DOE Final Report: Mindanao Feb. 27 blackout caused by a ‘confluence of uncommon events’
Blurb: 870 MW gone in 85 seconds
The Department of Energy has disclosed the results of its two-week investigation into the cause of the massive blackout which plunged the entire Mindanao Grid into darkness early dawn of Feb. 27, 2014.
In a press briefing held Friday morning (March 14) in Manila, Rolando T. Bacani, president and chief executive officer of the National Transmission Corporation (TransCo) said the blackout was caused by a “confluence of uncommon events.”
“A supply-demand imbalance caused by the reduced generation of STEAG coal-fired power plant due to a technical problem and the defective equipment of the government-owned Agus 1 hydro power plant led to the incident,” said Atty. Cynthia Perez-Alabanza, NGCP spokesperson in a phone interview.
According to Bacani’s report, the National Grid Corporation of the Philippines (NGCP) noted around 3:51AM of Feb. 28 that the power output of the STEAG State Power Inc.’s coal-fired power plant in Villanueva, Misamis Oriental mysteriously dropped from 200 megawatts (MW) to only 160 MW.
When a deficit like this happens in a power grid, the regulating frequency tends to drop which could be extremely destructive to power plants supplying power to the grid.
“Sixty (60) cycles is standard frequency, plus-minus 1% , or 59.4 cycles minimum, 60.6 cycles maximum,” said a former energy official charged with the operation of the Mindanao grid who declined to be identified. “Should the frequency drop below minimum, load is shed off automatically to restore to standard frequency.”
As its normal response to such situations, NGCP’s ancillary services automatically kicked in to release its regulating reserve from the Agus 1 plant in Marawi City. However, unknown to NGCP, the plant was experiencing a problem with the capacity voltage transformer (CVT) in its switchyard and so was unable to deliver the needed reserve to the grid.
A CVT is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay.
As a result, the grid instantly shifted to its second line of defense, automatic load dropping (ALD).
“Measures to uphold the security and integrity of the grid were in place at the time when two major events, namely STEAG’s sudden and continuous generation reduction and the tripping of Agus 1, happened within seconds of each other,” said Atty. Alabanza.
In just 85 seconds, around 870 megawatts were dropped from the grid.
“It was practically impossible for the system to recover from the catastrophic drop in overall system frequency, which directly resulted from STEAG’s generation reduction and the tripping of Agus 1.This, in turn, triggered the safety systems of the remaining generating plants as part of their equipment protection,” said Engr. Eugene Bicar, NGCP’s Head for Mindanao Systems Operations.
The “confluence of uncommon events,” as described by TransCo President, Mr. Rolando Bacani, was an unprecedented occurrence in the grid.
However, in a press statement released 14 March 2014, Dr. Bodo Goerlich, STEAG State Power Inc. (SPI) President and CEO, expressed surprise over reports that the massive blackout in Mindanao last 27 February 2014 was caused by or stemmed from Steag.
While admitting that SPI’s power generation output was greatly reduced prior to the collapse of the Mindanao grid, the SPI statement said “the gradual reduction will affect the electric supply condition, (but) it is not expected [however] to cause a cascading failure and tripping of other power plants and the collapse of the entire grid.
“The fluctuation of the load of power plants happens from time to time and the over-all effect is managed by adjusting either the supply or demand of the grid,” the statement quoted Dr. Goelich as saying. “ We have in the past experienced such a situation and it did not cause a massive blackout and total collapse of the grid.”
For its part, Atty. Alabanza said the results of NGCP’s internal investigation submitted to the DOE and TransCo, including the voltage and current profile at the time of the incident, showed that there was no fault in any of NGCP’s transmission equipment during the time of the incident.
Meantime, SPI said its Units 1 and 2 are offline since 27 February 2014 after sustaining damage to its turbine-generators and SPI experts estimate that barring any complications, Unit 1 is expected to be restored on 4 May 2014 and Unit 2 on 1 June 2014. Each unit has a net generating capacity of 105 MW.
The press statement further quoted Dr. Goerlich as saying “that SPI employees have been working round-the-clock to restore the units back to the grid noting the volatile power supply condition of Mindanao.”
“We empathize with those that are affected by the Mindanao power supply shortfall and rest assured that we are doing our best to restore the units back to the grid and help alleviate the island’s precarious power supply condition” Dr. Goerlich said. “We are also carrying out all maintenance activities on other systems of the plant that were originally planned/scheduled for August 2014. Thus, there will no more outage in August 2014,” he added.
The statement said SPI is cooperating with the Department of Energy (DOE), the National Power Corporation (NPC), the National Grid Corporation of the Philippines (NGCP), and other stakeholders of the Mindanao power industry, in addressing the situation.
“While our priority now is the repair and restoration of the units, we are also working closely with the DOE and other industry stakeholders in finding means of improving quality and reliability of power supply services in Mindanao” Dr. Goerlich added.
The National Power Corporation (Napocor) acknowledged NGCP’s assistance in correcting and restoring the defective Napocor-owned capacitor voltage transformer inside the switchyard of the Agus 1 plant.
Similarly, NGCP said it is asking power plants to coordinate and check with the system operator their own respective plants’ protection settings.
“NGCP remains steadfast in fulfilling its mandate as system operator, ” said Atty. Alabanza “We are one with the power sector in resolving this. As the system operator, NGCP will continue to uphold the security and integrity of the power grid.”