Zener SMARTSTART 6000, Инструкция по эксплуатации

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Appendix A
ZENER SMART‐TORQ ‐ Torque Control System
Technical Manual: Smartstart
®
6000 IMI0042 rev K
Page 44
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.
‘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 closing 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.
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
specific speed.
Below illustrates the constant acceleration torque applied for different load types;
1) Constant Torque type Load (eg. Conveyor)
2) Variable Torque type Load (eg. Pump/Fan)
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 specific 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
®
6000 combines this superior torque control
system with a robust design to suit all types of loads and applications. All models
include substantial heatsink mass with temperature controlled force ventilation to
accommodate the more severe (heavy) duty applications.
Total Torque
Load Torque
Speed
Torque
Acceleration
Torque
Load Torque
Speed
Torque
Acceleration
Torque
Total Torque
100%
100%
Load Torque
Speed
LRT
DOL (full Voltage)
Torque
100%
FLT
(100%)
Voltage Ramp
Torque
Acceleration
Torque