Utility distribution: what is this?

[iwire]

A cap is always trying to oppose changes in voltage. That means when the voltage dips, the cap opposes that change and supplies the needed voltage. So a cap is very effective at smoothing out dips in voltage.

That is not the same as boosting voltage, I am interested in the answer as well.

 

[peter d]

That is not the same as boosting voltage, I am interested in the answer as well.

No kidding. :roll:

I believe "boosting voltage" is an incorrectly applied term to a capacitor in this situation. Only a transformer can actually boost voltage.

 

[iwire]

No kidding. :roll:

I believe "boosting voltage" is an incorrectly applied term to a capacitor in this situation. Only a transformer can actually boost voltage.

I am open to learning something new.

 

[electrofelon]

A cap is always trying to oppose changes in voltage. That means when the voltage dips, the cap opposes that change and supplies the needed voltage. So a cap is very effective at smoothing out dips in voltage.

Yes but the amount of energy they hold is very small so they can only hold the voltage for a very short time. I suppose they could smooth out dips from things like motor inrush. The biggest motor this line likely has on it is 3 horse in someone's higher end table saw. Maybe that creates enough of a power quality issue under starting on a low, relatively low voltage line like this that a cap helps?

 

[mbrooke]

A cap is always trying to oppose changes in voltage. That means when the voltage dips, the cap opposes that change and supplies the needed voltage. So a cap is very effective at smoothing out dips in voltage.

Not only that, but capacitance "cancels" out reactive power. Reactive power has a current competent, and any current (amps) on a wire be it for watts or VAR produces voltage drop along the line.

 

[mbrooke]

No kidding. :roll:

I believe "boosting voltage" is an incorrectly applied term to a capacitor in this situation. Only a transformer can actually boost voltage.

Untrue. Utilities are always putting cap banks at substations to raise the voltage at the end of long transmission lines or in the system where low voltage is present or may become present. (see this excerpt from a utility's public proposal as one example). There are also times when line capacitance results in an unwanted rise:


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

 

[Bugman1400]

As mbrooke indicated, the cap is only to help cancel out reactive losses. This, in turn, reduces the I-squared losses which reduces the current. The reduction in current also helps with the voltage level. Make sense?

 

[Gary Glaenzer]

I don't see a system neutral. Maybe the arrester on the far side is connected to a cutout we cant see and two hot phases go to the capacitor. I have done this with 14.4kV Delta. Around here a static capacitor will usually be connected in the summer and open in the winter. All about air conditioning load.

If you look at the upper right corner of the 'box' you can see the very tip of another cut-out just barely visible.

 

[Bugman1400]

If you look at the upper right corner of the 'box' you can see the very tip of another cut-out just barely visible.

I don't see another cut-out.:?

 

[mbrooke]

As mbrooke indicated, the cap is only to help cancel out reactive losses. This, in turn, reduces the I-squared losses which reduces the current. The reduction in current also helps with the voltage level. Make sense?

Is this the same phenomenon that is responsible for elevating the voltage at substations? I ask because I have seen POCOs all over the world attach some giant cap banks directly to the 230 and 500kv bus bars to "boost" voltage.

 

[electrofelon]

As mbrooke indicated, the cap is only to help cancel out reactive losses. This, in turn, reduces the I-squared losses which reduces the current. The reduction in current also helps with the voltage level. Make sense?

Yes that makes sense.

 

[ron]

Interesting, could you elaborate? Would that be because the accumulated effects of many small transformers?

A utility company needs reactive power. Caps provide reactive power. http://electrical-engineering-portal.com/how-reactive-power-is-helpful-to-maintain-a-system-healthy

 

[meternerd]

Where is the neutral? It should be above the telephone line.

It's possible the left line is the neutral, since there is no cutout. Not all neutrals are "low". On single phase taps, the neutral may be run on the crossarm. Different jurisdictions have different allowable configurations. Also, not all poles have a grounding wire up to the neutral.

 

[mivey]

Anyone in the EE field know?

As for the reactance, mostly inductive as the capacitive portion is relatively small, particularly on overhead lines.

 

[mivey]

As mbrooke indicated, the cap is only to help cancel out reactive losses. This, in turn, reduces the I-squared losses which reduces the current. The reduction in current also helps with the voltage level. Make sense?

Exactly.:thumbsup:

 

[mbrooke]

As for the reactance, mostly inductive as the capacitive portion is relatively small, particularly on overhead lines.

Does this value change based on amps? I've read that reactive VARs go up on heavy loaded lines (if I remember correctly)

 

[GoldDigger]

A cap is always trying to oppose changes in voltage. That means when the voltage dips, the cap opposes that change and supplies the needed voltage. So a cap is very effective at smoothing out dips in voltage.

A cap smooths out DC very well. There is no way I can see for a capacitor to "smooth out" a dip in AC voltage except by cancelling the voltage drop otherwise caused by inductive current.

mobile

 

[mivey]

Does this value change based on amps? I've read that reactive VARs go up on heavy loaded lines (if I remember correctly)

The line impedance does not change with load. The vars go up mostly because of the load impedance. While present, the line var load is small compared to the endpoint load vars.

 

[fmtjfw]

It's possible the left line is the neutral, since there is no cutout. Not all neutrals are "low". On single phase taps, the neutral may be run on the crossarm. Different jurisdictions have different allowable configurations. Also, not all poles have a grounding wire up to the neutral.

Lightning arrestors are typically not connected to a neutral (at the top).

 

[kwired]

This is no different then selecting to put power factor correction capacitors near the motor vs having a common correction point for an entire plant.

If you put correction near each motor you will have less overall line loss (presuming you optimally corrected the power factor).

For situation like pictured in OP - POCO has to select which location best suits their needs. Putting a capacitor near every customer isn't going to be the most practical, especially in residential areas where the inductive loading will change frequently anyway. Instead they may find a reasonably consistent power factor is present over a certain area and strategically place that capacitor to get a reasonable correction for that area. Doesn't do much for line loss between the capacitor and the load in the area, but does improve line loss from the capacitor to the source, which also will improve voltage drop between the capacitor and the source because the reactive current is reduced in this same segment of the circuit. As I mentioned earlier in this thread - they may switch that capacitor out of the circuit if load conditions change, like if there is less reactive power present when air conditioning season comes to an end.