Seeing Harmonic Problems On The Grid

By Roy L Hales

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Modern grid operators have a more complex task than their counterparts did a generation ago. There was very little intermittent energy twenty or thirty years ago and little need for sophisticated instrumentation. Now the infrastructure is aging and operators need to deal with intermittent energy sources like solar and wind, energy storage, plug-in electric vehicles, interconnects and increasing demand. They need better information, so they can react to changes fast. National Grid UK selected National Instrument’s CompactRIO platform to increase their capability of seeing harmonic problems on the grid by 400%.

Think Of CompacRio As A Computer

Brett Burger, NI’s senior product marketing manager of smart grid systems
Brett Burger, NI’s Sr. Product Marketing Manager – Smart Grid Systems (NI)

National Grid UK realized their grid was changing, is changing and will continue to change. So they chose a platform that can be used for a variety of tasks. It can measure harmonics on the grid and display them visually on a screen so National Grid can literally see noise that wind turbines, solar panels and high voltage interconnects are putting on their grid. This same platform can potentially be used for software that handles response control, fault analysis or any number of other issues.

“We don’t specialize in one-off problems, we specialize in platforms,” said Brett Burger, NI’s senior product marketing manager of smart grid systems.

“Think of CompactRIO as a computer. We call it an embedded controller. It has the modules that connect into it and those modules allow the controller to connect to the sensors that are on the grid. A non-industry example is a smart phone, which changes what it does based on the software you load on it. That’s our take in the smart grid space.”

Using This Platform

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Photo credit: harmonics graph (NI)

National Grid UK increased their ability to measure grid harmonics by 400% using this platform. They can now look at the 100th order harmonics, while they were previously restricted to little more than the 20th.

This is important because, as the transmission operator for England and Wales, National Grid is incorporating a great deal of wind and solar energy.

“The offshore wind farms around the UK are the same order of magnitude, the same scale as a coal-fired power plant, but unlike coal powered plants the generation is very dynamic” said Burger. “The amount of energy a wind farm produces depends on how the wind is blowing, how much is blowing and what time of day.”

The Quality Of The Inverters

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National Grid UK

The electricity goes through digital electronics, inverters, that change DC to AC. The quality of that electricity is subject to the quality of the inverters. They have not been on the grid long enough for operators to gage their full potential.

“They have this growing wind generation capability, creating noisy harmonics. They have solar online which also creates noisy harmonics. They have large high voltage DC interconnects with neighboring countries. Those interconnects are also high voltage DC coming through inverters. So a growing percentage of their energy is going through digital inverters and maybe subject to poor quality,” said Burger.

He added, “Harmonics are the power quality problem that can cause problems with data centers. A lot of the data corruption people talk about can happen because of harmonics.”

Sources of energy being transmitted to the National Grid UK, from the video below
Sources of energy being transmitted to the National Grid UK, from the video “Preparing for the Grid of Tomorrow” (below)

From the perspective of power quality, conventional energy sources like nuclear and coal are much “cleaner” and reliable, but they have negative environmental and potential political impacts. The UK is shutting down some synchronous plants as part of a decarbonizing effort.

Digital inverters do not perform as well as the electromagnets used in conventional generation because their energy supply is not coming from the constant rotation of a generator.

“So all these challenges come to bear and the grid, today is not equipped to provide the operator with the information that will let them control that,” said Burger. “They either don’t have the instrumentation in place to see where the noise is coming from, or to see what the power levels are, or the instrumentation they do have is not advanced enough to let them see this phenomena.”

Seeing Harmonic Problems On The Grid

National Grid UK used the CompactRIO platform and some developed software to display a heat map of their grid. They can see harmonics displayed in colors ranging from green to yellow and finally red as the quality degrades. This allows them to see problems as they develop.

“That’s the 400% improvement,” said Burger.

Though renewable energy has a very positive environmental impact on the grid, it would be problematic incorporating it onto the grid without this kind of technological assistance.