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Appendix A
ZENER SMART-TORQ
Torque Control System
There are several methods available to soft start a motor. The more
traditional methods are Direct-on-line, Star/Delta, Auto transformer and
Primary resistance starters. The more sophisticated methods also provide a
soft stop and include Soft Starters and Variable Speed drives (VSD's). VSD's
can provide a better soft start with significantly lower starting currents and
many other benefits including energy savings. However, a Soft Starter may
provide a more economical solution to motor starting over the life of the
motor.
Soft Starters provide the following benefits:
1.
Reduced stresses and wear on the mechanics of the system
2.
Reduced starting currents
3.
Minimise voltage dips on the supply
4.
Lowered Peak demand charges
5.
Eliminate belt slippage on fans
6.
Smooth acceleration of motor / load
The conventional voltage ramp Soft Starter is a reduced voltage starter and is
similar to the traditional methods mentioned above. The problem with
voltage ramp soft starters is a non linear acceleration of the motor. This is
very noticeable on a pump type load where there is much higher acceleration
torque available at the beginning of the start. The diagram below shows the
variation in acceleration torque available for both a Direct on line (full
voltage) and the voltage ramp type soft start.
DOL (full Voltage)
Torque
LRT
Acceleration
FLT
Torque
(100%)
Voltage Ramp
Torque
Speed
®
'SMART-TORQ
' is a Torque Control System developed by Zener to overcome
this problem with greater control over the acceleration torque in the motor.
The torque is controlled in a manner which suits the type of load to achieve a
linear acceleration in motor shaft speed. This control system is also active
during the deceleration phase, providing a soft stop where the motor
decelerates at a constant rate. This can be used to overcome water hammer
problems associated with the c losing or slamming of check valves.
ZENER SMART-TORQ Key Benefits:
1.
A true linear acceleration of the load and motor for variable &
constant torque loads.
2.
Reduced stresses and wear on the mechanics of the system
3.
Ramp profiling to better match type of load such as variable
torque loads. Better control of pumps and fans.
4.
Torque Control available in Accel & Decel Modes and 3wire or
6wire motor configuration.
5.
Eliminate water hammer problems.
6.
Reduced peak current draw, especially at motor pull-in/pull-out
operating points.
7.
Reduced heating in motor at low speeds.
8.
No instability due to changing power factor. Closed loop system
to monitor and react to changing power factor.
9.
No instability due to slot ripple in 3 wire and 6 wire operation.
10.
Better control of deceleration through closed loop torque control
system.
11.
No external speed sensor required to produce superior
performance
Technical Manual: Smartstart
Load Torque
100%
®
6000
Page 34
The rate of acceleration is dependent on the additional torque
(Acceleration Torque) available in the motor.
Thus, we can achieve a constant or linear rate of Acceleration by providing
'constant' acceleration torque to the motor.
Since the torque required by the load may not be linear, the torque delivered
by the soft starter must match that of the load. To achieve this, the torque
developed in the motor must be the sum of the 'acceleration torque' and the
load torque at a spec ific speed.
Below illustrates the constant acceleration torque applied for different load
types;
1) Constant Torque type Load (eg. Conveyor)
Torque
Acceleration
Torque
Speed
2) Variable Torque type Load (eg. Pump/Fan)
Torque
Acceleration
Torque
Speed
How is this achieved ?
®
The SMARTSTART
6000 continually monitors start variables such as motor
current, voltage and power factor to determine the input electrical power.
From the motor parameters, the IR & magnetic losses are used to calculate
the Air Gap Power (ie. the power transmitted to the motor shaft). With an
instantaneous value of shaft power the instantaneous torque can be
determined. With this information we can vary the thyristor conduction to
achieve the desired torque. The torque is varied to follow a spec ific curve,
based on the initial torque setting, the final torque setting and the profile
selected. The end result is equal acceleration torque over the ramp period to
provide a linear acceleration in motor shaft speed. The profile is user
adjustable allowing for non-linear torques if required to other or unusual
types of loads.
Summary.
®
The 'SMART-TORQ
' Torque Control System provides smoother starting &
stopping, allowing ramp profiling to produce a linear acceleration and
deceleration of the motor speed. There are many benefits with variable
torque loads such a pumps. A linear acceleration and deceleration provides
better control to eliminate water hammer problems. The SMARTSTART
combines this superior torque control system with a robust design to suit all
types of loads and applications. All models inc lude substantial heatsink mass
with temperature controlled force ventilation to accommodate the more
severe (heavy) duty applications.
Total Torque
Load Torque
100%
Total Torque
Load Torque
100%
®
IMI0042 rev D
6000
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