1. Power Transformers- Economics of Refurbishment vs Replacement
Presenter: Mohammad R Siddiqui
National Grid, Saudi Arabia
Co-Authors: Abdullah O Bamousa

2. 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

3. 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 They would be 30 to 40 years by the year 2015

4. Transformers Commissioning Details from 1975 to 1985 in WOA National Grid
Area
Year of Commissioning
Total
From To
1975 To 1980
1981 To
JEDDAH 79 52
131
MAKKAH 19 27 46
TAIF 10 14 24
MADINAH
Nil 25
TABOUK 12
238

5. 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.

6. 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.

7. 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

8. 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

9. Planned study and timely replacement/refurbishment will prevent sudden deaths of Transformers that result in unplanned outages and possible extended damages.

10. 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

12. In Workshop

14. 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

15. The components that need inspection before deciding replacement / reuse:
Tap Changer / Diverter Switch.
Cooling Fans.
Protection Devices.
Bushings.
Current Transformers.

16. 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.

17. 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.

18. Item Description as % of total cost For New Trafo. To Refurbish
Cost Breakup
Item
Description
as % of total cost
For New
Trafo.
To Refurbish 1
Design 5 2
Project Monitoring, Installation Testing & Commissioning 15 3
Transportation + Duty 4
Transformer Components
4.1
Coil 20 12
4.2
Core 7
4.3
Tank, Conservator, Radiators, Piping, Gaskets, Consumables, fans and Control Cubicles

19. Item Description as % For New Tr. To Refurbish
Cost Breakup
Item
Description
as %
For New Tr.
To Refurbish
4.4
Coolant - Trafo Oil 8 5
4.5
Mech Protections, CTs 2
4.6
Tap Changer 10
Factory Tests 3 6
Dismantling and Assembly
Total
100%
49 %

20. 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.

24. 238 Transformers in the Western Region will be 30-40 years old by 2015
238 Transformers in the Western Region will be years old by 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.

25. An Assembly-plant sponsored by the Utility would be ideal to take up this work as the order-book 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

26. 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.

27. Facilities needed
A workshop with suitable unTanking facilities of the Live Part and replacement of coils by new ones.
Arrangement of Washing and Cleaning of Main Tank and Core and retightening of Core.
Oven facility for drying the assembly before sealing for transportation.
Testing facilities for the Transformer and its components.
Sufficient Storage and handling facility.
Oil regeneration unit(at site) with Oil Tanks for treatment and storage.

28. The Transformer oil will have to be regenerated
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%.

29. A Regeneration Unit in use in WOA,National Grid, Saudi Arabia
Paste picture-

30. 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 other metallic components are also reusable.
There are about 4000 H V Power Transformers in the Kingdom including National Grid, SEC Generation, SWCC, Aramco, Royal Commission and other Major Consumers. At an average cost of 3mSR they are worth million SR. They will need refurbishment/replacement turn by turn in the next 40 years. The choice to refurbish will result in a saving of about 6000 mSR.
The purpose of this paper is to initiate a healthy discussion on this subject of major maintenance to take timely steps to tackle the situation that would arise in the coming years.

31. THANKS
شكرا