8 Introduction 0.2 Why use Speed Control? There are numerous reasons for adjusting the speed of an application: • Save energy and improve effi ciency of systems • Match the speed of the drive to the process requirements • Match the torque or power of a drive to the process requirements • Improve the working environment • Reduce mechanical stress on machines • Lower noise levels, for example on fans and pumps Depending on the application one or the other benefi t is predominant. However, speed control is proven to bring signifi cant advantages in many diff erent applications. 0.3 How to Adjust the Motor Speed? There are three main technologies to realise speed control used in industry.
Each has its unique features: Hydraulic • Hydro-dynamic type • Static types They are often favoured in conveyor applications especially for earth-moving and mining equipment. This is basically due to inherent “soft start” capability of the hydraulic unit. Mechanical • Belt and chain drives (with adjustable diameters).
• Friction drives (metallic) • Variable speed gear Mechanical solutions are still favoured by many engineers – especially mechanical engineers – for some applications, mainly because of their simplicity and low cost Electrical • FC with electrical motor • Servo systems (for example servo amplifi er and servo PM motor) • DC motor with control electronics • Slip-ring motor (slip control with wound-rotor induction motor) Historically, electrical devices for speed control were complex to handle and expensive. They were used for the most challenging tasks where no alternatives were available. The provided list of technical solutions for speed control of motors is not exhaustive