vfd applications jeff miller · vfd installations - ambient • most drives are rated 0-40c –...
TRANSCRIPT
© 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?