Used where mechanical equipment is powered by motors, AC drives provide a safe, efficient, and dependable option. There are numerous ways that an AC Variable Speed Drive System can be of benefit, two of which will be covered here.
To understand the benefits of an AC variable Speed Drive System, we must first understand what it does. An AC variable Speed Drive System allows the motor to be controlled at startup by making available a range of speed and torque control as opposed to starting the motor across-the-line. Starting a motor across the line basically means that once it is turned on it runs at full power until it reaches its running speed and will continue to run at that speed until it is turned off. Since Christmas is right around the corner, we’ll use a Christmas tree as an example to help explain this. Once lights are strung on a Christmas tree and the chord is plugged in, the lights receive electric current and turn on. When the lights are unplugged they lose their current and turn off. Unless you’ve spent the extra money on dimmable Christmas tree lights, you will have two options: off or on. There is no option in between. When starting a motor across-the-line there is no variance in the speed given to the motor—either it’s on or it’s not. An AC Variable Speed Drive differs in its startup, which brings me to the first advantage:
Upon startup, AC Drives power on with a speed of zero and ramp up at a controlled pace until they’ve reached their set speed. To help explain this, think of your cellphone. When it’s powered on it takes a few seconds to warm up before you’re able to use it. While it’s not exactly the same, an AC drive essentially “warms up” the motor before it hits full speed. It does this to protect against jolts and harmful shocks which can be a result of starting across-the-line. The brilliant thing is that the speed the drive accelerates to is programmable—meaning it can be set to a fixed speed or the drive can be allowed to adjust speed so the load operates in the most efficient manner. It can even allow the motor to operate at a reduced speed as to conserve energy. Because of this ability to control speed so precisely, it can be used to accommodate fixed or variable load demands. In addition, AC drives are also designed to monitor and control multiple variables including voltage, current, and speed to make sure that the user has a safer motor operation.
Another key benefit of having an AC variable speed drive system is their significantly lower maintenance costs versus DC motors and drives. The main components of DC motors that require maintenance are commutators, brushes and rotating armature coils which are subject to centrifugal force. These components need frequent routine maintenance, and eventually require rebuild or replacement after a certain amount of wear. The costs associated with service and eventual replacement can be high—especially when there are multiple motors involved. This doesn’t even take into consideration what happens if a DC motor or drive fails. A technician is required to troubleshoot – and DC drives and motors are notoriously difficult to diagnose. AC motors have fewer components and require less maintenance. An AC drive protects the motor by monitoring for problems and correcting them if it can. In some cases, if the drive cannot correct the situation it will shut the system down to prevent serious damage. In either case, diagnostics are run to pinpoint the exact error—allowing the situation to be corrected as quickly as possible.
Whether you are looking to control speed or reduce high costs associated with DC motors, AC variable speed drive systems are a great option. They are compact, robust, and require little maintenance.