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MONITORING THE HEALTH

OF YOUR ELECTRIC POWER GRID Precision PC-Based 60-Hz Frequency Counter
by Doug Criner

Start ý Frequency and Time Errors ý A Struggling Grid ý Only Three Parts ý Sources and PDF

A STRUGGLING GRID

If the frequency is running slow and the time is running late, then it may indicate that the system is struggling. A sudden increase in frequency can occur if a large area is blacked out, either intentionally or by accident.

Although the entire grid runs at the same frequency, there is a phase angle between areas that are exchanging power. For example, if net power is being sent to Chicago from the East Coast, then the voltage phase of Chicago will be lagging slightly. A sudden change in power exchange between areas will show up as a change in the phase angle, which will be accompanied by an apparent frequency spike or dip. None of these events can be detected by monitoring the system voltage, which can be affected by any number of factors.

Measuring system frequency to within 0.01 Hz is not trivial and you must count a significant number of cycles to get meaningful results. Most commercial frequency counters lose precision at low frequencies. Luckily, you are only interested in frequency changes over 1 min. or so.

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