV/DT Spike

• What causes it?

• Who does it affect?

• What are the concerns with cable

distance?

AC Drive’s Output?

That is the dv/dt

spike.

D (delta) or change

in the Voltage

divided by the

change in Time

Shorter the time…

Bigger the spike

dv/dt Spike

• All transistors (switching power

semiconductors) create noise

– Not brand specific

• When is the Wave Reflected

– How can that be solved

• Terminator

• Impedance matched motor

• Standing Wave….

AC Line Reactor vs DC Link

Inductor

• Generally used to reduce Harmonic

Disturbances created by the drive

• Provides Impedance upstream of the drive

– Especially helpful with very large transformers

and small drives

• Magnetic structure rounds over (increases

time base) of disturbance

– Structure is developed by current

Reactor Attenuation

Time Base Time Base

AC Line Reactor vs DC Link

Inductor

• Basic difference in Magnetic Structure

– AC Line Reactors use current

– DC Link Inductors use Voltage

• Advantages of DC Link

– Magnetic Structure is fully developed anytime the

drive is energized.

– DC Link is effective regardless of load

• What does the DC Link not do

– Cannot protect a Drive from Line Disturbances

DC Link’s effect on the Dv/Dt

Time Base Time Base

Motor Theory

• List major differences between a Good

Inverter rated motor and Premium Efficient

Designs

• Multiple motor applications require what

additional components

• Insulation testing should be conducted at

what levels

Regulators

• Describe the basic differences between

V/Hz and Vector Regulators

– Volts “per” Hertz is a fixed ratio of Voltage to

Frequency

– Vector regulators are dynamic. They change

based on load and motor charactoristics

• Can be tuned

• Too smart for multiple motor applications

Common Mode Noise

• What creates CMN? – Anything with a Switch Mode Power Supply

• What are symptoms of CMN? – Devices connected to Neutral are affected when the

drive is energized

– Bearing Current

• How can CMN be detected? – Clamp on ammeter

• PowerFlex Drives combat CMN with what components or design features – CM Bus Caps, CM Magnetic Cores (CM Chokes)

Parameters

• Describe the Use or Value of:

– Programmable relays

– Flying Start

– PID loops

– Sleep Mode

Programmable Relays

• What basic functions are programable

• How many selections are available

• Describe 3 applications where the relays

could be employed

“Typical” Failures

• Converter faults relate to?

• Inverter faults relate to?

• What is the simple way to

determine health of drive

Energy Savings

• Drives have unity power factor

–Power factor is the ration of KW to KVA

• Remember Work (Torque) to Apparent (Magnetism)

–Drive can consume less current than the motor

• Affinity Laws

–Energy increases with the cube of Speed



Your “Apparent” Consumption

IE: Required Generation Capacity

Real Work

“Billed KWh”

Power Factor

Lagging PF

+20%

+10%

Standard

-10%

-25%

Unity PF



Power Factor

Lagging PF

+20%

+10%

Standard

-10%

-25%

Unity PF



Real Work

“Billed KWh”



Power Factor

Lagging PF

+20%

+10%

Standard

-10%

-25%

Unity PF

Real Work

“Billed KWh”



Energy

Consumed

Speed

Affinity Law

In Variable Torque “Ideal” Loads:

Energy Increases exponentially with speed

Energy Consumed = (speed)3

Consumption reduction

=(Speed reduction

)3

100 kWh Motor @ 50% Speed:

What does it Cost?

Er=(1/2)3

Now, how many rural

applications can you

think of?

List them on the critique sheet for

a “special” professional

development award

Robin Priestley

Power Control Manager

[email protected]

563-343-8862 © 2014 Robin Priestley & Rockwell Automation

mailto:[email protected]


MOTOR BEARING CURRENT

SOLUTIONS

• Background / Why is this an Issue?

• Bearing Damage / Failure Mechanisms

• Sine Wave Shaft and Bearing Currents

• Common Mode Voltages / Currents

• Solutions

• Measurements

• Conclusions


BACKGROUND

Q: Since bearing currents in

rotating machinery have been

documented for at least 90

years, why is this a

contemporary issue?


BACKGROUND

Q: Since bearing currents in rotating machinery have been documented for at least 90 years, why is this a contemporary issue?

A: Modern PWM inverters create both common mode voltages (CMV) and common mode currents (CMC) which provide new opportunities for current to flow through rotating bearings (along with couplings, gears, etc)


BACKGROUND

While the 90 year old sources of bearing

currents are well understood and

solutions exist, it is important to keep

them in mind to avoid resurrecting them

in trying to solve the challenges brought

on by common mode voltages and

currents.

BEARING DAMAGE /

FAILURE MECHANISMS

Fluting in outer race, from

prolonged operation after

damage from current flow

Individual arc damage spots

BEARING DAMAGE /

FAILURE MECHANISMS

Fluting on inner race, from prolonged

operation after damage from current flow Fluting in outer race


BEARING DAMAGE /

FAILURE MECHANISMS

• Interrupted current causes melting and

“re-hardening” of the race material,

creating untempered martensite, which is

brittle and prone to fatigue


BEARING DAMAGE /

FAILURE MECHANISMS

• Interrupted current causes melting and “re-hardening”

of the race material, creating untempered martensite,

which is brittle and prone to fatigue

• The normal bearing loads are then capable of breaking off

small pieces of this brittle material

• Subsequent running on this brittle surface and in the presence

of the damage “trash” material creates the “fluting”


BEARING DAMAGE /

FAILURE MECHANISMS

• If the damaged material does not progress to a fluted pattern

from subsequent running, two other patterns may be seen

• A “frosted” surface may appear, or

• A number of “pits” may be visible under

high magnification

• The verification of current flow as the root cause requires

more than visual inspection


BEARING DAMAGE /

FAILURE MECHANISMS

False Brinnel Damage with

Appearance of Fluting


BEARING DAMAGE /

FAILURE MECHANISMS

False Brinnel Damage

with Appearance of

Fluting


SINE WAVE BEARING

CURRENTS

• “If it were possible to design a perfectly

balanced and symmetrical machine, both

theory and practice indicate that no

bearing current could exist” - C. T.

Pearce, Bearing Currents - Their Origin

and Prevention, The Electric Journal,

August 1927.


SINE WAVE BEARING

CURRENTS

• Alternating flux “linking” the shaft …

• Net flux encircling the shaft is typically

due to asymmetric magnetic properties of

stator or rotor core

• Bearing current created by transformer

action in “single turn” secondary (shaft,

bearings, frame)


SINE WAVE BEARING

CURRENTS

Boyd and Kaufman, 1959

Shaft

Flux path


SINE WAVE BEARING

CURRENTS

• Currents flow thru shaft, bearings, endshields, and frame

• Axial voltage on shaft can be measured if a bearing is insulated (IEEE Std 112 - 1996)

• Small shaft voltage (500 mV) can lead to bearing currents above 20 amps

• Bearing damage is more likely to occur in larger machines


COMMON MODE

VOLTAGE / CURRENT

• Modern PWM drives create switching patterns

where instantaneous average voltage to ground

is not zero.

• Voltage has a rapid change of magnitude with

respect to time (dV/dt)

• High dV/dt results in capacitively coupled

currents from motor windings to ground

through several paths

I = C x dV/dt

COMMON MODE

VOLTAGE / CURRENT

PHASE

VOLTS

CMV


COMMON MODE

VOLTAGE / CURRENT

HIGH FREQUENCY CURRENT PATHS

I = C X DV/DT


COMMON MODE

VOLTAGE / CURRENT

BEARING CURRENT RELATIVE

MAGNITUDE

30

30.5

0

10

20

30

40

Stator Winding to

Frame/Shaft

Discharge dv/dt Charging

Peak A

mps T

hro

ugh B

earing


COMMON MODE VOLTAGE

/ CURRENT

HIGH FREQUENCY CURRENT PATHS


COMMON MODE

VOLTAGE / CURRENT

HIGH FREQUENCY END-END

CIRCULATION


COMMON MODE

VOLTAGE / CURRENT

ROTOR DISCHARGE CURRENT


COMMON MODE VOLTAGE / CURRENT

HIGH FREQUENCY CURRENT

PATHS –

CAPACITIVE CHARGING OF

ROTOR / BEARING

+

-

VCM

Bearing Frame

CSF CRF Cb

Stator Winding Rotor

+

-

Bearing Voltage : Vb = Csr

Csr + Cb + Crf VCM

CSR


COMMON MODE

VOLTAGE / CURRENT

ROTOR DISCHARGE CURRENT


COMMON MODE VOLTAGE /

CURRENT

TRANSIENT FRAME VOLTAGE

DISCHARGE


COMMON MODE

VOLTAGE / CURRENT

BEARING CURRENT RELATIVE

MAGNITUDE

30

30.5

0

10

20

30

40

Stator Winding to

Frame/Shaft

Discharge dv/dt Charging

Peak A

mps T

hro

ugh B

earing


BEARING CURRENT

SOLUTIONS

• Eliminate or reduce common mode voltage

/ current (Drive design issue)

• Create best high frequency ground paths

between drive, motor, and load

• Electrostatic shielded induction motor

• Insulated bearings

• Shaft grounding brush


BEARING CURRENT SOLUTIONS

INSULATED OPPOSITE DRIVE-

END BEARING FOR

CIRCULATING TYPE CURRENTS



INSULATED OPPOSITE DRIVE-END

BEARING AND DRIVE-END SHAFT

BRUSH

(BEARINGS IN COUPLED EQUIPMENT STILL AT PERIL)



INSULATED OPPOSITE DRIVE-

END BEARING, DRIVE-END

SHAFT BRUSH, AND COUPLED

EQUIPMENT BOND STRAP



TWO INSULATED BEARINGS,

DRIVE-END SHAFT BRUSH, AND

COUPLED EQUIPMENT BOND

STRAP


BEARING CURRENT

SOLUTIONS – FARADAY

(ELECTROSTATIC) SHIELD

• Add grounded conductive layer between

stator and rotor

• Eliminates stator to rotor coupling

• Will not eliminate stator winding to frame

coupling

• Still need good high frequency ground current path from

motor to drive ground



FARADAY SHIELD TO PREVENT ROTOR

CHARGING / DISCHARGING (BEARINGS

STILL AT PERIL FROM TRANSIENT FRAME

VOLTAGE DISCHARGE WHEN SHAFT IS

CONDUCTIVELY COUPLED TO GROUNDED

EQUIPMENT)



FARADAY SHIELD

AND COUPLED EQUIPMENT

BOND STRAP


BEARING CURRENT

SOLUTIONS

• Internal, end-end from magnetic

asymmetry

Insulate opposite drive-end

bearing

Insulate both bearings


BEARING CURRENT

SOLUTIONS

• Shaft Extension Current (stray ground current)

Insulate coupling

Insulate bearings

Bond strap from motor to load

Better low impedance ground in cable from

inverter to motor


BEARING CURRENT

SOLUTIONS

• Discharge of voltage on rotor

Faraday (electrostatic) shield

Shaft brush


BEARING CURRENT

SOLUTIONS

• Precautions

NO opposite drive end shaft brush with

single opposite drive end insulated bearing

Beware of shaft brush option in opposite

drive end encoder


MEASUREMENTS

(VOLTAGE)

Common

Mode

Voltage

Shaft

Voltage

250

V/div

12.5

V/div


MEASUREMENTS

(CURRENT) INTERNAL END-END

CIRCULATION

2 A/div


MEASUREMENTS

(CURRENT)

Common

Mode

Current

2A/div

(both).

Ground

Conductor

Current


MEASUREMENTS

(CURRENT)

Shaft

Extension

Current (30 Amp Pulse)


MEASUREMENTS

• Other than internally-sourced circulating

currents, all data is at high frequency

• Data tends to be non-repetitive

• Oscilloscope triggering technique

strongly influences perceived results


CONCLUSIONS

• Current flow in rotating bearings is not

new

• Common mode voltages and currents

from modern inverters can cause current

flow through bearings (plus couplings,

gears, etc)


CONCLUSIONS

• Corrective actions are dependent upon

the particular type of current flow

• Transient (high frequency) nature of the

voltages and currents imposes different

requirements than traditional 60 Hz

waveforms


CONCLUSIONS

• Since the sources of the currents as well as

the paths are typically outside the machine

whose bearings are taking the hit, a thorough

understanding of the system is key

• Grounding is important, but more in the sense

of point to point (low impedance) “bonding”

rather than “earthing”


COATED / INSULATED

BEARINGS


“CONDUCTIVE” GREASE

While the notion of a conductive grease as a solution may sound

appealing, the electrical behavior of bearing lubricants is not as

simple as "insulating" versus "conducting." Both the behavior of

the grease in bulk as well as the behavior of the thin oil film

separating races from rolling elements is strongly dependent on

external influences, including the presence of a voltage. As a

result, the current and voltage characteristics seen in a rotating

bearing are not simply described by a resistive value. In fact, it is

not simply described by a combination of fixed resistors,

capacitors, and other circuit elements. It has a "memory" effect,

based on past applied voltages and current flow, as well as

behaviors that may best be described as "stochastic."


“CONDUCTIVE” GREASE

• Different greases can have varying electrical

characteristics, based on their chemical composition, but

still would have the "inconsistent" behavior as described

above.

• Any proposed grease would obviously need to not

degrade the "normal" properties expected in a bearing.

• The conclusion of the points above is that a change to a

grease with different electrical properties is not a solution

to the basic problem of bearing currents (for neither VFD

nor line-fed motors).


SHAFT VOLTAGE ?


SHAFT VOLTAGE (NOT!)

INVERTER DRIVEN

INDUCTION MOTOR

BEARING CURRENT

SOLUTIONS

QUESTIONS ?

variable frequency drives: applications and power quality

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