Technology & Engineering
Variable Speed Drive
A Variable Speed Drive is a device used to control the speed and torque of a motor by varying the motor input voltage and frequency. It allows for energy savings, precise control, and reduced wear and tear on mechanical components. Variable Speed Drives are commonly used in industrial and commercial applications to optimize the performance of motors and machinery.
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7 Key excerpts on "Variable Speed Drive"
- Malcolm Barnes(Author)
- 2003(Publication Date)
- Newnes(Publisher)
1 There are many and diverse reasons for using Variable Speed Drives. Some applications, such as paper making machines, cannot run without them while others, such as centrifugal pumps, can benefit from energy savings. In general, Variable Speed Drives are used to: • Match the speed of a drive to the process requirements • Match the torque of a drive to the process requirements • Save energy and improve efficiency The needs for speed and torque control are usually fairly obvious. Modern electrical VSDs can be used to accurately maintain the speed of a driven machine to within ±0.1%, independent of load, compared to the speed regulation possible with a conventional fixed speed squirrel cage induction motor, where the speed can vary by as much as 3% from no load to full load. The benefits of energy savings are not always fully appreciated by many users. These savings are particularly apparent with centrifugal pumps and fans, where load torque increases as the square of the speed and power consumption as the cube of the speed. Substantial cost savings can be achieved in some applications. An everyday example, which illustrates the benefits of variable speed control, is the motorcar. It has become such an integral part of our lives that we seldom think about the technology that it represents or that it is simply a variable speed platform. It is used here to illustrate how Variable Speed Drives are used to improve the speed, torque and energy performance of a machine. It is intuitively obvious that the speed of a motorcar must continuously be controlled by the driver (the operator) to match the traffic conditions on the road (the process). In a city, it is necessary to obey speed limits, avoid collisions and to start, accelerate, decelerate and stop when required. On the open road, the main objective is to get to a destination safely in the shortest time without exceeding the speed limit. The two main controls that
- Mark Brown, Jawahar Rawtani, Dinesh Patil(Authors)
- 2004(Publication Date)
- Newnes(Publisher)
6 Troubleshooting Variable Speed Drives 6.1 Objectives 9 To understand the basics of VSDs 9 To understand the basics of converters 9 To understand the basics of inverters 9 To understand the installation, commissioning, and troubleshooting guidelines. The need for VSDs Fixed-speed motors and two-speed motors have been dealt with in previous chapters. Various industrial applications require motion control of machines with the help of such motors. VSDs provide continuous range control over the speed of the machines. Some applications, such as paper mills, rolling mills, pumps, and machine tools cannot run without these while others, such as centrifugal pumps, can benefit from the energy savings. In general, VSDs are used to perform the following 9 Match the speed of a drive to the process speed requirements 9 Match the torque of a drive to the process torque requirements 9 Save energy and improve efficiency. 6.2 Basic VSD Any basic electrical VSD consists of a motor, drive control unit, sensing unit, and an operator input. The basic block diagram of a variable speed electrical drive is show in Figure 6.1. The drive control unit is a device, which modulates power going from the source to the motor. Using the operator panel, one can increase or decrease the speed set point. A feedback unit gives the drive the actual speed feedback. The power modulator or the drive control unit then controls the speed, torque, and power, along with the direction of the motor and the machine. The power modulator may be used as a single device, for controlling a motor. It may have to be used in a combination type for certain other types of applications. The following are the types of power modulators or converters along with a brief description of each.
- Barbara Renner(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
CHAPTER 8 Variable Speed Drives 8.01 Plant operating personnel are generally not involved in the selection of Variable Speed Drive equipment for a given application. Instead, the design or consulting engineer makes the selection based on his preference toward one or more drive manufacturers and the requirements of the machine or pump that it will power. In addition, the contractor who installs the equipment may have a voice in the selection of the drive. This selection, however, may be based more on financial than design considerations but should be approved by the engineer or the plant owners before it is installed. 8.02 Many different methods are used to vary the speed of a machine, and many varieties of Variable Speed Drive equipment are presently being manufactured. Design features and component selection are different for each drive that is manufactured. Although some basic maintenance procedures can be applied to many units, most Variable Speed Drives require specific maintenance that applies only to their particular design. VARIABLE SPEED APPLICATIONS 8.03 Variable Speed Drives are used whenever the machine that they are driving cannot be run at a constant speed. Pumps, mixers, aeration, flocculation, and chemical feed equipment are only a few water or wastewater treatment plant devices that may require something other than a constant speed drive. For some machines, such as aeration blowers, the discharge valve may be modulated by special valves that permit the recirculation or bypassing of air while the blower runs at a constant speed, thereby eliminating the need of a Variable Speed Drive. 8.04 A Variable Speed Drive unit can be something simple or something very complex. In some instances, the drive device may be fairly simple, but the controls might be complicated. Most treatment plants use variable speed motors or belt-driven variable speed reducers to power various machines
- Boris M. Klebanov, Morel Groper(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
Section II Variable-Speed Drives The need to change the speed of driven units is com-mon. In many cases, it is made by changing the speed of the prime mover. For example, the rotational speed of car wheels or ship propellers is widely changed by the engine speed. Also, the speed of electric motors can be changed using electric and electronic devices. Modern appliances, such as variable-frequency drives (VFDs), allow the AC electric motor to change its speed from almost zero to the maxi-mum limited by the mechanical strength of the rotor, while the torque of the motor can be increased consider-ably. And what is more, the motor speed can be controlled by a computer to fit a predetermined program and/or changing parameters of the technological process. Similar appliances are available for DC motors as well. Not always can the speed of the prime mover be changed as needed for the driven unit. This depends on the speed versus torque characteristics of the motor and the driven device. There may also be other restric-tions. For example, the range of the speed variation of a combustion engine can be limited by the decreas-ing of its capacity and torque at lower speed, not to mention that the minimal speed of such engines is usually not less than one-fourth of its maximal speed. Further, in many cases, the equipment whose speed must be varied in operation is driven from power take-offs (PTO) mounted mostly on tractors or trucks. The PTO has a constant speed ratio with the engine that is to drive the vehicle, and its speed is adapted to this purpose. In these cases, the equipment that needs speed adjustment should be connected to the PTO through transmissions with variable speed ratio. These transmissions can be mechanical, hydrostatic, or hydrodynamic. This page intentionally left blank This page intentionally left blank
- Mukund R. Patel(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
397 15 Variable-Frequency Drives The power electronics motor drive comes in two major types: (1) the servo motor drive to control the precise speed and position of the rotor and (2) the motor drive for varying motor speed in response to a desired change in the load output, such as the air ventilation and fluid pumping rate. The response time and precision in position are important in the servo drive but not in the variable-speed motor drive. Our inter-est in this chapter is primarily focused on the variable-speed motor drives. The variable-frequency drives (VFDs) for ac motors were initially developed in the 1970s for oil refineries, where numerous motors are used to pump oil all year around. Although costly at the time, the significant energy saving at the end of every month paid back the drive cost within a few years. Then onward, for the rest of the drive’s life of 20–30 years, the VFDs added to the corporate profits. Most power installations now use VFDs with pumps for water, oil, and refrigeration, and with fans for air ventilation. Most cruise ships use VFDs for propulsion motors as well. The VFD primarily controls the speed, torque, acceleration, deceleration, or direction of rotation of an ac motor. Unlike the dual-pole—hence dual-speed— motor, the VFD allows a continuous resolution of the speed control within its operat-ing range. The benefit of the infinitely variable-speed motor is to increase the energy efficiency—doing the same work at a minimum expenditure of kilowatt-hours—or to optimize the product quality or the production process. In addition to their use with large motors in oil refineries and ship propulsion, the following are a few other examples in medium power ranges: • A pump supplying water in a high-rise building may run at low speed dur-ing night time and high speed in the afternoon to provide the required flow rate while maintaining the system pressure.
- Ali Emadi(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
6 Adjustable-Speed Drives and Their ApplicationsAs environmental and other concerns slow the growth of electrical energy generation in coming years, it becomes essential that we conserve and use limited and precious resources more efficiently. Conserving electricity and making it a better energy source relies on the widespread adoption of the power conversion process, which takes electricity from a source and converts it to a form exactly suited to the electrical load.Electric motors consume more than 60%of all electrical power in the United States. Adjustable-speed drives (ASDs) can improve the efficiency of these motors by about 50%in many applications. They can also reduce costs considerably. Power electronics allows us to develop efficient speed and torque control of electric motors at low costs. This, in turn, calls for development of optimized electromechanical power conversion units.Today’s technology requires different speeds in many areas where electric machines are used. Electric machines that use traditional control methods have mainly two states—stop and operate at maximum speed. Adjusting speed in these machines is costly and hardware dependent. This is because an increase in the machine size and mechanical parts requires more maintenance and less efficiency. After the discovery of semiconductors and the introduction of semiconductor devices such as diodes and transistors to industry, ASDs have become very popular because of their advantages over traditional control methods. The machine size is smaller and requires less maintenance and hardware.Using ASDs, the speed of a motor or generator (electric machine) can be controlled and adjusted to any desired speed. Besides adjusting the speed of an electric machine, ASDs can also keep an electric machine speed at a constant level where the load is variable. For example, if the desired speed of the conveyer showed in Fig. 6.1 is 1 m/sec at any time, changing the load will not change the speed (Fig. 6.2
eBook - ePub- Thomas Howard Blair(Author)
- 2016(Publication Date)
- Wiley-IEEE Press(Publisher)
CHAPTER 18VARIABLE FREQUENCY DRIVE SYSTEMSGOALS
- To understand the basic design and construction of variable frequency drives (VFD)
- To calculate the synchronous frequency and slip (in percent and rpm) of an induction motor fed from a VFD
- To describe the difference and benefits/limitations between a voltage source drive and a current source drive
- To be able to define the maximum safe speed of an induction motor based on NEMA standards
- To describe the difference between a constant-power load, a constant-torque load, and a variable-torque load
- To calculate the pulse number for a given rectifier design and determine the phase shift required for the source transformer
VARIABLE FREQUENCY drives (VFD) and Variable Speed Drives (VSD) are used to control the speed and/or torque of induction and synchronous motors at the power generation facility when speed control or torque control is required for the application. Their use varies from small pumps pumping water from one location to another for utilization to control flow or pressure of the water, to very large fans used to control the flow of air for combustion through the main furnace.The types of VFD technologies available are varied and each has its own unique advantages and disadvantages. While details of construction vary from manufacturer to manufacturer, the three main types of VFD are the voltage source inverter (VSI), the current source inverter (CSI) and the pulse width modulated inverter (PWM).A little clarification on terminology is in order. A rectifier converts AC voltage to DC voltage. An inverter
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