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Basics Construction of VFD Inside the VFD there are 4 major sections: rectifier (AC/DC Converter), intermediate circuit (DC Link), inverter (DC/AC Converter) and control/regulation (for interface)
Working of VFD The operation of the drive is as follows : Power first goes into the rectifier, where the 3-phase AC is converted into a rippling DC voltage. The intermediate circuits then smoothes and holds the DC Voltage at a constant level or energy source for the inverter. The last section, the inverter, uses the DC voltage to pulse the motor with varying levels of voltage and current depending upon the control circuit. The control section uses the frequency, voltage and phase angle to control the inverter.
Function of VFDVFD is a system for controlling the rotational speed of a motor by controlling the frequency of the electrical power supplied to the motorVariable speed drives gradually ramp the motor up to operating speed to lessen mechanical and electrical stress, reducing maintenance and repair costs, and extending the life of the motor and the driven equipmentVariable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand. By using VFDs the system can maintain a constant level or pressure without continuously cycling the pump or fan on and off. This allows for a better system control of a level or pressure, instead of cycling between a wide differential
How to analyze the necessity for VFD at a locationWe check for the pump valves that are throttledIf the valve is 30-40 % throttle (closed), then it indicates that flow required is lessIn such a case VFD can be installed, the valve can be opened fully and fluid’s speed and flow can be controlledFor example : Back water pump 2 at PM-1, was running at 1400 rpm taking 22 kW before installation of VFD. But after VFD installation, it consumes 12 kW while operating at 1100 rpm.
How VFD works at these locationsVFDs are installed at Fan Pump motors.Fan pump motor responsible for providing stock to the Head BoxHead Box requires a control of either head or levelControl of a level or pressure in Head Box is done by VFDA reference signal is fed to the VFD and using a comparator, an error signal is generated based on the deviation of current value from the reference value. The controller in the VFD, then, increases/decreases the speed based on the signals generated
Head Box Pressure and Level Control LP Air from Air ReceiverDrive End Tender End HP Head box LT PT Inlet Pulp PV PCV LIC 4-20 mA IP PIC Air Drain SP Air Supply 1.4 0.2 To 1 kg/cm2 kg/cm2 Fan VFD Pump 4-20 mA IP- Current to Pressure Converter LIC- Level Indicating Controller SP- Set Point VFD- Variable Frequency Drive PV- Process Value LT- Level Transmitter PCV- Pneumatic Control Valve PT- Pressure Transmitter
Major Considerations while installing a VFD Motor Specifications VFD Specifications VFD input/output current Cable Size Starting parameters Motor name plate Reference speed Overload current setting Operating option (keypad/remote) V/f ratio control
Conclusive advantages of using a VFD Energy Savings Better Process Control Reduced Maintenance Higher System Efficiency Remote Mounting