# power plants synchronized? **URL:** \ **Category:** Factual Questions\ **Created:** [September 18, 2006, 5:32pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200 "2006-09-18T17:32:50Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 19, 2006, 8:11pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/21 "2006-09-19T20:11:22Z")
[QUOTE=Chronos] One thing to wonder about… Everyone knows that a transformer will change the voltage and frequency of AC, but it’s less widely known that they also change the phase by 90 degrees. Would that mean that you have to keep track of how many transformers any given part of the grid has gone through? [/QUOTE] Someone has given you some very bad information. Why would the frequency change? The voltage and frequency will have some odd phase relationship in a transformer with an **open secondar** , but, except for small parasitic currents resulting from stray capacitance etc. the input voltage and current of the transformer are related in phase just as if the load (multiplied by the square of the turns ration) were connected directly to the source. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [September 19, 2006, 9:07pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/22 "2006-09-19T21:07:06Z")
[QUOTE=David Simmons] Someone has given you some very bad information. Why would the frequency change? The voltage and frequency will have some odd phase relationship in a transformer with an **open secondar** , but, except for small parasitic currents resulting from stray capacitance etc. the input voltage and current of the transformer are related in phase just as if the load (multiplied by the square of the turns ration) were connected directly to the source. [/QUOTE] Yep, frequency is not an issue but interconnection could be. Sometimes “like” voltages can’t be interconnected bare because of phase differences. This happens when one of the circuit voltages is the result of a different winding arrangement (autotransformer, Wye-Wye,Wye-Delta-Wye, WyeDelta). We had a circuit which had an interconnect switch with a neighborining utility but the switch could only be closed if one of the circuits lost power and was then isolted and “thrown over” to the other circuit. To close the swtch when they were both hot would cause some pretty nasty damage to equipment. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 19, 2006, 9:48pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/23 "2006-09-19T21:48:33Z")
Oops. Someone had good information, but not enough sleep. I meant to type that transformers change voltage and current, not voltage and frequency. It took me re-reading it until now to notice what folks were objecting to. It would take a rather complicated device, significantly more complicated than a transformer, to change the frequency (best I can come up with would be to put it through a nice smooth rectifier, and then another inverter), and I’m not sure why one would want to, anyway. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 19, 2006, 11:29pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/24 "2006-09-19T23:29:33Z")
[QUOTE=Chronos] …I’m not sure why one would want to, anyway. [/QUOTE] Lots of reasons; here’s one example from personal experience. Aircraft use 400 Hz, rather than 60 Hz, because motors and transformers can be made smaller and lighter for the same power-handling capability at higher frequencies. However, here on Earth, we are largely limited to 50 or 60 Hz, depending on geography. In order to manufacture and test equipment intended for use in aircraft, we need a ready source of 400 Hz power. Now, we _could_ build our own power plant to run at 400 Hz, but that gets rather expensive. A better way is to use a frequency converter. It works about like you’d expect: it’s basically a variable-frequency oscillator powered by 60 Hz mains voltage. We had a couple old tube-operated units at EWC where we used them to test various transformers built for use on commercial aircraft. Any place that repairs, tests or manufactures parts for aircraft will have at least one. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [September 19, 2006, 11:36pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/25 "2006-09-19T23:36:22Z")
Another reason is if you are an american company building equipment to be used in Europe, it is a good idea to verify by actual testing that it performs as intended on 50 Hz power. BTDT. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [September 20, 2006, 2:17am UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/26 "2006-09-20T02:17:33Z")
> [@](#): > > The preceding semi-humorous reply was to illustrate that yes, there will always be some phase issues due to the maximum speed of propagation (which is less than c, of course.) How the network is built to deal with this, or if it even has to or if simply matching phase to the local phase as per previous posters will be sufficient, I have no clue. Actually this is not fully understood or well modeled, and is actively being worked on. There are all sorts of feedback mechanisms, resonances, nonlinearities etc. in the milliHertz to Hertz range in the grid, some of them mechanical (in generators, etc.). These resonances are exited by load changes, weather (lightning, static electricity, etc.), and other events, and can cause stability problems. Here’s a sample of the current literature on this [Google search on “subharmonic stability electric grid ieee transmission”](http://scholar.google.com/scholar?num=20&hl=en&lr=&q=subharmonic+stability+electric+grid+ieee+transmission&btnG=Search). It’s only recently that power engineers have appeared who are also trained in control theory. Here’s a typical substation device to measure the absolute phase: [Arbiter 1084](http://www.arbiter.com/catalog/clock/1084/1084.php) with [phase option](http://www.arbiter.com/catalog/clock/power_mon/power_mon.php). This is a big issue when reconnecting generators after a big outage. Here’s an article from GPS World that describes the process involved: [Keeping the Lights On: GPS and Power Grid Intermesh](http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=75734&pageID=1&sk=&date=) Arjuna34 ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [September 20, 2006, 2:11pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/27 "2006-09-20T14:11:26Z")
[QUOTE=Chronos] Oops. Someone had good information, but not enough sleep. I meant to type that transformers change voltage and current, not voltage and frequency. It took me re-reading it until now to notice what folks were objecting to. It would take a rather complicated device, significantly more complicated than a transformer, to change the frequency (best I can come up with would be to put it through a nice smooth rectifier, and then another inverter), and I’m not sure why one would want to, anyway. [/QUOTE] They do that if they want to transfer power from one grid to another. You’ve pretty much described the basic concept of a DC tie. There are DC ties linking the Eastern and Western Grids and at least one I know of between Texas and the Eastern grid. The ties are expensive to build, but in cases of reliability or market inequeties, they can pay back pretty quickly. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 20, 2006, 3:20pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/28 "2006-09-20T15:20:55Z")
[QUOTE=BubbaDog] They do that if they want to transfer power from one grid to another. You’ve pretty much described the basic concept of a DC tie. There are DC ties linking the Eastern and Western Grids and at least one I know of between Texas and the Eastern grid. The ties are expensive to build, but in cases of reliability or market inequeties, they can pay back pretty quickly. [/QUOTE] And there is the [Pacific Intertie](http://en.wikipedia.org/wiki/Pacific_Intertie) running from Oregon to Los Angeles, a 1.2 (approx) million volt DC line. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [September 20, 2006, 5:50pm UTC](https://boards.straightdope.com/t/power-plants-synchronized/373200/29 "2006-09-20T17:50:42Z")
[QUOTE=David Simmons] And there is the [Pacific Intertie](http://en.wikipedia.org/wiki/Pacific_Intertie) running from Oregon to Los Angeles, a 1.2 (approx) million volt DC line. [/QUOTE] I forgot that application. That’s another reason to convert/invert AC/DC (Band Name!) even though its on the same grid. The ultra high voltage DC has fewer losses than an ultra high voltage AC line when used for long distances. Years ago I sat in on a concept meeting of a developer who wanted to build a DC line from California, up through Denver and then on to Kansas City or St. Louis. It was a great concept that would give the participants the ability to move markets in and out of hot zones and since it was a DC design it had the advantage of maximizing long distance _and_ deliverability into two grids. [Previous page](https://boards.straightdope.com/t/power-plants-synchronized/373200.md?page=1)