Cables and Lagging Reactive Power

I generally avoid power topics - having failed my power class in college, but I presume it's because a cable is basically inductive.

check here

Can you give me a reference of any book which support your statement.

There is a good article in Wikipedia on power factor.

You don't need a book. It is basic of electrical Engineering. read the transmission line chapter where the ferranti Effect is discussed.

Are you not supposed to discuss these in class? After all this is what the professors are paid for?

Professor doe not go in depth of topic. So, we have to find and study. I found my question answer as below.

Important results for lossless lines (EHV lines have low resistance, so lossless line approximation is valid).
	Voltage profile along the line is flat only if R= Zc is connected at receiving end (SIL). Under this situation, there is no demand of reactive power from either sending or receiving ends. Loads are decided by consumers and not by a system operator. As such, this exact condition is practically never met although it is ideal.
	If voltage at both ends is maintained at 1.0 pu (say, by controlling excitation of generators connected at both ends), the voltage tends to sag as we move towards the midpoint if Ps > SIL. The line absorbs reactive power.
	If Ps < SIL, voltage swells and the line generates reactive power.
	For a line which has one end maintained at 1.0 pu but kept open-circuited at the other end, overvoltage will be evident at the open end.

Cables have very high SIL (why?). The current at SIL usually exceeds the thermal rating of a cable. Therefore a cable is invariably loaded below its SIL. Cables, therefore, generate reactive power and usually voltages can be very high at low loading levels, especially for long lengths. Besides this, cables are much costlier than overhead lines and are more "unforgiving" towards overloads. Therefore, cables of lengths exceeding 30-40km are rarely used for ac transmission.

I would say, it is pretty basic concept of electrical power engineering.

You can get it clear with these simple questions and answers:

(1) Does the cable have capacitive nature? -> Yes

(2) Do the capacitors act as source of reactive power? -> Yes

(3) When considered as source, does it supply inductive reactive power or capacitive reactive power to the system? -> Inductive

(4) When considered as load, does it consume inductive reactive power or capacitive reactive power from the system? -> Capacitive

Pay attention to question 3 and 4, both must not have same answer.

Also keep in mind that

Inductive reactive power = - (minus) capacitive reactive power

Supply power = - (minus) consume power

Get it from another set of questions for PFI:

(1) Do inductive loads (motors) consume inductive reactive power? -> Yes

(2) Do capacitors compensate this inductive reactive power? -> Yes

(3) Then how actually capacitors do it? -> Either by supplying the type of reactive power that inductive loads consume (inductive reactive power) or by consuming the opposite type of reactive power that inductive loads consume (capacitive reactive power)

I understand, many times we rely mostly on books and have seen it in math or diagram, but if you think it in more depth, this is what really happening.

These links may also help:

http://www.uni-due.de/ean/downloads/papers/wilch2007a.pdf

http://www.nationalgrid.com/NR/rdonlyres/43892106-1CC7-4BEF-A434-7359F155092B/3543/Reactive_Introduction_oct01.pdf

http://www.alcorn-energy.com/pfc.pdf (try to understand Fig 4)

http://www.tvss.net/pq/pf.htm

http://www.nepsi.com/powerfactor.htm

- MS