if a power factor (pf) correction has been done to the main panel of electrical system, will it correct the power factors of down stream equipments. can the pf improve by install separate capacitor banks along with the main panel.
It is standard practice to install power factor automatic correction at the main panel, which does self correction with change in load. This is very effective system. It takes care for down stream equipment to most extent, Even though ideally it( correction capacitor) is to be installed at load, but this is not practical.
Power factor improvement is not a precise science, we normally improve to 0.95 lagging to avoid slipping into pf1 or unity as parallel resonance will occur and the capacitor fuses will blow. Improvement at the main panel is the most practical method as you are dealing with the average of the pf of all of the loads on the system. The advantage of this is that the pf is unlikely to change rapidly and the pf relay can keep up with these changes easily. Break times and lunch are exceptions to this. pf improvement must be automatic as loads such as electric motors have varying pf's according to the load on the motor. So a band saw motor will have a fairly good pf when cutting, but a low pf when idling, similarly, a welding transformer will have a fairly good pf when welding is in progress, but a low pf when no arc is struck. pf Improvement at the load will reduce the current drawn by the load and may assist in reducing cable size, but do not over correct, fit a smaller than expected capacitor bank to allow for the better pf on load.
Yes, it can be done . Use capacitor in parallel with the load .
First, it is good practice to install powewr factor correction capacitors to each large motor, 40Hp and larger. Then through a power factor meter installed in the main supply panel, check the power at the main bus bar. If the main panel is still lower than 0.8, install more power factor correction capacitors at the bus.
