A Watt transducer has line to line voltages and line currents as inputs. It calculates the Watts and outputs DC mA. The one i am working on is rated 1mA DC for 500W AC. The relationship is linear. A Var transducer does exactly the same, but it shifts the input AC by 90degrees to get Vars. My question is: How do we mechanically/electrically acheive the 90deg ph. shft. in the construction of the Var transducer ?