Trafo Rehab Vs New

National Grid, Saudi Arabia

Co Authors: Abdullah O Bamousa

National Grid, Saudi Arabia

Presenter: Mohammad R Siddiqui

Power Transformers Economics of Refurbishment vs Replacement

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

Introduction

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

In the early seventies, Utilities went for a H V Transmission Level of 110kV/132 kV.

The Need to Refurbish/Renovate

To

79 19 10 Nil Nil

MAKKAH

TAIF

MADINAH

TABOUK

1975 To 1980

From

JEDDAH

Area

To

12

25

14

27

52

1981 To 1985

From

Year of Commissioning

238

12

25

24

46

131

Total

Transformers Commissioning Details from 1975 to 1985 in WOA National Grid

The 2 Transformers in DSP Substation were not fully loaded and are still in service.

The two Transformers in City Substation were serving on full load and had to be replaced 2 years back near

In 1971 the first four 110/13.8 kV Transformers were put in service . Two each in City Substation and DSP Substation in Jeddah

Specific Precedence

Steps to be taken to make a decision whether replace or refurbish the Units.

To determine the aging effect on the units

This raises the following issues

The Number of Through faults that the Transformer has suffered

The loading cycles that the transformers have been subjected to over the years and

Aging depends on

Bipolar Test

Frequency Response Test (Previous Reference Results necessary)

DGA Analysis of the Transformer Oil

Insulating Strength of the Transformer Oil.

External inspection of the Transformer and its Auxiliary equipment.

Aging is best established by

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

The pictures in the following slides show different stages of assembly and dismantling of the Transformer in different locations

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.

In Workshop

The Main Tank The Core and Frame The External Metallic fittings Conservator, Piping, Radiator The Mechanical Protection Devices and Control Cubicles

Generally the components that remain intact over the years are:

Tap Changer / Diverter Switch. Cooling Fans. Protection Devices. Bushings. Current Transformers.

The components that need inspection before deciding replacement / reuse:

Press board material used for insulation and spacing.

New Gaskets for sealing and consumables

The Coils forming the H V /LV Windings have to be replaced

Major Components to be replaced:

Below is a cost comparison Table based on information exchanged with some manufacturers.

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.

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

Comparison:

20 7

12

Transformer Components Coil Core

Tank, Conservator, Radiators, Piping, Gaskets, Consumables, fans and Control Cubicles

4 4.1 4.2

4.3

3

15 15

Project Monitoring, Installation Testing & Commissioning Transportation + Duty

2

5

2

12 0

5 5

0

For New To Trafo. Refurbish

Design

Description

1

Item

as % of total cost

Mech Protections, CTs

Tap Changer

Factory Tests

Dismantling and Assembly

4.5

4.6

5

6

Total

Coolant - Trafo Oil

Description

4.4

Item

100%

0

3

10

5

8

49 %

10

3

5

2

5

To For New Tr. Refurbish

as %

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.

More Transformers will fall in this category with each passing year.

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.

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.

Alternatively it can be outsourced to one of the companies working with the required facilities within the Kingdom

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.

The Rating of the Transformer has to be retained, it cannot be increased.

DISADVANTAGES:

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.

ADVANTAGES OF REFURBISHMENT:

5. 6.

4.

3.

2.

1.

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.

Facilities needed

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

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.

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.

Conclusion