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5MVA Power Transformer 33/11kV Three Phase
 Release time:2013.04.04    Source:    View times:1609

 
5MVA TRANSFORMERS 33/11KV THREE PHASE
 

 

SCOPE

This specification covers the design, manufacture, supply, delivery installation, testing and performance requirements of POWER TRANSFORMERS

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
IEC  60551
Determination of Transformer and reactor sound level

General

Type of Transformer

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.

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.
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.

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.  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.

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 to cover through a separate bushing and earthed through removable link for inspection purpose.

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 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.

Tanks

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. 

Accessories

Each transformer shall be fitted with the accessories specified in the Schedules.

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.

Oil

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.

 
POWER TRANSFORMERS
 

SCHEDULE A: ZESCO MINIMUM TECHNICAL REQUIREMENTS

 
 
TECHNICAL DETAILS
UNITS
DATA
1.       
TYPE OF TRANSFORMER
 
Free breathing oil immersed power
transformers to IEC 60076
33/11kV transformers
 
2.       
Rated power
KVA
5000
3.       
Nominal Primary Voltage
kV
33
4.       
Highest system voltage - primary
kV
36
5.       
Nominal Secondary Voltage
kV
11
6.       
Highest system voltage – secondary
kV
12
7.       
Vector Group
 
Dyn1
8.       
Phases
 
03
9.       
Type of cooling
 
ONAN
10.   
Type of insulating oil: Mineral oil as per IEC 60296
Yes/No
Yes
11.   
PCB content (attach specification without fail)
 
Nil
12.   
Frequency
Hz
50
13.   
Winding Material
 
Copper
14.   
Minimum Impedance
%
7
15.   
Temperature rise limits
at rated voltage and power
Winding
0C
65
Top oil
0C
60
16.   
Lightning impulse withstand level at primary
kV
170
17.   
Lightning impulse withstand level at secondary
kV
95
18.   
Power Frequency withstand voltage – primary
kV
70
19.   
Power Frequency withstand voltage – secondary
kV
28
20.   
Bushing Type
 
Porcelain
21.   
Specific Bushing creepage distance
mm/kV
25
22.   
Equipped with Jacking pads
Yes/No
Yes
23.   
Equipped with lifting lugs
Yes/No
Yes
24.   
Bucholz for main transformer
Yes/No
Yes
25.   
Temperature Gauges (Windings)
Yes/No
Yes
26.   
Temperature Gauge (oil)
Yes/No
Yes
27.   
Pressure Release Valve (oil tank)
Yes/No
Yes
28.   
Earthing pad
Yes/No
Yes
29.   
Arrestor brackets-HV side
Yes/No
No
30.   
Arrestor brackets-LV side
Yes/No
Yes
31.   
Skid under base
Yes/No
Yes
 
TAP CHANGER DETAILS
 
 
32.   
Tap changer Type:
On load tap changer-Strictly MR type Germany.
Yes/No
Yes
33.   
Tapping range
105% to 85% in steps of 1.25% ( 17 taps)
Yes/No
Yes
 
34.   
Visual position indicator of tap position
Yes/No
Yes
35.   
Bucholz for tap changer
Yes/No
Yes
 
ENVIRONMENTAL CONDITIONS
 
 
36.   
Altitude above sea level
m
1400
37.   
Relative humidity (minimum)
%
85
38.   
Operating ambient temperature
0C
-1 to 40
 
DRAWINGS/TEST CERTIFICATES
 
 
39.   
Drawings showing dimensions/arrangement of connections/rating plate details of transformer offered to be provided with bid
Yes/No
Yes
40.   
Previous type test certificates/results to be provided with bid
Yes/No
Yes
41.   
Routine test certificates/results to be provided on delivery of transformers
Yes/No
Yes
42.   
Applicable standards
IEC60076
IEC60076
 
 
OTHER REQUIREMENTS
 
1.0 MARKINGS
 
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
 
 
TECHNICAL DETAILS
UNITS
DATA
1.       
TYPE OF TRANSFORMER
 
 
2.       
Rated power
KVA
 
3.       
Nominal Primary Voltage
kV
 
4.       
Highest system voltage - primary
kV
 
5.       
Nominal Secondary Voltage
kV
 
6.       
Highest system voltage – secondary
kV
 
7.       
Vector Group
 
 
8.       
Phases
 
 
9.       
Type of cooling
 
 
10.   
Type of insulating oil: Mineral oil as per IEC 60296
Yes/No
 
11.   
PCB content (attach specification without fail)
 
 
12.   
Frequency
Hz
 
13.   
Winding Material
 
 
14.   
Minimum Impedance
%
 
15.   
Temperature rise limits
at rated voltage and power
Winding
0C
 
Top oil
0C
 
16.   
Lightning impulse withstand level at primary
kV
 
17.   
Lightning impulse withstand level at secondary
kV
 
18.   
Power Frequency withstand voltage – primary
kV
 
19.   
Power Frequency withstand voltage – secondary
kV
 
20.   
Bushing Type
 
 
21.   
Specific Bushing creepage distance
mm/kV
 
22.   
Equipped with Jacking pads
Yes/No
 
23.   
Equipped with lifting lugs
Yes/No
 
24.   
Bucholz for main transformer
Yes/No
 
25.   
Temperature Gauges (Windings)
Yes/No
 
26.   
Temperature Gauge (oil)
Yes/No
 
27.   
Pressure Release Valve (oil tank)
Yes/No
 
28.   
Earthing pad
Yes/No
 
29.   
Arrestor brackets-HV side
Yes/No
 
30.   
Arrestor brackets-LV side
Yes/No
 
31.   
Skid under base
Yes/No
 
 
TAP CHANGER DETAILS
 
 
32.   
Tap changer Type:
On load tap changer-MRI type Germany.
Yes/No
 
33.   
Tapping range
105% to 85% in steps of 1.25% ( 17 taps)
Yes/No
 
34.   
Visual position indicator of tap position
Yes/No
 
35.   
Bucholz for tap changer
Yes/No
 
 
ENVIRONMENTAL CONDITIONS
 
 
36.   
Altitude above sea level
m
 
37.   
Relative humidity (minimum)
%
 
38.   
Operating ambient temperature
0C
 
 
DRAWINGS/TEST CERTIFICATES
 
 
39.   
Drawings showing dimensions/arrangement of connections/rating plate details of transformer offered provided with bid
Yes/No
 
40.   
Previous type test certificates/results provided with bid
Yes/No
 
41.   
Routine test certificates/results to be provided on delivery of transformers
Yes/No
 
42.   
Applicable standards
IEC60076