Discharge Study of 735-kY Lines by Analog Computer and Field Tests on 230-and 315-kV Lines

A study was done to analyze the discharge of a 735-kV line after its separation from the network. Two particular cases are treated: a short transmission line with saturable magnetic potential transformers at proper extremities, and a longer line with linear reactances also connected at both ends. A rapid discharge after the opening of the line allows an automatic reclosure some 25 Hz later without producing dangerous overvoltages. The magnetic potential transformer used for relaying and metering on the permanent system could reduce the residual voltage on the line due to its copper and iron losses, making it a preferable choice over capacitor potential transformers which do not have this latter property. The effects of different opening resistors on the breaker were also studied. The line discharge was studied by performing field tests (at 220 and 315 kV), and by using an analog computer having a capacity of 88 amplifiers. The first series of field tests was then simulated on the computer, and with the necessary corrections an extrapolation was done to study the 735-kV line discharge.