OT: synchronous condensers

[newshound]

A bit of technology I had not come across before (although apparently they used to be found at some sub-stations back in the 60's to 70's).

[Harry Bloomfield, Esq.]

newshound explained :

Why head it with a photo of a turbine?

[jon]

Because that is the heart of the inertial system that has to be supported when adding solar, wind and wave energy.

[The Natural Philosopher]

And batteries and interconnectors. In short anything DC that feeds the grid via an inverter.

[Brian Gaff (Sofa]

Yes well I have no real idea how all generating gear can be synchronised either. Seems a trifle crude but then I guess getting it wrong could be rather nasty, so how is it done when they import power from other countries, how do they go about deciding who needs to synchronise to whom? Brian

[Andy Burns]

You either have a fully synchronised grid covering a continent (remember how serbia/kosovo were causing all european mains to run slow a wile back?)

Or you link them using HVDC, and then you don't need to sync.

[Chris Hogg]

While I think I understand what they do, why are they called condensers?

[The Natural Philosopher]

My guess is that it is because they 'store a little electrical energy'...

[newshound]

I guess it is a historic term. Presumably they shift the phase in the opposite direction to inductors.

[Chris Hogg]

In the same way as capacitors were at one time called condensers? Nothing to do with condensing, then, as in converting vapour into liquid.

[Robin]

Dates back to the 18th century when electric fluid was condensed in a device (typically 2 plates and an insulator).

[Paul]

It's a phase angle thing, not particularly for energy storage.

They build them to stop people from smoking. This one is "hydrogen cooled". The perfect choice in a cooling gas. One thing I like about devices like this, is the stairwells are always designed so you can't get away in a hurry :-)

It's a big beautiful machine (as my instructor used to say). This picture shows what's inside the metalwork of the previous picture.

It creates leading or lagging VARs. Via a phaser diagram, you add the effects of it, to whatever the rest of your "plant" is doing.

Too many of those 0.7PF LED lamps, and you'll be needing one of those. It could become a requirement, simply by switching from incandescent lamps to LED lamps or CCFLs. The LED lamps are getting cheaper, but are also having lousier PF values now. The incandescent lamps drew only watts and no VARs. The power company might need to buy another one of those, to balance out all your LED lamps.

Since big industries are billed for both real and reactive power, it's the kind of device you might use to solve your reactive power problem (balance it out). If your plant is leading, the machine can be set to lagging to compensate. And vice versa, until the thing saturates. There's usually one side of the graph where bad things happen (and that's why it needs the fancy cooling).

The generator at the power plant, also has excitation control, and can be adjusted, but of the two directions leading and lagging, it can only safely provide about a 5% correction in one of the directions. It gets a bit warm if pushed too far in one direction. That's why the network as a whole, has capacitor banks at strategic locations. Like, if some industry creates a reactive power problem locally where it is connected to the grid, by "billing them for it", it gives an incentive for them to provide a capacitor bank or a synchronous condenser on their own property.

The synchronous condenser, being a moving machine, probably needs some serious maintenance every ten years or so. As that's how long some of the motor-generator sets last (the ones that create three phase power from a single phase supply).

The device pictured in the Wikipedia article, is "big enough for around four major industrial sites of the same type". Since it's that big, it is probably owned by the power company and used for grid stability maintenance. And via "billing for reactive power", that's how they pay for the nuisance installation of such. Someone has to build it, and there is a financial incentive for the person making the mess, to install one. Ultimately, the power company is responsible for grid stability, and has to "correct" whatever "mess" the customers make. If you expect "X" MVARs in an industrial park, eventually someone has to fork out to buy compensation for it.

Consumers don't necessarily get billed for reactive, and the correction of what consumers do, is a "freebie". All that the simple meters with the rotating plate did, was measure real power (watts) and not VARs.

Note that this may not stay that way forever - those nice smart meters you got, give the perfect means of billing for both real and reactive power. It's easy with the sigma-delta converters in there and that little processor in the meter, doing the maths, to compute your current VAR load.

Paul

[Clive Arthur]

<Explanation snipped>

Thanks for that.

[Paul]

And you see in the news today, that Texas is screwed right now, because it's not integrated into the rest of the grid. They live or die, on the power they create locally for themselves. And they're doing blackouts at the moment. The "ERCOT" in the picture here, is the island that does not have sufficient internal generating capacity at the moment. They did this, as a means to avoid federal regulation of their power by FERC.

There's a lot of this going around. These power islands are all over the place.

Power islands are clever, except when you don't have enough power.

Paul

[newshound]

+1

[newshound]

The good old Leyden jar!

[Roger Hayter]

Thirded. But I really cannot stop myself quibbling about reactive "power", though I suspect you didn't mean it.

[jon]

It's better to have a central power grid with all power stations piped into it.

[Paul]

The units of measure are volt-ampere-reactive.

To quote the instructor "reactive power sloshes around in the network, between the load and the generator". The current flow makes some of the conductors warmer as a result. It's not consumed as such.

"Reactive power - the delay between voltage and current at a given point - is subjected to transmission constraints. As a result, it is often necessary to produce reactive power close to the location where it is needed."

To carry reactive power, you still need the wire size for it. That's the transmission constraint.

Paul

[newshound]

Perhaps another example might be helpful. Most of the UK first generation civil nuclear reactors (Magnox) had to be down-rated after the discovery of unexpected corrosion problems. So the generators were operating at somewhat below their original design conditions. This meant that the copper windings in the rotor and stator were thicker than they needed to be. This in turn meant that they could be operated so as to generate extra "reactive power". Although the volts and amps are a bit out of phase, the resistive heating in the windings is just related to the current; thicker windings mean they can carry more current, and hence export MegaVARs as well as Megawatts, helping to contribute to grid stability. Under the original pool system I don't think MegaVARs were actually traded, there was some sort of fudged "Ancilliary Services" payment. I believe that under NETA MVars are traded similarly to MW.