About Sample3.png

About this drawing

What it is: Reactor protection single-line diagram (Fig. 7b) for a 765 kV line-connected shunt reactor bank (three-phase reactor plus spare phase reactor, neutral reactor plus spare neutral reactor) on a breaker-and-a-half bay (CB7-1, CB7-2, reactor breaker CBRX). It shows the CT circuits feeding high-impedance differential relays (87RXB/B7RX, 87RXB/87P, 87RXB/87SN) and the A-system relay 87RXA/O (87P-O, REF, 51N, 67N, 59N), plus sudden-pressure, gas and oil-level devices (63, 71G, 71Q, 49).
What it does: It detects faults in the shunt reactor, neutral reactor and their bus/connections and trips CBRX and the line breakers to isolate them. It does not show a supply path to a load.
Analyse next: Build a fault tree for the top event "a reactor/neutral-reactor internal fault is not detected and cleared". Model each zone (B7RX bus zone, phase reactor, neutral reactor, spare units) and its redundant A and B protection: CT cores, relays, batteries A and B, trip circuits and breakers (CBRX, CB7-1/CB7-2 or remote/transfer trip). Back it with an FMEA of the CT circuits (open/shorted secondaries, high-impedance differential stability) and of the spare-reactor switching (H1/H0 links). Later, an availability RBD of the line-reactor connection (bus → CB7-1/CB7-2 → line → CBRX → reactor) could be done, but only if a study defines it.
The drawing exists to show how protection is arranged: which CT core feeds which relay, the A/B battery redundancy and the zone overlaps. The question that matters is "fails to trip", or a false trip, and that is about failure logic of detection and tripping, not continuity of supply. The shunt reactor absorbs reactive power and does not serve a load. An "any path intact" RBD of the primary circuit would miss the CT, relay and DC-system redundancy the drawing is about, so an RBD is not the right first analysis.

An RBD doesn't fit this drawing, so none was built. The next step above is a recommendation for the engineer: we only build RBDs.

What we still need

Whole drawing: top event and trip logic: A fault tree needs the trip matrix, which this sheet does not show: which relays trip CBRX, which trip CB7-1/CB7-2, and whether direct transfer trip goes to the remote line end. It also needs to know whether the reactor may be left in service unprotected after one system fails. The note says the legend of device codes is in the document text, which we don't have.
Battery systems A and B, trip coils of CBRX / CB7-1 / CB7-2: The A/B suffix shows which battery each relay is on (note 2), but the DC distribution, dual trip coils and breaker-failure (50BF) arrangement are off this sheet. These set the common-cause and redundancy structure of the fault tree.
Spare Phase Rx / Spare Neutral Rx, H1/H0 connections, BNRX: The normal state of the spare reactors is unknown: in service, or connected only by manual links in place of a failed phase. This decides which CT circuits and differential zones are actually active.
Sudden-pressure/gas/oil devices 63, 71G, 71Q, 49 (dashed to 87RXB/B7RX, '6'): The drawing does not say whether these mechanical devices trip directly or alarm only, nor which battery system they use. That matters for credit as a protection path that does not depend on the CTs.
CT ratios/accuracy classes and relay settings: The CT data and relay settings are not shown. They are needed to judge whether the high-impedance differential stays stable during through-faults, and for the failure modes in the FMEA of the CT circuits.

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Sample3.png

draft no RBD r_20261101_165616_fa9a · 2026-11-01 16:56:16 UTC

An RBD doesn't fit this drawing: another analysis is recommended (see About this drawing)

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