Technical Audit of Sheikh Muhammadi 500kV Grid Station

The station has a transformation capacity of 900MVA connected to the grid out of the installed capacity of 1350MVA, feeding a major portion of KPK. The grid station is equipped with three 450MVA-500/220kV autotransformer banks, three 160MVA-220/132kV, one 250MVA-220/132kV autotransformer, and two 10/13MVA-132/11kV power transformers. The grid station was sabotaged on April 1, 2013, resulting in significant damage to equipment, including transformers and relay panels. Rehabilitation work is ongoing to restore the station to its original capacity. A technical audit team, comprising experts from the USAID Energy Policy Program, visited the grid station from April 29, 2014, to May 9, 2014, to assess the damage and identify necessary repairs. The audit team identified several key issues affecting the grid station's performance. Firstly, the loading condition of transformers is above the prescribed limits, with all transformers except T-8 loaded above 80% of their capacity. This exceeds the recommended limits per NEPRA grid code and IEC standards, which can reduce the expected useful life of transformers. Secondly, the 220kV Sheikh Muhammadi-Ghazi Barotha circuit is loaded above the prescribed limits, and auxiliary panels for several transformers are not functional. Furthermore, the grid station lacks essential maintenance, with major maintenance pending for five 500kV, fourteen 220kV, and thirteen 132kV circuit breakers due to unavailability of spare parts. Remote operating systems for several circuit breakers are not working, and opening/closing timing results and contact resistance tests for some circuit breakers are not within the permissible range. Additionally, several tests, including leakage current measurement, SF6 purity and moisture content, and capacitance and dissipation factor tests, are not being performed as required. The audit team also identified issues with the grid station's protection system, including the absence of thermal overload protection relays on some transformers, energy meters not installed on several transformers, and relays with their complete protection circuitry not in use. Breaker failure schemes and differential protection schemes are not working properly, and direct transfer trips are out of circuit for 500kV and 220kV systems. The audit team made several recommendations to address these issues, including conducting a proper load flow study and augmenting all 160MVA-220/132kV transformers. The relay panels for the 450MVA bank need to be arranged at the earliest to bring it back in service. Additionally, the grid station requires major maintenance for several circuit breakers, and remote operating systems need to be restored. The protection system also requires attention, with thermal overload protection relays, energy meters, and breaker failure schemes needing to be installed or restored. The grid station's SCADA control system was 80% complete before the sabotage but requires rechecking, re-verification, re-testing, and commissioning. The list of missing relays is attached, and retaining walls for several towers require construction due to soil removal. Braces are also short at certain locations of 220kV transmission circuits.