Study of VFD Installations

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 motor

Variable 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 equipment

Variable-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 location

We 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 controlled

For 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.

VFDs in Drive Room

VFD SHIFTING WORK IN PROGRESS VFD IN LINE

Wiring Diagram of Fan Pump Motor

VFD in Drive Room

How VFD works at these locations

VFDs 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 level Control 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

4-20 mA

IP- Current to Pressure Converter

SP- Set Point

PV- Process Value

PCV- Pneumatic Control Valve

LIC- Level Indicating Controller

VFD- Variable Frequency Drive

LT- Level Transmitter

PT- Pressure Transmitter

0.2 To 1 kg/cm2Air Supply 1.4 kg/cm2

Fan Pump

VFDVFD

Head box

IP

PTPT

PIC

LTLT

LIC

LP

HP

Inlet Pulp

PCV

Air DrainSP

4-20 mA

PV

Air from Air Receiver

Head Box Pressure and Level Control

Tender EndDrive End

Major Considerations while installing a VFD

Motor SpecificationsVFD SpecificationsVFD input/output currentCable SizeStarting parameters

Motor name plateReference speedOverload current settingOperating option

(keypad/remote)V/f ratio control

Conclusive advantages of using a VFD

Energy SavingsBetter Process ControlReduced MaintenanceHigher System

EfficiencyRemote Mounting

Thank You