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What Is a Variable Frequency Drive: Triol Corporation Response


Variable Frequency Drive VFD Meaning

Starting from the very first introduction of an electric motor in 19th century, a much concern connected to development technologies allowing to control its performance arose. Today almost a quarter of the electrical energy consumed worldwide falls on electric motors utilized within industrial applications. Apparently, it is almost impossible to find an enterprise without the electric motor application, enabling HVACs, elevators, conveyors, grinders, pumps, lifting systems, etc. Engineering aspects of the AC motor technology have resulted in emerging such an equipment as a Variable Frequency Drive, solving all the relevant key problems.

What is VFD

The Variable Frequency Drive (also alternatively referred to as VFD, adjustable-frequency drive, variable speed drive, or AC drive) is defined as an electrical device exercising a motor control function while driving the electric motor by means of varying the power supply frequency and voltage, providing that as a result the motor speed is adjusted respectively. For example, the VFDs are often utilized to convert a three-phase or single-phase AC power mains current with frequency of 50 (60) Hz into a three-phase or single-phase current with frequency from 1 Hz to 800 Hz. Modern VFDs enable digital control for equipment performance, which greatly simplifies technological processes at plants. The VFD is a versatile equipment protecting motors against overcurrent occurring in acceleration-deceleration conditions, involving various modes optimized for specific requirements for braking, power boost, failures avoiding, etc. Today the variable frequency drives are widely used in industry and are available in different types and modifications, such as single-phase and three-phase VFDs evolved to meet a wide range of applications requirements. VFDs types differences are contained in methods for frequency and voltage control, and harmonic mitigation technologies. The mostly used designs of the VFDs are a pulse-width modulation (PWM), an inverter of voltage source, and an inverter of current source. Currently, the PWM technology is the most common. It requires switching the power devices of the AC VFD inverter (transistors or insulated-gate bipolar transistors, that are also often referred to as IGBTs) on and off repeatedly in order to generate appropriate voltage levels of root-mean-square (RMS). In this case the output frequency and voltage are controlled via varying the width of the pulses.

Energy Consumption Optimization

One of the biggest advantages of the VFD is that it increases energy efficiency significantly. It means, that the controllable parameters of the motor are altered in accordance with load changes. The variable frequency drive reduces energy consumption comparatively to direct-on-line (DOL) operation mode, that provides the motor to run at a full speed irrespectively of the load demand. The VFD excludes excessive current supply to the equipment, gradually declining frequency and voltage to meet the current load requirements. As a result, the VFD decreases expenditure for power supply for more than 40 %, depending on a character of motor utilization. A commonly used starter for the electric motors often draws Locked Rotor Amps (LRA).  This means that the rotor becomes locked and enabled to move while the supply power is still applied. It occurs in a case of a bound pump, which results in overloads and a failure of the motor, as well as in a case of a startup. This phenomenon leads to a crucial increase in electrical demand at manufacturing plants where the LRA takes place in many electric motors. Since the VFD negates such downsides of electric motors operation and broadly decreases electric energy consumption, its purchase and integration to the technological processes are justified and to be reimbursed promptly due to an essential cut in total electricity costs.

Maintenance Expenditure Decrease

The main function of variable frequency drive is that the VFD eliminates a need to utilize mechanical drive elements (gearboxes, etc.), providing that those components are expensive and are a subject for complex additional maintenance, as well as require extra space for their arrangement. The variable frequency drives are controlled digitally and perform required operation without any mechanical mediator devices between the motor and the load. The VFD starts the motor at zero voltage and frequency, while the motor start without the VFD may require the current supply higher by up to eight times as the current of the motor full-load. Such an operation affects stator windings and generates heat, which results in reducing a lifetime of the electric motor. Also, this uncontrolled type of operation generates a significant drain that is dramatically harmful for power distribution systems at plants due to created supply voltage sags, which can lead to failures of some sensitive equipment (computers, static switches, sensors, contactors, etc.) within the distribution system. The variable frequency drive eliminates this hazard and thus protects not only the motor and the load equipment, but also every device in the network. But the most ponderable technical advantage of the VFD in this scope is that it provides smooth operation of the electric motor in accordance with the load requirements, excluding mechanical shocks, that increase the wear and tear of the connected equipment (both the motor, and the load). Consequently, repair intervals are increased, maintenance costs are decreased, and the facilities lifetime is extended.

Technological Processes Improvement

Every type of devices connected to the electric motors at plants should perform effective work peculiar for a definite kind of technological processes. In such a manner, a belt-conveyor feeder must move smoothly without jerks, and a pump engaged in water supply for public utilities must provide continuous operation at a stated output pressure. The motor utilized without a VFD maintains senseless and unable to conduct controllable and adjustable performance. Such a “blind” motor without an accurate control of a torque being applied to the load may create downtime and losses for enterprises. Unlike this nonprofit type of motor arrangement, the VFD optimizes technological processes by adjusting motor operational modes in respond to production specifications and supply network conditions. For instance, the VFD may be set to a torque limit, that cannot be exceeded by the electric motor. With the VFD it becomes possible to start the motor at a stated speed, control a ramped stop, enable reversing mode, exclude shocks and jerks, and alter equipment operation remotely due to a programmable process controller, all this results in controllable and adjustable technological processes.

Fundamentally New Opportunities with Triol VFDs

Low-voltage Triol AT24 and middle-voltage Triol AT27 Variable Frequency Drives have already proved their efficiency, reliability, and versatility at the electrical equipment market. Triol VFDs are successfully implemented in a wide range of areas, such as fuel and energy sector, housing and utilities, infrastructure, mining industry, construction industry, cement production, metallurgy, etc. Every line of these products is customized and constitutes a flexible and high-quality solution optimized for different kinds of technological processes. It is a ready resolving match for any challenges arising in any possible industrial fields. Contact us and find more details about Triol Variable Frequency Drives designed specially to remarkably increase profits for your particular business.

Discover a brand new way to control proven equipment with Triol solutions!

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