Abstract: A protective relay having means for adjusting a plurality of characteristic angles is disclosed. A characteristic angle is preselected to correspond to a desired reach representative of one or more zones of an A.C. high voltage transmission line desired to be protected. The adjustable characteristic angle means is interconnected to each of the one or more phases of the A.C. transmission line by a cascaded arrangement of one or more transactors and clamping means. The adjustable characteristic angle means comprises an operational amplifier, a plurality of resistors, a capacitor and selectable means for interconnecting each of the plurality of resistors one at a time to the operational amplifier. The plurality of resistors have values to correspond to the desired characteristic angles of the protective relay. The operational amplifier in combination with the plurality of resistors and the capacitor develop an output signal having a substantially constant magnitude as the characteristic angle is varied.

Abstract: A D.C. to D.C. converter is disclosed which includes a first and a fourth, and a second and a third, sequentially operating transistors. The D.C. to D.C. converter further includes a saturable transformer having a center-tap and resistive networks interposed among the four transistors. The D.C. to D.C. converter is adapted for energization by an input D.C. voltage. The transistors of the D.C. to D.C. converter cause one side of the input D.C. voltage to be sequentially applied to opposite sides of a primary winding of the transformer which, in turn, cause the transformer to be sequentially excited into positive and then negative saturation conditions. The sequential excitation of transformer develops a time varying square-wave type signal at the secondary windings of the transformer which is further converted into a D.C. signal by an A.C. to D.C. converter.

Abstract: Pulses generated by each of two normally synchronized oscillators are combined into a single pulse per cycle by feeding them to a monostable multivibrator and by differentiating the output signal of the monostable multivibrator.