Power Grid Synchronization and Reactive Power



I got an old tie clip that has that model on it. ;-)
At no load, I'd expect the excitation to be of the order of 2MW not including F+W of the exciter.
The 2 pole machines that I have in mind (both about 800MVA & 600MW) had full load losses of about 2% or less. About half were no load losses. With vacuum maintained the turbine losses were ? but small. My original 4MW is probably about half of what it should be but 40 still seems like a big number. If you saw it, you saw it. I made it a practice when I was working to not doubt what the operating types saw, only try to explain it. Sometime I found that they were right and sometimes their observation or instrument was off a little. But, we found out for each other's mutual benefit and education.

Probably about the same. They were set to about 175dF. They could also be a problem when going on line if the unit wasn't loaded fast enough. I don't recall ever seeing one trip but I'd guess anywhere from 5 to maybe 30 minutes depending on vacuum and any number of other things that take place during turbine run up.

The best inadvertent energization protection is an open disconnect switch and operators that check things out and think before they close a breaker or switch. Every other scheme fails eventually. In this day of remote indications and operation etc. this is a really tough problem. A single failure can turn the machine (including the turbine) into scrap.

I think that's probably it. When the unit protection operates the shutdown of everything is pretty much taken out of the operator's control. They don't like that. I don't blame them. But, I wish they'd calmly reduce the load to slightly motoring then trip the breaker.
During a strike, when I really learned how to operate a power plant, one of my fellow amateur operators in training would actually check the rotor of the unit watthour meter to confirm that he had 0 watts before he tripped a machine. I generally put the watt meter pointer just below 0. These were some 62.5MW 4 pole machines from 1930 or so that were very forgiving trainers. Protection was a differential relay and a smoke detector + an operator with good peripheral vision to catch that sudden meter twitch and a good ear for a disturbance in the hum. Those operating in the turbine room basement or on the firing floor had similar sensitivity for things that go bump in the pump or bang in the boiler. ;-)
I also took a 250MW off line the same way.

I've done this many times when simulating operation to check the unit protection. We didn't have generator disconnects so the phase bus straps were removed for this. I always personally inspected that the generator terminals were disconnected and roped and flagged off limits before we did these tests.

Well, according the the test engineer when we started the plant, about 1% goes into noise. I can believe it. Also, there are some 8 inch recirculation lines that bypass the turbine and there is a little leakage thru the wicket gates and the depression system vents stay open at least til full prime (maybe longer, it's only been about 40 years since I checked that system out). All I know for sure is that it's never been a problem and the unit wattmeter reads 50 MW almost exactly any of the few times I've watched a pump start. The generator/motors are 220MVA/260KHP and regularly pump at 230 to 250MW (which is at the 1.15 service factor limit). The air gap is about an inch.
The turbine/pump (it's a single machine that looks a lot like a pump) has an overall diameter of less than 15 ft. It's hard to estimate because most of the time I've only seen it from the draft tube which is about 6-8 ft in diameter (I'd estimate) or stood on the head cover which is 218 inches +/-. Seal clearance is probably of the order of 1/8 inch or less, probably less. The seals are 'lubed' with really clean water from the high head penstock. It's all encased in a huge monolith of concrete.
The original pump/turbine impellers were changed out about 15 years ago and I haven't attended a pump start with the new ones so the current rule of thumb times and loading may be different. The numbers were very repeatable with the old pumps.
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Fred Lotte
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You protect from reverse power (motorizing the generator) in two ways, reverse power trip protection or thermal power protection on the machine windings..reactive power power can result in heating which can cause thermal limits to be esceed and thermal trip to occur...simple explanation, little more difficult to engineer

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