Review Incident Shin.. - authority for electricity regulation, oman

3. INCIDENT
3.1. Immediately before the incident
At 22.00 h the load of the Shinas region was 51 MW. At this time the system was stable.
Moreover, no trips because of humidity were taking place 11 .
3.2. Immediately after the incident
At 22.07 h the 132 kV Circuit breaker of the Wadi Jizzi to Shinas line opened because the
distance relay at Wadi Jizzi operated. Since the Shinas 33 kV-network is only supplied by
this line, the trip led directly to the interruption in the power supply of this network. The reason
for the trip is not yet known.
The SCADA system informed the staff of the Load Dispatch Center immediately and provided
the information that a distance relay in the Wadi Jizzi grid station had tripped. From
the Shinas grid station no indication was received.
At 22.08 h the 132 kV Circuit breaker of the Wadi Jizzi to Shinas line reclosed automatically
and tripped again at Wadi Jizzi.
Because the staff of the Load Dispatch Center considered humidity as a likely cause, they
decided to manually reclose the circuit breaker at 22.22 h. This is not a normal procedure,
but taking into consideration a loss of load of the Shinas area and having the experience
that 90% of the faults in this region are caused by humidity the LDC staff took the risk of an
additional reclosure. The distance relays operated again to trip the circuit 12 .
We can understand the logic applied by the LDC staff to reclose the line manually, but we
note that reclosure of lines after a fault is not without risk for people and equipment. Although
nothing severe happened as a direct result of these auto-reclosures, it would be
11 Humidity combined with fine dust is causing lots of trips in the 132 kV system at present. However, during
the evening of the event no trips of this type were recorded.
12 The sequence of events of MJEC reports that at 23:36h there was another attempt to manually close the 132
kV Circuit breaker of the Wadi Jizzi to Shinas line, again without success. OETC reports do not mention this
third attempt to reclose the Circuit Breaker.
Review Incident Shinas August 2007 12 09.10.2007
vs. 2 (final)