Variable Speed Drives

INTRODUCTION

Variable speed drives are very useful in conjunction with supply &return fans & cooling tower fans, In addition to this these are also very helpful in virtually any type of centrifugal pump. In addition, centrifugal chillers are a leading applications. Engineers consider Speed Control and recognize such systems primarily for its energy savings benefits.

VARIABLE SPEED DRIVES

We can find large number of variable speed drive systems that are available in the market and that have been widely in use for control of fan or pump speed. These include following

·        hydroviscous,

·        eddy current clutch,

·        direct current, and

·        Variable frequency converters.

The distinctive advantage of the adjustable frequency drive is that we may use the standard AC motors. This implies that equipments such as cooling towers can be effectively converted to automatic control without making any change in the mechanical components and major design.

Examples of Variable speed derives is induction motor.

The variable frequency drives (VFD), which play role of interface b/w the AC power supply & the induction motor, should attain the following fundamental requirements:

1. they should have the ability of adjusting the frequency according to the desired output speed.

2. they should be able to regulate the output voltage in order to maintain a constant air-gap flux in the constant torque region.

3. it should have feature to supply a rated current without any delay i.e. on continuous basis at any given rate of frequency.