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Supercharger - Frederick, MD
- Thread starter Nilnoc
- Start date
Does that apply to utility transformers? Several people on TMC have mentioned that you can actually exceed the transformer’s rating for brief periods of time.
vdiv
Chief Grump
Derating applies to the circuit breakers after the transformer feeding the chargers. Power handling of the transformer itself would vary based on the cooling, i.e the ambient temperature and air circulation around its radiator.
mrElbe
Active Member
T3slaOwner
Member Extraordinaire
That is not what I am asking. I'm asking how they define "surge", not how they measure it.
T3slaOwner
Member Extraordinaire
According to the original poster of the links to the permit, it was for 12 units, but later was reduced to 10.
Supercharger - Frederick, MD
Supercharger - Frederick, MD
I can't really find any of the actual submissions at this point. Everything I pull up is just text from the county web site with status.
T3slaOwner
Member Extraordinaire
Yes, of course it is the peak kW. But what is it compared to? I'm not asking for guesses. I thought maybe someone here would actually know how it is calculated.
What do you mean "compared to"? There is a set price, $X/kW. If your peak is 3000 kW, then your demand charges will be 3000*X. If you want to see an example, below are the rates from a bill from Idaho Power and here's the document explaining the Large Service rates [pdf].
mrElbe
Active Member
Surge is defined by utilities as the highest steady current draw within a 15 minute period during the billing cycle.
T3slaOwner
Member Extraordinaire
What do you mean "compared to"? There is a set price, $X/kW. If your peak is 3000 kW, then your demand charges will be 3000*X. If you want to see an example, below are the rates from a bill from Idaho Power and here's the document explaining the Large Service rates [pdf].
Thanks, I failed to understand they charge for the peak kW separately from the kWh charges. I thought the peak kW use increased the kWh rate if it varied too much from the normal load. So if the peak is the average over 15 minutes, there would be no point in staging multiple motors that all start up within a minute or two. Maybe the details have changed over the years because my friend was the guy who did the rewiring to make the motors start up separately.
I see they also bill for "load capacity" which I assume means the size of the pipe coming into your facility. If they are charging so much for every possible source of expenses, I wonder why they need to bill $300 a month just for the basic account? My residential minimum is $6.
Businesses don't get much of a break unless they negotiate it. We used to have an aluminum smelting plant that paid less than residential users per kWh. After a couple/three decades the power company said they would not renew the deal and the aluminum company left not just the town, or the state, but the country! They went to Canada.
Funny, your Idaho tariff sheet looks just like a Potomac Electric tariff sheet. Maybe there's a federal guideline for these things. Or maybe they just all talk a lot. I know a lot of businesses share info through trade groups and end up standardizing things without standardizing. "de facto" is the term that comes to mind.
Reddy Kilowatt
Active Member
I assume the SC will be the traditional 150 KW units not 73 KW Urban chargers. so I would think we will be charging at a higher rate of charge. certainly better than Springfield. IF that was implied. We are still splitting between two pedestals though. I personally never see the high rates when I SC. I think 111 is the highest I have ever seen. 98 is more average or lower.
When I met the SC repairman at the Hagerstown site. He said the SC are simply the car's internal charge but a stack of them in Parallel. So this pedestal sharing will remain.
They just posted a good video on inside EV's detailing the Vegas V3 site. only a 2500 KVA feeding 24-V3 chargers as well as the destination chargers. We would be below 100 KW if the place filled up Also 4 pedestals seem to be shared on one SC cabinet. THe V3 Cabinets are a lot bigger so I can rule out Fredrick as a V3 site. The V3 dont have the side exhaust hood.
This applies for panels and wiring. Transformers are a grey area. technically I have seen them rated at 100% on most rating charts. I'm willing to bet the utilities probably over load them up to 50%. Also Since there transformers are liquid cooled I bet the ratings are much higher.
T3slaOwner
Member Extraordinaire
Did you mean 1,000 kW rather than 100 kW?
I'm not sure how liquid cooling makes a difference. Wouldn't that already be factored into the rating? While the internal is cooled by a liquid, the outside is still air cooled by convection. Or do they have fans on them? There's a power substation on East St in Frederick and it has a number of fans to blow on things.
East St Power
Reddy Kilowatt
Active Member
No the average per V3 charger at that site would only be about 100KW charge rate per car. Not bad. but not the 250 advertised.
I'm not sure how they would have listed a liquid cooled unit vs dry type. I would be pretty sure it could take the abuse of surges and high demand vs an air cooled unit. Otherwise the power companies wouldn't used them, is my reason to think so.
Baking vs boiling, overheating would more gradual with the oil filled???
T3slaOwner
Member Extraordinaire
The transformer has to be sealed in an enclosure to protect it from the elements. That inside is either an air space which does not conduct heat well or a liquid which does. I was not aware they used any transformers that were not liquid filled because of the cooling problems. Maybe we are not using the terms the same way. What are liquid and air cooled transformers to you?
I'm surprised they rate chargers at anything other than their peak rate which is what can and will happen. It doesn't happen long since the cars can only charge a higher currents over a smaller portion of the range/charge rate curve. Still, at some point there will be the max power draw which would be 250 kW for each pair of stalls or 125 kW on each stall. How long can a transformer built for 100 kW handle 125 kW? My area of expertise is much smaller and I treat max as absolute max. My designs have to worry about static discharges, not lightning. lol
Reddy Kilowatt
Active Member
Air cooled transformers are typically smaller indoor only, but they used and Air cooled 112.5 KVA at the vegas site with the nema 3R enclosure. I think 500KVA is the max size dry.
Liquid cooled transformers are outdoor or in an approved vault inside which is rare for commercial applications its just to expensive.
What Jim and I were talking about is with Tesla's networking hierarchy and networking between the pedestals. I'm assuming the super chargers are networked like the destination chargers. There is a dial inside the charger for you to state the maximum incoming feeder size. The super charger site maybe set to a maximum service size which in this case is 1000 KVA or 2776 amps at 120/208V. for a dry type transformer. The network will know that it can use 1000KVA. or 800KW. (I'm looking a quicky chart to convert to KW)
So fredrick will have 800KW divided by 150KW max per car is 5 cars at maximum charge rate before everyone starts loosing charge rate. So at this site 5 people plug in at the same "A" or "B" port at the same time wanting a full charge, everyone will be at full power. as soon as the 6th person plugs in the max would be 133KW charge if we can ignore the A&B issue. the 7th we drop to 114KW, 8th would be 100KW. so same example of 8 cars charging we would really drop down 50% to 50 KW if everyone is charging at their maximum sharing a pedestal with another car A&B plugged in now.
Of course the odds of this happening is slim. If you have someone almost fully charged they have already rolled back so someone else can take there KW increasing and or the A&B share directly rises 1 for 1 between the two cars.
So with sites like Springfield or Gaithersburg that are always full we get the low KW 37 or 57 charge rates with the smaller Utility transformers. This is why we don't get a high charge rate.
Tesla knows this and is playing the cost to install, fighting with the utility to install the larger transformer, demand factors, as viewed by the utility and or there in house demand calculation. So the doctorates at tesla came up with the great idea of the network share between chargers. this actually eliminates the argument of potentially costly demand factors, and there associated installation costs.
The NEC code now requires power distribution for car chargers to be build to 100% demand factor, Because it can easily happen. Look at the level two chargers at the mosaic District in fairfax there alway full, Expensive install low level charging to minimize installation charges. Look at Tysons it originally only had two 100 wall chargers fully rated to charge two P100D cars in six spaces. Ice one and everyone is pissed off. Tesla created the Network chargers that talk to each other and calculate the total load between the destination chargers and cap it at the 100A through simple dial wheels inside the chargers. Now you have 4 destination chargers sharing the same 100A feeder. As people come and go, max charge, or min charge, iced the Tesla computers are maximizing the charge rate to each cars. its 80 Amps max divided between 4 chargers, two 75 series cars can now charge at full rate for the same electrical installation cost as the original single non networked destination charger. you have to pay for the wall charger, but just saved a ton of money on the electrical installation cost. At a minimum each car can at least charge at a 20a rate. I believe the super charger locations probably work the same. The issue with the utiliities they need to see demand is now rapidly increasing and they need larger transformers.
vdiv
Chief Grump
Sorry again for hijacking the Frederick supercharger thread. 
Someone just needs to post a picture of a V3 charging cabinet label and that would clear up quite a bit of confusion. I also think they are rated at 500kW shared among four stalls, each capable of max. 250kW. The V3 plans for Vienna, VA showed 700A (80% rated), 480V 3-phase service feeding the cabinets. That's almost 500kW. Two of those are fed by a run of the mill 1000kVA transformer, along with a small circuit for the new site master/controller of the superchargers.
Think the sharing algorithm uses the original scheme, the last one to plug in pulls the leftover power, possibly from just a single charging module, but because the available power is now shared among four stalls it is better statistically multiplexed.
Someone just needs to post a picture of a V3 charging cabinet label and that would clear up quite a bit of confusion. I also think they are rated at 500kW shared among four stalls, each capable of max. 250kW. The V3 plans for Vienna, VA showed 700A (80% rated), 480V 3-phase service feeding the cabinets. That's almost 500kW. Two of those are fed by a run of the mill 1000kVA transformer, along with a small circuit for the new site master/controller of the superchargers.
Think the sharing algorithm uses the original scheme, the last one to plug in pulls the leftover power, possibly from just a single charging module, but because the available power is now shared among four stalls it is better statistically multiplexed.
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