1. ALTISTART 46 New TCS technology1

2. Introduction
Three phase AC motors are designed to provide quick acceleration from rest to rated speed.
In order to produce the extra torque, an AC motor will draw much higher current than is required during normal operation.
In some cases, the starting current requirements can exceed system capacity.
In addition, the amount of starting torque developed can damage the driven machine or work in process. 2

3. Introduction
The starting torque can be reduced by either mechanical methods - such as clutches or gears, electrical methods which reduce the applied voltage during starting or adjustable frequency drives.
A « soft start » is a solid state starter which uses Silicon Controlled Rectifiers (SCRs) to control the amount of voltage applied while the motor is starting.
Soft starts are ideal for meeting electricity utility requirements for reduced inrush current.
Soft starts also provide a multitude of benefits for process and machine applications by reducing the amount of excess acceleration torque. 3

4. Introduction
As little SCR development has occurred in the past 10 years, advancements in soft start technology are typically focused on increased flexibility in adjustments, ease of installation, advancements in protection and digital interface.
However, the ultimate goal is to provide a smooth, repeatable acceleration with the minimum amount of inrush current.
The key to optimizing the acceleration performance of a motor when using a soft start, is to control the motor torque development rather than simply applying a time based voltage ramp or maintaining a user defined current limit.
Providing control of the motor torque is the latest step towards optimizing starting performance - or taming the AC motor without varying the frequency of the voltage supply. 4

5. How does a soft start work
Soft starts control the firing angles of SCR pairs to adjust the amount of line voltage which is applied to the motor.
By changing the firing angle of the SCR, and since the frequency of the voltage applied cannot be changed using a soft start, the speed of the motor during normal operation will be the motor rated speed.
In addition, the torque producing capabilities and current inrush demands will be based on the motor performance rated voltage and frequency. 5

6. Reduced Current Inrush
A typical squirrel cage induction motor started at full voltage will draw current from four to ten times the current required to run the motor at full speed, fully loaded. When reduced voltage is applied to a motor, the motor will draw current in proportion to the voltage reduction;
I rv ~ I fv x ( Vrv / Vfv )
For a typical motor, the inrush or locked rotor current will be approximately 600% of the motor full load amperage (FLA) rating. If started with 50% of line voltage, the motor will then draw 0.50 x 600% or 300% FLA. 6

7. Reduced Starting Torque
When started at full voltage, a typical motor will produce approximately 150% of its rated torque. When a motor is started at reduced voltage, the torque is reduced by the square of the voltage reduction.
T rv ~ T fv x ( Vrv / Vfv )2
For example, if this motor described above is started at 50% of line voltage, the torque developed would then be 0.50² or 25% of the normal starting torque. 7

8. Main applications
Typical motor loads that are used with soft starts include centrifugal pumps, fans, batch centrifuges, unloaded compressors, and lightly loaded conveyors - or applications which do not require a high amount of starting torque to accelerate.
Controlling the motor torque expands the typical soft start application base to include machines that typically require more starting torque such as loaded conveyors and rock crushers 8

9. Voltage Ramping Soft Starts
The typical soft start available today provides a voltage ramp soft start. With this technology, the voltage is increased from an initial voltage to the line voltage in a linear fashion over a user adjustable period of time.
With a voltage ramping soft start, at each point in the speed ramp, the amount of acceleration torque available is completely dependent on the torque production capability of the motor given the applied voltage.
In addition, if the motor is not up to speed when the timed ramp is complete, the motor will draw the current required at that speed with full voltage applied.
As such, when using a voltage ramping soft start, the magnitude of the peak current is a function of both the motor locked rotor amps and the load requirements. 9

10. Voltage Ramping Soft Start Performance10

11. Current Limiting Soft Starts
Most manufacturers offer a current limiting soft start as an option. When using a straight current limit, the voltage is basically held constant for the duration of the user adjustable ramp time then increased to full voltage.
The acceleration performance of a motor when using a pure current limit soft start is similar to an electromechanical reduced voltage starter. 11

12. Current Limiting Soft Starts
The Altistart 23 was unique in that it provided a combination of voltage ramp with an overriding current limit function.
With the ATS23, the voltage was ramped to the motor linearly if the motor current requirement was below the current limit.
Once the current limit was reached, the voltage ramp was adjusted to maintain the current limit.
If the motor load requirements met the torque capability of the motor at that speed with the voltage applied to maintain the current limit, the motor would not be able to reach full speed. 12

13. Current Limiting Soft Starts
As shown in the figures below, the use of voltage ramping or current limiting technologies provided reduced current inrush and torque, but the motor performance was still dependent on the motor characteristics rather than the actual load requirement.
With either method, the motor acceleration typically started slow and finished fast. Previous technology did not allow for true reduction of peak inrush current for heavily loaded machinery and could not accommodate changes in the loading conditions. 13

14. 14

15. Soft Stopping
Deceleration control is widely offered to provide either a soft stop - longer than freewheel - or braking - shorter than freewheel.
A typical voltage ramping soft start will also provide a linear decrease in voltage to the motor for a soft stop.
This prevents an abrupt change in the initial decrease in the motor speed following a stop command.
For a pumping application in order to prevent water hammer the speed of the motor must be decreased gradually to prevent the check valve from slamming shut.
A standard soft stop does not provide this level of control. 15

16. Soft Stopping
Several soft starts are available specifically for control of pumping applications.
These units usually have a feedback mechanism to improve the performance of the acceleration and deceleration ramp specifically for a typical pump load requirements.
This technology is based on theoretical models of the motor performance and load requirements.
As such the performance of the application is based on how close the model is to the actual installed equipment performance. 16

17. Soft Stopping
The typical pump control algorithm also did not perform well on a lightly loaded motor.
When the motor load is below about 60% of the motor rated torque, the motor speed will not change until there is a significant decrease in the applied voltage.
As such, the speed drops off rapidly during the last part of the ramp.
While it is often possible to optimize the performance of the typical pump control soft start to one operating point, it will not be optimized if the loading conditions change. 17

18. New Technology in Soft Starts with Torque Control
The Altistart 46 soft starter offers an exclusive “Torque Control System”.
The torque control system uses an exclusive control algorithm to calculate real stator and rotor power for maintaining constant torque acceleration.
This is accomplished by continuously calculating motor power factor and stator losses throughout the acceleration and deceleration cycle. 18

19. New Technology in Soft Starts with Torque Control
The starter monitors voltage and current to determine power factor and subtracts the stator losses to determine the real rotor power or actual motor torque.
Previous technology soft starts required a tachometer feedback signal to indicate the motor speed in order to obtain a linear speed ramp.
The acceleration and deceleration ramps with the ATS 46 starter are not based strictly upon time and motor voltage levels, but are designed to provide a linear ramp of torque as long as the motor load does not exceed the current limit setting. 19

20. Functional Block Diagram20

21. We realize the same calculation for1 2 4 5 6 3
DOL
Ramp of
Torque Tr NC NT T1
Speed
Current I1
Iss I2 I3 ST
T= k U ² ~ k I ² Iss = I soft start
T1 ~ TDOL * Iss1 ² / IDOL ²
Iss1 ² = IDOL ² *TSS / TDOL
The user preset T1. We know Idol and TDOL
ATS deliver the current which give the right torque T1
I1 = T1.IDOL ²
TDOL
We realize the same calculation for
I2T2 …In Tn 3 21

22. TCS with Variable Torque Loads
The ATS46 is factory preset to provide a linear torque ramp from 0 to 100% of the motor nominal torque in 10 seconds with an initial torque offset of 10%.
This is a typical setting intended for use with most variable torque applications without adjustment.
As shown in the figure below, since the motor loading is approximately linear up to 70% speed, the linear torque ramp created by the ATS46 control algorithms result in a constant amount of acceleration torque. 22

23. TCS with Variable Torque Loads
Constant acceleration torque is the key to maintaining a constant rate of change in the motor speed to minimize pressure surges in pipes, belt slippage or mechanical wear.
In addition, if the load level changes on the machine, the difference in the motor torque and load torque will be different, but still constant along the speed ramp.
While a lighter load will accelerate faster than a heavy load, the acceleration will be linear for either loading condition. 23

24. TCS with Constant Torque Loads
Accelerating Torque
Constant Torque Load
Speed
Constant
Acceleration
When using the ATS46 TCS with a constant torque application, the initial torque and final torque settings can be used to provide a constant torque profile.
In order to optimize the performance, the actual load requirements can be read from the digital keypad.
Then the initial torque and torque limit settings can be used to ensure the motor torque is higher than the load requirement and constant along the speed ramp.
As shown below, even if the load changes, the amount of acceleration torque may change, but it will be constant each time the motor is started. 24

25. TCS with Constant Torque Loads
Accelerating Torque
Constant Torque Load
Speed
Constant
Acceleration
It is important to note that while the ATS46 can start any motor which can be started across the line, it may require current as high as the locked rotor amps if the maximum torque production capability of the motor is required.
The ATS46 current limit may be adjusted to the lower of 700% of the motor rated current or 500% of the device rating.
When using the ATS46 on a heavily loaded constant torque application, the heavy duty rating should be used so that the current limit may be adjusted to allow the required motor torque. 25

26. Initial torque FLT LRT BDT Speed Torque Time
Accelerating Torque
Constant Torque Load
Torque 0%
25%
75%
50%
100%
Constant Acceleration
Rated
Motor
Time 26

27. LSC Stator Losses Compensation
The power transmitted to the motor is calculated based on the motor current, voltage and power factor.
Then an estimation of the stator loses is subtracted from this to obtain the actual motor torque.
If using the ATS46 with a low slip, the LSC factor can be reduced to obtain the optimal motor performance.
If using a NEMA D motor, the LSC factor can be increased to change the motor profile to more closely fit a NEMA D motor.
For most applications, the factory preset should not be adjusted. 27

28. LSC Adjustment LSC Factory preset Decrease LSC Increase LSC
Factory preset is for a standard squirrel cage motor characteristic Torque/speed
and courant speed at full voltage and constant frequency.
LSC Factory preset Decrease LSC Increase LSC 28

29. Advantages of Torque Control
The ATS 46 torque control system provides motor torque performance that results in many application advantages. These advantages are as follows:
Linear speed ramp independent of motor loading
Control of power factor reduces current requirements on inrush
Standard torque ramp ideal for acceleration and deceleration ramp for variable torque loads such as pumps or fans
Torque ramp can be customized for constant torque acceleration profile
Motor torque value may be read and adjusted via the keypad to coordinate with the actual application requirements
Deceleration ramp starts at the torque load point to maximize linear ramp
No motor mounted feedback device required for optimal control. 29

30. Advantages of Torque Control
The ATS 46 soft starter with its torque control system (TCS) is microprocessor based making it very versatile.
It can vary the thyristor switching pattern to accommodate several different acceleration and deceleration ramp types as demanded by various applications.
It can be configured to provide constant acceleration torque for constant torque loads. This will provide a linear acceleration ramp for smooth constant acceleration from zero to full speed . 30

31. Advantages of Torque Control
Centrifugal pumps require acceleration torque that increases with speed based on the affinity laws.
The ATS 46 may be configured to linearly increase the motor torque over time starting from a user selectable motor torque percentage value to full load motor torque.
This configuration set up provides a linear acceleration ramp for centrifugal pumps and fans.
A linear acceleration ramp helps coordinating check valve opening with the motor/pump acceleration, eliminating water hammer. It can also eliminate belt slippage on fan loads reducing machine wear and maintenance. 31

32. Advantages of Torque Control32

33. Advantages of Torque Control
The ATS 46 is also capable of providing a linearly decreasing torque ramp for deceleration of centrifugal pump loads.
Similar to the acceleration ramp, the linear change in speed on deceleration ramp makes it possible to coordinate check valve closing without water hammer.
The ATS 46 continuously monitors the motor load torque and when a stop command is given it starts the deceleration ramp at that load torque point.
This allows for a linear deceleration ramp on pump loads even when the motor is lightly loaded or if the load changes. 33

34. Summary
The ATS 46 Soft Starter with its unique torque control system offers AC induction motor starting performance today that is unmatched by other reduced voltage starting methods.
This superior performance is provided by technology design with no additional cost to end user. The major power components of the ATS 46 soft starter are the same as used in the rest of the soft start market.
The difference is how the control algorithms are implemented to control torque during acceleration and deceleration.
The ATS 46 soft starter offers the best of performance by controlling the motor torque to meet the load requirements and provide the benefits of a reduced voltage start. 34