© ABBMonth DD, YYYY | Slide 1

VFD Applications

Jeff Miller

2010

Why use a VFD?

• Energy Savings – Running a centrifugal load at 50% speed on a 100HP

motor only uses 15HP but delivers 50% flow!

– Improves power factor to .98

• Soft start feature increases lifespan of

mechanical loads and helps reduce demand

charges, and water hammer, etc

– Much better than reduced voltage start

• Inherent protection for single phase,

overload, short circuit and ground fault

What is a Drive / VFD/ AFD/ASD?

0

230

460

Volts

Hertz

30 60

460 V

60 Hz= 7.67

V

Hz

230 V

60 Hz= 3.83

V

Hz

If 230 VAC Power Line:

What is a Drive?

Motor

L1

L2

L3

C

L

Input Converter

(Diode Bridge)

Output Inverter

(IGBT’s)

DC Bus

(Filter)+

_+_

+

_

+

_

+ +

_ _

RECTIFIER

Positive

DC Bus

Negative

DC Bus

+

-

INVERTER

RECTIFIER

Positive

DC Bus

Negative

DC Bus

+

-

INVERTER

RECTIFIER

Positive

DC Bus

Negative

DC Bus

+

-

INVERTER

Area Under The Square-Wave Pulses

Approximates The Area Under A Sine Wave

Frequency

Vo

lta

ge

Hoffman & Hoffman

Fundamentals of Variable Frequency Drives

Pulse Width Modulation (PWM)

High Frequency, Motor Noise and Stress

(2-20Khz)

VFD Installation

• Three separate

metallic conduits

– Control, input power

and motor wiring

• Should not be the

ground source

• Be cautious of buried

PVC conduit for EMC

issues!

• MCC mounted drives

too!

VFD Installation

• Motor – VFD

compatibility (long cable

runs). NEMA MG1, Part

31compliance & shaft

grounding

• Observe fuse requirements

and short circuit rating

requirements for base

drive and combination

drive and bypass (drive

and bypass protection)

• Shaft grounding

Surge / Transient Protection

• Protection from AC line

transients is important

• Generator testing

• Switching power factor caps

• Indirect lightning

• Need phase to phase and phase

to ground protection

• Micro Drives do not have as

robust protection scheme!

VFD Installations - Ambient

• Most drives are rated 0-40C

– Derating required for higher

temps (for 50C). Large impact

on drive lifespan. (MCC

mounted VFD’s)

– Heaters required for cold

temperatures (be smart)

• Corrosive environments

– Conformal coating for PCB’s

– Other protection

Enclosures Types

• Ambient Temperature

• UL rated

– UL Type 1 dry, clean indoor

– UL Type 12 dirty, dripping water

– UL Type 3R outdoor

– UL Type 4 hose down

• NEMA ratings are self certifying

– UL has very specific requirements

Enclosures – MCC’s

• Required for some applications due to space

limitations

• Run hotter = shorter product life

• More difficult to service / maintain

• Replacement cost / compatibility

• Harmonic filter options are limited

• More potential noise / interference issues

due to motor cable routing

• Higher initial cost

VFD Applications - Pumps

• Minimum speed at least 20-30% speed to open check-valves

and provide motor cooling

• Be cautious mixing variable speed and constant speed

pumps on parallel pumping systems

• Ramp times critical for most submersible pumps (thrust

bearing)

• The type of pump is very important (constant vs variable

torque)

VFD Applications - Fans

• VFD to interface with end switches

• Dampers: (isolation, etc.) to ensure dampers are

open before motor operation (VFD & bypass)

• Bypass considerations

• High static (dump damper, vav box override)

• Proof of flow from VFD (single motor application)

• Smoke purge / stairwell pressurization

• Control sequence

• Priorities

VFD Applications – Fan Array

• One VFD: Total motor FLA (all operate at the same

speed)

• Redundant VFD’s – one motor failure

OR

• Individual VFD per motor - VFD type

• OEM Packaged

• Local Service, design of panels

• Extended frequency operation

• Design by OEM

Interfacing with BAS

• Monitoring / Monitoring & Control

– Don’t waste your connection!

• S/S, Speed, Run & Fault

• VFD temperature, trip ID, trip reset (remote), load

“health” (plugged pump, stuck valve, etc), man-auto

control, KWH and much more!

VFD Types

Micro Drives – Small, cost reduced, short lifespan

Standard Drives – Robust, high volume, long life

Performance Drives – Capable, tight motor control,

PLC type functions, robust, long life

Questions?