Utility distribution: what is this?
- Thread starter electrofelon
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truck41trouble
Senior Member
- Location
- US
This is probably a dead end line, not a radial. And the fact that this is on a single phase delta feeder, means there probably isnt much power factor correction needed. Many utility's put a capacitor at set distances away from the sub, regardless of the load.
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mbrooke
Batteries Included
- Location
- United States
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- Technician
Common practice for some POCOs where there is a lot of single phase and perhaps one or two light 3 phase loads down a radial spur.
NewtonLaw
Senior Member
- Location
- Honesdale, PA USA
Power Factor Correction and Voltage Regulation
Power Factor Correction and Voltage Regulation
I agree with many of the replays you have received. The Capacitor appears to be connected Phase to Phase as there is no neutral. This not clear due to the position of the image supplied, but it appears correct. There are also two lightning arresters connected from each phase conductor to an earth ground (likely).
Almost without exception distribution lines (35kV and lower to about 2.4 kV) are inductive in nature. All lines have both capacitive and inductive values but for Distribution lines, the capacitive value is usually 5 to 30 times less than the inductive value. This mostly because they are short, 7 miles or less, and the inductive values are enhanced by the load current flowing through the lines adding to mutual induction also.
An unloaded long transmission line may have enough capacitance to ground to cause voltage rise exceeding the insulation levels. This condition termed Ferranti Rise can be a problem and may require series inductors placed into the line during light or no load conditions.
For your picture the capacitor is considered "fixed" (in service all the time) and it serves two purposes. Power factor correction and voltage regulation. Adding capacitance both corrects for inductive loads and raises the line voltage. The size of the capacitor is usually limited to ensure there is no more than a 5 volt increase (on 120 volt base) if it is a switched capacitor. (Capacitor banks may be fixed or switched in and out of service as needed).
Hope this helps.
Power Factor Correction and Voltage Regulation
I agree with many of the replays you have received. The Capacitor appears to be connected Phase to Phase as there is no neutral. This not clear due to the position of the image supplied, but it appears correct. There are also two lightning arresters connected from each phase conductor to an earth ground (likely).
Almost without exception distribution lines (35kV and lower to about 2.4 kV) are inductive in nature. All lines have both capacitive and inductive values but for Distribution lines, the capacitive value is usually 5 to 30 times less than the inductive value. This mostly because they are short, 7 miles or less, and the inductive values are enhanced by the load current flowing through the lines adding to mutual induction also.
An unloaded long transmission line may have enough capacitance to ground to cause voltage rise exceeding the insulation levels. This condition termed Ferranti Rise can be a problem and may require series inductors placed into the line during light or no load conditions.
For your picture the capacitor is considered "fixed" (in service all the time) and it serves two purposes. Power factor correction and voltage regulation. Adding capacitance both corrects for inductive loads and raises the line voltage. The size of the capacitor is usually limited to ensure there is no more than a 5 volt increase (on 120 volt base) if it is a switched capacitor. (Capacitor banks may be fixed or switched in and out of service as needed).
Hope this helps.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Very interesting. Thank you everyone that commented.
ofourcobra
Member
Cap
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ofourcobra
Member
Very odd to see 1 single cap like that
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truck41trouble
Senior Member
- Location
- US
Not as odd as you would think. Especially on a highly unbalanced feeder. Power factor/ voltage correction is usually only done on the phases required.
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ofourcobra
Member
Not at the power company I work for , I work in substations and we use larger scale capacitor banks that we put on line in the summer but I don't know of any single phase Caps in on our distribution feeders
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
So you are saying that they dont put caps on single phase lines period? This being a 4800 delta line, means its not the most modern system out there......
truck41trouble
Senior Member
- Location
- US
Those big caps at the substation can only work to certain distances. Line deployed pf correction is very prominent and very effective at distances further away, in addition to the caps substations. You may not know of any single phase caps in your system, but I would be surprised if you told me there were none.
As electrofelon stated, this is an older 4800v ungrounded delta. Lower voltage systems are more prone to voltage drop, which can indirectly affect power factor.
Power factor correction on delta systems fed from a wye system is even more important, as you are usually limited to the rating of the mid line pot, which changes your wye into a delta
Where I work we have some very long dead end feeders, some more than 22-28 miles from the sub. And I want to say we have single phase power correction on 85% of those lines, both delta and wye. Especially when the 3 phase drops out and its just a single phase feeder for 6-7 miles.
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