LTQ008 – LTQ230 Series 3-Phase
Products
User Instructions –
AIIOM000165
EN
Page
12
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40
5
Theory of Operation
Background:
Three-phase motors, regardless of size or horsepower, must have a reversing starter / contactor
to run in both directions as a result of some process control requirement. On single phase motors, the starter /
contact normally starts and run in a fixed direction. Reversing the starting winding causes the motor to run in
the opposite direction. In three-phase motors, the direction of rotation is reversed by switching any two of the
three phase lines into the motor. This is accomplished most commonly by utilizing a reversing motor starter. The
reversing starter can be located inside the actuator, or in a completely separate enclosure remote from the
actuator (i.e. switchgear “cabinet”), depending on site requirements and the actuator series chosen.
Flowserve offers several types of three-phase actuators that are designed to fit applications ranging from
basic controls to fully-optioned solutions. These various strategies form the levels described below which allow
a product to fit functionally and economically into most three-phase applications.
5.1
LTQ008 – LTQ230 NCU (230/3 – 575/3 On/Off Control)
Starting with the most basic design are the NCU
Series actuators. These models are designed for use
with existing 3-phase installations where motor
control centers are already established. A site-
furnished 120VAC control power circuit is required
for this series.
The inside of the actuator contains:
1.
No Reversing Motor Starter.
This actuator will run
in one direction only if the motor leads are not
connected to a reversing starter. The required
reversing motor starter must be already located
in an existing switch gear cabinet.
2.
No Phase Monitor Circuitry.
If phasing is incorrect
at the actuator, it will run in the wrong direction
at start-up. If phasing is incorrect, limit switches
and torque switches are not necessarily in the
correct circuit to protect the gear train or
actuator from damage. It should also be noted
that a three-phase service in a building may be
perfectly functional and phased correctly for
many years, then a transformer blows, the power
company comes to replace it, and it gets
connected out of phase. The building still has
power, but all three-phases motors now run in the
opposite direction. Proper phasing must be
verified immediately at initial start-up. Improper
phasing may immediately damage the actuator.
Always perform start-up with the actuator in the
mid-stroke position and watch the actuator
rotation when powering-up
.
3.
No Local Control Device.
There is no way to
operate the actuator locally. Only the existing
Motor Control Center (MCC) and the controls
already on-site can operate the actuator.
Without some type of MCC, there will be no way
to drive the actuator in either direction.
Figure 6: LTQ008 – LTQ230 NCU (230/3 – 575/3 On/Off
control) wiring diagram
