Mindanao outage caused by corroded gear

by Riza T. Olchondra, 18 April 2015
from Philippine Daily Inquirer

The power outage that crippled the whole of Mindanao was caused by a powerline component ruined by corrosion, according to a state-led probe.

“A corroded suspension insulator shank gave way, causing the transmission line to fall, hitting the other line conductors and the tower parts, resulting in a short circuit which was not isolated on time,” said Rolando Bacani National Transmission Corp. (Transco) president.

In a text message, Bacani said that since the incident, Transco recommended an immediate inspection and/or replacement of all suspension insulators in the area, noting that the pieces of equipment had been installed a long time ago.

Transco already sent a report to the Department of Energy and further recommended the immediate review of the timing coordination of protective relays and the installation of new and backup protection.

Transmission line insulators are devices used to contain, separate or support electrical conductors on high voltage power supply networks.

Transmission insulators come in various shapes and types.

Suspension type transmission line insulators suspend and support high voltage transmission lines, usually with a number of interconnected porcelain discs.

According to the initial results of the probe, released earlier this month, the April 5 outage was caused by a broken connection asset of the National Power Corp. (Napocor) in the Agus 6/7 hydroelectric power plant complex in Iligan City, Lanao del Norte.

In a DOE briefing, Bacani said a power conductor from the Agus 7 switchyard fell on the capacitor voltage transformer (a metering equipment) of the National Grid Corp. of the Philippines (NGCP).

NGCP head for Mindanao systems operations Eugene H. Bicar said that the line safety system of NGCP kicked in with a slight delay while Napocor’s corresponding safety system did not activate.

The resulting power disturbance flowed along the transmission line in the northern part of the grid.

Of Mindanao’s supply capacity of 900 megawatts (MW), 700 MW came from the northern part where Agus is located.

The isolation of the northern part due to the system reaction to the disturbance caused under-frequency in the southern areas. This brought the whole system down, said Cynthia Alabanza, NGCP spokesperson.

Napocor owns the power conductor, which is part of a “connection asset,” or a point-to-point transmission facility linking the Agus 6/7 switchyard to the transmission superhighways of NGCP.

However, private firm NGCP maintains the connection asset under an agreement with Napocor since the state firm no longer has linemen following deregulation of the energy sector.

Energy Secretary Carlos Jericho Petilla said the investigation was meant to prevent further disturbances in the Mindanao grid.

The Agus 1 and 2 power station complex is located in Marawi City, Lanao del Sur. The rest, are located in Lanao del Norte.

The island-wide blackout has delayed the full commissioning of the 300-MW Davao coal power plant of Therma South Inc. (TSI). The facility is supposed to be up and running by mid-2015, AboitizPower Corp. said.

Also, the disruption could result in a 10-month delay on the commissioning schedule of Unit 2 TSI’s power plant, TSI president and COO Benjie Cariaso Jr. said.

But Cariaso said the commissioning of Unit 1 of the Davao power plant would remain on schedule, and the facility should be fully operational by the end of June 2015.

“TSI is currently conducting a more detailed assessment of the extent of the repairs needed and a full review to determine all contributing factors that led to the plant incident to ensure appropriate measures are taken,” AboitizPower said in a statement.

Cariaso said the company would work with its contractors and suppliers to complete the repairs as quickly as possible.

Units 1 and 2 of the power plant have yet to be turned over to the company by its contractors, AboitizPower said.

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