How do I know if my project will have a harmonics issue and how do I determine the right harmonic solution?

So let's say you are doing a project and you want to know if you're going to have harmonic issues.

The first step is to understand what you're adding to your power system, whether it's an existing system or a new construction system. Are you adding nonlinear loads or perhaps multiple variable frequency drives or rectifiers, vehicle chargers or something that could cause harmonics? If you are, then you need to take into account what impact that harmonic current is going to have on your system and what potential problems it may cause.

The following questions need to be considered. What is on your power system that might interact with harmonics? Do you have capacitor banks? Do you need to think about harmonic filters? If nonlinear loads are in the system, what things could go wrong? What could go wrong is having enough current distortion to cause voltage distortion, resulting in equipment misoperation. Too much current distortion can overheat cables, transformers and other equipment on the system. 

An easy rule of thumb is at about 20% of a transformer's capacity. For example, having a 1000 kVA transformer, 200 horsepower or  200 kVA of variable frequency drives might be the place where you start to concern yourself with how much that is going to affect the system. Then you need to think about if those problems or potential problems are going to cost money. Just because you add nonlinear loads does not mean you are going to have a problem. If it costs money in terms of equipment failure, i.e., oversizing the generator, buying K-rated or HMT transformers, or spending more money on such things, that's where you need to start thinking whether you should be concerned or not. 

There are tools you can use to make sure you do or don't have a problem. At www.eaton.com/harmonics, there is a harmonics calculator that you can use to estimate some things related to whether or not you have an issue with voltage or current distortion. 

Then of course, you can always model the power system and simulate with just a four-, five-, six-bus system the harmonic loads, the current sources of harmonics and the system bus loads that are going to interact with other loads, and maybe the utility, to determine limits, measurements and things like that. 

If you do have an existing system or you have a system that you're going to add to over time, you are going to want to do some voltage and current measurements to try to understand what those limits and levels are going to indicate. You want to understand what those measurements mean in order to determine whether or not you're going to have a problem. 

There are tools you can use and people out there who you can talk to. Try to get the advice from people who have done this before. Also, go back to existing projects you've done that may be similar and look at the measurements to determine if the project you're working on—whether it's adding to a new or existing system, or creating a brand new construction system—is going to have harmonic issues.