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Class 8839 58M Enclosed AC Drives
Application Information
171
09/2003
© 2000–2003 Schneider Electric All Rights Reserved
Collectively, all facility loads and the building
electrical distribution network determines the
harmonic levels at the user & electric utility
interface. Commonly misapplied, the Electrical
Power Research Institute (EPRI) recognizes the
'Point of Common Coupling' or PCC as the
interface between user and electric utility (energy
meter) in the electrical distribution network. This
position will also be supported in the forthcoming
Application Guide (P519A) being prepared by the
Harmonics Working Group of IEEE. Square D
Company will typically provide 'drive isolation
transformers' or 'line reactors' as the most cost
effective method of harmonic abatement.
For specifications that are regulated by utilities
to the IEEE 519 guidelines, there are alternate
methods of harmonic abatement. Consult product
support or customer service for enclosed drives
for configurations and pricing.
Input Currents Ratings
(with and without Line Reactor)
Square D publishes input currents based on
distribution system impedance at various
available fault current ratings. Our literature
reflects multiple input current ratings based on
available fault currents
• 5,000 AIC (1–50 hp) or
10,000 AIC (60–200 hp) or
18,000 AIC (250–400 hp)
and
• 22,000 AIC
and
• 65,000 AIC
and
• 100,000 AIC
More common, line reactors are provided with the
majority of AC Drives today. The reasons
proliferate from abnormal line conditions, IEEE
519 guidelines, to power quality concerns. Line
reactors provide the most cost effective option to
minimize harmonic currents reflected back into
the distribution system. The use of line reactance
ahead of the AC drive will function best to:
1. Reduce line current harmonic injection into
the primary source, limiting the input ‘rms’
currents to less than or equal to motor full load
amps.
2. Reduce the available feeder short circuit
capacity.
3. Meet specified line impedance requirements.
5 KAIC, 10 KAIC, 22 KAIC, and 65 KAIC short
circuit current rating up to 100 hp, and 65
KAIC and 100 KAIC short circuit current rating
for 125–500 hp. By listing the alternate input
currents when using a series line reactor, the
user could benefit in savings reflected in
conductor and disconnect selection, as
required by the National Electric Code.
Drive Isolation Transformer
Drive Isolation transformers are designed for
maximum benefit when applied to an AC drive. In
addition to the functional comparison of a line
reactor, drive isolation transformers are normally
used for one of the following reasons over a
standard line reactor:
1. Match system voltage to drive rating.
2. Meet local or plant codes that require
isolation.
3. Capable of correcting line voltage unbalance
conditions commonly seen with open delta
and corner grounded delta distribution
systems.
4. Provides continuity of service for nuisance
grounding.
5. Reduces drive induced currents in supply
feeder ground and limit ground fault currents.
6. Isolate the electrical common mode noise
generated in solid state controllers from the
distribution system.
The Class 8839 58M Enclosed AC drives have a
high fault withstand capability (up to 65,000 A or
100,000 A depending upon configuration). For
these reasons, Square D does not suggest the
use of a drive isolation transformer for isolation
purposes unless the system requires one or more
of the six functions listed above.
Speed Range & Regulation
The Class 8839 58M Enclosed AC drives will
operate within the range of 0.1 to 60 Hz
(configurable up to 500 Hz). Please note, if
operating motors above base speed, the motor
manufacturer must approve operation for the
specified speed range.
Speed regulation is determined by one of several
modes of configuration. Most AC drives utilize the
volts/hertz mode where speed regulation is
determined by the motor slip, typically 3% or less.
The Class 8839 58M Enclosed AC drive utilizes
sensorless flux vector mode (SLFV) as standard
with 1% speed regulation; with optional
tachometer can be improved to 0.5%.