Hello,

When developing a model in order to run short circuit analyses, is it recommended to group LV motors <50HP? Upon looking at IEEE 399 and IEEE 551, this appears to be typical. Are individuals utilizing this technique or modeling all LV motors individually?

Thanks for the input.

I would use the red book as your go-to source, along w/ the purple/violet book. Per the red book, small motors are lumped into one "motor source" from a modelling perspective.

Mike

Hello, I'm in the UK where we typically run short circuit studies in accordance with IEC 60909. That standard suggests that "for simplification of the calculation" groups of asynchronous low-voltage motors "may be combined to a single equivalent motor". We generally follow this advice with our modelling and combine LV motors at each switchboard or MCC.

However, if there is a particularly large LV motor that may dominate a scenario (for example, an electric driven fire pump that is online when the system is in emergency mode) then we do model that as a standalone motor so we can switch it in/out as necessary.

Combining LV motors also reduces the task of data collection! We typically only ask for detailed motor data for the largest LV motors - this is in case we need to add them for a particular scenario, or for use in other studies such as coordination.