Another liquid-cooled GatesAir transmitter installation was completed for WYPR, Baltimore, MD. This unit replaced a Continental 816 which had a long life.
The area around the transmitter site is not the best neighborhood. The building was formerly the WBAL-TV transmitter site and was built circa 1947.
The transmitter room is a little tight, so it was difficult to get a good shot of the front of the unit.
The station is running HD Radio with -10 dBc.
This site has a strange 3-phase delta AC power configuration. The middle leg is at ground potential, and the other legs all measure 240 VAC to ground. I’ve never encountered that before. This is known as a corner grounded Delta, which gets rid of the high leg associated with most closed 3-phase delta systems.
Ultimately, all the leg-to-leg measurements are 240 volts, so the power supplies are satisfied. With these transmitters, the phase rotation does not matter because there are no actual 3-phase loads in the transmitter.
The sign says “Free Tools.”
I wonder why that strange electric service, never heard of it either. 1947, maybe the original transmitter needed it? Interesting, learn something new every day.
My local Target store has added lock-ups for the SOCKS.
THE SOCKS!!
But, what makes it especially delightful is that the socks are from a brand named “A Pair of Thieves”.
Crusty, it is an odd one, certainly I have never seen it before. I was able to find quite a bit of information about this setup on the internet. It actually makes sense to reference one leg to ground instead of having a high leg because the voltage on the other two legs is more stable. One has to remember that the legs are 240 volts to ground and not 120. They have a separate step-down transformer that creates the 120-volt legs and a neutral for that equipment.
Michael, I think we are living in an ironic divine comedy.
There is a TV station in Newton (MA) who’s transmitter site is fed with Open Delta. It’s rather “scary” for sure. I guess it’s common around Detroit?
I’ve been by that site, and yes, it’s not the greatest. TV Hill (where our sister station is, ironically, WBAL-TV) is a little nicer. Baltimore, like all cities, have the good parts and bad parts. In all my time travelling and photographing transmitter sites, the two worst areas where Cincinnati and Detroit.
There was a write up years ago about the odd power systems of older cities still in use. Areas still with 110/220 service. Lots of open delta 3-phase at odd voltages.
Especially prevalent were DC systems for elevators.
Boise Idaho had DC mains for downtown up to 1977.
Up to about 1977 the TV FM site on the 7200′ mountain NNE of Boise had 240 3-phase/120. When the power company swapped their transformers with 208/120 WYE feed, all the engineers were up there re-tapping transmitter transformers during the swap out.
How about 2-phase? 125v phase to neutral, 175v phase to phase. Center-city Philadelphia and Hartford, Connecticut are the only 2 places in the US known to still have it. From my reading, they use a “Scott-T transformer” to get from 3 phase to 2 phase. Instead of the 120 degree phase angle, 2 phase has a 90 degree angle.
https://en.wikipedia.org/wiki/Two-phase_electric_power
https://hackaday.com/2018/03/15/a-tale-of-two-phases-and-tech-inertia/
https://www.atlasobscura.com/articles/magnificent-photos-of-power-stations-in-the-early-1900s
I’ve come across a couple of open delta services, they are indeed scary and unpredictable. The two phase system is indeed a new one.
And that Scott-T transformer configuration can be used to take 2 phases and make 3. I inherited a site that’s had one for decades. I’ve been amazed the site hasn’t had more trouble with power than it has. The only 3-phase load is the Harris HT-10. I’ve already told them that their next transmitter should be configured for 240V single-phase to avoid voiding the warranty, unless they can convince the PoCo to pull another wire 2 miles to allow a proper 3-can transformer bank.
While, the corner ground does eliminate the high leg in theory, I think its real purposes is an alternative to the ungrounded delta service which is only permitted in establishments where “conditions of maintenance and supervision ensure only qualified individuals service the installation”. In addition it now requires the use of ground detectors, to ensure that the first ground fault is detected because the system will continue to operate normally. However a second ground fault will have catastrophic consequences. From what I have read this system is used in places where high reliability is desired, and a shutdown due to a ground fault would be catastrophic. Based on the presence of ground detectors, I have seen a radio and a TV station that were supplied by 480 volt ungrounded delta services. The radio station as might be surmised operates at 50 kw at least during the day.