Why Are the Lights Blinking?

Article Courtesy of Brad Schafer, Sales Director – Technical Solutions

When products don’t perform as anticipated, Gresco receives a phone call. Generally, this is not good news, but I do enjoy problem-solving as it presents an opportunity to learn something new and assist our customers.

In this case, Gresco sold a backup generator to one of our partners. The generator had been installed at a school and final testing was scheduled for a day that wouldn’t disrupt normal classes. As Murphy’s Law required, there was a power outage during this window and the school was surprised to find their lights flickering while running on the generator. So Gresco got the call.

Each call is unique, but the process has some reoccurring stages:

• Fog of War

• Discovery

• Research

• Solution Hypothesis and Testing

• Documentation

Fog of War

I describe the initial state as the ‘Fog of War’. This term has a military background. It essentially means that you are aware that something has occurred or is occurring, but the truth is hard to see. At this stage you must proceed cautiously and keep a careful list of your assumptions. The information you are receiving could be second-, third-, or fourth-hand, and may be filtered or altered. Also, human memory is imperfect. Even sincere, well-meaning, individuals can misremember events, thinking ‘ABC’ happened when it was actually ‘ACB’. This is especially true in emergencies or high-stress situations.

Discovery

You escape the Fog of War through discovery. In the role of detective, you gather data, interview witnesses, and verify assumptions. Your aim is to uncover solid facts. Often you have imperfect data, so you need to exercise judgement in determining the credibility of some information. Through discovery you try to gain as clear an understanding of reality as possible.

When we got the call on the lights blinking, we scheduled a meeting to visit the school. Before the visit we collected data on the types of lights and the generator. It was no surprise when we arrived onsite and found many of our initial assumptions were wrong. The flicker was a heavy strobe. The wiring inside the school was not what we expected. There was an additional step-up transformer between the generator and the school, and some circuits were running off a step-down transformer. The school had no wiring schematics of their buildings. We collected nameplate data for all the relevant equipment and made schematics of how equipment was wired.

Research

Research is an extension of discovery. As you gain a clearer understanding of the situation, you begin to see which missing puzzle pieces you need to collect. This might involve working with a manufacturer, collecting data logs from equipment, reading through a manual, but most often the best resource is a technical expert.

Solution Hypothesis and Testing

Hopefully at this point you are narrowing in on the root cause and a potential solution, or maybe you have more than one possible solution. Now you apply the scientific method by making a hypothesis determining a way to confirm/deny if that theory is correct. As you work through scenarios you are eliminating alternatives and driving towards the root cause.

At the school we believed we had a grounding problem. A step-up transformer after the generator was wired for three phase 480 delta. That was fine for the three phase motors running the freezer, but the utility system was wired for 480 grounded-wye and the lights circuits were wired to run off the single phase 277-volt circuits. That meant the neutral current didn’t have a path when running off the delta 480. We tested/demonstrated the theory by powering one of the lighting fixtures with the normal utility 277 voltage where the unit worked normally and then we powered the unit from the generator and the light would not turn on.

This also explained why some lights were working while others were not. There was an additional step-down transformer to power some 208/120 circuits. Those lights worked fine because the 480 delta could power the step down transformer and lights on the transformer secondary had a healthy neutral connection.

For the final solution we found an alternate transformer with the corrected grounded wye winding in stock. A week later the transformer was swapped out and the strobing effect was eliminated.

Documentation

The final step is documenting what happened. You never know years later when you might bump into a similar situation. It only takes a few minutes to collect your files and pictures and put them in a folder you can later reference.

Debugging can be frustrating, but it can also be an opportunity to learn and make something better.

If you need help with a tough situation, give your Gresco Sales Engineer a call. Let us be your sounding board and use our network of contacts to help you solve your problems.