The frequency of the mains voltage serves as a reliable indicator of the electrical grid’s load. The grid frequency meter outlined here monitors both this critical parameter and the mains voltage of the AC power supply.

Frequency Meter Design

A few years ago, I saw an article in Elektor by Dieter Laues which showed how you can determine the load on the National Grid electricity supply by measuring the frequency of the supply. In short: the greater the load, the more it slows down the generators and so the lower the frequency of the supply; the lighter the load, the faster the generators and the higher the frequency.

The National Grid is compelled in the UK to maintain the frequency of the supply to ±1% of the nominal frequency of 50 Hz, these limits being 49.5 Hz and 50.5 Hz. However, it aims to keep this to within ±0.2 Hz normally (49.8 Hz ... 50.2 Hz). A very large power cut across parts of the UK was caused by these limits being exceeded. Two large generating plants fail...