9424200994 Rev N 109
Phase Current Differential (87)
Protection
The phase-current differential (87) element monitors the differential current and provides primary
protection for generators. This element is available only in styles GxxxxxJxPxxxxx and GxxxxxJxTxxxxx of
the BE1-11g.
Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Phase Current Differential (87) settings screen in
BESTCOMSPlus. A summary of the logic inputs and outputs and operational settings appears at the end
of this chapter.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Current, Phase Differential (87)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Current
Protection, Differential 87
Element Operation
The phase-current differential element compares the currents entering and leaving the zone of protection.
In some applications, the zone of protection may include only the generator. In other applications, a power
transformer may be included in the generator zone of protection. If a fault is detected, the BE1-11g
initiates a trip signal to isolate the protected zone. This action limits equipment damage and minimizes
impact on the power system.
Functional Description
Figure 68 shows a detailed functional diagram of one phase of the phase differential protection function.
These functions and comparators are duplicated for each phase.
The measured currents are phase, zero-sequence, and tap compensated. The Configuration chapter
describes the setup of the BE1-11g for phase and zero-sequence compensation. Setup of the tap
adjustment compensation is described later in this chapter. The restraint current function uses the
compensated current to calculate the restraint current magnitude (in multiples of tap). Depending on the
setting, it calculates the maximum or average restraint current. The Operating Current function
determines the magnitude of the fundamental, second, and fifth harmonic differential current as the
phasor sum of those components of the compensated currents.
Figure 69 shows the characteristic of the phase current differential protection element. This comparator
has two slope settings and a minimum pickup setting. The slope settings are the ratios of delta operating
current to delta restraint current. The slope settings should be set above the maximum mismatch caused
by excitation losses, tap mismatch, and load tap changers. The minimum pickup setting determines the
minimum sensitivity of the restrained element.
BE1-11g 0BPhase Current Differential (87) Protection
(818 strony)
(82 strony)
(754 strony)
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