SynRM and flying start, can your drive control it?

Flying start is critical for many of today’s fine-tuned processes. Not all VSDs respond the same when controlling synchronous (SynRM) reluctance motors.

Imagine you are walking in a metals factory. Above you, a large ventilation fan is pulling hot air upwards. The factory you are in is working on making energy saving investments and recently installed a synchronous reluctance (SynRM) motor on that ventilation fan. They are saving energy and air quality is on target.


And then…

The power goes out. Not for a few milliseconds, but for several seconds, maybe minutes. The drive will recover energy from the spinning fan blade (load) as long as there is sufficient inertia to maintain control, but eventually it loses power. The drive’s capacitors feed energy for a while, but soon they are exhausted, and the fan now coasts. The fan’s inertia keeps the blades moving, slowing down slowly. And just as suddenly as the power went out, it’s restored and the drive kicks back online.

What does your VSD do?

Now your VSD has a choice: can it figure out how to detect the now unknown speed of the slowing fan and gracefully return the motor back to its previous speed of 1,000 rpm, or does it have to start the speed from 0 rpm, braking the motor and fan dramatically to rest before bringing it back up to speed? This dramatic braking effect can break belt drives or gearboxes, or even destroy the fan completely. That’s not good for any data center or process line.

That’s why it’s important to ask about flying start with your variable speed drive supplier. Not all drives for SynRM motors are capable of capturing a spinning fan, or a spinning decanter or a pump. It’s best to ask about these situations before you need the drive to respond.

Flying start is common

Of course this fan example is only one scenario. Flying start requirements are pretty common. Take for example another fan in a ventilation shaft. When not running, it’s possible that an updraft in the shaft will cause the fan to start spinning (either forwards or reverse). Here the drive needs to be aware of this spinning and ramp up accordingly. Sometimes pumps face a back-pressure that causes the pump’s impeller to spin backwards. The drive needs to be able to sense this and match the motor speed and direction to the moving impeller.

Make sure you get the control you need

Energy efficiency may have been one factor to select SynRM motors, but reliability and the performance control is the reason all of our ABB drives for SynRM motors are 100% flying start compatible. That gives you the real independence to choose ABB SynRM motors and drives.

Looking to learn more about drives for SynRM motors? Here are four things to consider when you are choosing drives for SynRM motors.

Ask your drives supplier about flying start control for SynRM. What is your experience with this issue? Leave a comment below, we’d love to hear from you.

Categories and Tags
About the author

Linda Stenman

I’m currently a Product Manager responsible for putting together drive and motor packages. I started working for ABB in 2008 as an Area Sales Manager for motors focusing on South Asia. During that time I got to see and learn about the value drive and motor packages give our customers. Now, SynRM packages are a main focus for me. I’m excited about the potential these packages offer our customers for energy savings and improved process performance.
Comment on this article