WHAT IS A LINE REACTOR
A 3-phase Line Reactor is a set
of three (3) coils (also known as windings, chokes, or inductors) in one
assembly. It is a series device, which means it is connected in the supply line
such that all line current flows through the reactor, as shown below:
Line Reactors are
current-limiting devices and oppose changes in current because of their
impedance. They hold down any spikes of current and limit any peak currents.
This resistance to change is measured in ohms as the Line Reactor’s AC
Impedance (XL) and is calculated as follows:
XL = 2 π f L (ohms)
f = Frequency in hertz (cycles
per second)
Harmonic frequency examples:
Harmonic (60 Hz) Frequency
(Hz)
5th 300
7th
420
11th 660
L = reactor inductance in henries
(H), millihenries (mH) – H x 10-3, microhenries (µH) – H x 10-6By inspection of
the XL formula, the Line Reactor impedance is directly proportional to the
frequency (f) and inductance (L).
That is, if the impedance of a
Line Reactor is 10 ohms at 60 Hz, then at the 5th harmonic (300 Hz),
the impedance is 50 ohms. If the inductance (L) is increased, then the
impedance will increase proportionally. This increase in Line Reactor impedance
will reduce the current in the line. The higher the frequency (Hertz) is, the
greater the current reduction. A Line Reactor’s DC resistance (R-ohms) is very
low by design so that the power losses (watts-I2R) are low.
Line Reactors are rated by %
impedance, voltage, and current. However, they are sized by % impedance,
voltage, and motor horsepower. The motor horsepower determines the necessary
current rating for the Line Reactor.
Line Reactors are rated by
impedance, voltage, and current.
1. Impedance (% impedance of load
Z)
The load impedance (Z) is
calculated by this formula:
2. Voltage rating
Since a Line Reactor is a
current-sensitive device, the voltage rating is needed for dielectric concerns
as a maximum voltage and horsepower.
3. Current rating (amperes)
This is the current required by
the load(s). It is total current flowing to the load(s) and through the
reactor. This current is measured in amperes (amps).
WHAT DEVICES REQUIRE LINE REACTORS?
Variable Frequency Drives, DC
drives, SCR drives, and Rectifier drives for motors are some of the names for
devices that require Line Reactors. These are grouped together and termed
Adjustable Speed Drives (ASDs) to encompass any type of drive for a motor which
changes the output speed. This happens because the current waveform is changed,
creating a non-sinusoidal waveform.
WHY ARE LINE REACTORS USED?
Until about 10 years ago,
isolation transformers (1 to 1 ratio) were used to control power transients,
provide line protection and isolate loads. Line Reactors accomplish these
functions, and more, at a lower cost and a smaller physical size. They are excellent
at providing isolation of the drive from the power system. This is important
because often, multiple drives are located near each other and cause
interference between each other. Line reactors are used to reduce voltage
notching caused by the rapid change in current draw by ASDs. They also provide
short-circuit protection and reduce spikes, sags, and harmonics.
Harmonics are currents flowing at
frequencies which are multiples of the fundamental frequency (usually 60 Hz).
Reactors are
“Harmonic-Compensated” units, allowing them to be used in any application.
WHERE AND HOW ARE LINE REACTORS CONNECTED?
If used on the output side of a
drive, the Line Reactor is connected in series with the motor leads which run
from the drive to the motor. If used on the input side of a drive for
non-harmonic applications (a Trap/filter is not used), then the Line Reactor is
connected in series with the power leads to the drive and should be on the load
side of the drive disconnect.
If used on the input side of a
drive motor for harmonic applications (a Trap/filter is used), then the Line
Reactor is connected in series with the power leads to the drive and on the
line side of the Trap/filter.
3-phase Line Reactors are
connected by three (3) input terminals labeled “A1,” “B1” and “C1” for the line
side and three (3) output terminals labeled “A2,” “B2” and “C2.” These
terminals are uniquely designed with a heavy-duty plastic shield covering them.
Where: Z = load impedance (ohms)
V = line voltage (volts)
I = line current (amps) LINE
REACTOR MANUAL
TYPICAL APPLICATIONS
Case 1
Nuisance Problems
Current surge
Voltage transients
Drive nuisance tripping
Voltage notching
High-voltage spikes from
capacitor switching
Multiple applications on the
same bus
If used on the input side of a
drive for non-harmonic applications (a Trap/filter is not used), then the Line
Reactor is connected in series with the power leads to the drive and should be
on the load side of the drive disconnect.
Case 2
Motor Drive Problems
Motor temperature
Motor noise
Motor efficiency improvement
If used on the output side of a
drive, the Line Reactor is connected in series with the motor leads which run
from the drive to the motor.
Case 3
Motor Drive – Harmonic Reduction
– No Power Factor Penalty Imposed by Utility
For harmonic reduction on the
motor drive circuits with no power factor correction capacitors on the
secondary side of the industrial plant transformer and no power factor penalty
imposed by the utility company, use the following:
If used on the input side of a
drive for non-harmonic applications (a Trap/filter is not used), then the Line
Reactor is connected in series with the power leads to the drive and should be
on the load side of the drive disconnect.
Case 4
Motor Drive – Harmonic Reduction
– Power Factor Penalty Imposed by Utility
In plants which have power factor
penalties and power factor correction capacitors are installed, or there are
plans to install power factor correction capacitors, the following should be
used:
If existing power factor
correction capacitors are installed and Adjustable Speed Drives (ASDs) are
being added, then harmonic filters must be installed on each ASD or group of
ASDs.
To isolate the in-plant power
factor correction capacitors, a Line Reactor must be installed on the line side
of the harmonic .Recommendation: Select a 5% Line Reactor sized per the voltage
and horsepower
If used on the input side of a
drive for harmonic applications (a Trap/filter is used), then the Line Reactor
is connected in series with the power leads to the drive and on the line side
of the Trap/filter.