Why We Use Variable Frequency Drive

Variable Frequency Drive is a common device in electrical work. I am responsible for several motor with different machinery in my factory and almost 65% of motor having own Inverter and 5% of motor are having share Inverter that means one Inverter can control two motor at a same time. Now come to the point, “Why we use Inverter or VFD?” In this post I am going to discuss all about it. So let’s go.

Inverter or VFD or AC Drive normally used to control load speed. Let’s consider you have a conveyer belt that needs to operate with two speeds. If you want to rotate it for 10 meter per minute and after an interval 5 meter per minute. Now how do you control the speed of conveyer belt? Fort this occasion you must use the Inverter / VFD / AC Drive to control the speed of the motor to control the conveyer belt.

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Let’s go for another example of using inverter. A motor can lift maximum weight of 20kg and now you want it to lift maximum weight of 10kg and if there is 11kg weight then your motor will stop automatically by overloaded. So making any program for any motor is very simple when you use an Inverter / VFD / AC Drive to control your motor. You just need to reduce the torque capacities by programming from Inverter and motor will operate automatically. So your demand can change by your required sector and logic.

If we use an Inverter / VFD / AC Drive to control our motor then famous Star Delta Connection don’t need to be use. First of all let’s discuss why we use star delta connection for a motor? Suppose you have a big motor and it starts with lot of start-up torque. For this reason motor need huge Ampere during its starting time. In this case, it impact on over-power protection system during the motor start running.

Just think, if your power consumption goes up too high and then suddenly decreases then your power supply system will affect badly as well as the other loads and the device will also face some trouble and it just for only one motor. Ok if the main power supply is coming from a generator then the situation can be more dangerous. For this reason we follow a simple system to get rid of this problem and it’s called Star Two Delta Connection. But Star and Delta con not control the speed of motor and Star connection take less current than Delta connection. For this reason for a big load we use Star connection for couple of second like 3 to 10 or may be more depending on our demand to stat it slowly with less current and when motor get enough rotation then we change it to Delta connection for further operation. Now for this operation if we use Inverter / VFD / AC Drive then Star-to-Delta Connection does not require. Just a simple program called Accelerator Time and Deceleration Time setting will set the starting and stop delay time for a motor to reduce taking more current.

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Another thing is that if we use an Inverter / VFD / AC Drive to control our motor then we don’t need to use Soft Starter. First of all let’s find out why we use Soft Starter and how can we replace Soft Starter by an Inverter. By the name of Soft Starter we can understand there is something that will start softly. And if it is a large motors then it will start softly and when motor start it will not cause harmful effects on the power system. So Soft Starter is responsible to start a motor slowly by programming. Now you can say an Inverter / VFD / AC Drive works by the same principle. Yes Inverters / VFD / AC Drives have some differences from the soft starter. Normally a place where we don’t need to control a motor when it running at full speed with full load then we can use a Soft Starter. But Inverter / VFD / AC Drive use where we need to control motor speed all time during its operation. In my factory we have some machine with ABB ACS880 Inverter and it control machine main motor by pattern with different speed.

ABB ACS880 Inverter
ABB ACS880 Inverter

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