ISLAMABAD: National Power Control Centre (NPCC) has urged CPPA-G to take up technical schedules of coal-fired power plants at Sahiwal and Port Qasim with companies and Nepra for finalization of generator frequency setting and de-synchronization time to ensure stability and reliability of power system network to avoid any undesired situation.
In a letter to Chief Technical Officer, General Manager (System Operation), NPCC, Sajjad Akhtar, said NPCC is negotiating since long with HSR Sahiwal Coal & PQEPC Port Qasim Electric Power company regarding technical limits of generating units, i.e., frequency ranges & de-synchronization times. However, the matter is still unresolved despite series of meetings and correspondence among the stakeholders.
Under the Nepra approved Grid Code, NTDC/ NPCC being system operator is mandated with operation of entire power system in the country and consequently is also obligated to ensure integrity, security, stability, and safety of the grid system. Therefore, any technical parameter in the system which may increase vulnerability of the system, thereby posing higher risk for system collapse is a cause of serious concern for system operator.
The technical issues of allowable generator frequency ranges and de-synchronization time are linked with stability of power system in the existing proposed upper frequency limit (51.5 Hz) of already commissioned coal fired power plants, i.e., M/s PQEPC & M/s HSR will be providing lesser support to avoid grid collapse when system frequency is abnormal and will trip earlier thereby reducing grid resilience and increasing risk for full collapse. This upper frequency limit (51.5 Hz) is not in accordance with the upper frequency limits of power plants established/ operating under Power Policy of 1994 & 2002 where the upper limit of frequency is 52 Hz & 52.5 Hz.
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In the operating committee meeting and many other correspondence M/s PQEPC & M/s HSR presented their view that requirement of generator frequency up to 52 Hz was not specified before the installation of major equipment of the power plant; therefore, it is not able to increase the generator frequency limit over 5t.5 Hz after COD.
NPCC stated that the steam turbines have been tested at 3300 rpm at the time of commissioning activities, which is 10% over-rated rpm. Thus, PEEPC & HSR project should be capable to meet with the proposed frequency ranges of NPCC, i.e., 52 Hz which is only 4% in excess of rated rpm of machines under abnormal circumstances; otherwise, there is no purpose to perform the commissioning tests if the machines could not meet with the prescribed criteria during its real time operation.
NPCC also referred to the PQEPC initial PPA schedule-5 signed in 2015 wherein numerous other factors were also agreed, i.e., minimum loading limit (40%) and number of allowable starts/ stop per year but power plant also intends to modify these limits, keeping in view the limitations at either PEEPC or its OEM end. Thus, PQEPC’s stance that generator frequency ranges were provided in the initiated Schcdule-5 and can’t be modified now, is not justified at all.
“Frequency settings by the plant were tentative; hence, NPCC has requested that matter be taken up with Nepra and concerned IPPs for finalization of generator frequency setting and de-synchronization time to ensure stability and reliability of power system network and to avoid any undesired situation,” it added.
Copyright Business Recorder, 2023
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