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Release time：2013.04.04 Source： View times：2840
5MVA TRANSFORMERS 33/11KV THREE PHASE
This specification covers the design, manufacture, supply, delivery installation, testing and performance requirements of POWER TRANSFORMERS
The requirements of the following standards/ specifications shall be met where applicable unless otherwise stated in this specification.
The transformer shall be double wound and be core type. The Transformer shall be suitable for outdoor use and shall have protection classification IP54W (IEC 60529). IEC 60076 recommendations shall be followed.
The transformer shall be fitted with bushings which satisfy the requirements for creepage distance and for impulse levels for altitudes up to 1400 m, such that the transformer can be interchanged one with another at any site.
Unless otherwise approved, the direction of winding of the higher and lower voltage windings shall be such that they are of subtractive polarity.
As specified in the Technical Schedules, tapings 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 test voltages when connected for the most severe 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. The 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.
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 to cover through a separate bushing and earthed through removable link for inspection purpose.
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 transformer is 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.
The tank (including the tank lid) of the transformer shall be of mild steel plate of sufficient thickness and it will have to stand 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. 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.
Each tank is to be designed to prevent the collection of moisture on any part and shall be sufficient rigid to resist any permanent distortion when the transformer is lifted complete with oil and subject to the rigors of road and sea transport.
Tank covers shall be provided with lifting lugs or lifting eyebolts.
The steel used shall comply with BS 4360 or corresponding ISO standard and must be of a quality suitable for deep drawing 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.
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.
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.
Each transformer shall be fitted with the accessories specified in the Schedules.
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.
The 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.
SCHEDULE A: ZESCO MINIMUM TECHNICAL REQUIREMENTS
RATING AND DIAGRAM PLATES: To conform to IEC 60076
In addition, the following markings must appear on the rating plate
q Zesco Indent No
q Clearly indicate : “OIL contains NO PCB's
2.0 Surge arrestor brackets shall be arranged as per figure 1 below:
Fig 1: Surge arrestor brackets on the 11kV side showing clearances.
3.0 Evaluation of losses
For bid evaluation of transformers, the lowest offered losses in kW will be used as reference. The load losses for the transformer will be evaluated at the rate of USD2000 per kW (excess) and added to the bid price. The excess in no load losses will correspondingly be evaluated at the rate of USD4000 per kW for the transformer and added to the bid price of the transformer. The losses in kW are the guaranteed values as indicated in schedule B by the bidder.
SCHEDULE B: TO BE FULLY COMPLETED BY THE TENDERER
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