Early Days of the Power Grid 3

[Mbrooke]

How did the power grid function in early 1900s by not being interconnected? How well did generation, such as a hydroelectric facility survive faults? Was step distance relaying or differential used on transmission feeders?

 

[davidbeach]

The rotary converters were used extensively to provide DC for street cars, interurbans, and other electrified rail systems. Ultimately supplanted by solid state devices, but not the vestiges of a dying DC system.

 

[Bill West]

You're right David. In the New York area in 1912, eleven major powerhouses belonged to streetcar, elevated, subway and railroad companies. Utilities NY Edison and Brooklyn Edison had about four major stations and substantially less total capacity. Interesting history at this link [link]https://ethw.org/The_Railway_Power_Stations_of_New_York_City[/url]

The limitations of rotaries also prolonged 25 HZ in America. It wasn't until the mid 1920's that the problems of large 60 HZ rotaries were solved.

Bill

 

[Bill West]

Here's a history thread I found years ago about our 120/60 and 220/50 voltage and frequencies. [link]http://www.physicsforums.com/showthread.php?p=974832[/url] . And Eng-Tips had this one [link]http://www.eng-tips.com/viewthread.cfm?qid=3663&page=218[/url]

As to the historical spread of these two systems, I feel that the principal factor in in their reach to the rest of the world was which country provided the money for the first electrification of a country. The investors bought from factories they owned and they used the volts/HZ that they built the most of. So all countries industrialized by the US are 60 Hz and all financed by Britain, Germany or France are 50 Hz. Brazil's choice for instance traces to Brazilian Traction, Light & Power, a Canadian company you may now know as Brookfield Properties.

Bill

 

[Bill West]

Bill Ross -Wikipedia mentions asymmetrical voltage drops on 3ph-3ph Scott transformers because of asymmetrical impedances. [link]https://en.wikipedia.org/wiki/Scott-T_transformer[/url] . I found the Xo tap there novel.

Bill

 

[waross]

Thank you, Bill.

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

 

[DM61850]

Does anyone know the reason for having two phase generators with the phases 90 degrees apart? Were the generators balanced by having 4 orthogonal vectors summed to two orthogonal vectors? Otherwise, it seems that the prime mover would have to have oscillating torque.

 

[waross]

It was a work in progress that progressed to three phases 120 degrees apart.
Two phase had advantages over single phase.
When it was recognized that three phase had advantages over two phase, the industry migrated to three phase.

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

 

[waross]

Otherwise, it seems that the prime mover would have to have oscillating torque.

I would state that as:
The load presents oscillating torque demands to the prime mover.
Flywheels?

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

 

[Bill West]

Those two phase motors replaced steam engines which were also an oscillating torque, lots of flywheel effect in the big pulleys of a factory's belt driven line shaft. Per your posts, the progress was positive so it was taken. Two phase got us self starting motors and seemed a simpler generator/motor design than three. Only later and in larger sizes was the value of three phase's steady torque and conductor utilization realized.

Bill

 

[waross]

Two phase gave an advantage in conductor utilization over single phase.
Three phase gave more.
Many years ago, BE Electric distributed commercial DC in downtown Vancouver.
It was used for elevator power.
When they phased out DC distribution, they installed rectifier banks for legacy customers.

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

 

[DTR2011]

A little bit off topic, but I spoke with a protection engineer some years ago and he was explaining to me a 6 phase system that was operated in New York for a while. I’m working in the area currently but can’t find anyone who knows about this system.

From wiki:

Between 1992 and 1995, New York State Electric & Gas operated a 1.5 mile converted from a double-circuit 3-phase 115KV transmission line to a 93KV 6-phase transmission line. The primary result was that it is economically favorable to operate an existing double-circuit 115KV 3-phase line as a 6-phase line for distances greater than 23–28 miles.

 

[Mbrooke]

Ok- now I have to know where that was. I thought I know everything about the NY power system- but I guess not.

 

[cuky2000]

DTR2011,

I hope I can help with what I can remember from working on this project back in the early 1990s for Ebasco. This project was contracted to us by NYSEG founded by the DOE to be deployed as a demonstration project that was based on the early work developed by in the early 1970s by PTI engineers H. Barnes and Lionel Barthold.

https://www.youtube.com/watch?v=HqZtptHnC2I

The project consisted of converting a double circuit 3 phase, 115 kV transmission line in a single circuit 6 phases, originally considered 230 kV but reduced to 161 kV because of corona concern. Stil the main benefit of the 6 phase system was to increase the line power transfer capabilities in 173% without the need of changing any insulator or conductor on the existing transmission line.

The six phases of the line were divided into two three-phase groups, one of them with a normal wye/delta transformer with 30^o phase-shift and the other connected to the inverted wye/delta transformer with -30^o. After superimposed created 6 phase in the line side at Goudey substation and reconverted back to 3-phase at the and Oakdale substation.

The protection system and SCADA at each end of the six-phase line consisted of several separate three-phase multi-functional relays tied together into a six-phase protection system by a common six-phase programmable IED implemented by an excellent P&C engineer H. Panke (deceased). The contiguous phases-to-phase and the phase-to-ground voltages were the same while the line-to-line voltages between opposite phases were double. The symmetrical 6 phase system is modeled with a 6x6 matrix rather than the conventional 3x3 transfer function.

_{PS: During the 80s and early 90s a lot of engineers from NYSEG, EPRI, IEEE, DOE, and other organizations in the US and abroad were actively involved in writing papers and discovering different options. Unfortunately, I do not see any interest in other utilities to take advantage of and benefit from the experience gained in this project. I hope that in the near future engineers and utilities could renovate interest in this technique to increase power delivery by a T. Line using High Phase Order.}

 

[Mbrooke]

173% increase you say?

 

[Bill West]

The Wiki is

https://en.wikipedia.org/wiki/Polyphase_system

. Reference 3 there is an extensive paper on the project.

Bill

 

[waross]

Convert two deltas to wye and reverse the polarity of one circuit and you have six phases.
The delta system would be insulated for 115 kV to ground and the voltage to ground would remain at 115 kV.
Six phase is touted as reducing corona but one note indicates that the voltage was reduced because of corona concerns.
That will cut into the +73%.
Oh well. I read it on the internet.
You will get the 73% increase or 173% of original capacity (depending on how you phrase it) that a conversion from delta to wye provides. That holds for three phase or six phase.
Takeaways from the summary of the 493 page report, Reference 3 in the Wiki article linked by Bill West.
Page 22,
Will it work? Yes
Did it work? Yes.
Is it worth converting existing double circuits? Probably not.
Is a single tower, compacted conductor scheme cost effective? No, but it may have applications on restricted Right Of Ways.
Why was it de-commissioned? The transformers were limiting the capacity of the line.

There may be special constraints on both the maximum voltage and ROW restriction.
In that case it may be a choice to go with a six phase system.
Normally, one would just choose a higher voltage for the required capacity on a new build.
Energized in 1992, de-energized in 1995. That says it all.

That internet article badly needs editing.

Compared to a single-phase, two-wire system, a three-phase three-wire system transmits three times as much power for the same conductor size and voltage.

Also;
The author seems to think that adding more poles to an induction generator implies higher phase orders.


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

 

[cuky2000]

.

Yes, conversion from 3 phase to 6 phase can increase the line power transfer capability up to 1.73 pu (173%). This is due to the fact the surge impedance loading, SIL (MW), is a direct function of the number of electrical phases.

For other reasons in this project, the transfer capability of the line was limited around 150% of the original line capability.

I hope this answers your question. For additional details, see the excerpt below.

 

[Bill West]

I'd look at it more sympathetically, Bill. It was only intended as an experiment, the chosen line was a matter of convenience rather than a defining example and their starting point was a region where ROW's too narrow to upgrade are an issue. They did suggest that it became worthwhile at 25-30 miles.

Bill

 

[Mbrooke]

So this begs the question. If we start all over, would we use 3 phase or 6 phase? Consider that most power systems through out the world are just two 3 phase systems operated in parallel. One could in theory operate one of them 60* out of phase with the other. Not much material to add, and a 173% increase.

 

[Mbrooke]

And Waross: I feel you buddy. I never trust wiki. Hate when people link me to it and then get mad when I call it out.