Continuing to think about the Navy data and its list of cities that may experience failures.

The list is skewed towards cities with Navy installations, so it's not a comprehensive list covering all cities, but it does say that 15% of the 400 naval installations are expected to experience the failure of all or part of the civilian infrastructure of power, natural gas, and water.

One of the conclusions of the NERC (North American Electric Reliability Council) was that a "significant disturbance" in one of the 4 primary "interconnections" in North America could bring down the entire grid.

Thus, one of my questions is, will the grid continue to work if 15% of it is experiencing a major disturbance?

It's likely that nobody knows the answer to that question, but I think people should ask it, a lot, in the next few days. Grid minus 15% = ?

Got printable flyers to distribute during y2k disruptions?

-- robert waldrop (rmwj@soonernet.com), August 20, 1999

Answers

"I know nothing" about the grid, but I think 15% may not be too bad. Demand in winter is down vs. summer with all the AC going full blast. I guess it depends on where the 15% is. I understand that the grid is really 4 seperate regional grids, so if most of the 15% happens in the northeast for example, then I think they (me) could be in trouble.

Mr. Cook or one of our other power guys should pick up this thread.

Tick... Tock... <:)=

-- Sysman (y2kboard@yahoo.com), August 20, 1999.

Robert,

It is not as easy to say that a certain percentage failure will bring the grid dow, or that the grid can even stand a certain percentage failure. It all depends on variables called Spinning Reserve and reserve transmission capacity.

To try and describe thes terms to you; Imagine a generator at a power station that is capable of producing 100 MW, but at the time of a system incident it is only producing 75 MW. It would be said to have a spinning reserve of 25 MW (or 25% of capacity). This additional 25 MW can be picked up very quickly to replace generation that may have suddenly and unexpectedly been disconnected.

At the time of the rollover there will be many such generators connected to the grid that are not generating at maximum, and will all be contributing to this spinning reserve. I do not know just what amount of reserve will be carried in USA at that time, but here in NZ we will carrying around 25%. Thus a failure of up to 25% of generation can be tolerated without there being any significant shortfall in generation.

The other aspect is reserve transmission capacity. Consider an area being fed from the grid via 4 transmission circuits, where 2 circuits are the minimum number requiredto maintain full supply to the area. The loss of any single circuit would cause no problems, but the loss of a second circuit would have the grid controllers watching the line loadings very carefully. These 2 additional circuits are the reserve transmission capacity, and they are there to allow any circuit to taken out for maintenance while still maintaing supply.

Where problems may occur is if some generation fails in an area that has little reserve transmission capacity, and the that could cause locallised outages. Or if a lot of generation fails in one area, causing unplanned overloads in the transmission system. Add a few of these together and that whole section of grid starts to look a bit brittle.

Malcolm

-- Malcolm Taylor (taylorm@es.co.nz), August 20, 1999.

Hi Malcolm:

Thanks for the informative post.

Since you seem quite familar with power systems generally, I wonder if you might be able to shed some light on a question that's been puzzling me for some time now: Given multiple generating faciltites, exactly how is each of those generators phase synchronized with others feeding a common grid?

Many thanks for any help you might offer.

Kindest Regards,

-- Yan (no@no.no), August 20, 1999.

The grid could keep going if 80% of generating capacity went down, provided that (a) it went down in a controlled way and (b) control over remote switching operations was maintained. The end result would be a large percentage of the grid's load deliberately disconnected, so demand equalled reduced supply (via rolling blackouts so that essential services got continuous power and everyone else got power maybe one hour in five).

This is of course begging the question. The real risk is a loss of control. If something suddenly fails (because of Y2K, natural disaster, self-barbecued squirrel or whatever) the load has to be redistributed virtually instantly, often leading to overloads. This can and has led to a cascade of failures, in the past shutting down entire areas for a few hours. If remote switching telecomms were badly degraded, a few hours might stretch to days or weeks or (according to doomers) years or forever.

-- Nigel Arnot (nra@maxwell.ph.kcl.ac.uk), August 20, 1999.

Winter is not as bad as summer with Air conditioning going. People have other modes of heat..gas etc. However, no matter which companies are compliant if there are enough that aren't ...baboom! We be in the dark and the cold! :< This means we prepare even when our companies "say" they are compliant.

-- Moore Dinty moore (not@thistime.com), August 20, 1999.

regarding the 15% loss on the grid. One of the above threads mentions that it will not be in the middle of summer so the demand won't be that great. If the Naval document is accurate and all those cities lose Natural gas, that would mean all those citizens that use gas for heat and cooking would resort to using electric for their heating and cooking, i.e., buying electric heater etc. what impact would that have??

-- David Butts (dciinc@aol.com), August 20, 1999.

Not being an expert, wouldn't it depend on the amount of damage done to physical plants and equipment if the shut down is not controlled? What kind of physical damage could occur with an uncontrolled shut down? Would also assume that the kind of damage vs. spare parts would also have something to do with the length of time the power would be down.

-- Valkyrie (anon@please.net), August 20, 1999.

Under the possible conditions described in the Navy report, how could we expect electric utility employees to 1) be at work and 2) be at their best to remediate the mess? I'd like to know the range of how many employees these companies have and the distance to work that many would have to traverse to get there. Many utilties are located in the central business district of the downtown area it seems. Bad, bad potential areas...

Again the contingency plans of these people MUST be strong. Are they? Obivously not...

-- PJC (paulchri@msn.com), August 20, 1999.

Hi Malcolm:

Thanks for the informative post.

Since you seem quite familar with power systems generally, I wonder if you might be able to shed some light on a question that's been puzzling me for some time now: Given multiple generating faciltites, exactly how is each of those generators phase synchronized with others feeding a common grid?

Many thanks for any help you might offer.

Kindest Regards,

-- Yan (no@no.no)

Yan,

I think you are actually asking two distinct questions about synchronising of generators, but they are ones that people outside the electricity industry often get confused about.

A generator can be synchronised either manually or automatically. In order to explain the process I'll describe a manual sequence. When a generator is being started, it must first be run up to speed. A high speed 2 pole turbo/alternator must run at 3600 RPM in order to generate ac power at 60Hz. (60 cycles per second multiplied by 60 secs per minute = 3600 rpm). This speed control is maintained by the governor to a very precise degree, but the actual speed can be altered slightly either faster or slower.

Once the 3600 RPM is achieved an excitation current is supplied to bring the alternator up to its rated voltage. The operator would now alter the voltage slightly so that the incoming generator voltage is matched to the running system voltage.

Next the generator frequency is compared to the system frequency via a device called a synchroscope. This device is like a clock with only one hand that is free to spin in either direction. If it is spinning clockwise then the generator is running to fast, and if it is spinning anti-clockwise then the generator is spinning to slow. Once the hand is spinning very slowly this indicates that the incoming speed and frequency speed are similar. The position of the hand indicates the phase relationship between the generator and the grid. When the hand is at the top (0 degrees phase difference), and moving very slowly (speed is correct), and the voltages are matched, the operator will close the synchronising circuit breaker and start loading the generator. Naturally most generation stations now do this autmatically using a synchronising relay, but the overall process is still the same.

Once the generator is synchronised to the grid, it is held in synchronism by its magnetic coupling. I think that this may the question that actually intended to ask, but to anyone in the industry the question of synchronising only relates to the intitial closing of the circuit breaker.

To understand how every generator on the system can be held at a constant relative speed due to magnetic coupling it is only necessary to consider what happens when you try to put 2 bar magnets together. If you place them both North pole to south pole, they will lock together hard, but if you try to place them North pole to North pole they will flip around and you will find it hard to hold them. This is precisely what is happening inside a generator. It has a pair of poles (some lower speed generators such as hydro plant have many pairs of poles) that actually lock them to the system frequency. The rotor poles are powered by DC excitation current, and each pole is always of the same polarity. The stator windings are a set of large wires which cause a magnetic field that alternates as the generator spins, and as such the stator and rotor always form a north pole - south pole coupling. The current that causes this is known as reactive (or magnetising) current, and it is this coupling that keeps the grid synchronised.

There is no need for any outside timing devices, or other outside influence in any of these processes. I hope that this gives you some understanding of how the generators are coupled.

One point that does appear to be raising some confusion is the part that GPS plays. Here in New Zealand we do not use GPS timing at all (we use radio signals), but I believe that some areas of USA do have GPS clocks. The purpose of GPS timing is merely to check on something known as frequency time error. Imagine that the grid control center and the power stations had no way of knowing just what the standard time was. It is possible that the grid frequency could be running at 60.01 Hz instead of 60.00 Hz. In 100 seconds the sytem time would have gained 1 cycle, and in 6000 seconds it would be fast by 1 second. In other words, all over the coutry electric clocks would be running fast by 1 second every 1 hour 40 minutes, or 14 seconds per day. Every four days these electric clocks would have gained a minute, and so on. So GPS timing is used to measure this error, and allow the ststions to correct it.

Malcolm

-- Malcolm Taylor (taylorm@es.co.nz), August 20, 1999.