Hypothetical question

[mivey]

160121-1003 EST

mivey may be able tell us what a real world power distribution line with an open circuit at about 700 miles would do at the source.

Using about 9400-9500 amps available fault at source:

500 kV A-frame transmission structure:
700 miles: 500 kV at source rises to about 2.5 MV at open end, 5-5.5 kA at source
70 miles: a few percent rise in voltage, 150-165 amps at source

12.5 kV cross-arm MV structure:
700 miles: rises to about 27 kV at open end, 48-50 amps at source
70 miles: a few percent rise in voltage, 3-5 amps at source

480 volt cross-arm MV structure:
700 miles: rises to about 1 kV at open end, 1.8-1.9 amps at source
70 miles: a few percent rise in voltage, 120-130 mA at source

480 volt UG cable:
700 miles: drops to about 63 volts at open end, 2.8 amps at source
70 miles: a few percent rise in voltage, 1.3 amps at source
2000 ft: voltage about the same, about 7 mA at source

 

[mivey]

I should have noted approximate ground currents. Keep in mind these are for comparison and can't be absolute without an accurate model of the specific condition. I did assume grounding at every span and every 500 ft for the UG except in the 2000 ft case.

500 kV A-frame transmission structure:
700 miles: 18 A
70 miles: 6.6 A

12.5 kV cross-arm MV structure:
700 miles: 550 mA
70 miles: 68 mA

480 volt cross-arm MV structure:
700 miles: 21 mA
70 miles: 2.6 mA

480 volt UG cable:
700 miles: 380 mA
70 miles: 220 mA
2000 ft, grounded both ends: 1.7 mA
2000 ft, grounded source end only: 3.1 mA

 

[gar]

160124-1424 EST

mivey:

Thanks for the analysis.

Can we assume that the voltage multiplying factor at 1/4 wave decreases as the source voltage drops is the result a relatively more lossy transmission line at the lower voltages?

Also does your modeling software take into consideration the propogation velocity in the real world vs free space? Thus, should some other distance be used for the electrical 1/4 wavelength than 700 miles?

.

 

[mivey]

160124-1424 EST
Can we assume that the voltage multiplying factor at 1/4 wave decreases as the source voltage drops is the result a relatively more lossy transmission line at the lower voltages?

Not sure. I just figured the change in rise was a result of the relative voltage pressure and capacitance. I did not note the per unit loss.

160124-1424 EST
Also does your modeling software take into consideration the propogation velocity in the real world vs free space? Thus, should some other distance be used for the electrical 1/4 wavelength than 700 miles?

It was a frequency domain analysis so it should not matter in the steady-state result. Of course we would never get those rises I posted in a real world system as the protection would not allow it.

Realistically, you would want to make a time domain analysis if you are analyzing a tie point on a long, uneven transmission loop.

 

[gar]

160130-0817 EST

mivey:

Does your model assume lumped L, R, and C or distributed?

.

 

[Ingenieur]

Wow
very interesting and wide ranging discussion
120 to 500kv dc

recently completed a grad couse on facts/hvdc
had no idea that the tech was so widely used for so long

currently in a grad course 'power system analysis 2'
the eastern blackout was a case study

the program I am enrolled in is a 15 credit grad cert in power engineering
the credentials of the instructors are impressive
lot of smart folks in this thread too

as far as the op I'm not clear on the question
could he draw enough open ckt to trip thermal or mag? Probably not
ground fault/leakage? Yes if long enough and if the system is grounded