hi,
I used to work with adoptive var compensators in the past.
Capacitor banks are mainly used for Power Quality applications, such as voltage sags, voltage flickers, and power interruptions. Sags are short term reduction in voltage and power interruptions are zero-voltage events. Both can be helped by using UPSes. But flickers are rapidly occurring voltage sags which can be smoothed by using capacitor banks for voltage control. These capacitor banks can be STATIC or DYNAMIC.
Static capacitor banks are good in price and have their applications on utility loads (just Google static var compensators utility) or in motors. The value of kvar is once calculated and the capacitors are deployed in the field....they sit there on the line.
On the other side, dynamic var compensators usually comprise electronic controls to add or reduce the amount of capacitors that will be switched up or down as per the demand for vars on the line.
A higher level of VAR requirement will require fast additions of capacitors versus low demand of VAR which requires lesser capacitors to be disconnected from the shunt. Usually, there are also reactor cabinets involved into dynamic var compensators, in order to absorb switching harmonics.
for dynamic var compensators there are many companies out there such as S&C electric, ABB, and I believe SIEMENS is active in that area of Power Quality as well. The websites of these companies provide great information from application point of view on your question.
I hope that helps.
Bilal
K-Bill