Technical Audit of Guddu 500kV Grid Station

Commissioned on December 16, 1986, the station has a total transformation capacity of 1350 MVA and serves as a vital link between major 500kV grid stations of Sindh and Punjab. The station is directly fed from Guddu thermal power station at 220kV level and dispatches power to other grids by stepping up to 500kV level. The station's infrastructure includes three 450 MVA-500/220kV autotransformer banks, owned and maintained by the National Transmission and Despatch Company (NTDC). The autotransformers are overloaded, with maximum loading exceeding 96.96% of their nameplate ratings. This exceeds the permissible limit of 80% as per the National Electric Power Regulatory Authority (NEPRA) grid code and International Electro-technical Commission (IEC) standards. Overloading can reduce the expected useful life of transformers in proportion to the amount and duration of overload. Oil leakage or seepage exists in several transformers and shunt reactors, including the Blue-phase unit of transformer T-3, shunt reactors on 500kV Guddu-Dadu-2, Guddu-D.G. Khan, and Guddu-Dadu circuits. Circuit breakers and lightning arrestors are not installed on shunt reactors of the 500kV Guddu-Dadu circuit-2, Guddu-D.G. Khan circuit, and Guddu-Dadu circuit-1. Major maintenance of thirteen 500kV circuit breakers is pending due to unavailability of spare parts, which is essential to ensure the healthiness and reliability of the system. The station's transmission circuits also exhibit several discrepancies, including line to ground clearance issues on the 500kV Guddu-Dadu circuit-1 and 2, and the 220kV Guddu-Sibbi and Guddu-Uch circuits. The 220kV Guddu-Uch circuit is overloaded, exceeding the prescribed limits per NEPRA grid code. The SCADA system is installed but final testing and commissioning is pending. Recommendations for addressing these issues include transformer augmentation, load flow study, and immediate action to attend to seepage in shunt reactors. Circuit breakers and lightning arrestors need to be installed on shunt reactors, and major maintenance of circuit breakers should be conducted with spare parts. Local operation of 500kV isolators should be made functional for remote operations, and regular dissolved gas analysis and detailed oil testing of transformers should be carried out. Conductor capacity needs to be upgraded for the 220kV Guddu-Uch circuit, and discrepancies observed on transmission circuits need to be rectified.