Metro power question

[YOLO]

Anyone know how WMATA decided on using 750V power, instead of something like 600V in NYC or 1000V in SF?

General question but are there any benefits to running a higher voltage, say 1000-1500V?

[Sand Box John]

"YOLO"
Anyone know how WMATA decided on using 750V power, instead of something like 600V in NYC or 1000V in SF?

750 VDC became the de facto standard for new systems powered by third rail and lightrail / streetcar power distribution during second half of the last century.

General question but are there any benefits to running a higher voltage, say 1000-1500V?

Yes. The need for fewer substation for given length of route, greater spacing between substations. It also requires greater insulation to prevent arching to ground.

[farecard]

General question but are there any benefits to running a higher voltage, say 1000-1500V?

Higher voltage is lower current for the same wattage. Lower current is less losses, less heat. That's why BART went that way.
The tradeoff is you need better insulation/larger air gaps.
When BART opened w/1000vdc, they had repeated motor failures, as the usual DC motor suppliers were not used to the higher voltage.

With the switch to VFD-driven AC motors, burnouts/arcs are far less of a problem -- a 3ph AC induction motor is dirt simple compared to a commutatored DC one.

[srepetsk]

Speaking of WMATA power, they just awarded a $5mil contract to upgrade 6 tie breaker stations on the OR/BL (K & G) lines: http://wmata.com/business/procurement_a ... on_id=3442" onclick="window.open(this.href);return false;

The fun document in the pile is the Contact Rail Schematics doc that shows how the 3rd rail is laid out and connects back to the TBS/TPSS.

Edit: looks like SandBoxJohn already linked a better schematic showing more info on more lines previously.