Dynamic Electric – An industrial drive system basically consists of a mechanical working equipment or load, which has to be kept in motion to turn out mechanical work, equipment to do this job, called the prime mover, and a transmission to transfer energy from the prime mover to the mechanical load. Transmission equipment such as a gearing or belt may be used to match the speeds of the prime mover and the load. The transmission may also be required sometimes to convert rotatory to linear motion and vice versa. Thus, a combination of a prime mover, transmission equipment and mechanical working load is called a drive.
I.C. engines, steam engine, turbines or electric motors may be used as prime movers. However; in industrial drives electric motors are predominantly employed for this purpose due to their inherent advantages, such as overload capacity, efficiency, better dynamic and transient behaviour, availability in various sizes and designs compatible to load requirements, etc. An electric drive can be defined as a drive, using an electric motor as a prime mover, and ultimately converting electrical energy to mechanical energy. The electric motors used may require some types of control equipment to achieve speed control and/or torque control. These controls make the motor work on a specific speed-torque curve, and may be operated using open loop or closed loop control.
Advantages and Disadvantages of Dynamic Electric:
- Availability of electric drives over a wide range of power a few watts to mega watts.
- Ability to provide a wide range of torques over a wide range of speeds. DC motors are very versatile in this aspect. However, with the advent of thyristors and thyristor power converters, ac motors are also now capable of giving a smooth speed control.
- Adaptability to almost any type of environmental or operating conditions, such as natural, forced ventilation, totally enclosed, submerged in liquids, exposed to explosive, or radioactive environment, etc.
- No hazardous fuel is required. No exhaust gases are emitted to pollute the environment. The noise level is also low.
- Electric drives have an overload capacity which can be made use of in selecting a smaller motor for short time duties. The efficiency is very
- The speed control of these motors is straightforward. Using a proper control they can be made to operate on a desired speed-torque curve to suit the mechanical load. Gear less coupling to the mechanical load, especially for low-speed rolling mills is possible. A smooth transition from one set of operating conditions to another is possible, with a high quality of dynamic performance.
- An electric drive is capable of operating in all four quadrants of the speed-torque plane, i.e. motoring and braking in either direction of Regenerative braking, in which the kinetic energy of the rotating parts is advantageously returned to the mains is possible only with electric drives.
- The motor can develop a steady torque because of symmetry, on a balanced sinusoidal supply. The operation is quiet. However, non-sinusoidal supplies to the motors when, fed from converters may cause some torque pulsation due to the time harmonics of the supply voltage/current which may become objectionable particularly at low
- Electric motors are available in a variety of design ratings to make them compatible to any type of load.
- The drive can be started and accelerated to the design speed at very short notice. Full load may be applied almost immediately. There is no need for refuelling or warming up of the motor, and it requires little However, electric drives do have certain drawbacks:
They require a continuous power supply, particularly in vehicle propulsion if there is no power rail available. The power supply equipment needs to be carried on board, requires a lot of space, and is bulky. Problems of saturation of iron and cooling make the electric motors have a lower power/weight ratio.