High-Rise Voltage Drop Solutions

[joozu6]

Our city skyline is getting taller. So much so that the new taller high-rises are limited by voltage drop. We are having this issue on our Network system, where we typically service customers from the ground floor with either 480V or 208V. We considered running primary up the building and installing transformers on upper floors closer to the load, but obviously access to these transformers becomes an issue. We also considered primary metering, serving them with our higher source voltage and having them install their own transformers, but most customers do not want to be in the medium-voltage business.


What solutions are utilities with taller high-rises applying to the secondary voltage drop issues?



Thanks.

 

[waross]

This is for discussion;
How about a network solution.
Run the same 480 Volt and 208 Volt systems as now, but instead of feeding from one point, feed the LV network with multiple, smaller, transformers installed at various levels.
There will be both advantages and there will be challenges.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

It's very common to have multiple spot networks in tall buildings with the primary feeders in risers. Provisions have to be made for utility access.

 

[Mbrooke]

For buildings over X stories you have MV distribution running up the building with MV-LV transformers in the basement, mid rise mechanical equipment room and the penthouse. There is simply no other practical way.



If the building isn't ridiculously tall you can provide 1000 or 1,200 volts and run that up the building to 480 and 208 volt step down transformers. I read a report where they did that with a new high rise residential apartment building in Manhattan. 1000 volts is typically the highest voltage you can use without going into the MV world. In fact the NEC is working on revising their code to reflect that- 600 volts is gradually being changed to 1000 volts each code cycle.

 

[joozu6]

These are helpful. Thanks.

Has anyone heard of using capacitors to raise voltages in this scenario? I'm thinking of leveraging AMI meter data to monitor voltage, and using controlled capacitors on the secondary voltage side to raise secondary voltage as needed when the loads are high. Then we could keep the large medium-voltage utility transformers on the ground floor, run secondary cable up, and add (smaller) capacitors on upper floors where the voltage issues occur. The capacitors are smaller and would be easier to get to the upper levels.

 

[itsmoked]

Ooo.. I can't see that working well especially with today's typical distortion power factors.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crshears]

Could work provided smaller-capacity caps were switched in and out in stages; it would be expensive, though.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Mbrooke]

Here is a typical example for an office building:

https://imgur.com/qirIkPI

 

[Bill West]

Capacitors work when the load is inductive (motors) and the PF correction meaningfully reduces the line current. They also work for MV because the line series inductance becomes significant compared to the resistance and the capacitor can leverage that to level or even raise the voltage along the line. But at LV, if your load is largely resistive then I not sure you'd get much advantage.

If your projects are still moderate in scale, maybe you could trade cost for simplicity by just doubling up the upper floor feed conductors to twice what is needed for the current.

Bill

 

[joozu6]

Good point Bill. It would be mostly resistive load.

I'm curious how far (how tall of a building) increased cable size would get you before it is no longer cost effective, versus installing additional transformers on multiple floors. Also, could you have the customer install step-transformers (LV regulators if there is such a thing) on 208V? This would maintain the goal of avoiding the utility having to install MV transformers on upper floors and still serve the customer with 208V from the ground floor.

 

[waross]

Also, could you have the customer install step-transformers (LV regulators if there is such a thing) on 208V

At this point a transformer will probably be cheaper than a regulator.
You will have an added saving on the cost of supply conductors.
Utility access is handled with key lock-boxes.
Many utilities are reading the meters remotely, no need for monthly access.

Bill
--------------------
"Why not the best?"
Jimmy Carter