1. 1 Electronic Soft Starters How and Why they Work, and What they can do for You. Fairford North America

2. 2 The Starting Point n The performance of a soft starter is crucially dependent on the performance of the motor it controls. n Therefore, it is essential to understand motor characteristics in order to understand soft starter applications.

3. 3 Statements of Fact - 1 n Energy cannot be created or destroyed - but it can be converted from one form to another. n In a conversion system, an event such as a surge in demand, experienced in one form of energy is immediately reflected in the other form of energy.

4. 4 Statements of Fact - 2 n An induction motor is an energy conversion device, converting electrical energy into mechanical energy and some heat energy. n For an induction motor, torque is proportional to the motor terminal voltage squared. (V 2 ). So, for example, half the voltage produces a quarter of the torque.

5. 5 Induction Motors - 1 n Were invented about 100 years ago. n Because of their simplicity and efficiency, they are the workhorses of industry throughout the world.

6. 6 Induction Motors - 2 n The induction motor has two basic functions to fulfil : n 1To accelerate itself and its load to full speed. n 2To maintain the load at full speed efficiently and effectively over the full range of loading.

7. 7 The motor speed-torque curve Locked Rotor Torque (LRT, MA) 0SSpeed Pull Up Torque Pull Out (Peak) Torque (M K ) Full Load Torque (FLT, MN) Torque

8. 8 The load speed-torque curve 0SSpeed Full Load Torque (FLT) Torque 0SSpeed Load Torque Motor

9. 9 Putting the two curves together we get Torque Load Torque Motor Locked Rotor Torque Peak Torque Full Load Torque (FLT) S’ The accelerating torque at any speed S’ is (T2 - T1) 0SSpeed T2 T1

10. 10 n Because the load starting torque is usually near zero, an induction motor will develop far too much torque when connected directly to the supply. So, n At the instant of start-up, there is an un- necessary heavy power surge on both the electrical supply and the mechanical drive components. What does this mean in practice?

11. 11 The mechanical effects n The sudden impact at start up on the load, followed by the rapid acceleration to full speed causes excessive wear on :- n Belts and pulleys n Gears and chains n Couplings and bearings and :- n Cavitation in pumps etc........

12. 12 The electrical effects n A heavy current surge on the electrical supply which can be severe enough to cause voltage dips and flickering lights. n Pitting and burning of contacts due to high currents which are many times the motor full-load current.

13. 13 The user experiences:- n Continuous maintenance. n Greater chance of unscheduled shutdowns n Oversized mechanical and electrical components to cater for the power surge on start up. n Short component life.

14. 14 n Primitive, but familiar - Just a simple contactor in circuit between the motor and supply giving only unsynchronised on-off control n No control over inrush currents or torque surge at start up n Very rapid acceleration of load with large transient forces placed on drive train and electrical system Direct-On-Line Starters

15. 15 Direct-On-Line Starting CURRENT TIME 600%

16. 16 Star-Delta Starters n Uses three contactors and a timing mechanism to switch between them. n Installation costs are greater because of the need for 6 connections between the motor and starter. n If the transfer occurs at less than 80% of normal speed, large current and torque surges can arise.

17. 17 The Star-Delta Trauma

18. 18 Star/Delta Start

19. 19 n Inserts a resistance in one or more of the stator phase connections. The resistance is progressively reduced as acceleration occurs. n Starts are limited n Installation and running costs are high. n Smoothest and least stressful method of electro - mechanical starting Primary Resistance Starter

20. 20 Other Means Of Starting n Auto transformer n Primary Reactance

21. 21 Semiconductor Motor Controller n Is based upon the silicon controlled rectifier or ‘thyristor’. n By pulsing a thyristor, it switches from ‘off’ to ‘on’ until the current stops flowing though it - which occurs every half cycle in an AC. supply. n By controlling electronically the thyristor turn on point, it is possible to regulate the energy passing through it.

22. 22 Thyristor Control

23. 23 Semiconductor Motor Controller (cont.....) n By starting with a large delay angle and gradually reducing it, the motor terminal voltage is increased from a low value to full voltage, giving a smooth, stepless, start.

24. 24 A Soft Start compared CURRENT 6-700% DIRECT-ON-LINE STAR-DELTA SOFT START 100% TIME

25. 25 The Result is :- n In a simple, reliable and cost effective piece of equipment, all the problems of electro-mechanical starting have been banished to the past!

26. 26 Running Induction Motors LOAD 0 1/21/1 EFFICIENCY 100%

27. 27 The Action of the Optimising Mode - 1 n Optimising continually monitors the motor to improve the part-load efficiency by reducing the degree of over-fluxing of the stator. n The part load pF of the motor is improved.

28. 28 The Action of the Optimising Mode - 2 n This produces a significant reduction in kVAr and kVA, as well as a useful reduction in kW. n Electrical losses in the stator and feed cables are reduced. n Motor performance is unimpaired.

29. 29 Applications n There is virtually no fixed-speed application of an induction motor which cannot benefit from the fitting of a QFE soft-starter. n In particular, pumps and pumping systems benefit from the soft-stop feature and the reduction in cavitation effects.

30. 30 Applications n Fans, particularly high inertia ones, enjoy smooth, stepless acceleration at controlled current levels without the damaging effects of the star-to-delta transfer. n The life of frequently-started drives and of reversing drives is considerably extended by the soft start action.

31. 31 Applications n Compressors, n Chillers, Escalators, n Conveyors, n Mixers, n Rollers, n Screw feeders. n MG sets (elevators)

32. 32 Applications n Ball mills, Crushers, n Blowers, Pelletisers n Grinders, Presses, n Saws, Washers, n Moulders, Sifters, n Screens, Tumblers, etc..,etc...,

33. 33 Applications n All these and many other applications have been successfully softstarted by the QFE.

34. 34 Reliability n IEC 60947-4-2, EN 60947-4-2 AC Semi-Conductor Motor Controllers and Starters’ defines the soft starter in every important aspect. Purchasing a controller conforming to this standard will safeguard the user from poor equipment. n UL listed for the United States and Canada

35. 35 The End