wwhitney
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Re: Expanding EV charging in Yosemite

Tue Oct 04, 2016 9:55 pm

GRA wrote: if we're going to provide a couple of 32A L2s on a 25kVA (20 kVA usable) 208V transformer plus 4 L1s, they need to be 12A.

Who owns the transformers? Most service equipment is rated in terms of its allowable continuous load (unlike residential circuit breakers), so I would think you could draw 25kVA all day long from a 25kVA transformer. I also believe power companies will allow their transformers to be overloaded for a few hours a day, when they know that the load will be lower overnight, so that long term thermal behavior is acceptable.

Thus I would think that a dedicated 25kVA transformer could handle (3) 32A L2s and (3) 16A L1s, given that it will be rare to never that all 6 are in use flat out for more than, say, half a day. Also some consideration should be given to balancing the loads across all three phases, so multiples of 3 are good.

Cheers, Wayne

GRA
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Re: Expanding EV charging in Yosemite

Wed Oct 05, 2016 2:58 pm

wwhitney wrote:
GRA wrote: if we're going to provide a couple of 32A L2s on a 25kVA (20 kVA usable) 208V transformer plus 4 L1s, they need to be 12A.

Who owns the transformers? Most service equipment is rated in terms of its allowable continuous load (unlike residential circuit breakers), so I would think you could draw 25kVA all day long from a 25kVA transformer. I also believe power companies will allow their transformers to be overloaded for a few hours a day, when they know that the load will be lower overnight, so that long term thermal behavior is acceptable.

Thus I would think that a dedicated 25kVA transformer could handle (3) 32A L2s and (3) 16A L1s, given that it will be rare to never that all 6 are in use flat out for more than, say, half a day. Also some consideration should be given to balancing the loads across all three phases, so multiples of 3 are good.

Cheers, Wayne

Thanks. For some reason I was thinking this might count as a feeder, and thus would need the de-rating. SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass. I'll re-write the technical section accordingly. Unfortunately, my copy of the NEC dates from the early '90s, and the book I have that explains just what the hell the NEC means is also keyed to that edition, long before EV charging was an issue. It looks like I need to read Art. 240 (X-former feeder protection) and Art. 450 (X-former protection) of the 2014 NEC. The x-formers I was able to find a rating plate on in the T. Mdws area were all 208Y/120, as expected. The one @ Tioga Pass was 25kVA, that at the Tuolumne Meadows Lodge was 75kVA. The one at the gas station didn't have a plate I could find, but appeared to be identical to the Tioga Pass one. They're all pad-mounted, unlike some of those I saw at Curry Village which were pole-mounts, but those seemed to be related specifically to a cellphone tower set up in the parking lot.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

wwhitney
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Re: Expanding EV charging in Yosemite

Wed Oct 05, 2016 4:51 pm

GRA wrote:SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass.

That doesn't necessarily mean that the POCO (power company) owns the transformers, in some case the "service point" is upstream of the transformers and the customer owns them. So you need to find out where the service point is and who owns the transformers.

If the customer installs loads that are larger than can be carried by the existing POCO-owned transformer, then sometimes the POCO just upgrades the transformer without charging the customer. Or sometimes the POCO wants to be paid by the customer for the upgrade. That's a question for the POCO in each case.

Of course, if the customer (the Park Service?) owns the transformers, then any cost of upgrading them is on the customer.

GRA wrote:I was thinking this might count as a feeder, and thus would need the de-rating.

Ratings tend to be continuous on the POCO side of the serivce point, while the NEC applies on the customer side of the service point. So if you have a 25kva 3 phase transformer at 208Y/120, that means the transformer can provide up to 25000/120/3 = 69.4 amps on each phase continuously. If the customer has a continuous load that draws 69.4 amps on each phase, then the NEC requires sizing the conductors after the service point with a factor of 125%, or a minimum of 86.8 amps. In practice you'd install a "100 amp" service (a standard size), using conductors sized for at least 100 amps under the NEC, all fed by that 25 kva POCO transformer.

In fact, the NEC load calculations are generally very conservative. So the NEC might tell you that you need a 200 amp 208Y/120 service, and you'd install 200 amp conductors from the service point to your main panel. But the POCO knows that calculation is conservative, so depending on your load type, it might choose to feed your 200 amp service with only a 25kva transformer. It knows that in practice your demand per phase will seldom exceed 69.4 amps, and that the transformer will be OK with occasional short term overloads.

If the load consists principally of EVSEs, that that is one case where the NEC calculation isn't overly conservative, other than the 125% multiplier for continuous loads. So three 32 amps 208V EVSEs really could draw 64 amps on each phase for a long period of time.

BTW, if you want to balance the EVSE loads across all 3 phases, another option is to install (2) 32 amp 208V EVSEs, one on, say, phase A and B, one on phase B and C, and then (4) 16 amps 120V EVSEs or (single) receptacles, two on phase A and two on phase C. When all 6 are then running flat out, the current on each leg will be 32 amps.

GRA wrote:They're all pad-mounted

Did you take photos of the name plates?

Cheers, Wayne

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Re: Expanding EV charging in Yosemite

Thu Oct 06, 2016 2:52 pm

Here's my first try at the Suggested Charging Sites section. Constructive criticism is welcome.
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Suggested Charging Sites. [Note: the Technical section which immediately follows this goes into more detail about the types and numbers of charging stations recommended for each site, and the reasoning behind the recommendations]

I believe the most critical areas in the park for the initial expansion of charging are at concessioner-operated lodging, retail and activity centers, which have both grid-electricity and excess capacity. In decreasing order of priority:

1. Tuolumne Meadows: at the former gas station and at Tuolumne Meadows Lodge.

The Tuolumne Meadows area is furthest in both distance and elevation gain from existing charging sites in the Valley and outside the park, and also tends to see a higher percentage of environmentally-motivated visitors, who are more likely to opt for PEVs. The gas station already has power, and a transformer which appears to be going unused now. Charging stations located there can serve both the store/grill and campground guests.

Charging stations at the Lodge serve both overnight guests and those there just for breakfast or dinner.


2. The Valley: Yosemite Village, Yosemite Valley Lodge, Half Dome Village and the Majestic Yosemite Hotel.

An expanded number of stations in Yosemite Village will better serve short-term day-use visitors to the Village, who are currently restricted to just a single charger there. If it's in use they have to wait or go elsewhere and hope to find an available, working charger. If it's out of service they may well be out of luck, and will need to be towed to somewhere they can charge. Many BEV owners won't take that chance, and will just opt to drive their fossil-fuel powered vehicle instead. As is stressed in the Technical section, redundancy at each charging site is essential.


Charging stations at Yosemite Valley Lodge would serve overnight guests there as well as Camp 4 visitors, and also some day-use visitors visiting Yosemite Falls or the Merced River.

Half Dome Village would serve lodgers/dining guests, as well as the Pines Campgrounds and Happy Isles trail users.

The Majestic Yosemite Hotel sees a relatively large number of overnight users with higher-end PEVs, and expanding charging there will encourage that trend.


3. Badger Pass and Wawona.

Badger Pass needs charging in two areas, one for day skiers and one for wilderness permit overnight users in winter, and to encourage people to park and use the shuttle in summer.

The Wawona area is closest to existing charging sites in the Valley and outside the park, and can be left to last. Charging is needed at the Big Trees Hotel to serve overnight guests, and at the store/Pioneer Yosemite History Center parking for day use.


Once those facilities are provided for, follow-on charging sites should be aimed at NPS Visitor Information/Wilderness Permit Centers and trailheads with grid electricity either at them or nearby. Examples include the Big Oak Flat and Tioga Pass entrance stations; Happy Isles, Dog Lake/JMT, and Glen Aulin/Tuolumne Stables parking lots; Tuolumne Meadows and Wawona Visitor Centers, and Tuolumne Meadows Wilderness Permit Center.
Last edited by GRA on Thu Oct 06, 2016 4:26 pm, edited 1 time in total.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

GRA
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Re: Expanding EV charging in Yosemite

Thu Oct 06, 2016 3:08 pm

wwhitney wrote:
GRA wrote:SCE provides power at Tuolumne Meadows, and PG&E covers the Valley, Wawona and presumably Badger Pass.

That doesn't necessarily mean that the POCO (power company) owns the transformers, in some case the "service point" is upstream of the transformers and the customer owns them. So you need to find out where the service point is and who owns the transformers.

If the customer installs loads that are larger than can be carried by the existing POCO-owned transformer, then sometimes the POCO just upgrades the transformer without charging the customer. Or sometimes the POCO wants to be paid by the customer for the upgrade. That's a question for the POCO in each case.

Of course, if the customer (the Park Service?) owns the transformers, then any cost of upgrading them is on the customer.

Don't know who owns them, but I think I can leave that to the park to handle.

wwhitney wrote:
GRA wrote:I was thinking this might count as a feeder, and thus would need the de-rating.

Ratings tend to be continuous on the POCO side of the serivce point, while the NEC applies on the customer side of the service point. So if you have a 25kva 3 phase transformer at 208Y/120, that means the transformer can provide up to 25000/120/3 = 69.4 amps on each phase continuously. If the customer has a continuous load that draws 69.4 amps on each phase, then the NEC requires sizing the conductors after the service point with a factor of 125%, or a minimum of 86.8 amps. In practice you'd install a "100 amp" service (a standard size), using conductors sized for at least 100 amps under the NEC, all fed by that 25 kva POCO transformer.

In fact, the NEC load calculations are generally very conservative. So the NEC might tell you that you need a 200 amp 208Y/120 service, and you'd install 200 amp conductors from the service point to your main panel. But the POCO knows that calculation is conservative, so depending on your load type, it might choose to feed your 200 amp service with only a 25kva transformer. It knows that in practice your demand per phase will seldom exceed 69.4 amps, and that the transformer will be OK with occasional short term overloads.

If the load consists principally of EVSEs, that that is one case where the NEC calculation isn't overly conservative, other than the 125% multiplier for continuous loads. So three 32 amps 208V EVSEs really could draw 64 amps on each phase for a long period of time.

BTW, if you want to balance the EVSE loads across all 3 phases, another option is to install (2) 32 amp 208V EVSEs, one on, say, phase A and B, one on phase B and C, and then (4) 16 amps 120V EVSEs or (single) receptacles, two on phase A and two on phase C. When all 6 are then running flat out, the current on each leg will be 32 amps.

Okay, thanks, I'll mention it, but I think I can probably leave most of that to the Park Engineer and maintenance people. I'll recommend some options, but they're the ones who know what kind of excess capacity they've got in many of the areas, load profiles etc.. I'm definitely going to recommend ToU pricing on any L2s with PoS systems, to keep them as free as possible during the day for short-term users.

wwhitney wrote:
GRA wrote:They're all pad-mounted

Did you take photos of the name plates?

Cheers, Wayne

Unfortunately not. My cell phone remains just that, and I haven't bothered to haul out my 35mm SLR in years. Besides, I had to check some of them out surreptitiously ("What, officer? You say the road is marked 'Closed to the Public' 1/2 mile back? I must have taken a path here that missed it. My apologies, and I promise not to do it again (until next time)." So, in the case of Tuolumne Meadows Lodge, which had closed for the season and was being dismantled, my inspection was somewhat hurried and had to make use of twilight. Meant to write the info down, but naturally I'd left my notebook in my other pack.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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Re: Expanding EV charging in Yosemite

Mon Nov 14, 2016 9:16 am

Just wanted to note that, a couple of weeks ago, we were able to take our new-to-us Tesla S-85 on a trip to Zion National Park in Utah. Getting there was a piece of cake - we maintained "normal" highway speeds and Supercharged only at Primm, NV and briefly at St. George, UT.

What's relevant here is that it really worked well to have access to L2 charging (ranged from 22-30 amps) during our time at Zion. The two charging stations by the main Visitor Center are right by the shuttle stop, so it was easy to charge while doing day hikes out of the main canyon. They are also walking distance to both of the canyon campgrounds (South and Watchman).

Why, one might ask, would we want/need to charge at or directly adjacent to a national park when the nearest Supercharger or fast charger is less than 50 miles away? Simple - to enable day trips and to enable skipping a charge stop on the way home. On one of our days camped at Zion, we took a day trip to Bryce Canyon National Park, away from any fast chargers. (The round trip to Bryce from Zion required nearly four hours of driving and was about 180 miles, which we completed on a single charge with about 75 miles of range to spare.) On another day, we drove up Kolob Terrace Road in Zion National Park and did a higher-elevation hike there. Plus, Zion Lodge (in the canyon) hosted a nighttime ranger program and the only way to travel there after hours was by private automobile. At the conclusion of our Zion visit, we drove directly to Valley of Fire State Park in Nevada without a charge stop (we paid for an RV site with electrical hookups at Valley of Fire and stayed one night).

So, while I'm a proponent of using shuttles to reduce congestion, and of encouraging people to get out of their vehicles and hike, it must be acknowledged that private vehicles will continue to play a key role in enabling the exploration of our most beautiful places. To the extent permitted by electrical infrastructure and park regulations, I hope to see more EV charging opportunities arise inside and around the parks. This will give EV driving visitors a level of freedom that's competitive with fossil fuel cars, as it did for us at Zion.

By the way, L2 charging at the Zion visitor center is a flat $5 for three days. Because we drew a significant amount of energy (over 100 kWh), I voluntarily paid extra! We only briefly saw one other EV (another Tesla) using the charging stations, and there are also some hotels near the park entrance that offer charging.
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Re: Expanding EV charging in Yosemite

Mon Nov 14, 2016 10:02 am

Thanks for the informative report. National parks are my favorite places to visit. For the first time, I am beginning to think I might eventually need a Tesla.

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