Variable Frequency DriveIn short VFD, is an energy saving device by converting fixed frequency to adjustable frequency to control AC induction motor in variable speed base on the load's changes, also know as variable speed drive, frequency inverter and adjustable frequency drives. VFD also works as a phase converter to convert single phase input to three phase output in small ratings.
As one of the professional manufacturers of low voltage variable frequency drives in China, we can supply a wide range VFD ratings, from 1/2 hp to 500 hp, with single phase 220V to three phase 380V.
Our variable frequency drives are widely used in China domestic companies, and have been export to India, Pakistan, Australia, South Africa, and much more countries. our VFD can be used in pumps, fans, injection molding machines, HVAC system, constant pressure water supply system and lots of other applications which need vary motor speed.
The cost of the synchronous motor itself over the asynchronous motor, with increased in frame size, added copper and other materials, is another base reason synch motors are seldom, if ever used in the overhead hoist and crane industry. As far as precise travel and lifting speeds with cranes, variable frequency drives with the hardware and software fairly standard on most variable frequency drives (VFD) designed for the application, is more than adequate. These variable frequency drives not only deliver excellent efficacy and significant energy savings by maintaining very good Volts/Hz/RPM ratios. Utilizing motor speed regulation at 0.5% without an encoder and 0.1% with asynchronous motors, makes the most opted for joint overhead crane control package.
MV VFDs are - almost exclusively - three phase connections both upstream and downstream from the variable frequency drive. Although a LV VFD can be similarly connected to three phase, there are a large percentage of LV VFDs that are single phase devices (either upstream, downstream, or both).
When using single stage pumps, the pump speed is critical, and the pump curve should be verified. But when using submersible pumps, these are typically multi-stage (maybe 15+ stages) and can be reduced much lower in speed. With centrifugal pumps, of course efficiency drops off. Fans have a much lower threshold as where they become ineffective. We have done many pump and fan variable drive applications in the last 30 years, and turning the speed down has never been a problem... With constant-torque applications, it is not recommended to go below 30% even when using a severe duty motor.
This is a control system in which the ratio of frequency to the output voltage is constant when the frequency is changed. In this system, if the voltage to be actually valid decreases due to a voltage drop in a wiring or the primary coil of a motor, enough amount of torque cannot be output (the slower the speed is, the more this phenomenon affects.). Therefore, the amount of voltage drop estimated in advance is set higher (torque boost) to cover the shortage of the torque at low speed.
Detect a motor speed with an encoder and calculate a motor slip to identify the load magnitude. This control is a system which divides the variable frequency drive output current into an excitation current (a current necessary to generate a magnetic flux) and a torque current (a current proportional to the load torque) by vector calculation and controls a frequency and voltage optimally to flow a necessary current individually according to this load magnitude.
A variable frequency drive (VFD) is a static unit mainly consisting of semiconductor devices. Daily inspection must be performed to prevent any fault from occurring due to the adverse effects from the operating environment, such as temperature, humidity, dust, dirt and vibration, changes in the parts with time, service life, and other factors.
2) The external thermal relay may operate unintentionally due to the leakage current between cables.
One of the most common methods of varying pump shaft speed is to use a VFD. These VFDs take advantage of the fact that torque, speed and horsepower of an AC electric motor are related to the frequency and voltage of the electrical power supply.
For the VFD to be a sensible solution to your pumping application the system curve would have to fall on, or close to this best efficiency point line, or you will experience radial loads that will translate to shaft deflection. Most centrifugal pump companies want you to operate within 5% to 10% of the best efficiency point. Heavy duty pumps that have a low L3/D4 (shaft diameter to shaft length ratio) have a much larger operating window.
They also feature better operator interface features, including:
- start, stop and speed adjustment
- reversing and toggling between manual and automatic speed adjustment from an external process control signal
- alpha-numeric display, indicator lights, and meters to provide text information for communication and maintenance
- a front-mounted or cable-connected keypad for input
- input/output terminals available for push buttons, switches and other interface devices
- serial communication port for variable frequency drive configuring, monitoring and controlling using a computer
- loading of parameter settings from one VFD to another
- multi-day timers
- broadcast function to control dozens of VFDs from one advanced operator panel.
China industry and commerce can save 30% of its energy costs, which represents a significant 3% addition to the bottom line. All it has to do is implement a single, simple energy saving measure - fitting VFDs to its electric motors. However, I'm quite conscious that there are plenty of technologies out there claiming to be the panacea of all environmental ills. But in the case of the variable frequency drive, there is a real, mathematically demonstrable, argument.
Energy Savings result from reduced electrical costs by reducing the speed of the pump and by better temperature control - preventing temperature over-shoot (over heating) in the zones. In many applications the pumps are oversized (10 to 15%), so even in maximum heat load conditions, the maximum pump speed with the variable frequency drive is less than before the retrofit.
When compare with a variable frequency drive (VFD), the motor peak design ratio is basically preserved throughout the acceleration ramp. To put this in a general, simple explanation, when a 460 VAC/60 Hz motor is running at 30 Hz, the corresponding voltage to the motor should be in the vicinity of 230 VAC. Changing one value in the Volts to Hertz ratio without changing the other results in significant motor torque loss. A VFD will provide smooth starts from zero to peak speed as with the Hz/Voltage ratio maintained, near peak motor torque is preserved. Unlike a soft starter, it will provide the same balance ratio and control effect in a deceleration ramp as well.
With damper control, the input power reduces as the flow rate decreases, however under variable frequency drive control the power reduction is far more dramatic. The variable torque characteristic of the fan means that the relationship between flow and the speed of the fan is such that the input power reduces in a cube law relationship with the speed reduction, as shown in the graph.
Note: When operating at near full speed there is a crossover point where variable frequency drive control can use more energy than fixed speed control with dampers. This is due to the losses in the variable frequency drive exceeding the savings from the speed reduction.
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Variable Frequency Drives control AC motor for energy savings by adjustable speed, for short VFD, also named variable speed drives and frequency inverter.