Wacky Weekend: NERC to relax power grid frequency strictures
The North American Electric Reliability Council is planning to relax the standards for how closely power utilities must hold to 60.00Hz. Here's my absolute favorite quote of all time: Tweaking the power grid's frequency is expensive and takes a lot of effort, said Joe McClelland, head of electric reliability for the Federal Energy Regulatory Commission. "Is anyone using the grid to keep track of time?" McClelland said. "Let's see if anyone complains if we eliminate it." http://hosted.ap.org/dynamic/stories/U/US_SCI_POWER_CLOCKS?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT I believe the answer to that question is contained here: http://yarchive.net/car/rv/generator_synchronization.html [1] This is gonna be fun, no? Cheers, -- jra [1]Please, let's not start in on the source.[2] [2]No, really: *please*. :-) -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
On Fri, Jun 24, 2011 at 06:29:14PM -0400, Jay Ashworth wrote:
This is gonna be fun, no?
If your definition of fun is spending a year watching an old microwave clock lose or gain a few minutes. I don't see how this has anything to do with syncing two generators. The grid is in sync, and if the frequency of the grid changes (as it does all the time) it will stay in sync. It has nothing to do with the absolute frequency.
----- Original Message -----
From: "Jussi Peltola" <pelzi@pelzi.net>
Perhaps I read the piece incorrectly, but it certainly sounded to *me* like the part that was hard was not hitting 60.00, but *staying in sync with others*... Cheers, -- jra -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
On Sat, Jun 25, 2011 at 10:49 AM, Jay Ashworth <jra@baylink.com> wrote:
Way I read it, when they occasionally run at 59.9hz for a few hours (and according to my UPS monitoring software this is a regular occurance), they're no longer going to run at 60.1 hz for a while so that the average comes out to 60. Regards, Bill Herrin -- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004
On 06/25/2011 08:06 AM, William Herrin wrote:
This paper describes what they currently do to keep clocks accurate with Manual Time Error Correction (which is what they are going to suspect for a year): http://www.naesb.org/pdf2/weq_bklet_011505_tec_mc.pdf As I said in my last post, I'm not an EE, but just follow some of topics on that side of the house. What I gather is that Manual TEC, which is done by purposely running the frequency away from 60Hz to correct an average deviation, can actually cause more problems. "NERC is investigating the possibility of eliminating Time Error Corrections. NERC has been collecting data regarding Interconnection frequency performance, including the number of clock-‐ minutes during which actual frequency dropped below the low Frequency Trigger Limit (FTL) of 59.95 Hertz. During the period of July 2005 through March 2010, approximately 44% of the minutes during which clock-‐minute actual frequency dropped below the low FTL occurred during Time Error Corrections when scheduled frequency was 59.98 Hertz (1,875 of the 4,234 total minutes observed below 59.95 Hertz). Upon further investigation, it was found that almost all of those minutes (1,819 of the 1,875 total) represented frequency deviations that would likely not have dropped frequency below 59.95 Hertz if the scheduled frequency had been 60 Hertz. In other words, approximately 97% of the Low FTLs were of such a magnitude that if the Time Error Correction had not been in effect, the exceedance of the low FTL would not have occurred. These Frequency Trigger Limits in and of themselves are only indicators of system behavior, but the nature of their relationship to Time Error Corrections calls into question the potential impact that Time Error Corrections can have on frequency behavior overall. While it is intuitively obvious that any frequency offset that moves target frequency away from the reference point to which all other frequency sensitive devices (such as relays) have been indexed will have a potential impact on those devices’ performance, the industry has by and large regarded Time Error Corrections as harmless and necessary as part of the service it provides to its customers. However, in light of this data, NERC’s stakeholders are now questioning whether or not the intentional movement closer to (or in some cases, further away from) the trigger settings of frequency-‐based protection devices as is evidenced during Time Error Correction events is appropriate. Accordingly, NERC is planning a Field Trial during which the practice of doing Time Error Corrections will be suspended. Because of the fundamental nature of this 60Hz signal, NERC is reaching out to various industries to get their thoughts on whether they anticipate any problems with the elimination of Time Error Corrections. Those industries include appliance manufacturers, software companies, chemical manufacturers, companies that make automation equipment, computer manufacturers, and many others." Source: http://www.wecc.biz/library/Lists/Announcements/Attachments/9/June%2014%20Ti... The main point I gather is that trying to do manual Time Error Correction actually makes the power grid less stable at times, and as such they want to do away with it (thus making the power grid more stable). Think of it the same as patch management risk assessment. If there are no security or bug fixes that directly affect you or even feature enhancements that you don't need, do you apply a patch/upgrade to critical systems? Nah, you skip those, because we all know every patch/upgrade carries with it risk of an unknown bug or even security flaw. That's what they're doing here, opting to skip "patching" the time error. They're not ignoring frequency altogether, but rather only minding that aspects that have to do with grid stability, not your alarm clock. This is for the better anyway, and NTP/GPS/WWV/WWVH is the way to go to keep clocks accurate and hopefully will be the outcome of any consumer complaints. I've seen conversation in various forums and lists I read that they are going to ignore or not care about the 60Hz standard. This is incorrect. They just aren't going to purposely deviate from the scheduled frequency to perform manual TEC. Mind you, that they still care about why the frequency is off, and when things are not able to quickly compensate, they want to know and be able to pinpoint it and fix it: http://www.nerc.com/filez/standards/Frequency_Response.html Specifically, read this PDF: http://www.nerc.com/docs/oc/rfwg/NERC%20Balancing%20and%20Frequency%20Contro... The AP piece was focused on hype and word-spinning (I couldn't find an AP.org link, so used one that I could find, http://www.huffingtonpost.com/2011/06/24/clock-problems-power-grid-clock-dis... ): "The experiment would allow more frequency variation than it does now — without corrections." The NERC BAL standards already hold the NERC entities to very high frequency standards, and this will be unchanged, except for manual TEC. All it is doing is eliminating the corrections made purely for time's sake, which actually eliminates more frequency variation. This may, or may not, create more average frequency variation, and that is part of this test. "Officials say they want to try it to make the power supply more reliable, save money and reduce what may be needless effort." This is the real goal, and should have been the focus of the news story - but that doesn't make headlines. I'm going to go shop for a new clock. I had one that used the WWV/WWVH stations, but then they messed with DST and it was off for a few weeks around each DS change. That forced me me to pull it off the wall and change the TZ at one time of the year to correct it, but the other time of the year I could not correct it (as it only had 4 TZ settings), so I took it down. Beware "Automatic Time Set" clocks which don't really learn the time from the WWV/WWVH stations (like the Sony ICF-C218, which has a preset time and battery, but still uses the frequency from the wall to maintain time). The best bet is a clock that requires batteries as you know it won't get time from the power grid. Jason Roysdon
----- Original Message -----
From: "Jason Roysdon" <nanog.20110127@jason.roysdon.net>
Thank you, Jason. I did some searching before I posted that, to see if I could locate better information, but clearly, I didn't search hard enough. Cheers, -- jr 'my google-fu requires 60.01Hz :-)' a -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
On 06/25/2011 02:02 PM, Jay Ashworth wrote:
NERC's site is very hard to find info on if you don't know where to look. Even when you've found something before, it can be hard to find again. I run into that nearly monthly and have a document just to help me navigate to certain areas. http://www.nerc.com/page.php?cid=6|386 http://www.nerc.com/page.php?cid=6|386|391 http://www.nerc.com/files/NERC_TEC_Field_Trial_Webinar_061411.pdf http://www.nerc.com/filez/Webinars/tec_webinar_061411/index.htm <webinar Jason Roysdon
On 06/25/2011 03:52 PM, Jason Roysdon wrote:
Interesting... Normally slow is not a problem since it happens normally when the grid is running near capacity... The "frequency runs" (when I worked IT/comms with a power company they were on Thursday nights after midnight...) were almost always fast (I was involved in this in the mid 70's mostly; our company rarely reached capacity but could if the weather was hot enough.) Given that the slew command has to be done almost simultaneously at most of the power plants in US and Canada, in order to avoid the throttle hunting problem that JDA mentioned (yes, even big plants can hunt, just ask the NE folks (twice!!!) though both of them were caused by circuit faults (network partitions) and not time corrections) Now that most clocks are run by 32khz crystals and not counting cycles, the corrections don't matter as much. I guess the experiment is to find out who complains... Then again, as a kid I remember So Cal Edison sending out new rollers for phonographs (I know - what's that?) when they changed from 50 to 60hz. Talk about inaccurate clocks (and I don't know what they did about those either.) And most of LA's hydro was still running generators that were built for 50hz even into the 70's, so lost some efficiency. politics of how the ISO's fit into this; they complicated things a lot from when I was involved in the power biz.)
On 06/25/2011 07:49 AM, Jay Ashworth wrote:
Generators all stay in sync. Generator owners have expensive devices that sync the phase before the generator is connected to the grid. Once a generator is connected to the gird, it will stay in sync - in fact that is why they have the expensive devices to make sure that they are in sync before they connect them, as if they are not, it will instantly jump to being in sync, which may destroy the generator. I'm not an electrical engineer, but I do IT "Cybersecurity" for a local utility. The electrical engineering / power utility side of the house starts to rub off - but I say this as I might not have all the terms exactly right. I follow the FERC/NERC discussions as CIP compliance is one of my primary job duties. In fact, if you want to see what happens if you connect a generator out of phase, just look into the AURORA out-of-phase circuit breaker re-closing issues which were brought to light last year. Here's some links: http://www.atcllc.com/oasis/Customer_Notices/ATCNetworkCustomerMeeting052411... Here's another link I read in the last week when trying to get up to speak more: http://yarchive.net/car/rv/generator_synchronization.html Jason Roysdon
Big generator are synchron maschines, as they can generate also reactive power. If a out of sync synchron maschine is connected to the grid, theres a big "kawumm" and then the maschine is in sync or dead. Only the angle between the rotor and the magentic field make the difference between generator and motor. A synchron motor can not self-start and only run at fixed grid freuency / rpm's. A overloaded motor suddenly stops. Smaller generators are asynchron maschines, that can run faster or slower than network frequency - ie run as generator or motor - but they always consume reactive power. They can self-start. Synchronising maschines to a grid is not a big problem, the bigger problem is to syncronise 2 disconnected grids. Some years ago in europe a grid operator violated the n+1 redundancy rule as he needed to switch of a big power line over the river "Ems" - to allow a big ship to leave the shipyard. The result was a netsplit trough whole europe - a lot of "big" line-breakers flipped and switched of north-west and south-east power lines. The whole european grid was split into 3 parts, running at higher and lowet frequencies. Details: http://www.bundesnetzagentur.de/SharedDocs/Downloads/EN/BNetzA/Areas/Electri... Kind regards, Ingo Flaschberger
On 6/25/2011 15:12, Leo Bicknell wrote:
Most of these come in open, delayed, or closed transition models: http://www.gedigitalenergy.com/powerquality/ATSHome.htm For open and closed transitions you'll most certainly want to sync to utility to transition between the two. For the delayed transition model it'll stop at the intermediate "open" point for a configurable amount of time during which the load is disconnected from everything (i.e. let all the motors spin down first). ~Seth
On Jun 25, 2011, at 4:47 PM, Andrew D Kirch wrote:
motors don't produce DC? tesla vs edison? human safe dc voltage requires comically large conductors for the sorts of loads we energize? transmission loss except at very high voltages... http://en.wikipedia.org/wiki/High-voltage_direct_current
On 06/26/2011 05:55 PM, Jussi Peltola wrote:
Sometime look at break ratings for AC and DC breakers and compare the relative sizes. Shows this effect. Easy answer is: don't use mechanical switches for routine switching... (easy if there is an inverter present, like in a VF drive or switching power supply). Big enough AC breakers maintain the arc over more than one cycle so have this problem too. (plasma quench time at atmospheric pressure can be a while...) Given the technology of the time, AC won rightfully. Still better for most distribution. -- Pete
On Jun 25, 2011, at 4:59 PM, Joel Jaeggli wrote:
They can.
tesla vs edison?
Tesla was right, Edison was a better marketing person. AC works better for long-distance transmission. AC could have been made much safer had we chosen a 2Khz+ frequency rather than a 60Hz frequency.
human safe dc voltage requires comically large conductors for the sorts of loads we energize?
So does human safe AC voltage. The key difference is that AC voltage is much easier to change efficiently (transformers) whereas DC-DC voltage transitions require either an inverter (DC->AC->DC) inefficient and usually mechanical, a motor/generator set (inefficient and mechanical), or a DC-DC converter circuit which tends to be horribly inefficient and expensive, especially at high amperage. Owen
On 6/25/2011 16:43, Paul Graydon wrote:
Also depends on the operator, so ask to see their xfer switches and how they're programmed if that's a concern. All of the non-residential models in that link for three-phase have motor/load disconnect signaling capability. If the operator is clued enough to use it then it's all good: shut off signal to motor/compressor loads, phase sync and switch, signal reconnect after delay. But if they're not... run away. Even with the delayed transition models the "hold open" delay can be too short and end up re-energizing the motors too quickly. There's always plenty of ways to f*ck things up good. ~Seth
Another couple of reasons to use a delayed transition ATS: 1) Motor lock. Delays on HVAC equipment never get triggered if the system never goes offline. Having a correct "open" period allows the motors to spin down, and start back up on the delays that are programmed keeping them from being synchronized 2) Allowing transformer fields to collapse. Even in phase, without a delayed transition ATS you can end up with a partially collapsed transformer field with a new field being created at non-ground state. This can cause a transient back wave that can snap circuit breakers. Yep, this one happened to us a few times before we switched to a delayed ATS, was a PITA to debug and resolve. -----Original Message----- From: Seth Mattinen [mailto:sethm@rollernet.us] Sent: Saturday, June 25, 2011 8:49 PM To: nanog@nanog.org Subject: Re: Wacky Weekend: NERC to relax power grid frequency strictures On 6/25/2011 16:43, Paul Graydon wrote:
Also depends on the operator, so ask to see their xfer switches and how they're programmed if that's a concern. All of the non-residential models in that link for three-phase have motor/load disconnect signaling capability. If the operator is clued enough to use it then it's all good: shut off signal to motor/compressor loads, phase sync and switch, signal reconnect after delay. But if they're not... run away. Even with the delayed transition models the "hold open" delay can be too short and end up re-energizing the motors too quickly. There's always plenty of ways to f*ck things up good. ~Seth
On 06/26/2011 05:43 PM, Ingo Flaschberger wrote:
The collapse can take more than one cycle, especially in a 3-phase transformer... As can the startup transient. In our case, if a big thunderstorm came, we started one generator ahead of time and synced it to the line, then did a 0-delay (overlap) switch. Avoids this problem, though the generator had better be a bunch bigger than the load to bring this off. Short delay ATS (less than 1sec) is a disaster, though. If you always wait till the power actually fails before starting the gen, you should wait 5-10 secs (or more) before putting the load on it, at least if there are any motors involved. (our generators were 1mw brushless ones that took 10-15secs for the voltage to come up anyhow...) And HVAC compressors have their own problems; once fully stopped you have to wait for the liquid to clear the compressor before restarting, or have LOTS of torque (like a car unit) available (and a supply of new belts :-)
It isn't this simple... Switching on involves transients that overwhelm the sinusoidal waveform for a few cycles. Also the above is only strictly true for an unloaded transformer; if it has a matched resistive load the current and voltage are (mostly) in phase. (leakage inductance notwithstanding, though it isn't very high for high-power transformers.) Unfortunately most larger feed transformers are integrated 3-phase units where the current-voltage curves are shared between windings and get much more complicated, and there is no time (in normal operation) when all the voltages or currents are 0. Also for high enough ratios the interwinding capacitance is important (480 to 120/208 isn't high for this purpose; 8 or 16kv to 120/208/240 is). Big data centers (most bigger buildings) have 2 stages of transformers, one from "distribution" (8, 16, 20, 34kv) to 480 and a transformer per floor from 480 to whatever. Sometimes the generator is between these two and the UPSs are after the floor transformer(s). Big enough UPSs run at 480 so are between also. To complicate things even more, (modern) computers look kind-of capacitive, modern fluorescent lighting (electronic ballasts) looks kind-of capacitive, and motors and most other loads, and older lighting look inductive. That means it is hard to predict how to switch loads; either no-delay (need to sync the generator, though) or lots-of-delay operation is safer; short delay isn't. (and synchronous motors can actually look capacitive if they have enough of a flywheel on them, but the startup transient for a non-VF drive can be a killer.) BTW - in reply to a misconception long before in this thread, 3-phase sync motors self-start easily, and most older single-phase clock motors had enough of a shaded-pole to start in induction-motor mode then transition to sync once close to speed. The means to do this were subtle; sometimes it involved clever multilayer plating on the rotor and/or very clever shaping of the holes in the rotor. What I mean by kind-of capacitive is a bit odd; it looks capacitive on the voltage rise but resistive and/or a little inductive on the peak and fall, and the current is 0 when the voltage is below some threshold. Actually these days the feds (and I believe EC also) spec power-factor correction for switching power supplies so this effect is less. The main way this is arranged is to make sure the input-rectifier filter capacitors are SMALL enough; then have the switcher waveform compensate for the voltage droop. Bigger VF motor controllers do this also. -- Pete
Kind regards, Ingo Flaschberger
On Sun, Jun 26, 2011 at 06:46:09PM -0400, Pete Carah wrote:
[begin OT lecture about refrigeration] If you have liquid in your compressor you are very screwed, it will dilute the oil and cause the surfaces of the compressor to wear out very quick (and if enough liquid gets far enough to actually get compressed, the compressor will very likely self destruct because liquids will not compress) To avoid this, many larger systems actually have a solenoid valve before the metering device which completely stops the refrigerant from moving the instant the compressor stops - the liquid refrigerant will then stay in the condenser, and the machine will cool instantly on the next start-up as an added benefit. These machines start against their normal working pressure. Some bigger systems have automatic pump-down which will actually run the compressor after shut-down against the closed valve with a pressure switch that makes sure all the refrigerant is in the condenser (and receiver) - this is required if the charge is sufficiently large that the amount of liquid in the evaporator (that hasn't evaporated yet) is enough to flood the compressor after shutdown. These systems can start against more than the normal operating pressure. The only ACs that have problems with restarting due to backpressure are single phase units - my window rattler has a bad thermostat that sometimes bounces the compressor off for a second. The result is a very loud hum and dim lights until the circuit breaker blows. But even single phase compressors with a proper start relay and capacitor can start against pressure, and these are fitted (called a hard start kit) if the system has a solenoid valve, or if the compressor is not starting due to wear or weak mains power (but these uses are band-aids.) All single phase ACs with electronic controls that I've seen have either a start up delay (often a few minutes, which I think is mostly to avoid excessive inrush when the power comes back) or they will not start at all without pressing the button manually. This usually works very well, but in some the logic is in the indoor unit, which in some cases can be powered separately from the outdoor unit.
This is true, but if you are feeding them through on-line UPSes they should look pretty resistive again. The EU has pretty strict specifications for PFC, and practically all modern servers I have tested are visually indistinguishable from a light bulb when viewed on a scope (I know that is not a very good measure of distortion.)
----- Original Message -----
From: "Seth Mattinen" <sethm@rollernet.us>
And more to the point, if you're installing 2-5MW of generation capacity, it's not all that uncommon to make it a cogen plant, at which point yeah, you're gonna run in sync. Leo: note that your body text was an *attachment* for some reason; new mailer? Cheers, -- jra -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
In a message written on Sat, Jun 25, 2011 at 03:32:09PM -0700, Seth Mattinen wrote:
Most of these come in open, delayed, or closed transition models: http://www.gedigitalenergy.com/powerquality/ATSHome.htm
I think we're missing something, which is where these ATS's are installed. I don't think most utilities allow (largeish) ATS's to do a closed transition from a genset to the utility grid, but I may be wrong. There may be other ATS's in your facility that do a closed transition though. For instance, consider this (somewhat simplified) dual UPS design: Utility Generator | \/ | | /\ | ATS #1a ATS #1b | | UPS #1 UPS #2 | | \ / \ / ATS #2 | Load ATS's 1a, 1b, sense utility power for quality. Should the utility power quality not meet specs (e.g. go out), they disconnect from utility, tell the generator to spin up, wait 5-15 seconds for the generator(s) to spin up and then close to the generator. They are in an open state for perhaps 20+ seconds, generators are never closed to the utility. Going back the drop may be shorter, perhaps 10 seconds, but there's still a long-ish open gap. Definately not sub-second. ATS #2 takes the dual UPS output (from synchronized UPS's) and does a closed transition between the two sources. Indeed, a previous employer had ATS's at this location that could switch between sources in less than 1/4 wave, the equipment never knew the differenece. Very impressive. It's not that you couldn't install a closed transition ATS in the ATS 1a/1b location from an electrical point of view, but I don't think codes, power companies, or common sense make it a good idea. As others have pointed out, the grid can do weird things because your neighbors did something stupid, or a car hit a power pole and shorted 3 phases together. Syncing to it is, well, crazy. Maybe small plants are different, but I've never seen a 1MW+ plant where the generators synced to utility. I can imagine CoGen might have some different requirements, and I've never worked with that, but I don't think that's what we are discussing. -- Leo Bicknell - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/
On Sun, Jun 26, 2011 at 05:27:10AM -0700, Leo Bicknell wrote:
It makes little sense to sync to the grid when the generator is only used when the grid is down - and unless you run your generators 24/7 your UPS will have to make up for the comparatively long time it takes for the generator to start, so it's rather useless to sync the generator when the power comes back so you can avoid a sub-second break when transferring back to utility power. UPS's shouldn't mind a break-before-make transfer, and motor loads are more and more often inverter/VFD driven types that should have their own delayed start logic that will hopefully handle most power glitches gracefully. Power distribution downstream of UPSs is a different animal with different goals, and there synchronized UPSs and make-before-break makes sense. To at least pretend to be relevant, the absolute frequency of the grid is, again, not relevant at all - and when the power is out, you won't be able to sync to it anyway.
IMHO, this design is overly complex, and will lead to the most usually form of failure - human. There is lot to think about in the above, especially during maintenance. You also have an interested situation on retransfer (gen -> normal) when 1a and 1b do not transition at precisely the same exact moment, which almost never happen. And if one of 1a or 1b gets 'stuck', you have UPS's paralleled being fed from unsynchronized sources, which leads to other problems (such as bypass not being available, etc).
That is not typical. The normal contactor/breaker doesn't usually open until the emergency source is available. It remains closed to the dead normal until emergency is ready to be transferred to.
So are you saying that the load was directly connected to utility (no UPS protection) until utility had a problem?
Closed transition should not really be thought of as syncing to the grid. Closed transition infers a very, very short overlap. A few cycles. Mainly so that downstream load does not get interrupted on the retransfer.
It ismy understanding also that most commercial grade gensets have built into the ATS logic that when utility power comesback online, that the transfer back to utility power is coordinated with the ATS driving the generator until both frequency and phases are within a user specified range? - mike On Jun 25, 2011, at 3:12 PM, Leo Bicknell <bicknell@ufp.org> wrote:
Well, that depends. If you have a open-transition ATS, where there is a 'neutral' (read: not connected to any source) position, it doesn't matter (much). Well, it matters a little. There is really two types of open transition. Something called "open transition" will provide a transfer by going closed-open-closed (in both directions). The issue is the open portion of that transfer can be very short; sometimes only a few cycles at 60 hz. If you have an electric motor connected as load (fan, compressor, whatever), if the sources are out of phase, it can be an interesting event for said motor. Typically, a open transition switch will wait until the phasing is 'close enough' (usually programmable by way of degrees.). We have an old russ electric ats somewhere that is happy at about 15 degrees +/-. There is also a type, "delayed transition", which is closed-open-wait-closed. Wait is typically programmable, it may be 500 msec, it might be a minute. It's up to the user. This is regarded as the safest type of switch (imho) because you do not run the risk of any of the above mentioned badness. However, in a datacenter scenario, you do have a battery hit (ranging from tens or hundreds of millisecond to many seconds depending on what you want). How good is your UPS and battery plant? Will your fans inertia keep air moving for a little while? All things to consider. If you have a closed-transition switch, typically the retransfer from emergency to normal is closed-closed, meaning that emergency gen, normal utility, and load are all connected together for a short while. Typically in the tens or hundreds of msecs. Anything longer than that kinda falls into the cogeneration category. That is another discussion. At least here in JCPL territory (northern NJ), closed transition is frowned upon. Too much risk, they think. They are correct, really, but the risk is mostly yours. If you lock to the utility out-of-phase, you will surely lose and they will surely win. The fault you create that they will see will probably not hurt them. Unless it is extraordinarily large and you are very close to the nearest substation. You must really trust your utility and your transfer gear and your generators to do this. Personally, I'm not a huge fan of this, but that is just religion. Personally, I like delayed transition, and that is what we do on anything recent. Short, usually, like 3 or 5 seconds. If anyone wants a demonstration, let me know. Long enough for motor controls to say "oh, hey, we lost power so let's do a nice soft restart of motors" and compressor controls can do delayed restarts as well. Works quite well, in practice. Much is overlooked in this discussion, as to things people should do about ATS and UPS programming.. but it is outside of the scope of NANOG unfortunately. Perhaps we need a NADCOG or something. What does this have to do with the whole 60 hz discussion and clocks? Not much. Other than I will have to rely on the cell phone more and the microwave less for time.
On Sun, Jun 26, 2011 at 12:23 AM, Alex Rubenstein <alex@corp.nac.net> wrote:
At least here in JCPL territory (northern NJ), closed transition is frowned upon. Too much risk, they think. They are correct, really, but the risk is mostly yours. If you lock to the utility out-of-phase, you will surely lose and they will surely win. The fault you create that they will see will probably not hurt them. Unless it is extraordinarily large and you are very close to the nearest substation.
Utilities concern themselves with not only their gear and your gear, but also your neighbor's gear. I would not like to be next-door to a large genset that is connected to the grid out-of-phase. My equipment would be affected by such an event. -- Jeff S Wheeler <jsw@inconcepts.biz> Sr Network Operator / Innovative Network Concepts
----- Original Message -----
From: "Jeff Wheeler" <jsw@inconcepts.biz>
More to the point, as I note in another reply, you don't want to be *the lineman down the road with his hands on a "dead" wire*. Pretty much the *first paragraph* in NEC 700 (700.6) says this: """ Transfer equipment shall be designed and installed to prevent the inadvertent interconnection of normal and emergency sources of supply in any operation of the trans- fer equipment. """ So, if your transfer switch is *physically* capable of connecting your genset to the incoming power wires, then it violates 700.6, unless you're in a cogen sort of environment, in which case you're following Article 705, and a whole different set of rules apply. Cheers, -- jra -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
You didn't keep reading. Or, you don't have the annotated version :) "Transfer equipment and electric power production systems installed to permit operation in parallel with the normal source shall meet the requirements on 700.5" This is from 2008, but I don't recall a change in 2011.
----- Original Message -----
From: "Michael DeMan" <nanog@deman.com>
I don't believe that's actually true, Mike. In a *load transfer* configuration, it's really not all that critical if the power presented to the load skips phase a touch on the transfer; there's a 50-500ms gap in the power anyway, since such transfer switches are required by the NEC to be non-shorting, so they don't electrocute power workers. Cheers, -- jra -- Jay R. Ashworth Baylink jra@baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com 2000 Land Rover DII St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274
On Fri, 24 Jun 2011 18:29:14 -0400 Jay Ashworth <jra@baylink.com> wrote:
I blinked too after hearing of this. They say it's an economic issue because it costs millions of dollars to maintain a steady frequency. Excuse me...we probably spend over $50 billion per year on electricity and they're complaining about a few million. Talk about pinching pennies! matthew black e-mail postmaster california state university, long beach
On 6/27/11 1:19 PM, Matthew Black wrote: the grid. Power flows from the higher frequency area to the lower frequency area (not exactly but close enough for this discussion). It limits the ability to generate power in areas that have excess and loads transmission lines with power being used to correct frequency. Mark
participants (18)
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Alex Rubenstein -
Andrew D Kirch -
Ingo Flaschberger -
Jason Roysdon -
Jay Ashworth -
Jeff Wheeler -
Joel Jaeggli -
Jussi Peltola -
Leo Bicknell -
Mark Radabaugh -
Matthew Black -
Matthew Huff -
Michael DeMan -
Owen DeLong -
Paul Graydon -
Pete Carah -
Seth Mattinen -
William Herrin