What’s this all about?
These meters show the status of New Zealand’s power grid as seen from the basement of G Block, University of Waikato.
The estimated imbalance between supply and demand is a very crude estimate, based on the first derivative of frequency. A positive value means there is more generation than demand.
Frequency is of particular interest, since it shows the balance between generation and demand. Frequency will be the same at all points on a power grid. In New Zealand, the frequency is normally 50 Hz; higher than this indicates that more electricity is generated than is being consumed, and similarly a lower frequency indicates that not enough electricity is being generated. Frequency-keeping generators are constantly balancing their output based on current demand in the short term, while additional generating capacity is switched on during peak demand.
This is the RMS voltage between the Active and Neutral conductors. It is affected by demand in the same area as it is measured; the scale is currently unknown, but is suspected to be within a building or neighbourhood. Due to the resistance of transmission lines, an increase in power consumption will cause a decrease in RMS voltage.
This is the RMS voltage between the Neutral and Earth conductors. Normally, Neutral and Earth are physically connected close to the point that the electricity is used, e.g. at the switchboard of a house, so the voltage between them should be close to zero. A small voltage is caused by current flowing through the neutral conductor and not the earth conductor, and therefore provides an indication of power consumption on the circuit.
This value is calculated based on the first derivative of frequency. A surplus of generation will cause generators around the country to increase in speed, while a shortage causes a decrease in speed. This is much like driving a car up a hill; more power from the engine is required to maintain speed up the hill, and the car will slow down unless the power output of the engine is increased.
The device for measuring the parameters on this page is called the “IDSLM Grid Monitor”, and is based on two PIC microcontrollers: one on the ‘live’ side that
measures the voltages, and an optically isolated PIC that provides a USB interface and measures frequency.
Voltage is sampled at roughly 30 kHz for 12 cycles on each channel (Vna, Vne), while frequency is measured by precisely timing 25 cycles.
Measurements are currently recorded at the University of Waikato every 500 milliseconds; the frequency should apply equally to the entire North Island, while the voltages show local variation and are not representative of other locations.
Starting on the 23rd of August 2010, measurements have been recorded at 500 millisecond intervals, 24/7. These measurements may be useful for data mining purposes and feature extraction. For example, the data could be used to detect changes in load and generation in the grid, major circuit breakers tripping, local changes in demand or even people watching TV.
The graph to the right corresponds to the grid frequency during the 2010 Canterbury Earthquake – the effect of a sudden loss of load is clearly evident.
If you are interested in obtaining this data for analysis, let me know.