what will be the result when more KVAR is added to a transmission line?

Question

I am doing a project on micro controller based powerfactor correction system.We use a capacitor bank for powerfactor correction automatically.If more capacitors are added to the circuit what will be the net effect.Please answer...

Answer 1

This is impossible to answer because the power transmission lines have large capacitance values and those values are determined on the size of the line, the material the line is made of and how long the lines are. You may not need a capacitor bank at all. KVAR is unusable power and goes out of the line through motors and equipment in the form of heat. So adding KVAR to a line is not always a good idea unless you want to compensate for your line impedance.
Your goal should be to move the wave forms (voltage and amperage) to unity at the point of use not out on the transmission line. The utility company will take care of that.

Just some info. Hope it helps.........

Answer 2

you are not really asking what would happen if you add more KVARS. you are asking what would happen if you add more capacitors to a power factor correction unit. I assume that you are not really talking about transmission lines, but the connection point of most PFC units which are located on the transformer side of most main switch boards. If this isn't what you are after then the following will probably not be that useful.

Mostly this will depend on what power factor your load is running at. If the power factor is low 0.8 lagging for example (typical value for most commercial and industrial users, then adding more capacitance is a good thing as it reduces your current use relative to the power usage.

If you have a high power factor load, say 0.98 (typical datacentre load) then adding aditional capacitors will push the lagging power factor to a leading. Most energy distributors get upset about this so try not to do it.

Getting the balance right with the power factor correction unit is important, as is having a good controller to switch the banks of capacitors in and out as required. Please note that the repsonse of a PFC unit is usually slower than typical power surges so can cause problems if you push the correction value too high (i.e. 0.98).

If you are looking at adding more Capacitors to an existing PFC unit, then check what level you are maintaining the power factor at currently and whether the existing capacitor banks are fully utilised.