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30MVA 25MVA 16MVA, 88-132/33kV transformers
 Release time:2013.04.04    Source:    View times:9188
Technical Specifications
1.         
2.         
3.         
3.1.        SCOPE
This specification covers the design, manufacture, supply, delivery, testing and performance requirements of POWER TRANSFORMERS for the following Substations:
·             Fig tree Substation       
1 x 16MVA, 88-132/33kV transformers with online tap changers specified for an 88kV primary voltage.
·             Roma Substation         
2 x 25MVA, 132/11kV Transformer with an online tap changer.
·             Chibombo Substation  
2 x 30MVA, 88-132/33kV transformers with online tap changers specified for an 88kV primary voltage.
3.1.1.      General Requirements
The supplier will take the following into consideration for the complete design and must provide with his offer explanations of the influence thereof:
·            The effect of the difference in height above sea level for the manufacturing plant and the site of installation on the design.
·            The effect of the difference in maximum/minimum and yearly average temperatures between the manufacturing plant and the site of installation on the design.
Manufacture, testing before shipment, all transport & delivery of the new transformers to various substation locations in Lusaka Zambia.  The rates provided must make provision for all loading, off-loading, insurances against loss and/or damage, import duties, taxes and logistics within the time specified. Tap Change Control Panels does NOT form part of the scope of supply.
Transformers shall comply with the requirements of IEC 60076. Check this std.
Transformers of the same rating shall have matched impedances to allow parallel operation.
A copy of the transformer manufacturer's certificate of quality assurance, issued by an acknowledged institution, shall accompany the Tender.
Provision shall be made for a set of two HV current transformers and one neutral current transformers on the transformer HV and Neutral bushings respectively.
 
3.2.        Normative References
The requirements of the following standards / specifications shall be met where applicable unless otherwise stated in this specification.
 
Specification / Standard Number
Title
IEC  60076
Power Transformers
IEC  60137
Insulated bushings for alternating voltages above 1000V
IEC  60214
On-Load Tap Changers
IEC  60296
Specification for unused mineral insulating oils for transformers and switchgear
IEC  60529
Degrees of protection provided by enclosures
3.3.        general
3.3.1.      Type of Transformers
All transformers shall be double wound and be either of the core or shell type.   Transformers shall be suitable for outdoor use and shall have protection classification IP54W (IEC 60529). IEC 60076 recommendations shall be followed.
All transformers shall be fitted with bushings which satisfy the requirements for creepage distance and for impulse levels for altitudes up to 1600 m, such that transformers can be interchanged one with another at any site.
3.3.2.      Electrical Connections
Unless otherwise approved, the direction of winding of the higher and lower voltage windings shall be such that they are of subtractive polarity.
When specified in the Technical Schedules, tappings shall be provided on a three-phase set of transformer windings to provide an alternative ratio of transformation.  The transformer shall be capable of delivering the rated power when connected for the alternative ratio and the unit must be capable of withstanding the specified voltage tests when connected for the most severe condition.
3.3.3.      Duty Under Fault Condition
Except where modified below, it is to be assumed that the amount of generation simultaneously connected is such that normal voltage will be maintained on one side of any transformer when there is a short circuit between phases or to earth on the other side. 
Any transformer may be directly connected to an underground or overhead transmission circuit and switched into and out of service together with its associated transmission circuit.
All transformers shall be capable of withstanding for three second without damage an external short-circuit between phases.  Transformers without tertiary windings shall be capable of withstanding a short circuit between one phase and earth.
Transformers with tertiary windings shall be capable of withstanding for three second without damage any short-circuit to earth with the neutral points on both HV (132/88)kV and MV (33/11)kV windings directly connected to earth.
3.3.4.      Cores
The cores, framework, clamping arrangement and general structure of the transformers shall be of robust design capable of withstanding any shocks to which the transformers may be subjected during transport, installation and service.
The magnetic circuit shall be of cold rolled grain orientated steel and the flux density shall be between 1.65...1.75 Tesla when the voltage applied to any tapping is not in excess of that for which the tapping was designed.
All reasonable care shall be taken in the design and construction of the transformers to reduce noise and vibration to a minimum.  Each core shall be earthed to the tank and securely fastened to prevent movement relative to the tank.  Suitable hooks shall be provided to allow for the lifting of the core from the tank.
The framework and core bolts shall be efficiently insulated from the core so as to reduce circulating current to a minimum.
The core shall be earthed at one point only by means of a link or bolted connection which must be located in an accessible position requiring the minimum amount of oil to be drained from the tank.. Preferably the link shall be brought out through a separate bushing and earthed through removable link for inspection purpose.
3.3.5.      Windings
The windings shall be fully insulated for continuous working at the specified service voltage.
The insulation of windings and all connections shall be of approved materials which shall not deteriorate under the action of hot oil or from other causes when the transformers are operated continuously at the maximum permissible loads.
The windings shall be braced in an approved manner to withstand the effect of short circuit and shocks which may occur during transport.
3.3.6.      Tertiary Windings
The product of the number of turns of the tertiary windings and the cross-sectional area of one such turn shall not be less than 33% of the corresponding product for the untapped main winding.  Facilities shall be provided for earthing the tertiary winding external to the tank.
3.3.7.      Tanks
The tank (including the tank lid) of each transformer shall be of mild steel plate of sufficient thickness to withstand static pressure up to 130 kPa.  Each tank shall be designed to prevent the collection of moisture on any part and shall be sufficiently rigid to prevent distortion when the transformer is lifted complete with oil and subject to the rigors of road and sea transport..  Suitable lugs shall be provided for this purpose and tank cover shall also be provided with lifting eyebolts.
Inspection openings shall be provided in the tank cover to give access to changeover links, bushing core earth links etc. and these inspection covers shall not weigh more than 25 kg each.
Bidders may offer transformers enclosed within a tank incorporating corrugated metal walls and/or ends. The base and tops of such transformers shall be of  mild steel plate having  minimum thickness of 5 mm.
Tank covers shall be provided with lifting lugs or lifting eyebolts.
The corrugated wall and ends of the tank shall be formed by folding and welding of the sheet steel of  a minimum thickness normally not less than 1.2 mm..
The steel used in the formation of corrugated walls and ends shall comply with BS 4360 or corresponding ISO standard and must be of a quality suitable for deep drawings not prone to work hardness and accepting the welding processes used in the tank manufacture.  The manufacturing process used shall not introduce any permanent elongation within the steel.  Stretching of the walls of the corrugations is not acceptable.
The complete tanks shall be pressure tested for oil tightness and tank rigidity and strength.  Such testing shall be completed and proven satisfactory before the core and windings are installed.  The methods of construction testing and quality control of the tanks shall be subject to the approval of the Engineer at all stages of construction.
The Bidder shall submit comprehensive details of the methods of construction and testing procedures employed and shall be prepared to demonstrate to the Engineer the complete operation.
The Bidder shall submit details of previous experience in the manufacture of corrugated tanks and shall indicate the number of years manufacturing corrugated tanks, the number and ratings of the transformers, the site location and the failure rate due to the tank defects.
Details shall be submitted of the standard method of packaging employed to protect the transformers from mechanical damage during transportation to site.  The Bidder shall indicate in detail what additional packing will be provided to protect the transformer during shipping by sea and road and handling on sites due consideration being given to the limited resources available en route.  The method of packaging shall be to the approval of the Engineer.

 
3.3.8.      Accessories
Each transformer shall be fitted with the accessories specified in the Schedules.
3.3.9.      Earthing Terminal
Stainless steel or a mild steel earthing flag approximately 63 mm square and a thickness not less than 6 mm with a centre hole of 14 mm diameter shall be welded externally to the tank.
3.3.10.  Lifting Lugs
Lifting lugs shall be designed to lift the completely assembled transformer with oil.
3.3.11.  Jacking Pads
Not less than four suitably and symmetrically placed jacking pads shall be provided in positions, which will not be impeded when the transformer is loaded on to the transport vehicle.
Each jacking pad shall be designed to support at least half of the total weight of the transformer base and complete with oil the unimpeded working surface of the jacking pads shall be as follows:
·            Minimum/maximum height of jacking pad above base in mm:  460/530. 
·             Unimpeded working surface mm:  230 x 230.
3.3.12.  Skid Under-Base
Skid under-base shall be reinforced to permit moving the transformer in the direction(s) specified.  Hauling eyes shall be provided on the under-base.
3.3.13.  Oil
Each transformer shall be supplied with a sufficient quantity of oil suitable in all respects for continuous service under tropical conditions.  The oil shall be of approved grade and comply with IEC 60296 Cl I or II.
3.4.        Dual ratio transformers
3.4.1.      132-88/33 kv transformers
When requested, facilities shall be provided for changing the voltage for the higher voltage winding from 88kV to 132kV and vice-versa with the transformer disconnected from the supply system.
3.4.2.      On-Load Tap-Changers
On-load tap changing equipment shall be provided of the high speed transition resistor type for varying the transformation ratio whilst the transformer is on load and without producing phase displacement.
The variations shall be made in steps not greater than those specified over the total range specified without phase displacement.
The taps shall be arranged on the windings specified in the schedules.
The taps shall be brought into a separate oil filled compartment with connection links and bridges so that in no case can tap positions be short circuited.
Details of the system shall be indicated on an instruction plate mounted on the tap change equipment.
Equipment for local and remote electrical and local hand operation shall be provided and shall comply with the following conditions :
                                                              i.          It shall not be possible to energise the electric drive when the hand operating gear is in use.
                                                            ii.          It shall not be possible for the local electric and  remote electrical control to be in operation at the same time and a local/remote changeover switch shall be provided for this purpose.
                                                          iii.          Operation from the local or remote control switch shall cause one tap movement only unless the control switch is returned to the “off” position between successive operations.
                                                          iv.          All electrical control switches and the local operating gear shall be clearly labelled in an approved manner to indicate the direction of rotation.
                                                            v.          The local control switches shall be mounted in the Marshalling Kiosk or the control panel.
                                                          vi.          The control equipment shall be so arranged as to ensure that when a tap change has been started it shall be completed independently of the operation of the control relays or switches.  If the failure of the auxiliary supply during a tap change or any other contingency would result in that movement not being completed approved means shall be provided to safeguard the transformer and its auxiliary equipment.
                                                        vii.          The supply available for electrical operation of the control and indication equipment shall be as stated in the schedules.
Apparatus of approved type shall be provided:-
                                                              i.          To give indication of the transformation ratios in use on each transformer both at the local and remote control points.
The indicators shall show clearly the actual tap position and voltage ratio in use at any time and shall show simultaneously the number representing this ratio.  The number shall range from 1 upward depending on the number of ratios and size of position and shall show the total number of positions specified.  Number 1 shall be the tapping position corresponding to the maximum number of 132kV or 88kV winding turns (i.e. the plus percentage position).  The highest number shall represent the tapping position corresponding to the minimum number of 132kV or 88kV winding turns (i.e. the minus percentage position).  The accuracy of indication of these devices shall not be affected by a variation from plus 15% or minus 15% of the normal applied voltage
                                                            ii.          Indication will be given at the remote control point that a change of ratio is in progress by illuminated signal and buzzer type alarm both to continue energised if a change is not completed.
                                                          iii.          To make the equipment suitable for supervisory control and indication a multi-way make-before-break type switch shall be provided at the transformer having one fixed contact for each tap position.  This switch shall be provided in addition to any that may be required for the purpose of remote tap position indication.  Supervisory indication shall also be provided in the form of contacts to close on “Tap Change Incomplete”.
Any switches forming part of the main tap changing apparatus shall be oil immersed and readily accessible. It shall not be possible for the oil in those compartments which contain contacts used for making and breaking current to mix with the oil in any other compartment.
The tap-changing switches and mechanism shall be mounted in oil tanks or compartments placed in an accessible position on the transformer tank and shall be supported from the main tank or its base.  Drop down oil tanks which necessitate the provision of pits in the foundations shall not be used.
Any “drop down” tanks associated with the tap changing apparatus shall be fitted with guide rods to control the movement during lifting or lowering operations.  The guide rods shall be so designed as to take support of the associated tank when in the fully lowered position.  Lifting gear fitted to “drop down” tanks shall include an approved device to prevent runaway during lifting and lowering operations.
Any enclosed compartment not oil-filled shall be adequately ventilated to restrict condensation.  A metal-clad heater shall be provided in the driving mechanism chamber.  All conductor relay coils and other parts shall be suitably protected against corrosion or deterioration due to condensation.
The oil in the compartments of the main tap changing apparatus which do not contain contacts used for making breaking current shall be maintained under conservator head by means of a pipe connection from the highest point of the chamber to the conservator.  This connection shall be controlled by a suitable valve and shall be arranged so that any gas leaving the chamber will pass into the gas and (oil) actuated relay.
It shall not be possible for the oil in those compartments of the tap change equipment which contain contacts used for making or breaking current to mix with the oil in the main transformer or to mix with the oil in the compartments containing contacts not used for making or breaking current.
When a conservator is provided and used to maintain oil level in compartments which contain contacts used for making and breaking current it shall be clearly separate from the main transformer conservator.  An oil gauge and a silica-gel breather shall be fitted to each such conservator.
Each compartment in which the oil is not maintained under conservator head shall be provided with an oil gauge of approved design.
Limit switches shall be provided to prevent over-running of the mechanism and shall be directly connected in the circuit of the operating motor.  In addition a mechanical stop or other approved device shall be provided to prevent over-running of the mechanism under any condition.
Limit switches may be connected in the control circuit of operating motor provided that a mechanical declutching mechanism is incorporated.
Thermal devices or other approved means shall be provided to protect the motor and control circuits.  All relays, switches fuses, etc. shall be clearly marked to indicate their purpose.  Switches for the initiation of a tap change shall bear the inscription “Raise Tap Number” or “Lower Tap Number”.
Tripping contacts associated with any thermal devices used for the protection of voltage control equipment shall be suitable for making and breaking 150 VA at voltages ranging from 30 V to 230 V a.c. or d.c. and for making 500 VA between the limits of 110 and 250 volts d.c..
A device shall be fitted to the tap changing mechanism to indicate the number of operations completed by the equipment.
The whole of the apparatus shall be of robust design and capable of giving satisfactory service without undue maintenance under the most severe conditions likely to be met including frequent operation.
A permanently legible lubrication chart shall be fitted within the driving mechanism chamber.

3.5.        automatic voltage control (For information)
Approved means shall be provided for automatically maintaining within adjustable limits a predetermined voltage at the lower voltage busbars to which the transformer is connected.  The transformer may be required to operate in parallel with other transformers and the voltage control equipment shall be designed on the principle of prevention of circulating current in accordance with IEC 60076 and IEC 60214.  The circulating current shall be limited to 10% or less of the rated current. The equipment shall be suitable for control of up to four transformers and shall be so designed that where control of less than four transformers is initially required it shall be possible to extend the facilities to cover up to four transformers at a later date.
Local control shall be arranged that it is necessary to have the remote selector on a non-automatic position and the Local/Remote changeover switch in the marshalling kiosk positioned on the “Local” before operation is possible.  If the remote selector switch is on any other position the Local/Remote switch shall be inoperative.  Under these condition the local switch shall have over-riding control.
Where specified a voltage regulating relay of an approved type designed to operate from each transformer.  The no-load voltage level of the relay shall be adjustable between 90% and 110% of the nominal energising voltage independent of  any other relay shall be suitable for pre-determined adjustment at any value between the transformer tap set percentage and 1.5 times the transformer tap step percentage.  The relay shall be insensitive to frequency variation 48-52 Hz.
Approved means either by switch or links shall be provided for each transformer to give complete isolation of all supplies at the remote control point without preventing the operation of tap-changers on the other transformers.
A device shall be provided for each transformer to render the automatic voltage control inoperative if the control voltage falls below 80% of the nominal value with means of restoration of the automatic control with the application of at least 85% of the normal energising voltage.  Unless otherwise specified the apparatus shall stay at the tap in use at the instant when the automatic voltage control is rendered inoperative.
Means shall also be provided to indicate at a remote point a partial or complete failure of the voltage transformer supply to the voltage regulating relay.  The alarm shall operate only when the transformer 11kV or 33kV circuit-breaker is closed and when the tap-changer is on automatic control.  The tap-changer shall remain in the position at which it stands when the alarm is given until such time as the control voltage is restored.

3.6.        radiators
Radiators fitted direct to the vertical walls of tanks shall have valves of an approved design top and bottom so that the radiators can be removed when the tanks are full of oil.  Means shall be provided for draining the radiators separately.  Radiators shall be suitable for the attachment of fans at a later date if required. Radiators shall be hot dip galvanised to ensure withstand against corrosion.
3.7.        conservator vessels and breathers
A conservator vessel fitted with a sump and suitable means of drainage shall be provided on each transformer and an approved breathing system shall be supplied.
The oil pipe connection to the conservator shall be of approved design and shall be connected to the highest point or points in the oil system of the transformer tank before passing to the conservator so that all gas rising from the transformer shall pass into the oil pipe towards the conservator.
The conservator shall have a capacity between the highest and lowest visible levels of not less than 10.5 % of the total cold oil volume of the transformer and cooling equipment.
A separate conservator vessel shall be provided for the tap changer having a suitable means of drainage and an approved breathing system.
An oil level indicator shall be fitted to each conservator.
3.8.        gas and oil actuated relay
The surge float contacts shall close at a rate of steady oil flow between the following limits.  As far as possible the limits shall also be met when the relay is subjected to oil surge conditions produced by rapid opening of a lever operated gate valve.
A test facility will be provided by means of a pushbutton to operate the alarm and trip contacts for test purposes.
 
Oil pipe connection internal diameter
Operational limits for relay rising angles of 1o to 9o 
mm
Steady Oil flow
(millimetres/second)
up to 25
700 - 1300
25 - 50
750 - 1400
50 - 75
900 - 1600
 
The gas collection contacts shall operate for a gas accumulation not less than 100 cm3.
Care must be taken when mounting the Buchholz relay to ensure that the free passage of oil surges and gas bubbles are not restricted in the pipework between the tank and relay.  Provision shall be made for a straight run of piping at least five pipe diameters in length on the transformer side and three pipe diameters on the conservator side.  These straight runs of piping shall slope up from the tank to the oil conservator at an angle between 1 to 9 degrees to the horizontal.  Care shall also be taken when mounting the Buchholz relay to ensure that the arrow on the relay is  in the same direction as the oil flow to the conservator.
Suitable pipework and petcock shall be provided accessible from ground level to draw off accumulated gases from the Buchholz relay.
3.9.        Cleaning and Painting
All surfaces liable to corrosion shall be painted and before painting shall be cleaned of all scale and rust by approved means.  All external rough surfaces on castings shall be filled.  After cleaning the interior surfaces, tanks shall be painted with an approved oil-resisting varnish or enamel.  For all other metal parts a priming coat of approved paint shall then be applied and no further painting shall be done until the Work’s Tests have been carried out.  After inspection and testing but before despatch all surfaces shall be thoroughly cleaned and receive two further coats of paint of approved quality and composition. See also SP-GGE-001 “Cleaning and Painting”.
3.10.  inspection and tests
3.10.1.  GENERAL REQUIREMENTS
As provided in the conditions of Contract, the whole of the materials used in the Works shall be subject to such inspection and test at the manufacturer's works as the Engineer may direct from time to time as the work proceeds. The equipment also shall be subject to inspection prior to shipment.  The cost of such inspection and tests, including the provision and use of test equipment, shall be included in the Contract.
Not less than fourteen days’ notice of all tests shall be given to the Engineer in order that he may be present if he so desires.  As many tests as in the opinion of the Engineer are possible shall be arranged together.  Six copies of the Contractors' records of all tests shall be furnished to the Engineer.
The approval by the Engineer of the results of such inspection and tests shall not relieve the Contractor of his obligations under the contract for the satisfactory performance of the plant and materials.
If, due to the Contract Works and/or component materials not complying with this specification and further tests are deemed to be necessary, the Contractor shall pay all additional costs which may be incurred in re-testing.
During the execution of the Contract, test specimens, if required by the Engineer, shall be taken from the materials for the purpose of check tests or analyses by Independent Authorities.  Such specimens shall be prepared for testing and forwarded at the expense of the Contractor to the Testing Authorities selected by the Engineer.
The Engineer reserves the right to call for further tests which are in his opinion necessary to confirm satisfactory performance.  Tests shall as far as possible simulate site conditions.
The contractor shall submit certified type test certificates for all equipment covering the type tests detailed in this section.  Evidence to this effect shall be submitted at the time of tendering.
Type tests will normally only be required when certified test certificates are not available for identical equipment.
Routine tests will be required on all equipment as described in this Section.
Except where otherwise indicated all electrical tests shall be carried out at rated frequency with an approximately sinusoidal waveform.
All instruments shall be approved by the Engineer and if required shall be calibrated at the Contractor's expense.
3.10.2.  Type Tests
One transformer of each type shall be subject to the following type tests:
a)                                    Impulse withstand Test.
b)                                    Temperature-rise type test (IEC 60076-2).
c)                                    Dielectric type tests (IEC 60076-3).
d)                                    Determination of sound level (IEC 60076-10) for each method of cooling for which a guaranteed sound level is specified.
e)                                    Measurement of the power taken by the fan and liquid pump motors.
f)                                    Measurement of no-load loss and current at 90 % and 110 % of rated voltage.
g)                                   Measurement of dissipation factor (tan d) of the insulation system capacitances.
h)                                    Vacuum deflection test on liquid immersed transformers (IEC 60076 (11.9)).
i)Pressure deflection test on liquid immersed transformers (IEC 60076 (11.10)).
3.10.3.  ROUTINE TESTS
Routine Tests as specified in IEC 60076 will be conducted on each transformer.
3.10.4.  TAP-CHANGERS
3.10.4.1.Type Tests
In accordance with the requirements of IEC 60214, the power frequency withstand voltage test is to be applied between electrically adjacent contacts. The test shall be carried out at half normal service voltage.
3.10.4.2.Routine Tests
Routine Tests as specified in IEC 60214 will be conducted on each tap changer.
3.11.  packing and despatch
Packing shall comply with the general requirements of the specification.  Each transformer shall be dried out before leaving the Manufacturer’s Works and shall be despatched with a filling of oil or gas as may be approved by the Engineer.  Each transformer shall be despatched complete and small accessories which can be removed shall be securely packed and attached to the transformer.  Full instructions shall be provided with each transformer for all work necessary to complete its installation setting to work and maintenance.
3.12.  operation and maintenance instructions
Maintenance Instruction shall be provided in English.
3.12.1.  Contract Drawings
Drawings for approval shall be submitted in duplicate as soon as possible, but not later than 4 months after the contract has been placed (unless a shorter period is stated).  The Contractor shall guarantee to supply the drawings within the specified time.  After these drawings have been approved an original copy of each drawing shall be supplied.
Drawings shall be of a convenient size to permit clear interpretation and the minimum size of condensed drawings will be subject to individual approval.
The following drawings shall be supplied:
a)                                    Outline and general arrangement;
b)                                    Internal arrangement of the core and windings, showing lead supports and winding clamping arrangements;
c)                                    Details of core and core clamping;
d)                                    Sectional arrangement drawing of the windings showing sufficient details of the conductors and insulation for local maintenance purposes;
e)                                    Rating and diagram plates;
f)                                     Tap-changer switch;
g)                                    Wiring diagram, outline and drilling details of each item of loose control equipment;
h)                                    Wiring diagram and dimensioned outline drawing of control panels or cubicles, which shall show base fixing arrangements.
The approval of drawings by the Engineer shall not relieve the Contractor of responsibility for correctness thereof, or from the consequences of error or omission on the Contractor's behalf.
3.12.2.  Instruction Manuals
Four copies of instruction manuals in English shall be supplied before the transformers are delivered to site.  The manuals shall be complete with all relevant drawings to enable the equipment to be assembled, checked and overhauled.
Information shall be included on the following:
a)                                    Mechanical operation of tap changers;
b)                                    Setting and testing of winding temperature, oil temperature indicators and Buchholz relay.
3.13.  bushings and insulators
Bushings and insulators shall be according to IEC 60137.
3.14.  marshalling boxes
Connection from various protection, temperature  and alarm devices shall be terminated in a suitably positioned weatherproof  box. The box will be provided with means of breathing, drainage, and anticondensation heater. 
3.15.  FORCED AIR AND FORCED OIL COOLING
Transformers shall be capable of the continuous maximum rated output specified with ONAN cooling unless otherwise specified in the technical schedules.
Where only ONAN ratings are offered , transformers shall be suitable for the addition at a later date of forced air cooling equipment for ONAF cooling to allow for a 30 % increase in rating.
3.16.  current transformer accommodation
Provision shall be made for mounting current transformers in the terminal housings and this shall include approved terminal boxes, conduit and wiring or cables for the secondary connections which on each transformer shall be terminated in the main marshalling kiosk near ground level.
Provision shall also be made for the mounting of current transformers in the neutral earth connection of the HV (132/88kV) or MV (33/11kV) windings of main transformers.
3.17.  capitalisation
3.17.1.  Calculation of equivalent Annual cost of transformer
The equivalent total annual cost of the transformer shall be calculated as follows:
AC = 0.12*C + 511*Fe + 154*Cu
where    AC   =       Annual Cost (US$)
              C      =       Capital Cost of Unit(US$)
              511    =       a US$/kW factor for this application
              Fe     =       Total Iron Loss (kW)
              154    =       a US$/kW factor for this application
              Cu    =       Total Copper Loss(kW)
The above factors of 0.12, 511 and 154 are the results of calculations of a much longer formula using Long Run Marginal Costs (LRMC) of power and energy, discount rates and Loss Load Factors determined elsewhere, which is not stated in this enquiry document to simplify the use of the document.
3.17.2.  Capitalisation of losses for evaluation & guarantees purposes
The capitalisation of losses for the purposes of bid evaluation and penalties for the functional guarantees for copper and iron losses is considered over a period of 20 years with a discount rate of 8%. Over this period the Net Present Value of the cost of losses is 9.82 X the annual cost of losses.
Although the lifetime of the transformer usually is considerably longer than 20 year the NPV for the years beyond that have comparatively small value. For example the NPV over 30 years is 11.36 X the annual cost of losses.
The 20 year period is a reasonable period to consider for the evaluation purposes and the formula shall be as follows:
NPV cost of losses (20 Yr) = 9.82 X (511*Fe + 154*Cu)
 

IEC 60076-1
Annex A
Chibombo substation
2 x 30MVA 88-132/33kV
SCHEDULE A
SCHEDULE B
A.1.1
DESCRIPTION
Minimum Requirements
Equipment Details. (To Be Completed By Contractor)
a
Specifications
IEC 60076
 
b
Transformer construction
Three winding
 
c
Phases
Three
 
d
System Phases
Three
 
e
Frequency
50 Hz
 
f
Transformer type
Oil immersed
 
f
Insulating medium
Mineral oil
 
g
Indoor/Outdoor
Outdoor
 
h
Cooling
Specify
 
i
Rated power:  ONAN/ANAF
25/30MVA
 
j
Rated HV voltage
132kV with 88kV tapping
 
j
Rated MV voltage
33kV
 
k
Tapped winding
132kV
 
k
Number of taps
17
 
k
Tapping range
+5/-15% on 132kV
 
k
Tap steps
1.25%
 
k
On/off load
On load
 
l
Highest HV voltage(Um)
145kV
 
l
Highest MV voltage(Um)
36kV
 
m
HV earthing (132kV)
Neutral SA Specify data
 
m
MV earthing (33kV)
NER
 
n
HV Lightning impulse withstand level (132kV)
650kV
 
n
MV Lightning impulse withstand level
170kV
 
n
HV Short Time AC withstand (132kV)
275kV
 
n
MV Short Time AC withstand (33kV)
70kV
 
o
Vector group
YNyn0 d
 
p
Accelerometer
Yes, 3 axis
 
A.1.1
DESCRIPTION
Minimum Requirements
Equipment Details. (To Be Completed By Contractor)
q
Auxiliary supply voltage
400V 3ph
 
q
Protection & control VT secondary voltage
110V
 
q
DC control voltage
110V
 
r
Conservator With Oil Gauge
Yes
 
r
Dehydrating Breather
Yes
 
r
Buchholz Relay (Main Tank & Tap Changer)
Yes
 
r
Pocket For Oil Top Temperature Thermometer
Yes
 
r
Dial Type Oil Temperature Indicator with Alarm and Trip Contacts
Yes
 
r
Dial Type Winding Temperature Indicator with Alarm and Trip Contacts
Yes
 
r
Cooler Fan Control Circuit
Yes
 
r
Drain Valve
Yes
 
r
Oil Filtration Connections
Yes
 
r
Oil Sampling Facilities
Yes
 
r
Pressure Relief Device
Yes
 
r
Earthing Terminals (To Be Suitable For 40mm x 3mm Flat Copper)
Yes
 
r
Lifting Lugs
Yes
 
r
Jacking Pads
Yes
 
r
Cooling Radiators
Yes
 
r
Surge arrestor brackets
Yes
 
s
Oil preservation
Diaphragm
 
w
33kV Terminals arrangement
Air bushings
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A.1.2
DESCRIPTION
Minimum Requirements
Equipment Details. (To Be Completed By Contractor)
c
Impedance at nominal tap (132kV)
10%
 
e
HV Winding connection configuration
88kV
 
f
Short Circuit Current Withstand (kA for 3s)
Specify
 
g
Noise Level (dB)
Specify
 
j
No Load Losses (kW)
Specify
 
j
Load Losses @ 75˚C (kW)
Specify
 
j
Power Required for Cooling equipment
Specify
 
t
Altitude
1600m
 
t
Seismic Hazard ( ground acceleration)
Attached
Low(0.2-0.4m/s²)