OT - Daily Mail Eco Bollocks - "Big brother to switch off your fridge"

[harry]

I think they can alter smart meters by changing a chip or reprogramming so it can do virtually anything. Maybe even reprogramming remotely. This is just the thin edge of the wedge.

[whisky-dave]

Well they are smarter than the journos :-)

[polygonum]

Right - that certainly makes sense, thanks.

[polygonum]

It is a grid but not as we know it. :-)

[whisky-dave]

Doubt that, due to cost.

That would make sense but for what purpose, until I replace my fridge and f reezer and every other applience it won't be able to talk to them any more than talk to my cat with her RFID chip. What it can do it's altere the price per unit, buyt I'm not convinced that turning appliancies off in times of high demand is the aim.

The slippery slope that the snowball is on is my concern. ;-)

[John Rumm]

With an "online" UPS then computer would be running from the inverter all the time, and never see the grid frequency.

[Man at B&Q]

Even that is not sufficient. A real smart meter is one which is integrated into a smart grid network and takes part in grid balancing by dynamically switching loads, so called "demand side management".

Try

MBQ

[Andy Champ]

Yes. And?

If you get an increased load, surely you can maintain speed by reducing the excitation current - can't you?

Andy

[Ian Jackson]

This will result in a reduction of generator output voltage.

[John Rumm]

No, frequency and load are closely related....

[The Other Mike]

There is automatic voltage control at the generator to keep the terminal voltage near constant, terminal voltage being a predefined generator design parameter and controlled to within a few % of that figure. It's typically somewhere in the region of 15 - 25kV on the majority of UK coal/oil/nuke/gas generating capacity) This is then stepped up to a transmission voltage (400/275/132kV) The grid systems with one or two exceptions is always run at their nominal voltage, the transformers between these three voltages are usually autotransformers or in a few cases double wound. So the lower voltage networks run at a strict ratio to the higher voltage ones with no adjustment possible.

The variable tapping takes place at the interface between the transmission voltage and the distribution voltage and often on the secondary of a transformer having 132kV on its primary. Metering of power leaving the grid system is normally performed at these nodes. (Contrary to the norm are a small number of

400kV and 275kV to 66kV/33kV/11kV transformers on UK power networks)

[F Murtz]

If it shut down for a few seconds, would not it use more energy switching back on again than it saved by switching off?

[The Natural Philosopher]

that is possible. high current transients cause extra losses in power lines because its I squared R, So delivering the same average power down a resistive line is less efficient at lower duty cyles.

When the idea s to use less power overall, its rather more complex.

A problem many have encountered in the RC electric plane world, where controllers blow up at part throttle, not full (throttling being done by chopping the supply) .Its critically linked to the leakage inductance of the motors: low inductance (the best motors) will have massive peak currents at part throttle.

[The Natural Philosopher]

yes, but they are still separate issues.

[John Rumm]

separate issues, but codependent if you prefer.

[harry]

freezer and every other applience it won't be able to talk to them any mor e than talk to my cat with her RFID chip.

t turning appliancies off in times of high demand is the aim.

Possibly not. Everything is driven by money.

[harry]

But that also reduces voltage. If you reduced it sufficiently the "generator" would be run as a "motor".

[harry]

(Andrew

As any generator is in parallel with others, the speed/frequency, cannot change. So torque is increased and excitation. As torque is increased, the load angle increases until eventually pole skipping occurs. (Which is why excitation is also increased)

[polygonum]

I think that is entirely possible if you take your current refrigerator and add a simplistic device that switches off at least the motor for a few seconds. But if the device has been designed to support brief interruptions, then it could be designed to behave more intelligently. Maybe to wait until the motor switched off anyway before applying the interruption. Sure, that reduces the speed at which load is shed, but maybe that is not so very important?

[harry]

No. The generators are driven at constant speed. They are linked magnetically with every other generator in the country. As demand increases, the torque and excitation are increased. If demand exceeds availabilty then the voltage falls/is allowed to fall. No more torque can be applied, no more excitation can be applied or the machine will overload by too much current in the stator.

Al of the above is near impossible with wind turbines which run most efficiently at different speeds for different wind speeds. which is why their output is first rectified and then inverted to mains frequency. This overcomes a major control problem