Power Transformers Economics of Refurbishment vs Replacement - Presenter: Mohammad R Siddiqui

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   Total

                 1975 To 1980             1981 To 1985

   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    To
                                           Trafo. 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

       Tank, Conservator, Radiators,
 4.3
       Piping, Gaskets, Consumables,
       fans and Control Cubicles            12          2

as %
Item           Description                       To
                                  For New Tr.
                                              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 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

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.

‫شكرا‬