A drive to save energy
By S.P. Suryavanshi
In today's competitive scenario, industrial manufacturers strive to maximise efficiency in all possible areas. Improvement in energy efficiency can be achieved only if the losses in various processes are minimised in an industry. Energy losses are categorised as under:
Electrical losses: Due to multistage power conversion and high staring current requirement in electromechanical equipment.
Mechanical losses: Due to conventional means of speed variation (belts, pullys, PIV gears etc.)
Thermal losses: Due to frictional losses in the mechanical flow control mechanisms and higher starting currents in electromechanical equipment.
Optimal energy solution
Keeping the above in mind, Siemens Ltd has consistently focused on products that help in conserving electrical energy and contributes in minimising losses. Variable speed AC/DC drives form an integral part of the manufacturing industry. Today, these are extensively used to increase the speed of operation, improve accuracy, faster response and higher efficiency subsequently resulting in increased productivity and consistency. When drives are used in place of conventional means of flow control, substantial amount of energy can be saved.
How energy can be saved?
A significant amount of energy is used by industrial processes involving equipments like fans, pumps and compressors. These equipments are seldom used at their full capacity and hence it is required to control the generated flow by one or more external means. The conventional method by far is to use constant speed motors and to control the flow mechanically by using dampers, throttle valve, inlet vanes etc. These mechanical means of achieving flow control have a major disadvantage, in terms of heat and friction, resulting in overall poor efficiency. By using variable speed drives it is possible to vary and regulate the speed of motor driving the pump or fan, in a step-less manner. This results in controlling the flow at the output very easily and efficiently.
Flow control using speed variation
The other method of flow control is to change the speed of the motor itself. It results in reduced power consumption. The situation is reversed in case of variable speed operation. When the pump is driven by a variable speed drive, flow reduction is achieved by reducing the speed from full speed to the required speed. For this speed a set of new pump head capacity curves is drawn through the new operating point.
How much energy can be saved depends upon various parameters. These are:
* The actual flow requirement over a period of time (utility profile)
* The rated capacity of the motor and actual load
* The conventional method of flow control currently used
Typical operating cycle
The centrifugal fan is generally sized to handle 100 per cent maximum volume requirement. However, peak volume requirements are minimal. The fan is operating at the reduced volume, 60 per cent to 70 per cent, most of the time. Once the operating cycle is known, by using typical load torque-speed characteristics of the pump or a fan, it is possible to work out the achievable energy saving with variable speed drives. Further, by knowing the number of days of operation, it is possible to work out the payback period of investment on the drive.
(S.P. Suryavanshi is Manager Marketing - Motors at Siemens Ltd)
Energy driven solutions from Siemens
The Siemens Master Series of drives is designed not just to improve industrial productivity but also to reduce the consumption of power. The company's drive range incorporates digital technology that accurately controls and regulates speed and torque. This technology is modular and can be easily and cost effectively adapted to various demands. Siemens provides a complete spectrum of variable speed drives to suit all applications, spread over a wide output range. These drives adapt to all voltages levels of international standards. The comprehensive range allows the user to optimally and economically choose the drive corresponding to application requirement.
In addition, there are many other advantages that the drives offer, such as: Accurate control of flow over a wide range; step-less control leading to a possibility of finer adjustments; reduced shock loads on piping systems; fundamental system power factor near unity; lower maintenance; and, possibility of interface with automation systems.
A drive to save energy