Sri Lanka’s CEB faulted for ‘significant lapses’ over 2020 cascading failure
ECONOMYNEXT – Sri Lanka’s state-run Ceylon Electricity Board has been faulted for bad maintenance procedures and significant lapses in not carrying out recommendations in previous investigation reports in an interim report on probe on a cascading failure in August 2020.
The grid had also failed seven times during restoration. The reasons for five failures had been found. The reason for at least two failures involving an unanticipated drop in load still remained a mystery.
It could be due to tripping of sections of the distribution system or solar power coming on, the interim report said.
An error made by an Electrical Superintend at the Kerawalapitiya grid sub-station by incorrectly switching on an isolator after routine maintainance while a section had been earthed had led a short circuit.
A mechanism called an ‘interlock’ which would have prevented the isolator from being switched on had been disabled during maintenance, leading to the short circuit, which led to a spike in the grid frequency which should be around 50 Hertz.
This had led to generators including coal plants being disconnected for safety setting off a cascading failure.
The error should never have happened, members of the committee told reporters.
An interim committee report said there was “no robust maintenance protocol in place”.
“The maintenance practices of high risk areas are to be identified and best practiced protocols in maintenance to be incorporated in particular in the said areas rather than having a general maintenance philosophy,” the report said.
During restoration of the grid had failed several times. Attempts to restore the system with generators at Victoria dam had failed three times, partly due to generator failures. Attempts to restore with Kotmale hydro generators had failed three times, some of which were due to generator failures involving a faulty governor.
The grid was gradually restored on the seventh attempt.
The grid had also failed due to ‘load side mismatches’, where demand suddenly dropped, Lilantha Samaranayake, from the University of Peradeniya said.
There was no method for system control to accurately see the distribution load, he said.
‘The failures in the restoration of the second and sixth attempts can be attributed to a over frequency caused by one of the many of the large loads in the selected thirty three kV feeders got tripped or a large solar PV system coming into operation which is reflected at the generators as in over frequency,’ the report said.
Committee members said further investigations had to be done to find whether solar power was the cause of the load drop. (Colombo/Aug2/2020)