Coupling Capcitor

Because capacitors pass AC but block DC signals (when charged up to the applied dc voltage), they are often used to separate the AC and DC components of a signal. This method is known as AC coupling or "capacitive coupling". Here, a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the signal frequency, is employed.

How the checking of three phase capacitor?

Capacitors are reactive elements. An ideal capacitor is 100% reactive and does not offer any resistance while a practical capacitor has some resistance as well. So a little voltage out of the voltage applied to the capacitor drops in the resistance. Every capacitor name plate will have the KVAR rating and voltage rating. KVAR = sqrt3 X V X I X sin(Phi). For new capacitor resistance is very small and hence has to be neglected. So sin(phi) =1 and KVAR = sqrt 3 X V X I. Calculate the current from the formula. This is the rated current of the capacitor. As the capacitor gets older, the capacitance decreases causing it to draw less current. From the above formula calculate KVAR to know how effective the capacitor is. Also standard charts are available from capacitor manufacturers for checking the KVAR value against the current drawn from which KVAR can be known for the current drawn by the capacitor.

3 phase capacitor checking method ( in delta ) give the power supply then check the amps ( all phase currents are same

Main purpose of coupling capacitor is, it removes the ripple voltage present in AC