5-128L90 Line Differential RelayGE Power Management5.6 CONTROL ELEMENTS 5 SETTINGS52. The relay measures frequency and Volts/Hz from an input on a given Source with priorities as established by the con-figuration of input channels to the Source. The relay will use the phase channel of a three-phase set of voltages ifprogrammed as part of that Source. The relay will use the auxiliary voltage channel only if that channel is pro-grammed as part of the Source and a three-phase set is not.The are two identical synchrocheck elements available, numbered 1 and 2.The synchronism check function is intended for supervising the paralleling of two parts of a system which are to be joinedby the closure of a circuit breaker. The synchrocheck elements are typically used at locations where the two parts of thesystem are interconnected through at least one other point in the system.Synchrocheck verifies that the voltages (V1 and V2) on the two sides of the supervised circuit breaker are within set limitsof magnitude, angle and frequency differences.The time while the two voltages remain within the admissible angle difference is determined by the setting of the phaseangle difference ∆Φ and the frequency difference ∆F (slip frequency). It can be defined as the time it would take the voltagephasor V1 or V2 to traverse an angle equal to 2 × ∆Φ at a frequency equal to the frequency difference ∆F. This time can becalculated by:where: ∆Φ = phase angle difference in degrees; ∆F = frequency difference in Hz.As an example; for the default values (∆Φ = 30°, ∆F = 0.1 Hz), the time while the angle between the two voltages will beless than the set value is:If one or both sources are de-energized, the synchrocheck programming can allow for closing of the circuit breaker usingundervoltage control to by-pass the synchrocheck measurements (Dead Source function).T 1360°2 ∆Φ×------------------ ∆F×--------------------------------=T 1360°2 ∆Φ×------------------ ∆F×-------------------------------- 1360°2 30°×------------------- 0.1 Hz×------------------------------------------- 1.66 sec.= = =
