DC at wall outlets, NYC, around 1963 iirc -- Surprise! - Page 1
Forum section: electronics / general

author: Vell
author_rank: Contributor
timestamp: May 30, 2019, 08:58:06 pm
content: This was the Audio Engineering Society's annual Convention and Exhibition. The AES had rented the ballroom (iirc) in the New Yorker Hotel (almost sure). Wall outlets looked "bog-standard". When they started to plug in and power up their gear, nothing happened. Pretty soon, motors and power transformers overheated, although I don't think there were any fires. Turned out that the room was fed with 110(120?) VDC, and had not yet been changed over to 115 V 60 Hz. I didn't learn how they discovered that it was DC.

author: tooki
author_rank: Super Contributor
timestamp: June 01, 2019, 08:23:26 pm
content: Nice!For those that don't know about NYC's DC power grid:https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 01, 2019, 11:12:54 pm
content: How did they deal with the arcing problem back then? That seems to be the main problem with DC power distribution above 50V or so.

author: bloguetronica
author_rank: Frequent Contributor
timestamp: June 02, 2019, 05:58:07 pm
content: Quote from: Vell on May 30, 2019, 08:58:06 pmSorry, but something doesn't add up. Although some motors will work in DC (say, universal motors), transformers don't like that kind of current at all. Not only they won't work, they will get instantly saturated and go with a bang and an arc. Doesn't it sound suspicious that they didn't notice anything at first?Also, what is the purpose of having DC in one room, or only in one building, especially in 1963?Kind regards, Samuel Lourenço

author: Vell
author_rank: Contributor
timestamp: June 02, 2019, 06:48:04 pm
content: Thanks for your link to NYC DC!I lived on W. 108th St. for 23 years, and almost survived.(Now, suburban Boston)My apt. building was erected iirc in 1920, and had a DC elevator drive. As the contactors clattered to start the motor, the noise was memorable. Live-front switchboard, of course. Nice commutator sing.Regarding other power, as late as maybe 1980, there apparently still was 25 Hz power in the subway system. I remember going down into a station past a lone, forlorn, but lit bare incandescent bulb (emerg. lighting?) that was flickering, quite likely from 25 Hz power.Why 25 Hz? Steam engine-driven alternators from many decades back had speed limitations, unlike turbines. Somebody posted magnificent engineering drawings of one of those alts., and as I recall, the rotor was a 40-ft dia. disc. Engine cylinders were both vertical and horizontal.AC would have permitted relatively distant power distribution, of course.At 96th St., a short walk on the south side toward the river took you past a substation which converted AC (likely 25 Hz) to local DC for the trains; ~600 V as I recall. The building housed a few rotary converters, and had doors open to the sidewalk, but with metal mesh to keep people out. You could plainly see and hear the converters; their wondrous commutators had several hundred bars, and made a lovely, quiet singing noise. Ooodles of brushes picked off lots of DC. The other end of the single rotor had three sliprings for AC input; it was likely to be synchronous. Rotor was maybe 9? feet in diameter, and there was a pit below the machine, so its shaft (and much more) were easily accessible. Stator was ordinary group of coils, DC, possibly a dozen. Machine speed was perhaps 90? rpm.If you were patient and had a good ear, you could hear subtle changes in the sound when trains starting up drew more current.I had to leave NYC in 1986, so I know essentially almost nothing about present status.

author: David Hess
author_rank: Super Contributor
timestamp: June 02, 2019, 10:13:31 pm
content: Quote from: NiHaoMike on June 01, 2019, 11:12:54 pmThe fire departments handled it, poorly.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 02, 2019, 10:35:35 pm
content: Another of the weird idiosyncrasies of New York City's power distribution, is that live steam is still delivered to many buildings in Manhattan.It is used for heating.https://en.wikipedia.org/wiki/New_York_City_steam_system

author: tooki
author_rank: Super Contributor
timestamp: June 02, 2019, 10:48:36 pm
content: Many cities have steam systems (or more generically,district heating, since some use steam and some use water). It's hardly unique to New York.

author: David Hess
author_rank: Super Contributor
timestamp: June 02, 2019, 10:49:57 pm
content: Quote from: schmitt trigger on June 02, 2019, 10:35:35 pmThat is not unique to New York.Part of Seattlealso has steam heating. Being ever practical, the Soviets even distributed steam from nuclear power plants in some cities.https://en.wikipedia.org/wiki/District_heating

author: tooki
author_rank: Super Contributor
timestamp: June 02, 2019, 10:54:17 pm
content: Quote from: NiHaoMike on June 01, 2019, 11:12:54 pmWell, themainproblem was that it's difficult to transform DC power, meaning that you had to distribute the power at its final voltage, resulting in high transmission losses or the need for extraordinarily thick wire. With AC you can easily use transformers to shift to high voltages for transmission and then back down to low voltages for consumption.Anyhow, I also wondered about arcing, both in switches and in outlets. Did the DC grids actually use the same plugs and sockets as the AC ones??

author: David Hess
author_rank: Super Contributor
timestamp: June 02, 2019, 11:01:29 pm
content: Quote from: tooki on June 02, 2019, 10:54:17 pmI assume so. I doubt they used different plugs onAC/DC receivers.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 02, 2019, 11:07:23 pm
content: I knew that Iceland does have an extensive live steam distribution system, coming from its abundant geothermal activity, but wasn't aware that other North American cities also employed it.Thanks for sharing.

author: tooki
author_rank: Super Contributor
timestamp: June 02, 2019, 11:08:25 pm
content: Not just North America. It's common anywhere it gets cold.

author: IanB
author_rank: Super Contributor
timestamp: June 02, 2019, 11:09:11 pm
content: Quote from: Vell on June 02, 2019, 06:48:04 pmApparently the reason for 25 Hz is that the system in the early days used rotary converters to rectify the AC into DC, and it was much easier to design rotary converters operating at 25 Hz than at 60 Hz. (The speed of a rotating AC machine is proportional to the frequency, so either the converter at 60 Hz would run too fast and increase mechanical stresses, wear and tear, or it would need more poles in the design to slow it down increasing the design cost and complexity.)

author: langwadt
author_rank: Super Contributor
timestamp: June 02, 2019, 11:12:17 pm
content: Quote from: tooki on June 02, 2019, 10:48:36 pmyeh, here the powerplant, trash incineration and cement factory all supply hot water for district heating. In another city there was plans for a big new Apple datacenter to also contribute to the district heating using their server cooling and heat pumpsthere is also places that distribute cold water for cooling

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 02, 2019, 11:20:39 pm
content: Quote from: tooki on June 02, 2019, 10:54:17 pmThe voltage conversion problem is much less nowadays than it was back then, but arcing remains to be the main obstacle to widespread use of DC power distribution at the building level. HVDC at around 170V or 340V would make a lot of sense for off grid homes, for operating electronic devices (anything with a switching power supply) as well as PoL inverters for motors that can vary the voltage and frequency to exactly what's needed. With a central inverter as is commonly done for off grid, the V/Hz scaling possible is very limited.

author: tooki
author_rank: Super Contributor
timestamp: June 02, 2019, 11:28:34 pm
content: Quote from: NiHaoMike on June 02, 2019, 11:20:39 pmHence why I chose the word "was" and not "is".Quote from: NiHaoMike on June 02, 2019, 11:20:39 pmActually, I'd argue that themainreason today is legacy compatibility, since the cost of switching to a new standard would be enormous, and the benefits unclear or insignificant. As far astechnicalreasons against HVDC, arcing might be the main technical obstacle today, but it certainly wasn't the main reason back then.

author: soldar
author_rank: Super Contributor
timestamp: June 02, 2019, 11:53:28 pm
content: When I was a kid knife switches were widely used and the ones I remember all had a spark arresting system where the blades had secondary contacts pulled back by springs. I am surprised by how hard it is to find photos of these and most are of the simple knife with no arrestor.If you look carefully in these photos you can see the secondary contact on the blades.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 03, 2019, 12:18:45 am
content: Quote from: tooki on June 02, 2019, 11:28:34 pmThe nice thing about 170V or 340V DC is that most switching power supplies will work. The only change that might be needed is a fuse designed to break DC, which could be installed externally. Likewise, off the shelf VFDs can be used for motor loads, allowing V/Hz scaling with far more range than the central inverter can do.The biggest advantage of HVDC in off grid is lowered standby losses. It's much easier to design a DC/DC converter to have a low quiescent current than an inverter.As a compromise, I have proposed the idea of pulsed DC that needs little more than a transistor switching at a low frequency to convert from constant DC. The interruptions extinguish arcs just like AC does, but the circuit ends up way simpler than an inverter.

author: David Hess
author_rank: Super Contributor
timestamp: June 03, 2019, 12:59:23 am
content: Quote from: NiHaoMike on June 02, 2019, 11:20:39 pmDC to DC conversion has become more economical but transformers are still better in most applications. The same applies to AC motors versus electronically commutated motors.DC to DC conversion is used where power to weight or size is important and at very high voltages where AC has higher corona and dielectric losses than DC. For motors, I suspect it only makes sense where flexible operation or higher power per weight and size are required. Motors by themselves are pretty efficient.Quote from: NiHaoMike on June 03, 2019, 12:18:45 amIf anyplace, I could see DC distribution being used in data centers where as you point out, the changes needed for the power supplies are minimal. This can also combine well with battery based backup systems with the primary example being the old -48 volt POTS (plain old telephone service) standard.QuoteI doubt the difference is significant compared to the load. This same question comes up with high efficiency low power supplies where the benefit is marginal but the cost is high.

author: Nusa
author_rank: Super Contributor
timestamp: June 03, 2019, 01:47:07 am
content: Quote from: Vell on May 30, 2019, 08:58:06 pmFrom:https://en.wikipedia.org/wiki/Wyndham_New_Yorker_Hotel#Power_plantWhen it was built, the New Yorker Hotel had coal-fired steam boilers and generators sufficient to produce more than 2,200 kilowatts of direct current electric power. At the time, this was the largest private power plant in the United States. The hotel's own direct current generators were still in use during the Northeast Blackout of 1965, but by the late 1960s the hotel's power system had been modernized to alternating current. In a dedication ceremony held on September 25, 2008, The Institute of Electrical and Electronics Engineers (IEEE) named the New Yorker Hotel's direct current power plant a Milestone in Electrical Engineering. A bronze plaque commemorating the achievement was presented to the hotel by IEEE.

author: amyk
author_rank: Super Contributor
timestamp: June 03, 2019, 02:27:46 am
content: More ironically, from that article too:QuoteSome more info I could find on the DC system in the hotel, including a few pictures:http://sites.ieee.org/ny-monitor/files/2012/04/2006_08.pdf(starts on page 10)http://sites.ieee.org/ny-monitor/files/2012/04/2006_09.pdf(continues on page 13)Some newer pictures of the power plant, in a bit of a sad state:https://untappedcities.com/tours/behind-the-scenes-tour-of-the-new-yorker-hotel/

author: tooki
author_rank: Super Contributor
timestamp: June 03, 2019, 07:54:05 am
content: Quote from: NiHaoMike on June 03, 2019, 12:18:45 am...and all wall outlets, switches, circuit breakers, GFCIs/RCDs, arc fault interrupters, the entire distribution grid, power plants...Why change to DC at the enormous cost required to essentially rebuild the entire power infrastructure??

author: GlennSprigg
author_rank: Super Contributor
timestamp: June 03, 2019, 11:51:33 am
content: Quote from: soldar on June 02, 2019, 11:53:28 pmDamn it... Yes you re right !!!!!!!!! I can't find them (images) either !!!!I started my Apprenticeship at E.T.S.A. (Electricity Trust of South Australia) Sth Aust Power Authority.I used to build them myself by hand, for use in Sub-Stations, and large switch-boards....Unlike the VIDEO though, the actual 'snap-release' part was only like 2" long, at the very top of the(say) 14" knife-switch main Blade. Purely to rapidly break the circuit/arc after the main blade opened.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 03, 2019, 12:40:51 pm
content: Quote from: tooki on June 03, 2019, 07:54:05 amIt's easier to change AC to DC than the other way around. In a data center, there's considerable efficiency gain to do it at a centralized device, eliminating losses with a distributed PFC architecture.https://en.wikipedia.org/wiki/Rectifier#Twelve-pulse_bridge

author: soldar
author_rank: Super Contributor
timestamp: June 03, 2019, 04:52:16 pm
content: Quote from: GlennSprigg on June 03, 2019, 11:51:33 amIf you look at the photos you will see the "snap release" parts are, as you say, a separate part which is only a fraction of the length of the blade. I think the video is only meant to illustrate how the thing snaps back, not drawn to scale.

author: Seekonk
author_rank: Super Contributor
timestamp: June 03, 2019, 06:11:46 pm
content: DC sockets will be the future. Some big players are working on a standard to supply power for many small devices that are DC operated anyway. Power factor for these devices is driving the utilities nuts. Solar is also a big driver for this.The first AC standard was 167Hz.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 03, 2019, 06:20:00 pm
content: There's already a 12V "standard" that a lot of small network devices use.

author: tooki
author_rank: Super Contributor
timestamp: June 04, 2019, 12:21:35 am
content: Quote from: NiHaoMike on June 03, 2019, 12:40:51 pmStop moving the goalpost. We were talking about power at the grid level. And by “change”, I didn’t mean rectifying thepower, I meant converting thegrid, since that’s what we were talking about

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 04, 2019, 05:07:26 am
content: Quote from: tooki on June 04, 2019, 12:21:35 amThere's no need to change the whole grid to DC in order to get some benefits of DC. As shown in the link, if power factor matters, it's a lot more efficient to rectify AC for DC distribution at the building level than it is to have individual active PFC rectifiers on every major load. It makes even more sense if there's a desire to integrate battery backup and renewable energy on site.

author: tooki
author_rank: Super Contributor
timestamp: June 04, 2019, 01:23:23 pm
content: Quote from: NiHaoMike on June 04, 2019, 05:07:26 amThe topic of this thread was DC at the grid level (especially as to why it fell out of favor). Internal DC buses surely make sense for many applications, but that’s not what the topic was... DC grids went away because of the difficulty in transforming it. AC allowed this easily, and could easily be converted to DC where needed.

author: Nusa
author_rank: Super Contributor
timestamp: June 04, 2019, 06:42:08 pm
content: Quote from: tooki on June 04, 2019, 01:23:23 pmAlthough the specific example posted by the OP was technically NOT a grid-level issue. That hotel has a major DC power station in their sub-basement, which was still in use at the time of the example. I'm sure their primary reason for updating to grid-based AC was because they were out of sync with society and the rise ofportableAC-only appliances that guests traveled with (of which there were very few prior to the 60's).

author: tooki
author_rank: Super Contributor
timestamp: June 05, 2019, 01:21:20 am
content: Quote from: Nusa on June 04, 2019, 06:42:08 pmUmm, the issue was specifically an outlet that was a relic of the DC grid. How do you see that as NOT being a discussion of DC mains power?!?

author: Nusa
author_rank: Super Contributor
timestamp: June 05, 2019, 02:45:26 am
content: Quote from: tooki on June 05, 2019, 01:21:20 amRelic of the DC era, yes, but not of the grid. The New Yorker Hotel was built in 1929 with its own DC power plant in the sub-basement to be self-sufficient. One of their generators was diesel-powered, so they did not need expensive grid access for backup purposes when the steam system (which heated the building as well as powered it) was under maintenance.That doesn't mean you can't discuss the DC grid of course. It just happens the example given by the original poster isn't part of it.

author: Vtile
author_rank: Super Contributor
timestamp: June 05, 2019, 07:03:48 pm
content: Quote from: David Hess on June 02, 2019, 10:49:57 pmYes, in cold climate it is most energy efficient to produce combined heat and power, heat is steam/water and power is electricity. Example City of Helsinki do have approx. 840 miles of pipes (to point out the temperatures are low, only a bit over boiling point at open air. So no spectacular steam leaks as in NY).https://www.euroheat.org/knowledge-hub/case-studies/helsinkis-combined-district-heating-cooling/