GE B90 User Manual

CHAPTER 9: THEORY OF OPERATION SATURATION DETECTOR
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 9-7
9
Figure 9-4: Directional principle operation during external faults
Figure 9-5: Directional principle operation during internal faults
The B90 implementation calculates the maximum angle for the considered currents and compares it against a fixed
threshold of 90°. The flag indicating whether the directional protection principle is satisfied is available as the FlexLogic
operand BUS 1(4) DIR A/B/C.
9.5 Saturation detector
9.5.1 CT saturation detection
The saturation detector of the B90 takes advantage of the fact that any CT operates correctly for a short period of time,
even under very large primary currents that would subsequently cause a very deep saturation. As a result, in the case of
an external fault, the differential current stays very low during the initial period of linear operation of the CTs while the

GE B90 Specifications

General

Brand	GE
Model	B90
Category	Relays
Language	English