Lack of coordination in the supply and demand of electricity caused the national grid’s frequency to drop, tripping the Bheramara sub-station and causing a cascade effect that rapidly shut the whole system down.
This was the conclusion contained in the 24-page final report of the Power Ministry committee to probe the November 1 blackout, submitted on Wednesday to the state minister for power, seen by the Dhaka Tribune.
State Minister for Power Nasrul Hamid said the report would be formally announced at a press conference on Sunday or Monday.
The Dhaka Tribune was the first to report that the Bheramara sub-station had tripped causing the national grid to collapse on November 2. The findings of the Power Ministry investigation confirmed that this was the primary reason for the November 1 blackout.
According to the probe findings, the national grid failure commenced at 11:28am when the National Load Despatch Centre (NLDC) system frequency rapidly dropped to below 45 Hz, well beneath the minimum threshold of 48.9 – 51 Hz.
On the day, the forecast demand was 4553MW and forecast power generation was 4674MW, but a sudden spike in demand caused the grid’s frequency to dip, ultimately causing the system to fall.
When frequency drops, voltage declines, and the low voltage registered at Bheramara sub-station caused it to trip.
Following this, one of the circuits connecting the Bangladeshi grid to Indian power supplies, Bheramara-Behrampur Circuit 1, also tripped.
At the time, India was supplying 444MW of electricity to Bangladesh. The tripping of Circuit 1 caused a major deficit in supply of power to the grid, causing it to become unbalanced.
This imbalance, in turn, caused all the power stations in the country to shut down. The whole process took just 14 seconds to transpire.
The NLDC, the report said, was not able to foresee the spike in demand because the load calculation used to forecast demand is not done properly.
Simply put, the demand spike was not foreseen because November 1 a weekend, a Saturday, and NLDC load calculations assumed lower-than-weekday demand.
The report said under-frequency relay operations failed to automatically cut the load and the NLDC was not manually able to use load management, commonly known as load shedding, because the whole process took place in such a small time span.
The eight-member probe body, comprised of a former Power Development Board (PDB) chairman and seven current government high officials, submitted 32 recommendations to avert similar shut downs in the future.
Md Shahinul Islam Khan, member of PDB (generation) and one of the eight members of the probe committee did not sign the report that was submitted because he is away on a trip to the United States.
Twenty-two are short-term measures and the rest middle- or long-term measures.
The committee visited the NLDC, the Hasnabad grid sub-station, the Bheramara sub-station, the Ashuganj, Haripur and Ghorashal power plants, and interviewed 13 power sector officials and several outside experts to prepare the report.
A day after the first deadline expired on November 6, instead of submitting a report, the committee submitted “primary information” about the blackout to the state minister for power and sought a 10-day extension.
The committee completed its fact-finding on November 11. It said a detailed study on transmission fault analysis, protection system and restoration process should be carried out at later date.
Recommendations of the committee
The report did not name or blame any official or functionary for the black out.
The committee’s key short term recommendations include the update and maintenance of grid sub-stations and power plant equipment, especially transformers, circuit breakers, isolators, arresters, battery-chargers.
It said the scope of load control could be increased by adjusting the under-frequency relay settings to enable automatic load controls and by enabling Supervisory Control and Data Acquisition operations, a remote device management system.
It said relay settings had to be set-up between rental or quick-rental power plants and grid sub-stations.
The committee said digital fault and disturbance recorder’s clocks at grid sub-stations and power plants ought to be synchronised with GPS to enable near-real time observation of system difficulties.
It called for a technical team to study the reason for the High Voltage Direct Current (HVDC) sub-station to trip, including looking into whether there are network setting problems.
Since its establishment in October 2013, the HVDC sub-station at Bheramara has tripped 8 times, including, most recently, on November 7, a week after the country-wide blackout.
The Power Grid Company of Bangladesh, the owners and operators of the national grid and the Bheramara sub-station, told the probe committee that a software problem could be the cause of the frequent trips.
The report recommended that the reasons for the frequent trips at the HVDC sub-station be determined with certainty.
It recommended that NLDC officials monitor the power plants on four six-hour shifts to ensure that the frequency is controlled, and that closed-circuit television cameras be installed at the NLDC office.
It called for the establishment of an advisory technical panel to make recommendations for the modernisation of the national grid.
Among the committee’s middle- and long-term recommendations, was the creation of an independent system operator over the power transmission system.
It called for all sub-stations and power plants connected to the NLDC to be linked up digitally to enable easy data storage and management.
The committee called for self-starting auxiliary power sources to be installed at the major power stations instead of the current grid-dependent auxiliary power system.
The Power Ministry probe body called for Electricity Grid Code 2012 to be effectively enforced with regard to transmission and for the draft Electricity Distribution Code to be finalised.
Md Kizir Khan, former PDB chairman and a member of the investigation committee, yesterday told the Dhaka Tribune: “We have worked on a very thorough report and I believe it should be published and circulated so that the public is aware of the situation.”
He also said: “Blackouts do take place, even in first world countries, and may happen again here. While one cannot absolutely rule out that it will happen again, the recommendations we have made will go along way to decrease the possibility that it will happen again soon.”