Results & Answers

The PicoLog graph below shows the measured results.


Fig3. Screen capture of PicoLog

The results appear to show a cycle occurring daily between Monday and Friday. The voltage at night rises to around 240 Volts. During office hours, the voltage drops significantly below 240V, which may indicate a higher demand on the national grid. This higher demand is probably due to heavy plant machinery and office usage.
During the weekend, the voltage is generally at a higher level and does not show the daily fluctuations described above.

Using PicoLog, the Minimum, Maximum and Average values for the mains voltage and frequency were recorded and calculated as shown below:

Parameter
Min
Max
Avg
Voltage (Volts)
232.432
243.846
239.384
Frequency (Hz)
47.97
50.24
49.99

Observations

  • The average frequency is very close to the specified frequency.
  • The average voltage is approx. 10V above the specified voltage.
  • The voltage remained within tolerance during the week.
  • The frequency appears to have a couple of low spikes.

Discussion

Originally, the UK mains voltage supply was specified at 240V RMS +/-6%. Some while ago, the specifications were changed (230V +10%, -6%) to allow harmonisation across Europe. The average value clearly indicates 240V.

At first sight, the spikes in the frequency data are outside the specified tolerance, indicating that the generating company is not meeting their published specification. Closer research into the specification small print shows that the frequency is allowed outside the specification provided that the average frequency over one minute is within the spec. The experiment sampled the frequency every thirty seconds, therefore the spikes are reasonable. A one minute sampling rate would be more suitable for checking completion

Credits, Comments and Further Info

This experiment was written by James Carey at Pico Technology. If you have any comments about this experiment or suggestions for improvements please e-mail experiments@picotech.com