Technical Audit of Burhan 220kV Grid Station

The station was commissioned on June 1, 1977, and has a total transformation capacity of 640MVA connected to the grid. It feeds portions of KPK and Rawalpindi. The station has four 160MVA-220/132kV transformers and one 13MVA-132/11kV power transformer, all owned and maintained by NTDC. The technical audit team, comprising transmission and protection experts, visited the station from May 27, 2014, to June 6, 2014. The team's findings revealed several issues, including overloading of the 220/132kV transformers, which are operating at 108.6% and 102.9% of their maximum capacity. This exceeds the 80% loading limit prescribed by NEPRA's grid code. The overloading is attributed to the breakdown of one 160MVA-220/132kV transformer at Mardan 220kV GS. The audit team also identified issues with the loading of Tarbela-Burhan 220kV transmission circuits and Burhan-ISPR 220kV transmission circuit, which are loaded above 80% of their capacity. Additionally, severe oil leakage exists from the main tank and radiators of transformers T1, T2, and T3. The team noted that several tests, including dissolved gas analysis (DGA) and detailed oil testing for transformers, capacitance and dissipation factor (C&DF) test of current transformers (CTs), potential transformers (PTs), and capacitor voltage transformers (CVTs, SF6 purity and moisture content test for circuit breakers, and leakage current measurement (LCM) test of lightening arresters, have not been performed as required. The team also identified issues with the condition of the equipment, including five 132kV BBC make Minimum Oil Circuit Breakers (M.O.C.B) that are excessively leaking, very old, and worn out beyond repairs due to unavailability of spares. Most isolators in the 132kV switchyard are being operated manually, and two line isolators in the 220kV switchyard are operated locally to avoid air leakage in the compressed air distribution system. Spares are unavailable for twelve 220kV and twelve 132kV SF6 gas CBs for overhauling, which is due in the near future. The audit team made several recommendations to address the issues identified, including shifting the load to adjacent GSs, conducting proper load flow studies to maintain loading of transformers per NEPRA grid code, and replacing the five 132kV M.O.C.B with SF6 gas CBs. The team also recommended arranging adequate spares for major overhaul of the twelve 220kV and twelve 132kV SF6 gas CBs, sealing the seepage points on transformers T1, T2, and T3, and replacing the pole-mounted 200kVA auxiliary transformer with a pad-mounted transformer to avoid any mishap. In terms of protection, the team noted that the tele-protection (carrier-aided) tripping facility is missing on almost all 220kV and 132kV circuits, and that two distance protection relays on 132kV circuits are defective. The team recommended installing the missing tele-protection facility, repairing the defective distance protection relays, and installing the missing relays and other defective equipment. The audit team also identified issues with the condition of the equipment, including retaining walls that are required at tower Nos. 33, 42, 52, and 72 of Burhan-Tarbela double circuit line and at tower No. 7 and 36 of 220kV Burhan-ISPR Line. The conductor from tower Nos. 9 to 11 is in deteriorated condition and requires attention. Overall, the technical audit of the Burhan 220kV Grid Station identified several issues that need to be addressed to ensure the safe and reliable operation of the station. The recommendations made by the audit team aim to address these issues and improve the overall performance of the station.