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VFD/Motor Compatibility,

Harmonics, Upgrading an

Existing System – Retrofits

Presented for WMEA by

Jim Wilson, Yaskawa Electric America

November 18, 2015

Why Retrofit Existing Systems

With VFDs?

If you are Controlling Temperature,

Pressure or Flow with a Valve, Vane or

Damper…

You have an Opportunity to Improve

Process Control and Significantly

Reduce your Power Consumption.

20% Reduction in Speed Results in

50% Lower Energy Consumption.

VFD / Motor Compatibility


Inverter Duty Motors

NEMA MG1-31.4

Windings Designed for =/>1600V Peaks


Long Motor Lead Length

Countermeasures

* Minimize Conductor Length

* NEMA MG1-31.4 Inverter Duty Motor

* Output Line Reactor

* Reactor at the Motor

* Motor Protecting Output Filter


PWM Voltage Rise Times generally from .1 to .3ms

referencing the formula

Surge Voltage can Appear at 52 to 156 feet

Keep Motor Lead Lengths under 150 feet

Note – Long Motor Lead Lengths are only an issue for 480vac Systems


NEMA MG1-31.4 Inverter Duty Motor

Simplest and Most Cost Effective Solution:

“Inverter Duty Motors shall be designed to

withstand 1600 Volts Peak and Rise Times

of Greater or Equal to .1ms on Motors

Rated less than 600 Volts RMS.”

Applying Motors that meet this standard will

afford the user years of error free operation

at virtually any motor lead length.


Output Line Reactor

Cost effective solution when applying VFD to

an existing non NEMA MG1-31.4 Motor

Reliable Operation to 300 feet Lead Length

Installed at VFD Output Terminals, also

protects 600V Motor Leads


Reactor at the Motor

Positives:

Allows Lead Lengths up to 650 feet

Negatives:

Reactor Deteriorates over Time

Does not protect 600V Wire


Motor Protecting Output Filter

* Insures Error Free Operation to 2000 feet

* Designed to Strip High Frequency Component

from the PWM Output

* Reduces Voltage Rise Time to approx 1.2ms

Waveform at 1000’ with Output Filter… And at 1000’ Without Filter

Minimum Motor Speed

• MMS (Turndown Ratio) is a function of motor

design, ambient temperature, and MOSTLY

driven device limitations.

• For fans and pumps, minimum motor speed is

usually 20-30% of full load.

• Under low ambient conditions, VFD and motor

are not the limiting device.

Shaft & Bearing Pitting

• In general, with proper grounding, continuously variable

applications do not suffer from shaft & bearing pitting.

• Fixed frequency for sustained periods of low speeds may

lead to bearing failure

• Proper Grounding, Shaft Grounding Kits and Insulated

Bearings will prevent this failure.

200 V class: ground to 100 Ω or less

400 V class: ground to 10 Ω or less

Bearing Protection Ring

Ceramic Bearings

http://www.est-aegis.com/shaft-grounding-brush.htm

http://www.est-aegis.com/shaft-grounding-brush.htm

Existing Equipment

Retrofit Considerations

Existing Equipment


Fans & Pumps

Do I need a special motor?

Is there an existing PI control loop?

Is there an existing Damper Control?

Do I need to interface with a PLC System?

Where do I mount the VFD?

How far away is the motor from the VFD?

Existing Equipment


Fans & PumpsDo I need a special motor?

Existing Motors can be used. If the Motor is

older, use an Output Line Reactor to protect it

Replace the motor with a Premium Energy

Efficient design if possible

Consider using a Permanent Magnet Motor

Existing Equipment


Fans & PumpsIs there an existing PI control loop?

Convert Pneumatic Controls where possible

Many VFDs have Built in PI Controllers

Interface with Existing PLC System

Existing Equipment


FansIs there an existing Damper Control?

If the Dampers are Fixed or Variable, precautions

must be taken to prevent Duct Work Damage

Converting Variable Vane Fans requires that the

Vanes be Mechanically Locked in the

Open Position

Existing Equipment


Fans & PumpsDo I need to interface with a PLC System?

Consider using Communication Options

Considerable Data can be available to the

PLC System

Can be used in Concert with Analog Control

Existing Equipment


Fans & PumpsWhere do I mount the VFD?

In a Space that is Dry & Temperature Controlled

Motor Control Room

In the Plenum

NEMA 3R Outdoor Enclosure

Existing Equipment


Fans & PumpsHow far away is the motor from the VFD?

Always mount the VFD as Close to the

Motor as Possible

Motor Lead Lengths often differ between

VFD Manufacturers

Existing Equipment


Radio Frequency Interference

Radio Frequencies are emitted by the

VFD’s transistor section (essentially an FM

Radio Station)

Radio Frequency Interference is an often

overlooked potential problem. Some VFDs

have RFI Filters built in, others do not.

Power Quality and

Harmonic Distortion

Explanations and Various

CountermeasuresAmplitude of Sine-Wave with 5th and 7th

Harmonic

0 30 60 90 120

150

180

210

240

270

300

330

360

Degrees

Amplitude

Topics

• What are Harmonics?

• What are possible Sources of

Harmonics?

• Effects of Harmonics

• What Solutions are Available?

Harmonics

Definition

• Harmonics are defined as currents or voltages with frequencies that are integer multiples of the fundamental power frequency

What is Harmonic Distortion

• Harmonic Distortion is a mathematical way

of describing a non-sinusoidal wave shape

Every Wave shape has Harmonic Distortion!

THD = 1.2% THD = 78.3%

Possible Effects of Harmonics

• Increased Transformer HeatingTransformer K-Factor (4 to 13 recommended)

• Increased Conductor HeatingWiring per NEC - usually not a problem

• Electromagnetic EquipmentPLCs - more sensitive to Voltage Notching

• System resonance - Power Factor Correction Utilize input reactors to reduce likelihood of resonance

• Lower Power Factor for Entire SystemHigher utility bills (pay for energy you can’t use)

HarmonicsactalalTotalTrue PowerPowerPowerPowerPFPF .ReReRe /

Devices that Increase

Harmonic Distortion• Copy Machines

• Fax machines

• Computers

• Elevator Controls

• Solid State Lighting Ballasts

• Devices that incorporate Static Power Converters - SCRs, Diodes .. etc.

• Adjustable Frequency Drives

Common Issue among Common Devices

Different Types of HarmonicsDC Drive - SCR Based AC Drive - Diode Rectifier

New Technology May Solve Old Power Quality Problems

SCR Rectification - Line Notching, Increase Voltage Distortion

Diode Rectification - Pulsed Current, Increase Current Distortion

Common

SpecificationsIEEE 519 - 1981 - Focused on Voltage Distortion

IEEE 519 - 1992

- Focused on Current Distortion

- Does not clarify PCC

- Does not increase sufficiently

closer to associated device

Custom Specs

IEEE

Std 519-1992

Table Three: Current Distortion Limits for General Distribution Systems

(120 V through 69 kV)

Maximum Harmonic Current Distortion

in Percent of Load Current

ISC/IL <11 11 h<17 17 h<23 23 h<35 35 h TDD

<20 4.0 2.0 1.5 0.6 0.3 5.0

20<50 7.0 3.5 2.5 1.0 0.5 8.0

50<100 10.0 4.5 4.0 1.5 0.7 12.0

100<1000 12.0 5.5 5.0 2.0 1.0 15.0

>1000 15.0 7.0 6.0 2.5 1.4 20.0

Even harmonics are limited to 25% of the odd harmonic limits above.

where

ISC = Maximum short-circuit current at PCC.

IL = Maximum demand load current (fundamental frequency

component)

at PCC.

Table Two: Voltage Distortion Limits

Bus Voltage at PCC Individual Voltage

Distortion (%)

Total Voltage

Distortion THD (%)

69 kV and below 3.0 5.0

69.001 kV through 161 kV 1.5 2.5

161.01 kV and above 1.0 1.5

Harmonic

Countermeasures• Correctly Sized Input Transformer

• DC Link Choke

5% Impedance Results <38% iTHD

Improves Displacement Power Factor

• AC Input Reactor

Reduces Line Voltage Transients

• Harmonic Filters

Capacitor Bypass Contactor below 80% Load

• 12 or 18 Pulse Transformer

• Active Front End / Matrix Technology

The Solution to fit the Application

Harmonic

Countermeasures

Harmonics are a Function of the Ratio of

Available Short Capacity (Isc) vs the Load (IL)

Correctly Sized Input Transformer with K-Factor Rating of 4 - 13

Lightly Loaded Transformers are

Subject to Higher Current Distortion


Harmonic

Countermeasures


Impedance has a Big Effect on the Magnitude of

Harmonics

Add 3% Impedance iTHD drops by 45%, vTHD

drops by 3%

5% Impedance Results <38% iTHD

Improves Power Factor

Adding >7% Impedance Represents a

Diminishing Return on Investment

Harmonic

Countermeasures

Harmonic

Countermeasures

Harmonic Filters Utilize Inductors (Reactors)

& Capacitors to “Tune Out” Undesired Current

& Voltage Harmonics

Harmonic

Countermeasures

Bypass Contactors should be provided

to remove the Capacitors from the Circuit

below 80% Load (to Prevent Leading

Power Factor)

Harmonic

Countermeasures

12 Pulse Front End- Utilizes Dual Wye/Delta Secondary Transformer

In Combination with Dual Diode Rectifiers

- Typical Performance 7.5 – 12% THD at the Input Terminals

Harmonic

Countermeasures

18 Pulse Front End- Utilizes Triple Secondary

Phase Shifting Transformer

With 3 Diode Bridge Rectifiers

- Typically Performance

5.5% THD at the VFD Terminals

Harmonic

Countermeasures

Active Front End

Typically Performance

=/<5% THD at the VFD Terminals

AFEAC drive

AC reactorPower Supply Motor

Harmonic

Countermeasures

Matrix AC to AC

Typically Performance

<5% THD at the VFD Terminals

Power Supply Motor

U1000

Harmonic Countermeasures

vs % Load

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

25.0% 50.0% 75.0% 100.0%

iTH

D

Load

iTHD-U1000 iTHD - 12p iTHD-18p

Harmonic Countermeasures

vs % Load

0.0 %

2.0 %

4.0 %

6.0 %

8.0 %

10.0 %

12.0 %

14.0 %

16.0 %

18.0 %

20.0 %

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

0.0 Hz 20.0 Hz 40.0 Hz 60.0 Hz 80.0 Hz

THD[%]

Mo

tor

Pow

er[

%]1

00

%=

40H

P

Fout[Hz]

Fig.1. iTHD comparison with Variable Torque profile

Load

Conclusion

It is important to note that use of an

IEEE Standard is voluntary.

The scope of the standard is to

establish GOALS for the design of

electrical systems that include both

linear and non-linear loads.

Conclusion

If current harmonics are a problem, the

result is increased voltage distortion.

IEEE’s standards on voltage distortion

are very clear and accurate.

If voltage distortion exceeds 5%, the

power factor of the system will be

reduced.

Conclusion

Utility data can be used to determine if

any corrective procedures should be

instituted to mitigate poor power factor

penalty charges.

One important issue not to overlook is

if power factor is a problem, it can

result in higher utility bills.

Thank for this opportunity to discuss

VFD/Motor Compatibility, Harmonics and

Existing System Retrofits

Additional information can be found at

www.drives.com

If you have future questions or need

specific guidance, I can be reached at

[email protected]

http://www.drives.com/

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