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Enamelled Round Winding Wires
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Enamelled Rectangular Winding Wires
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Continuously Transposed Conductor
|
Paper Insulated Copper Conductor

Continuously Transposed Conductor

story_big

WHAT IS CTC?

CTC consists of a group of enamelled rectangular wires, which are connected up parallel to the ends. In the group each strand (enamelled rectangular wire) successively and repetitively takes up every possible position in the whole cross section. The bunch is wrapped with oil compatible pure cellulose paper.

 

 

 

 

WHAT IS TRANSPOSING?

The enamelled wire conductors within CTC are arranged in two parallel stacks. One stack having one more conductor that the other. The conductors are continuously transposed by machine action moving them from position to position in discrete steps:

Step1: Conductor 1 is moved from the top of the left hand stack to the top of right hand stack.

Step2: The right hand stack is moved down one conductor thickness in relation to the left hand stack.

Step3: Conductor 3 is moved from bottom of right hand stack to the bottom of left hand stack.

Step4: The left hand stack is moved up one conductor thickness in relation to the right hand stack.At the end of four transposing step, as shown in the figure, the CTC conductors have returned to the original geometry, but each conductor advanced one position clock-wise.

INTRODUCTION OF PRECITRANS™¹ CTC:

PWIL is proud to introduce the PRECITRANS™¹ family of CTC comprising the following:

Sr.No.
Description
Type of Enamel Insulationand Thermal Class °C
Type of Insulating Paper
1.
PRECITRANS-PVA™¹
PVA,Class 120
Kraft, Thermally Upgraded, Dennison Crepe, Nomex™ or others as per Customer request.
Remarks
Suitable for large Oil Filled Power and Distribution Transformers
Advantages
Improved transformer performance by reducing eddy current losses.
Considerable increase in space factor due to very small thickness of singleconductor insulation.
Uniform temperature distribution throughout winding.
2.
PRECITRANS-BOND™¹
PVA + Epoxy, Class 120(The epoxy coating is cured to B-stage and is tack free
Kraft, Thermally Upgraded, Dennison Crepe, Nomex™ or others as per Customer request.
Remarks
Suitable for large Oil Filled Power and Distribution Transformers
Advantages
Improved transformer performance against unstable electrical network and short circuit risks.
Exceptional bond between Enamelled rectangular wires offers increased strength.
Increased short circuit forces resistance due to conductor bonded like a solid beam.
Excellent B-Stage storage stability.
Strands bonding during drying process, hence no special treatment necessary at users end.
Epoxy resin coating cure in the same process as paper drying at 100-120°C.
Best hot transformer oil resistance.
Each insulated conductor has improved insulation due to Epoxy.
Tack free and dust-free surface of insulated conductor for easy handling of Strips without powder residue.
No pollution since B-stage Epoxy is free from harmful solvents.
Small thickness of Epoxy bond coat needed (0.020-0.050 mm)
Better sliding amongst the strands, improving CTC windability.
3.
PRECITRANS-200™¹
Polyesterimide +Polyamideimide Class 200
Thermally Upgraded, Nomex™ or others as per Customer request.
Remarks
For dry type Transformers requiring high temperature resistance
Advantages
High Temperature Resistance.
Improved transformer performance by reducing eddy current losses.
Considerable increase in space factor due to very small thickness of single conductor insulation.
Uniform temperature distribution throughout winding.
Increased short circuit force resistance, particularly with epoxy bond coat insulation.

Remarks:

The copper conductor used is Electrolytic Tough Pitch (ETP) or Oxygen Free Copper With High conductivity, for controlled low losses in electrical machines.
The number of strands includes all numbers between 5 to 43; odd numbers can give higher cross section are in CTC. Paper tapes up to 24 wrapping is applied as external insulation over the transposed conductor bunch.
Besides fully annealed copper conductor, PRECITRANS CTC is available with copper conductor with controlled proof stress, for increased mechanical strength for Transformer Winding. Standard Proof Stress Grade are as under:
CONTROLLED PROOF STRESS CTC, REF STANDARD EN 13601:2002OR BS 1432
Grade
RP (0.1%) MPa
Special grades supplied against customer requirement
CPR-1
140-200
CPR-2
170-220
CPR-3
220-260
FULLY ANNEALED
Annealed
Rp (0.2%) 60-100
Standard grade supplied

 

PRECITRANS CTC CURRENT MANUFACTURING RANGE:
CONSTRUCTION DETAILS
No of Single conductors(Strands) in CTC
Upto 43
Generally odd nos. give max C.S area in CTC
Min. dimensions of conductor (mm)
Thickness: 1.25Width: 4.0
Max. dimensions of the single conductor (mm)
Thickness: 3.00Width: 11.5
Width to thickness ratio (Preferred) for Single Conductor
From 2.6 min.to 6.0 max.
Hiight to width ratio (Preferred) of CTC
Preferred height to width ratio of CTC will be intimated during contract review stage
Inter column separator
0.1 mm thick
Other thickness on request
Inter paper wrapping
0.050-0.080 mm Kraft paper Max 22 nos.
Other thickness on request
Outer paper wrapping
0.080 mm thermally upgraded, high tensile crepe paper, last 2 paper coverings
Other thickness on request
Packing on Wooden drums
From 250-4000 KG With separators(Delivery Spools)
As per customer requirement

 

ENAMELLED RECTANGULAR WINDING WIRES USED IN CTC:

Enamelled Rectangular Winding Wires are one of the key ingredients of CTC. Wire Enamel being a critical input of Enamelled Rectangular Winding Wires is carefully chosen to give the desire properties like abrasion resistance, transformer oil resistance, temperature resistance, dielectric strength, etc.

Please refer to the following table for guidelines regarding Enamel Selection and increase in dimensions due to Enamel insulation.

Designation
Enamel Insulation and Class
Grade/Thickness of Insulation
Increase in Dimensions (mm) due to Insulation
PRECIFORM
Poly Vinyl Formal, Class 120
1
0.10 ± 0.02
2
0.13 ± 0.02
PRECITHERM- PLUS
Polyesterimide + Polyamideimide
1
0.10 ± 0.02
2
0.15 ± 0.02
PRECIFORM- BOND
Poly Vinyl Formal, Class 120 +B-stage cured Epoxy
1
0.14 ± 0.02
2
0.17 ± 0.02

Note: The above increase in dimensions can be used as a guideline. Specific requirements can be executed as per Customer request.

DEFINITIONS:

 

TRANSPOSING PITCH :Transposing pitch “P” is the distance between two transposing.

TRANSPOSING LENGTH:Transposing length “lt” is the length measured on the CTC between two points where the stand goes from one side to the other side of the CTC stack. The transposing length is generally less than 50% of the Transposing Pitch “P”.

MINIMUM WINDING DIAMETER AND TRANSPOSING PITCH:The first property to be satisfied during the manufacture and use of the CTC is the windability on the transformers core.

Generally the length in which there is a complete transposing of one strand (called stranding pitch) should be less than the circumference of the transformer core.

The requirement is due to the flexibility of the CTC in order to avoid any damage of the CTC structure.

CTC Plan Transposing Head

Minimum winding diameter is in relationship with the dimensional charcteristicsand the stranding pitch by the following formula:

Where:
S = Transposing distance (Transposing pitch), distance between twotransposotions
M = S/h = Proportionality coefficient – transposing factor (if less than 6, themaximum plus tolerance in redial dimension shall be ‘k’.
if M is lower than 6 it can be difficult to produce the CTC for strand width greater than 6mm,because the pitch can be too small for the transposing machine. if n is large, the pitch mustbe short but not too short to get M lower than 6.

 

CTC DIMENSIONS:

CTC DIMENSIONAL DATACalculation of the cable outer dimensionsMaximum dimension in axial direction:Maximum dimension in radial direction

Where:H = Axial cable dimensionB = Radial cable dimensionh = Axial strand dimensionb = Radial strand dimensionKh = Maximum plus tolerance 0.10 mm for axial dimensionKb = Maximum plus tolerance for radial dimension (values in table)n = Number of strands in the cableiE = Increase in dimensions due to enamel (0.13 for pva and 0.19 for pva plus epoxy)ip = Thickness of separator between the strands stacks.ic = Paper covering (in case of cable without paper ic/2 is the thickness of the plastic wire)

 Table : Kb values

Numbers of strands
s/h ≥ 7 and b < 2 mmand Rp 02 < 180 Mpa
All others cases
Up to 21
0.20
0.30
From 23 to 27
0.25
0.50
From 29 to 35
0.35
0.60
Greater than 35
0.70
1.00

S = Transposing distance (Transposing pitch), distance between two transpositions.

External dimensions are tested under pressure of IN/mm² or the value required by the customer.

INTERCOLUMN SEPARATOR:An intercolumn separator between the two stacks of CTC conductors is inserted, for all stack heights more than 10 mm, unless otherwise agreed to with the user.

The standard paper thickness for this is 0.100-0.110 mm thick.

Intercolumn paper is generally inserted if:

Standard thickness of intercolumn separator paper, besides 0.100 mm, are 0.20, 0.30, and 0.40 mm

PAPER ARRANGEMENT:

Transposed Enamelled Conductors / Strands are wrapped with multiple layers of oil resistant Kraft and/or other special papers to give high dielectric and mechanical strength to the CTC. The paper rolls can be slitted into required width tapes.

TYPES OF PAPERS:

Paper Type
Thickness(Recommended)(mm)
Application
Salient Properties
Kraft Paper
0.055-0.080
 General purpose,inner layers
 High purity 5A2-1M3
CalenderedKraft paper
0.110-0.140
 General purpose,outer layers
 High tensile strength
Aramid paper(Nomex)™
0.050
 Thermal Class 200
 High temperatureresistant, for dry typetransformers

Special papers, depending on customers requirement can be used.

Unless otherwise agreed with the customer, the insulation shall consist of at least 3 layers of 0.080 mm thick Kraft paper.

The paper covering is applied in the following arrangement:

Papers are wound up to 8 papers in the same direction
Above 8 papers, in groups of maximum 8 papers
All inner layers are but lapped and staggered from 25 to 40%
The two outermost layers are wound interlocked with about 50% overlap

Agreement with customer is required for any change in thickness of papers and the type of wrapping arrangement, in order to reach required paper insulation thickness.

WINDING GUIDELINES FOR PRECITRANS CTC:

For optimal performance of CTC during the winding it is necessary to follow certain basic precautions.

During winding operations it is necessary to use some criteria in order to get the best winding of the Transposed Conductor on the transformer core, particularly if the CTC has a high ratio B/H.

When the diameter core is greater than 25 times the radial dimension B, It is possible to wind the CTC leaving it free in the region between CTC and winding core (see figure a).
In case of core with diameter less than 15 times the radial dimensions of the CTC, is possible to wind the Transposed Conductor using the following hints:
Distance between transformer core and the drum axis shall be multiple of the stranding pitch S.
CTC shall be held up and guided by rollers (see figure b) in order to avoid flexions in the length between core and drum.
In order to avoid CTC twisting, rollers shall have adjustable flanges (see figure c and adjustable flanges d).
DRYING AND HEIGHT ADJUSTMENT PROCESSES AFTER WINDING:

PRECITRANS-Bond CTC generally gives best bonding after curing in the range of temperature between 110 and 130 degree C. In our Quality Assurance laboratory the adhesive strenght test on Epoxy bond coated conductors is done by heating for 24h at 120°C.

Many customers use the following drying cycle with great success

During the transformer manufacturing, drying under vacuum, a pressure of 3-5 N/mm²(on the spacers of the helical coil winding) is applied and the temperature is raised to 115°C for 48-72 h. (excluding 6-8 h preheating and 10 hours of cooling periods)
A dimensional adjustment is done at a pressure, in order to reach final dimensions
A vapour phase drying is done at 130°C for 48hrs. (after 2-3 hrs. preheating to reach the temperature)
Before the heat treatment, ensure that at the two ends of the strands are separated sufficiently, to avoid undesirable bonding between them.

 

WHERE IS CTC USED?

Transformer coils wound with CTC
Large Power Transformers, generally > 1 MVA
Furnace Transformers
Traction Loco Transformers
Chokes
Inductance Coils

 

APPLICATION OF CTC

Transformer coil winding with CTC helps in compact design of transformers, campared to Paper insulated copper conductor.
Paper less (netted) CTC is used in special transformers such as Furnace and Freight Loco, for improved cooling.

 

 

 

 

Engineering DataPackagingOrdering Info 

CTC DIMENSIONAL DATA

Calculation of the cable outer dimensions
Maximum dimension in axial direction:

Maximum dimension in radial direction

Where:
H = Axial cable dimension
B = Radial cable dimension
h = Axial strand dimension
b = Radial strand dimension
Kh = Maximum plus tolerance 0.10 mm for axial dimension
Kb = Maximum plus tolerance for radial dimension (values in table)
n = Number of strands in the cable
iE = Increase in dimensions due to enamel (0.13 for pva and 0.19 for pva plus epoxy)
ip = Thickness of separator between the strands stacks.
ic = Paper covering (in case of cable without paper ic/2 is the thickness of the plastic wire)

 

 Table : Kb values

Numbers of strands
s/h ≥ 7 and b < 2 mm
and Rp 02 < 180 Mpa
All others cases
Up to 21
0.20
0.30
From 23 to 27
0.25
0.50
From 29 to 35
0.35
0.60
Greater than 35
0.70
1.00

S = Transposing distance (Transposing pitch), distance between two transpositions.

External dimensions are tested under pressure of IN/mm² or the value required by the customer.

 

INTERCOLUMN SEPARATOR:
An intercolumn separator between the two stacks of CTC conductors is inserted, for all stack heights more than 10 mm, unless otherwise agreed to with the user.

The standard paper thickness for this is 0.100-0.110 mm thick.

Intercolumn paper is generally inserted if:

Standard thickness of intercolumn separator paper, besides 0.100 mm, are 0.20, 0.30, and 0.40 mm

Delivery Spools

 

PRECITRANS and PRECITRANS-Bond CTC is generally supplied on wooden non-returnable drums. On agreement with the customer CTC can also be supplied on returnable wooden spools.

CTC is also supplied with separators to permit two or more parallel winding of CTC in transformer coil, for improved winding efficiency at customer.

 

Spool
Type
Flange
Diameter
Barrel
Diameter
Bore
Diameter
Overall
Width
Traverse
Capacity
in KGS.
 P 900
1100
800
82
660
560
990
 P 1250
1400
900
82
440
340
1200
 P 1750
1400
900
82
580
480
1700
 P 2200
1400
900
82
710
610
2200
 P 2900
1300
900
82
1150
1050
2900
 P 3500
1400
900
82
1110
1010
3500
 P 4500
1700
1000
82
900
770
4500

 

All dimensions in mm

Ordering Information

 

While ordering PRECITRANS CTC, please use PWIL’s contract review form or furnish the information stated hereunder to mumbai@pwil.net or fax it to +91-22-2431087

 

 

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