The Increasingly Persistent Problem of Momentary OutagesBack to Top
If all faults were persistent, then establishing protection along feeders would be simple. All a utility would have to do is place single-operation devices, such as fuses, coordinated so they operate faster as you get further away from the substation. Utilities wouldn’t have to worry about momentary outages at all.
The fact is, utilities do have to worry about momentaries. A lot.
Until recently, short interruptions were somewhat hidden, like the portion of an iceberg under the surface. I am old enough to remember my first ‘digital clock radio’… digital because it had numbers instead of analog hands. But when the power went out, it didn’t reset to 12:00 and blink. When the clock flipped to the next minute, it was just a bit behind the actual time when power was restored. Contrast that to today, and the millions of Wi-Fi routers and connected devices in our homes and businesses, most without power backup. A loss of power for even a few seconds drops connections, wastes time, and loses online transactions.
What I am getting at is, the grid-performance criteria set up in the Seventies and Eighties was thought up during a time when short interruptions would go virtually unnoticed. A rise in social media outrage shows that momentary power outages today are more than just nuisances. They cost electricity users real money.
A preliminary update to an earlier report from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory suggests the annual U.S. cost of short interruptions (lasting 5 minutes or less) is rising, from $52 billion annually in 2002 to $60 billion in 2014. As a result, there’s a growing trend of customers, utilities, and certain regulatory agencies around the world that are taking notice of short interruptions.
Compounding the issue, distributed renewable generation is being connected at a growing rate to the distribution system. It’s on the roofs of both homes and small businesses. The reason this is important is that this generation source is now also depending on distribution network reliability to provide energy to the network.
Different types of generation have different recovery times. They all get knocked offline by a short interruption. Some recover quickly, within a few minutes, and others may be subject to manual intervention of complex startup sequences, meaning they are offline longer, even though the service is restored to the feeder and the load is fully present. Taken in scale, such as during a large storm with many scattered outages, this is bad news for utilities because a growing portion of the generation is not available when they need it most. This can aggregate from a small local problem to a larger distribution network problem as generation availability is shifting on and off.
We are at a very interesting apex within our industry in that distributed energy resources are highlighting that today’s grid is not the grid we need for tomorrow. There are challenges here that are not as apparent or as simple as increased “blinks” noticed by consumers.
The growing problem of short interruptions clearly exists. We need to have a broader vision of what “reliability” is, meaning momentary interruptions do matter and must be addressed.
I’d be interested in learning your thoughts on this issue in the Comments section below.
July 19, 2018