ISLAMABAD: National Transmission and Despatch Company (NTDC) has raised many ‘Ifs’ and ‘buts’ on proposed power evacuation plan of 330 MW Siddiquesons Thar coal-fired power plant that is supposed to supply power to K-Electric.
Deputy Managing Director, NTDC( NPCC- System Operator) , Zain Banatwala in a letter to Managing Director PPIB has stated that excess generation capacity vis-a-vis demand in the South poses system stability problems that restrict power transfers from south to north, lead to sluggish demand in the south (HESCO and SEPCO), lack of balancing energy/regulating reserves in the south due to which baseload plants are used for load-following and balancing the natural variation in wind power, low system inertia in winter (due to lower generation) and reduced margin for down regulation as all power plants are already operating on minimum loading, systemic vulnerabilities in the south and Lahore regions.
He maintained that several commercial points need to be addressed by the main stakeholders (KE, CPPA-G and NTDC) before the scope of a system impact assessment study can be determined.
With respect to unit commitment and security-constrained economic dispatch: the System Operator is often required to dispatch “baseload” Thar plants as load-following due to lack of mid-merit plants in the generation stack. This includes operation at minimum load when down regulation from more expensive plants is exhausted.
The proposed SEL power plant would be treated like any other power plant connected to the NTDC network in Thar. In order words NPCC will start, stop and vary the plant’s set-point as and when required, similar to other plants. “Who will pick up the cost differential due to mid-merit operation of SEL? The cost differential includes energy as well as efficiency loss from operating at a lower set-point?” questioned NTDC.
Banatwala further stated that an equivalent Thar power plant (e.g. TEL) would have to be shut down to maintain a stable balance between Northam and Southern generation when system demand is low, balanced operation is essential for system stability including voltage stability of the HVDC link.
While, this makes no difference to system operation (as SEL would simply replace TEL), CPPAG could potentially lose up to 300 MW of cheap energy in its pool.
Once the operating Reserves Policy is approved by NEPRA, KE would be required to contribute primary reserve and secondary reserve. SEL would be required to provide 30to 50 MW primary reserve at all times. Secondary reserves could be provided from any power plant that is owned or contracted by KE that is technically capable. In case the required secondary reserves are not provided by SEL, KE would have to provide the reserves from Bin Qasim 3. Otherwise, K-E would be required to compensate CPPAG for providing the necessary secondary reserve on its behalf from the national pool.
NTDC argues that starting/stopping TEL will invoke startup costs and additional stresses on the plant (higher maintenance costs). Similar start-up and load variation costs (PLAC) are allocated to CPPAG consumers. NPCC will not be liable for any additional costs for KE consumers or any plant degradation suffered by SEL due to non-baseload operation.
The 50% annual dispatch of Port Qasim and China Power Hub is yet to be settled by CPPA-G. In case it is extended, then Thar coal plants (incl. SEL) will have to be dispatched less, Banatwala maintained.
With respect to outages of the NTDC network, he said all southern coal power plants (i.e., Port Qasim, China Power Hub, Lucky and all Thar coal plants) are part of the HVDC stability control system (SCS) strategy table. SEL would also be required to be part of the SCS strategy table and be remotely tripped in case of a bi-pole blocking event.
“SEL would be required to accept over-frequency disconnection settings provided by NPCC and implement cross-trip schemes similar to the other Thar coal plants,” Banatwala continued. Failure to trip may result in tripping of other plants out of sequence and even a failure of SCS which may be penalized by NEPRA for loss of cheap power to CPPA-G consumers.
Copyright Business Recorder, 2023
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