Naked Science Forum
General Science => General Science => Topic started by: Bab on 11/05/2017 13:26:57
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Different appliances run off a house electricity grid. Do the different appliances draw power at different frequencies that a sensor on the main feed line to the grid would be able to sense and then display the different consumption in say kWh used?
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No.
You can signal around the local ring main network within, say, a house, but the incoming meter will block most outgoing signals.
The best way to determine the power used by an appliance is to look at the label on the back. Selfregulating, continuously operating machines like refrigerators will also have an "average consumption" specification.
The key question is "what are you going to do about it?" Will you eat part-cooked food, or sit on the dark? If not, why not just use whatever you want, switch off anything you aren't using, and pay for whatever the meter reads?
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Do appliances consume power at different frequencies?
They used to.
In the past, devices with electronic controls would switch transistors on and off to consume power when they wanted, often consuming power at different frequencies or different times than the mains AC frequency would expect of a resistive load. Examples are:
- Variable-speed motors in lifts or factories, that could inject variable-frequency noise on the mains
- Triac light dimmers that would switch on part-way through an electrical cycle, injecting considerable high-frequency noise on the mains.
- Many electronic devices that injected considerable amounts of third-harmonic (or 5th, 7th etc) back into the mains
- These higher frequencies cause increased loss in distribution transformers
However, all this electrical noise started interfering with radio and TV reception, so now worldwide regulations strongly limit the amount of conducted interference devices can inject on the mains; this is is achieved by passive electrical filters and by smarter electronic regulators that consume the power at mains frequency, but generate different frequencies towards the device being controlled. And power supply authorities penalize industrial users who inject non-supply frequencies back on the mains.
There is another way that devices in the electricity box claim to recognize individual appliances in the house - by looking at the pattern of electricity consumption - the on/off cycles of a refrigerator, microwave oven, dishwasher or electric jug are all distinct, and with some guided training, they can recognize individual appliances with reasonable accuracy.
Hopefully this information will be used for good, and not hacked by criminals to determine the best time to rob your house!
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Tx Evan, your second to last paragraph touches on what I was looking at. I have the idea that some monitor providers run fancy algorithms to monitor this and so allows one to track one's power consumption and hopefully identify wastage.
I hope to get more clarity on this from forum users.
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Here is the story of a company that is doing something like this for commercial premises.
They sample the current in the electric wires at an 8kHz rate - enough to detect harmonics up to almost 4kHz (around the 70th to 80th harmonics).
http://spectrum.ieee.org/view-from-the-valley/energy/the-smarter-grid/want-to-know-whats-happening-in-a-building-listen-in-at-the-breaker-box
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Amazing. Much obliged.
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8)This topic is helpful.
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Up until about 30 years ago TV,s had very crude PSU,s that injected a considerable amount of DC back into the mains which must have had a bad effect on transformers .
I am sure that by now they have all been scrapped.