Three factors caused the national grid failure on October 4, found the probe body of Power Grid Company of Bangladesh. The power grid malfunction had left large swathes of Bangladesh without electricity for four to eight hours, affecting over 130 million people. 

The main factor behind the grid failure occurred due to power distribution companies "not reduce lessening the load in due time," as per the National Load Dispatch Centre's (NLDC's) instruction, said Yeakub Elahi Chowdhury, the chief of the probe committee. 

The other factors were Ghorashal substation transforming power above its capacity and tripping; and the sudden increase in demand when a private steel mill started consuming electricity directly from the national grid without informing NLDC, according to probe committee members, who spoke to The Daily Star yesterday. 

"The National Load Dispatch Centre told the distribution companies -- DPDC, DESCO, PDB and REB -- to shed load instantly, but they failed to do so and the grid couldn't take the load at 2:05pm [on October 4]," a member of the probe body told The Daily Star, on the condition of anonymity.

"All those things happened, but the main reason behind it was that they (power distribution companies) did not follow the NLDC's instruction," said Yeakub Elahi Chowdhury. 

All four power distribution companies — identified as not heeding to the NLDC's instruction — formed separate internal committees to identify what happened and verify PGCB's claim.

Referring to the probe report, a source at the power division said the grid failure was a result of a lack of coordination between the NLDC and distribution companies.

He said the Ghorashal grid substation on October 4 had the capacity to transform 900MW, but it was dealing with about 1,100MW, and tripped.

After connection between the eastern and western parts of the grid was lost, the NLDC failed to get distributors to decrease load which caused the grid failure, and power plants tripped one after another, the source said.

The PGCB probe body submitted the report to the Ministry of Power, Energy and Mineral Resources on Sunday and suspended two of its engineers for negligence.

The engineers -- Allama Hasan Bakhtiar and Md Mostafizur Rahman -- used to work for Single Programme-Multiple Data (SPMD) of Dhaka-1 section of PGCB. SPMD is a data management system for power transmission.

On the same day, the state minister for power, energy and mineral resources Nasrul Hamid told reporters that action would be taken against those who were involved in the incident.

Contacted, managing directors of DPDC and DESCO -- power distributors in the capital, said they always follow the instruction of the NLDC.

"I never heard that such an incident of a blackout happened due to not shedding load," said Bikash Dewan, managing director of DPDC.

Md Kausar Ameer Ali, MD of Desco, said, "There were no such records of not following the instructions of the NLDC. The committee will check."

Another committee from the power division is investigating the incident and is yet to submit its findings.