Power Transformers Economics of Refurbishment vs Replacement Presenter: Mohammad R Siddiqui National Grid, Saudi Arabia Co Authors: Abdullah O Bamousa National Grid, Saudi Arabia
Introduction This paper is based on Data obtained from the Grid Interaction with some Transformer manufacturers. Technical Papers published on the different components of Power Transformers Ongoing Projects in the Grid
The Need to Refurbish/Renovate In the early seventies, Utilities went for a H V Transmission Level of 110kV/132 kv. In the Western Region Grid, 238 of a total of 730 Transformers were commissioned between 1975 to 1985. They would be 30 to 40 years by the year 2015
Transformers Commissioning Details from 1975 to 1985 in WOA National Grid Year of Commissioning Area From To From To 1975 To 1980 1981 To 1985 Total JEDDAH 79 52 131 MAKKAH 19 27 46 TAIF 10 14 24 MADINAH Nil 25 25 TABOUK Nil 12 12 238
Specific Precedence In 1971 the first four 110/13.8 kv Transformers were put in service. Two each in City Substation and DSP Substation in Jeddah The two Transformers in City Substation were serving on full load and had to be replaced 2 years back near The 2 Transformers in DSP Substation were not fully loaded and are still in service.
This raises the following issues To determine the aging effect on the units Steps to be taken to make a decision whether replace or refurbish the Units.
Aging depends on The loading cycles that the transformers have been subjected to over the years and The Number of Through faults that the Transformer has suffered
Aging is best established by External inspection of the Transformer and its Auxiliary equipment. Insulating Strength of the Transformer Oil. DGA Analysis of the Transformer Oil Frequency Response Test (Previous Reference Results necessary) Bipolar Test
Planned study and timely replacement/refurbishment will prevent sudden deaths of Transformers that result in unplanned outages and possible extended damages.
A Power Transformer is a stationary device and does not contain components that require precision Engineering. Dismantling a Transformer and replacing the components is relatively an easy procedure. The pictures in the following slides show different stages of assembly and dismantling of the Transformer in different locations
In Workshop
In Factory
Generally the components that remain intact over the years are: The Main Tank The Core and Frame The External Metallic fittings Conservator, Piping, Radiator The Mechanical Protection Devices and Control Cubicles
The components that need inspection before deciding replacement / reuse: Tap Changer / Diverter Switch. Cooling Fans. Protection Devices. Bushings. Current Transformers.
Major Components to be replaced: The Coils forming the H V /LV Windings have to be replaced New Gaskets for sealing and consumables Press board material used for insulation and spacing.
Comparison: The cost of a new 40 MVA 110/13.8 kv Transformer, including Design Manufacturing, Transportation, Installation Testing & Commissioning in 2012 is 2.8 to 3.2 msr and a 67 MVA trafo costs 3.5 to 4.0 msr Refurbishment of an existing 40 MVA Transformer will cost about 1.5 msr. The cost of refurbishment of a Transformer is about 50 % as compared to the cost of replacement. Below is a cost comparison Table based on information exchanged with some manufacturers.
as % of total cost Item Description For New Trafo. To Refurbish 1 Design 5 0 2 Project Monitoring, Installation Testing & Commissioning 15 5 3 Transportation + Duty 15 5 4 Transformer Components 4.1 Coil 20 12 4.2 Core 7 0 4.3 Tank, Conservator, Radiators, Piping, Gaskets, Consumables, fans and Control Cubicles 12 2
as % Item Description For New Tr. To Refurbish 4.4 Coolant - Trafo Oil 8 5 4.5 Mech Protections, CTs 5 2 4.6 Tap Changer 10 5 5 Factory Tests 3 3 6 Dismantling and Assembly 0 10 Total 100% 49 %
In 2006 a 100MVA 13.8kV/132kV Transformer had all its Winding HV and LV, replaced for 1.3 msr. The cost of such Transformer then was about 5mSR.
238 Transformers in the Western Region will be 30 40 years old by 2015. If 10 % of these 238 Transformers are identified for refurbishment each year over the next ten years, it will be required to refurbish one Transformer every 2 weeks. If extended to the entire Country that has 4 such Regions in all, the refurbishment rate can be estimated as 4 Transformers in 2 weeks that is 2 Transformers per week. More Transformers will fall in this category with each passing year.
An Assembly plant sponsored by the Utility would be ideal to take up this work as the orderbook will be full for the next so many years. It will be a first step towards indigenous Heavy Industry for production of Transformers and generate employment for skilled and semi skilled workers in the country. A New Team will have to be set up. Alternatively it can be outsourced to one of the companies working with the required facilities within the Kingdom
ADVANTAGES OF REFURBISHMENT: Cost Saving. No design cost. Environment friendly. No Civil Work required. Control and Indications remain unchanged. Short cycle operation Can be aimed for 16 weeks. DISADVANTAGES: The Rating of the Transformer has to be retained, it cannot be increased.
Facilities needed 1. A workshop with suitable untanking facilities of the Live Part and replacement of coils by new ones. 2. Arrangement of Washing and Cleaning of Main Tank and Core and retightening of Core. 3. Oven facility for drying the assembly before sealing for transportation. 4. Testing facilities for the Transformer and its components. 5. Sufficient Storage and handling facility. 6. Oil regeneration unit(at site) with Oil Tanks for treatment and storage.
The Transformer oil will have to be regenerated. The cost of regeneration is about 60 % as compared to the cost of new oil. This is an environmentally friendly procedure and the success rate as experienced in the existing substations is 100%.
Paste picture
Conclusion The refurbished Transformer will have a life nearly as good as that of a new Transformer, as studies of the silicon sheets used to form the core of the Transformers have revealed no aging effect. The purpose of this paper is to initiate a healthy discussion on this subject to take timely steps to tackle the situation that would arise in coming years.
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