Calculating line impedance for distance relaying

[mbrooke]

Since the other T-line is not in the same ROW then no mutuals should factor.

Question, how much does the mutual coupling vary between lines in the same right of way vs 2 circuits on the same tower? Or 345kv and 115kv on the same tower? Just gauge my understanding.

They other parameters that are need to estimate the line impedance are:

1.) What type of static wire is being used and how many (1 or 2)?

2 static wires.

2.) What is the avg structure height from the ground up (don't include 10%+2' embedment)?

80 feet

3.) What is the physical spacing of the conductors with respect to the CL of the structure and the top of the structure?

CL? Let me double check the specs.

4.) Give me an idea of the soil impedance (or soil type).

Errrr... Id say clay soil? Certainly not an erade region.

5.) Lastly, can you provide more info on the T-Line length? If you have to give the structure spans (str. by str.), that is good. For a ~14 mile line, a difference of 1.4 miles is 10% error (0.7 mile = 5%) and is considered too much of an error. 10% error could easily cause an over or under trip event, result in mis-coordination, or simply fail to adequately protect the line.

So the exact length is needed here? Let me get it, for this line it is indeed very close to 14 miles.

 

[mbrooke]

I guess my question is why doesn't the relaying/protection group or the line engineering group of a public utility have the basic software tools to do this?

Well, think about it like this. How was it that utilities were able to get millions upon millions of transmission lines to work in the 40s, 50s and 60s without a single computer program?

 

[Ingenieur]

Well, think about it like this. How was it that utilities were able to get millions upon millions of transmission lines to work in the 40s, 50s and 60s without a single computer program?

Lower voltages
less understanding of the science, less concern with the consequence
less sophistication with protective systems
their numbers were loose approximations

but now we have computers
I've had several courses that addressed this subject using pencil/paper (and computer)
but it was made clear that this was for understanging the physics
in the real world a computer is used

once the basic geometry, sizes, etc are known it can be solved in minutes on a computer

 

[Bugman1400]

Question, how much does the mutual coupling vary between lines in the same right of way vs 2 circuits on the same tower? Or 345kv and 115kv on the same tower? Just gauge my understanding.

Same principle applies but, obviously, the closer the T-lines are to each other, the more influence they have on each other. Because of EMF principles, the voltage level is another main factor. The last main factor is the distance the two lines are together relative to the total length of the line.

2 static wires.

What type....3/8" EHS?

CL? Let me double check the specs.

Centerline

 

[Ingenieur]

here's a typical basic program output
you put in the conductor properties from the tables and the geometry
soil resistivity, temperatures, etc are in a set-up block
calculates the Z matrix on a per mile basis

when I get some time I'll plug your numbers in
this was a HW problem

 

[mbrooke]

Lower voltages

There were 345 and 115kv lines (400 and 132kv in Europe) as much in the 1960s as today. For example, what fed NYC in the 1960s?

less understanding of the science, less concern with the consequence

Do computer programs that just spit out a number help the average EE gain a better understanding of the how and why?

less sophistication with protective systems

Yup, a huge plus.

their numbers were loose approximations

In some aspects yes, but it certainly worked well all over the world.

but now we have computers
I've had several courses that addressed this subject using pencil/paper (and computer)
but it was made clear that this was for understanging the physics
in the real world a computer is used

Which is good thing.

once the basic geometry, sizes, etc are known it can be solved in minutes on a computer

I agree, but Id still like to know the why.

 

[mbrooke]

here's a typical basic program output
you put in the conductor properties from the tables and the geometry
soil resistivity, temperatures, etc are in a set-up block
calculates the Z matrix on a per mile basis

when I get some time I'll plug your numbers in
this was a HW problem

Thanks, but I am truly stumped on what temperature to select. My understanding is this effects the R portion of every calculation, and the conductor temp can vary from room temp to over 100*C depending on load and ambient.

 

[mbrooke]

Same principle applies but, obviously, the closer the T-lines are to each other, the more influence they have on each other. Because of EMF principles, the voltage level is another main factor. The last main factor is the distance the two lines are together relative to the total length of the line.

And this can act almost like infeed to a line, correct?

What type....3/8" EHS?

Yes

Centerline

Let me check that.

 

[Ingenieur]

There were 345 and 115kv lines (400 and 132kv in Europe) as much in the 1960s as today. For example, what fed NYC in the 1960s?

In general voltages were lower
lower loads

Do computer programs that just spit out a number help the average EE gain a better understanding of the how and why?

you learn the math first
then you know how a computer calculates it

Yup, a huge plus.

In some aspects yes, but it certainly worked well all over the world.

It works better now or the std would be hand calcs
it is not

Which is good thing.

I agree, but Id still like to know the why.

the point is if this work is being done professionally and will be implemented we owe it to the customer to use the best means available

the only way to learn
an instructor familar with subject
a good text, the usda doc is a good primer
take a course, trig, geometry, algebra, basic calculus and perhaps lihear algebra will be required
study 2 to 3 nights per week for a few hours each and continue for a few months
there is no magic sauce lol
It still baffles me, the math can be intense to develop the equations for a fundemental understanding
less so for plugging numbers into them

 

[mbrooke]

the point is if this work is being done professionally and will be implemented we owe it to the customer to use the best means available

the only way to learn
an instructor familar with subject
a good text, the usda doc is a good primer
take a course, trig, geometry, algebra, basic calculus and perhaps lihear algebra will be required
study 2 to 3 nights per week for a few hours each and continue for a few months
there is no magic sauce lol
It still baffles me, the math can be intense to develop the equations for a fundemental understanding
less so for plugging numbers into them

Any recommendations on text? BTW, I am up for the challenge


But, I disagree. The math is whats key, not just plugging in the numbers.

 

[Ingenieur]

Any recommendations on text? BTW, I am up for the challenge

But, I disagree. The math is whats key, not just plugging in the numbers.

previously posted
http://www.cengage.com/search/produ...alysis|9781111425777&Ntx=mode+matchallpartial

4. TRANSMISSION-LINE PARAMETERS.
Case Study: Transmission Line Conductor Design Comes of Age. Case Study: Six Utilities Share Their Perspectives on Insulators. Resistance. Conductance. Inductance: Solid Cylindrical Conductor. Inductance: Single-Phase Two Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing. Inductance: Composite Conductors, Unequal Phase Spacing, Bundled Conductors. Series Impedances: Three-Phase Line with Neutral Conductors and Earth Return. Electric Field and Voltage: Solid Cylindrical Conductor. Capacitance: Single-Phase Two Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing. Capacitance: Stranded Conductors, Unequal Phase Spacing, Bundled Conductors. Shunt Admittances: Lines with Neutral Conductors and Earth Return. Electric Field Strength at Conductor Surfaces and at Ground Level. Parallel Circuit Three-Phase Lines.

next level
https://www.crcpress.com/Computer-A...sis-Second-Edition/Kusic/p/book/9781420061062
actually took the course from the author last spring
started with 9 in the class finished with 3 lol

Each has a few chapters on lines
the first single lines
the second networks



never said the math isn't important
just seldom used
more important is the understanding of electromagnetic fields garnered in a basic tech physics course and upper level BS EE program
the math quantifies, the physics leads to understanding, they go hand in hand

 

[mbrooke]

previously posted
http://www.cengage.com/search/produ...alysis|9781111425777&Ntx=mode+matchallpartial

4. TRANSMISSION-LINE PARAMETERS.
Case Study: Transmission Line Conductor Design Comes of Age. Case Study: Six Utilities Share Their Perspectives on Insulators. Resistance. Conductance. Inductance: Solid Cylindrical Conductor. Inductance: Single-Phase Two Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing. Inductance: Composite Conductors, Unequal Phase Spacing, Bundled Conductors. Series Impedances: Three-Phase Line with Neutral Conductors and Earth Return. Electric Field and Voltage: Solid Cylindrical Conductor. Capacitance: Single-Phase Two Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing. Capacitance: Stranded Conductors, Unequal Phase Spacing, Bundled Conductors. Shunt Admittances: Lines with Neutral Conductors and Earth Return. Electric Field Strength at Conductor Surfaces and at Ground Level. Parallel Circuit Three-Phase Lines.

next level
https://www.crcpress.com/Computer-A...sis-Second-Edition/Kusic/p/book/9781420061062
actually took the course from the author last spring
started with 9 in the class finished with 3 lol

Each has a few chapters on lines
the first single lines
the second networks



never said the math isn't important
just seldom used
more important is the understanding of electromagnetic fields garnered in a basic tech physics course and upper level BS EE program
the math quantifies, the physics leads to understanding, they go hand in hand

But its that seldom use where theory withers. I see more and more college students jump to powerworld, powertechnolgiesinc, ect without giving the math studied a consideration. Remember that in the 50s campuses did not have it.

Anyway, thank you for those resources. But if someone knows the basics Id like to try them out here too. I have some experience, so in my eyes it should not be all that hard.

 

[Ingenieur]

But its that seldom use where theory withers. I see more and more college students jump to powerworld, powertechnolgiesinc, ect without giving the math studied a consideration. Remember that in the 50s campuses did not have it.

Anyway, thank you for those resources. But if someone knows the basics Id like to try them out here too. I have some experience, so in my eyes it should not be all that hard.

My experience differs, nothing 'withers'
been taking grad courses for the last 3-4 years and my peers would not pass the courses without a fundemental understanding obtained by using the math to derive the equations from the physical system

but you can't model or simulate/analyse a 16 bus 16 line system by hand lol

to get a basic approximation of a single line's parameters is easy
there are tables for fixed configs which can be adjusted for spacing and height
ref the USDA manual
good for general losses voltage rise/drop, etc
not for relaying imho

 

[mbrooke]

My experience differs, nothing 'withers'
been taking grad courses for the last 3-4 years and my peers would not pass the courses without a fundemental understanding obtained by using the math to derive the equations from the physical system

but you can't model or simulate/analyse a 16 bus 16 line system by hand lol

Correct, but Id just like to figure out a simple line and its distance relay. Nothing more. Theoretically anything can be done by hand, even ERCOT, but the equations would take up a tractor trailer truck worth of paper.

to get a basic approximation of a single line's parameters is easy
there are tables for fixed configs which can be adjusted for spacing and height
ref the USDA manual
good for general losses voltage rise/drop, etc
not for relaying imho

But once you know the paramters, you can then obtain the positive, negative and zero sequence components to begin setting the distance characteristics. My understanding even if the line is modeled perfectly, normal variants will always shift the relay's reach.

 

[mbrooke]

Same principle applies but, obviously, the closer the T-lines are to each other, the more influence they have on each other. Because of EMF principles, the voltage level is another main factor. The last main factor is the distance the two lines are together relative to the total length of the line.




What type....3/8" EHS?


Centerline

here's a typical basic program output
you put in the conductor properties from the tables and the geometry
soil resistivity, temperatures, etc are in a set-up block
calculates the Z matrix on a per mile basis

when I get some time I'll plug your numbers in
this was a HW problem

Ok, so I got these positive sequence values for a 12 mile (approx) line using Lapwing conductor:


R=0.01034

X= 0.06995

B= 0.00975

All units are in per unit value. Sound kosher? Normal continuous rating of 220 MVA.


Given these values, how would you set an Mho?

 

[Bugman1400]

Ok, so I got these positive sequence values for a 12 mile (approx) line using Lapwing conductor:


R=0.01034

X= 0.06995

B= 0.00975

All units are in per unit value. Sound kosher? Normal continuous rating of 220 MVA.


Given these values, how would you set an Mho?

Not sure how you got those values. What was the conductor spacing and static wire type? Or, have you moved onto arbitrary values to figure out your Mho setting?

Mho's are typically set in at least 2 zones for this length of line. Zone 1 would be 85-90% of the positive sequence line impedance and would have no intentional tripping delay. Zone 2 would be set to 120% of the pos seq line imp and would have a 20 cycle tripping delay. The Zone 2 time delay could range from 15-40 cycles (typ. 20 cyc) depending on the time delay of the remote ends and if there is severe overlap of the Zone 2.

 

[mbrooke]

Not sure how you got those values. What was the conductor spacing

8 feet from the bottom center of the insulator to the pole, 10 feet from arm tip to arm tip and 7.5 feet from top arm tip to the static wire.

and static wire type? Or, have you moved onto arbitrary values to figure out your Mho setting?

3/8 HSS

Mho's are typically set in at least 2 zones for this length of line. Zone 1 would be 85-90% of the positive sequence line impedance and would have no intentional tripping delay. Zone 2 would be set to 120% of the pos seq line imp and would have a 20 cycle tripping delay. The Zone 2 time delay could range from 15-40 cycles (typ. 20 cyc) depending on the time delay of the remote ends and if there is severe overlap of the Zone 2.

Correct, but my question is how do you take the final impedances and plug them into the mho settings.

 

[mbrooke]

http://faculty.mu.edu.sa/public/upl...1cba17ff378633_SymmetricalComponents_2013.pdf


Ok, reading up on this is getting really easy. But... Im somewhat stuck on determining the positive and zero sequence line impedance angle (not magnitude).

 

[rian0201]

Hmmm... If you dont have computer for this, it is kind of tedious process, you could through matrices of complex impedances of the lines. If you have mathcad i could share to you the file i have. And edit it.

But, in my place, this is no longer required. You can measure the line impedance, which is way more accurate than calculating it. They require to measure it rather than calculate it.

As for the settings, you need to check the in feeds if it exists.. If there is no in feeds you can just do it directly, relays are accurate if the lines are radial, if not, consider the infeeds, the other protection as well.

For the final settings, you need to convert them to the unit that the relay accepts. Most relay units are in sec ohm format, others accepts primary format, you need to enter the magnitude and angle of positive and zero sequence, and k0 factor - as per relay manual, they the settings.

In general, it depends on the relay, after which, relay test will follow.


Sent from Mars

 

[mbrooke]

Hmmm... If you dont have computer for this, it is kind of tedious process, you could through matrices of complex impedances of the lines. If you have mathcad i could share to you the file i have. And edit it.

But, in my place, this is no longer required. You can measure the line impedance, which is way more accurate than calculating it. They require to measure it rather than calculate it.

As for the settings, you need to check the in feeds if it exists.. If there is no in feeds you can just do it directly, relays are accurate if the lines are radial, if not, consider the infeeds, the other protection as well.

For the final settings, you need to convert them to the unit that the relay accepts. Most relay units are in sec ohm format, others accepts primary format, you need to enter the magnitude and angle of positive and zero sequence, and k0 factor - as per relay manual, they the settings.

In general, it depends on the relay, after which, relay test will follow.


Sent from Mars

Id be interested. Great info btw. I found this on converting primary ohms into secondary ohms:

http://www.relaytech.com/files/34789987.htm


Infeeding... is it correct I do not have to worry about it unless I have a generator directly attached to the line?