GE 845 Instruction Manual page 380

MONITORING
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For wye-connected VTs, the power factor value is calculated from the valid phase(s) with a
voltage that is above a user selected threshold and a current that is above 0.002 x CT.
Power Factor element delay timers are only allowed to time when the supervision
conditions are met and the Power Factor remains outside of the region between the
programmed Switch-In and Switch-Out levels. In the same way, when a Power Factor
condition starts the Power Factor 1 or 2 delay timer, if one or more valid phases no longer
satisfy the supervision conditions, the power factor will be re-calculated based on the still
valid phase(s). If the element is continuously asserted with the new power factor value, the
timer will continue timing, otherwise, the element will reset without operating.
The following figure illustrates the conventions established for use in 845 relays, where the
negative value means the lead power factor, and the positive value means the lag power
factor.
Figure 4-117: Conventions for Power Factor
For example, the applications of Switch-In and Switch-Out levels are shown in the figures
below.
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS