Accident waiting to happen?

Electricity grid system has weaknesses, says OUR committee

BY CAMILO THAME Business co-ordinator

Wednesday, February 27, 2013

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THE electicity grid is so vulnerable to system shutdowns that its deficiencies and weaknesses could be viewed, in some instances, as an 'accident waiting to happen'.

The factors leading to the last islandwide blackout, not related to a natural disaster, was found to be "typical of those which precipitated the three earlier system shutdowns, including the first major incident in 2006", by the Office of the Utilities Regulations (OUR) investigation committee into electricity grid shutdown last August.

"While the initiating circumstances are different in each case, the underlying sequence of system collapse from generators and transmission circuits tripping follow a familiar and parallel path," said the Jamaica Public Service Company (JPS) Power System Integrity Investigation report, which was completed three weeks ago. "Human error and maintenance shortcomings have played a part, as well as manifested deficiencies in the islandwide grid and generation infrastructure."

Last August, lightning strikes at a pole located on the Duhaney to Naggo Head 69kilovolt (kV) transmission line, as Tropical Storm Ernesto passed nearby the island, led to a shutdown.

But it was the lack of a protection relay, which apparently malfunctioned or was removed from the system the April before, which was "primarily blamed for precipitating the subsequent island-wide system collapse.

Similarly, in 2006, the failure of distance relays to operate at Duncans substation following a lightning strike to the Duncans to Bogue 138kV transmission line caused a system-wide shutdown.

In 2008, a fault on the Duhaney to Tredegar 38kV transmission line wasn't cleared, after a pole fell to the ground.

The 2006 system shutdown was reviewed by Gowlings Consulting Incorporated and Rusnov Associates Limited, whose recommendations were complied with, in the main.

But the OUR technical staff believes that the most recent episode showed that where a "crucial protection relay was not repaired or replaced for some four months at Duhaney substation, that the intent of this system is not being achieved".

Either way, the Duhaney substation is considered to be a "major weak link in the transmission grid integrity" because it serves as the only link between generators in the Corporate Area with the generating plants in Old Harbour and Bogue, St James.

"Any failure on either the 138kV, or in particular the 69kV, is likely to precipitate an islandwide System shutdown," said the report.

The technical team found that the protective relaying system for the Duhaney substation was urgently in need of a complete review.

Also, "the 10 substations reported as not having SCADA visibility need to be put on the system as soon as possible".

The SCADA (Supervisory Control And Data Acquisition) system allows control engineers to remotely monitor and control the power system, and JPS has 53 substations in all.

"The current philosophy for grid restoration, based on JPS documented policy and operating instructions currently in place, appears satisfactory to adequately address system restoration procedures following a partial or complete shutdown of the system," wrote the review committee.

However, the system restoration policy appears not to include a provision for a full analysis of the shutdown to be undertaken by technically competent personnel prior to grid restoration activities, in specific instances when the reason for the System shutdown is in doubt. It is recommended that the policy be revised to include analysis by technical personnel.

The committee did find the general system protection philosophy, which governs the basis of JPS's installation of protective relays at generating stations and also at substations for busbars, transformers and transmission line protection, to be "generally adequate and meets international standards for reliable utility operation".

"Nevertheless, it is recognised that the human factor plays an important role in the effectiveness of maintenance, together with the dedication to detail and a process of rigid management follow-up on defects is an issue of considerable concern," said the report. "Indeed, recent system shutdowns have highlighted this problem and JPS needs to urgently remedy the human factor in order to prevent a repeat occurrence."

In light of the frequency of total system shutdown events in the Jamaican power system (four in since 2006), the committee also recommends that the OUR considers the establishment of an on-going Grid Reliability Committee (GRC) as an added means of addressing issues impacting the reliability and security of the power system.

The group would meet regularly to identify items which currently threaten or could threaten grid integrity and ensure expediting of agreed remedies.




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