Geomagnetic Disturbance: What Is It?


PJM issued a warning Tuesday, May 14, that a potential geomagnetic disturbance could impact the PJM transmission system between 5:45 a.m. and 8 a.m. that morning.

This is a fairly rare event, but one with potential impacts to the electrical grid.

As is most often the case, there was no reported effect on the PJM system during that time; the alert served to warn generation and transmission operators in case they would have to take prescribed steps in their operations to offset the impacts of such a phenomenon.

Which raises the question…

What Is a Geomagnetic Disturbance Anyway?

Geomagnetic disturbances, which are also called solar magnetic disturbances, are caused by activity on the surface of the sun.

Sunspots, solar flares or other phenomena can produce large clouds of plasma, called coronal mass ejections, which can induce electric currents within the earth and on high-voltage transmission lines. These currents can flow up from the earth or down into the earth through grounded grid equipment, usually transformers.

High levels of these currents have the potential to damage transmission equipment.

For example, a major disturbance on March 13, 1989, caused a nine-hour power disruption in Quebec and also severely damaged a transformer at the Salem Nuclear Power Plant in Salem County, New Jersey.

The Space Weather Prediction Center of the National Oceanic and Atmospheric Administration (NOAA) monitors both solar activity and the earth’s magnetic field and issues alerts and warnings to grid operators so they can prepare for the impacts of space weather events. It was an NOAA notice on May 13 that prompted PJM’s alert.

How Does PJM Protect against Geomagnetic Disturbances?

When the NOAA Space Weather Prediction Center issues an alert to PJM rated above a certain threshold, PJM issues a warning to generation and transmission operators to prepare for a potential disturbance.

To help anticipate problems, PJM’s members have installed special equipment to detect and measure ground-induced currents caused by geomagnetic disturbances. When a disturbance is forecasted, PJM monitors the installed detectors at various locations. If sustained ground currents at a certain level are detected, PJM operates the system in a more conservative mode until the space weather event has ended. Read more about geomagnetic storms and their impacts outside of the electricity industry on the NOAA website.