Inductors and capacitors in Power Systems

Inductors and capacitors are very common in power systems. Normally people say inductive loads consume reactive power and capacitive loads produce reactive power. But I have different thought on this. My opinion is that there is no such a reactive power thing, but created simply for calculation convenience. Why??

Inductors and capacitors never consume power, but they can store energy!

Inductors store energy in the form of magnetic field, while capacitors store energy in electric field.

Magnetic field can be generated due to three reasons: (1) moving electric charges (which is current) (2) time-changing electric field (3) natural magnet.


If we put a charged inductor (with current in it) short-circuited, it will contain the energy in it forever (if it is superconductor)

If we put a charged conductor (with non-zero voltage) open-circuited, it will contain the energy forever (if it is the ideal capacitor).

 

Remember, for inductors, larger current means larger magnetic field, therefore more energy stored!
For capacitors, large voltage means larger electric field, therefore more energy stored!

(1) Understanding of reactive power
Based on the above analysis, my opinion is there is no such a reactive power in power system!!! The concept is only for calculation convenience.
Why? We see that inductors and capacitors do not consume energy, they basically return those stored energy sooner or later to power systems. But why we feel there are losses, because there are time difference!!! What we lose here is the time value!

If we only inductive loads in systems, then it will borrow system energy, and return in next cycle when the current is decreased. If a load need 2S power at a time, but the system gives it S-Q at time t1 and S+Q at time t2 for compensation. You think it is enough? No! The lost value here is TIME!  It is like somebody borrows money from you, and returns to you next month, but how about interest (time value, opportunity cost)??  Inductive load: current lagging voltage because u=L*di/dt, if i is sin(theta), u then is cos(theta)=sin(theta+90), which means u leading i 90.

In our textbooks, we know that inductors absorb reactive power, and capacitors produce reactive power. This statement gives us misunderstanding that more capacitors can decrease the reactive power loss! Absolutely not!!  Since there is no reactive power, if a system contains conductive loads, the current will lead the voltage, they are still not on the same boat, time value is still lost! So not: the more the better!

But why we are in need of capacitors in power system, because the power system nature is inductive (store power first and then return). So if capacitors return power first and then store, they will perform like nothing, the power returned and stored cancel!!


When system load is very light, the capacitance> inductance, current is small, therefore, system voltage will increase (more energy stored in electric fields); when system load is heavy, current is large, the capacitance <  inductance, current is large and voltage will drop, because u=di/dt, voltage drop increase!

Ok, then, let's summarize. When system is inductive, more energy stored in magnetic field rather than electric field, voltage drops a lot; when system is capacitive, more energy stored in electric field, voltage increase a lot!