RODRIGUEZ GUZMAN CARLOS ALBERTO (CO)
GUERRERO MORENO GERMAN ALONSO (CO)
RODRIGUEZ PALACIOS RICARDO (CO)
MORENO ZEA RAUL ERNESTO (CO)
GARZON MARTINEZ MIGUEL EUGENIO (CO)
RODRIGUEZ GUZMAN CARLOS ALBERTO (CO)
GUERRERO MORENO GERMAN ALONSO (CO)
RODRIGUEZ PALACIOS RICARDO (CO)
MORENO ZEA RAUL ERNESTO (CO)
| US2488628A | 1949-11-22 | |||
| EP1887588A1 | 2008-02-13 | |||
| JPH0723526A | 1995-01-24 | |||
| GB612191A | 1948-11-09 |
WINDERS, J. J.: "Power transformers: principles and applications", 2002, CRC PRESS, pages: 49
| CLAIMS 1. A winding connection configuration characterized by having three sets of windings distributed in three columns wherein each winding set consists in two coils, the first of said coils is sectioned into two parts with a two to one turns ratio between sections, and the second coil located in another column has a turns ratio equal to the lower section of the first coil, said first coils of windings are connected to each other in delta configuration, and in each saying winding set, common point of sections of the first coil supplies the second coil located in other column; end parts of said second coils of each column are connected to each other constituting thus the neutral, and beginning parts of first coils in each column supply output phases. 2. A winding connection configuration according to claim 1, wherein the connection to the coil located in other column is made so that the common point of the first coil in first column supplies the second coil located in the second column, the common point of the first coil of second column supplies the second coil located in the third column, and the common point of first coil located in the third column supplies the second coil located in the first column . 3. A winding connection configuration according to claim 1, wherein the connection to the coil located in other column is carried out so that the common point of the first coil in the first column supplies the second coil located in the third column, the common point of the first coil of third column supplies the second coil located in the second column, and the common point of the first coil of second column supplies the second coil located in the first column. 4. A winding connection configuration characterized because primary windings are connected in inverted V configuration, and secondary windings have a connection configuration according to claim 1, allowing said configuration supply a three-phase load from a two-phase feeding. 5. An electric energy distribution transformer characterized because all its windings are mounted on a magnetic core, and: • Primary windings are in an inverted V connection. • Secondary windings are in a connection configuration according to claim 1, supplying said transformer three-phase service from a two- phase feeding. 6. An electric energy distribution transformer according to claim 5, which is reducer. 7. An electric energy distribution transformer according to claim 5, which is elevator. 8. An electric energy distribution transformer according to claim 5, which is constructed with a column type core. 9. An electric energy distribution transformer according to claim 5, which is constructed with a shielded core . 10. An electric energy distribution transformer according to claim 5, which is constructed with an amorphous core. 11. An electric energy distribution transformer according to claim 5, which windings are made of copper and/or aluminum. 12. An electric energy distribution transformer according to claim 5, constructed with any type of magnetic sheet . 13. An electric energy distribution transformer according to claim 5, which nominal power is selected from 5, 10, 15, 30, 45, 75, 112.5, 150, 225, 300, 400, 500, 630, 750, 800, 1 000, 1 250, 1 600, 2 000, 2 500, 3 000, 3 750, 5 000, 30 000 and 90 000 kVA. 14. An electric energy distribution transformer according to claim 5, which rated voltage is selected from the following series, HT <= 15 kV, LT <= 1.2 kV; HT <= 46 kV, LT <= 15 kV; HT <= 220 kV, LT <= 46 kV. |
BACKGROUND
The present invention refers to a novel winding connection specially designed to be fed from two-phase grids and supplying tree-phase service, and with a 2x3 distribution transformer .
In the generation and transformation of electric energy, there is no system able to supply three-phase energy from a two-phase input of only two lines. For example, in the medium voltage distribution grid of electric energy, the need exists of supplying said three-phase energy from only two wires of the grid.
In urban areas having high density of mixed commercial, industrial and residential loads, said medium voltage grid generally uses a three-phase network system, which assures a higher reliability but with significantly high costs.
In other hand, rural distribution grids are characterized because in most of them distribution transformers are fed by two-phase lines, through low capacity single-phase distribution transformers, because load demand is lower. However, said load demand in rural sectors has been increased recently because of the technification of farm jobs and industrialization of processes, surpassing in many cases the installed capacity in the single-phase transformer or transformer bank. This demand has forced reconfiguration of the medium voltage system requiring, among others, installation of the third conductor wire in medium voltage grid, causing elevated costs and excessive delays in the provision of the service.
In order to try to satisfy this growing demand in rural sector, single-phase transformer banks have been installed in traditional connections, open Δ-Δ or open Y-Δ. Unfortunately, medium voltage grid configuration for this type of transformers cannot be of only two wires, but three phases are required in the case of open Δ-Δ connection (See Figure No. 1, Shoemaker, T., Mack, J. "The Lineman's and Cableman' s handbook" 11th edition, McGraw-Hill Companies Inc., New York, 2007, page 15.13) and two phases plus a neutral for open Y-Δ connection (See Figure No. 2, Winders, J. J. "Power transformers: principles and applications" CRC Press 2002, page 49). Additionally, single-phase transformers should be over-sized to be installed in the bank, because the power availably for each case, corresponds to 58% (and not to 66 V3 % of the power that would expected by having two units) and 86.6% (from the addition of nominal powers of two units) , respectively.
Therefore, within the technical field there is a clear necessity of supplying three-phase power service from a two-phase feeding with only two wires, for example, for distributing energy to the final user, without making modifications on the medium voltage distribution grid already existent.
BRIEF SUMMARY OF THE INVENTION
A first object of the invention is to provide a novel winding connection able to transform two-phase tension to three-phase tension, that is, phases which are 120° out of phase with each other and possibility of neutral. Another object of the present invention is to provide a novel distribution transformer able to supply three-phase loads with possibility of neutral from two-phase grids.
The invention provides, for the case of distribution transformers, a distribution system adapted to transform the primary input tension level from two phases to a three- phase system at industrial frequency, able to supply single-phase and/or three-phase loads.
The invention provides a novel configuration of winding connection herein called "delta series", Α, characterized by the use of several columns or phases of the magnetic core for the same winding.
Also, the invention provides a novel configuration of winding connection, in this case used for distribution transformers, inverted V (incomplete Y) - "delta series", Δk, which surprisingly and with a very good performance, allows the three-phase supply from a two-phase power input.
A preferred embodiment of the invention consists in a 2x3 distribution transformer, characterized by having a configuration of winding connection, inverted V - "delta series", Δ, allowing the tree-phase supply from a two- phase feeding.
BRIEF DESCRIPTION OF FIGURES
Figure No. 1 is the circuit diagram and the phase diagram for the connection known as open Δ - Δ, commonly used in three-phase distribution. Figure No. 2 shows the circuit diagram and the phase diagram for the connection known as open Y-Δ, commonly used in three-phase distribution.
Figure No. 3 corresponds to a scheme of the first coil making part of the winding sets of the connection according to the present invention.
Figure No. 4 shows the delta connection of first coils of winding sets according to the present invention.
Figure No. 5 corresponds to a scheme of the novel connection herein disclosed, called "delta series"£& .
Figure No. 6 shows the winding connection in an inverted V configuration (incomplete Y) .
Figure No. 7 corresponds to the scheme of the power distribution system used by the traditional system, compared to that contributed by the present invention.
Figure No. 8 represents the column type core commonly used in constructing distribution transformers.
Figure No. 9 corresponds to the schematic circuit diagram of the configuration of windings of the distribution transformer according to the present invention.
Figure No. 10 (A) corresponds to the schematic circuit diagram of the configuration of primary windings of the distribution transformer according to the present invention on a magnetic core Figure No. 10 (B) shows the schematic circuit diagram of the configuration of secondary windings of the transformer according to the present invention on a magnetic core.
Figure No. 11 corresponds to the phase diagram of Δ connection, included in the transformer according to the present invention.
Figure No. 12 illustrates one of possible connection sets in "delta -series" Δ configuration, in a distribution transformer according to the present invention.
Figures No. 13, No. 14 and No. 15 correspond to Magnitude, dB vs. Frequency (Hz) graphs, obtained from the SFRA analyses .
DETAILED DESCRIPTION OF THE INVENTION
A first aspect of the present invention is a winding connection allowing supply a three-phase system from a two- phase feeding.
Said winding connection consists in a series of coils distributed in a novel configuration named in the present description "delta series",Δ .
This delta series connection combines delta connection, with a connection similar to that used in auto transformers, and Y connection (star) .
Thus, delta series connection is characterized by having three winding sets distributed in three columns, using two columns for a same winding. Configuration of each winding set consists in two coils, wherein the first one of said coils is sectioned into two parts with a two to one turns ratio between sections (Figure No. 3), and the second coil, located in another column, has a turns ratio equal to the inferior section of the first coil. First coils of each winding set are connected each other in a delta configuration (Figure No. 4).
In other hand, in each winding set common point of sections of the first section supplies the second coil, located in another column. Connection may be done as follows (Figure No. 5) : common point of the first coil in the first column (1) supplies the second coil located in the third column (4), on other hand, the common point of the first coil in second column (2) supplies the second coil located in the first column (6) and finally, common point of the first coil located in the third column (3) supplied the second coil located in the second column (5) . All the final parts of second coils of each column are connected to each other to provide the neutral, whereas initial parts of first coils in each column supply output phases.
Connections of common points of the two sections of the first coil may be connected to the second coil in inverse order to that above described, that is, the first coil of the first column with the second coil of the second column, the first coil of the second column with the second coil of the third column, and the first coil of the third column to the second coil of the first column.
Also, the direction of delta connection of first coils may be made in an opposite way.
This connection supplies three phases and a neutral, with the possibility to have a feeding only of two phases. Said input is made through a winding connection in a configuration commonly known as inverted V (or incomplete Y) , wherein windings are connected as two arms of a Y or star (Figure No. 6) .
Inventors has been able to prove surprisingly that this novel winding configuration inverted V- delta series subject of the present invention, allows the supply to three phases and a neutral from only two input wires.
This connection system may be used in any type of transformer to obtain three-phase power from two phases, no matter which input phases are (UW, VW, WU) .
A second aspect of the present invention consists in a 2x3 distribution transformer supplying four lines (three phases and a neutral) such as in traditional transformers, but it receives power only from two medium voltage lines. Figure No. 7 shows a scheme of an energy distribution system wherein distribution transformer of the present invention may be used.
Said transformer according to the present invention uses a winding configuration inverted V- delta series &, which means that its primary windings are in inverted V configuration and are fed by two lines of the distribution system, and secondary windings are in a delta series configuration supplying three output phases and a neutral.
Figure No. 8 indicates the typical construction used in distribution transformers. The core is built of magnetic sheet with three columns, identified in the figure as: 1, 2 and 3. Coil packages both of primary and secondary are built concentrically on each phase or column.
In the present specification, windings are identified as follows :
Primary windings : IP, the number corresponds to the column where the winding is located and letter P refers to the Primary side of the transformer.
Secondary windings : 43S-1, number 4 corresponds to a generic identification of windings, number 3 corresponds to the column wherein the winding is located, in this case number 3, S means secondary winding of the transformer and 1, number of section of secondary winding of the transformer. For all cases, identification of the point in coils will be assumed as its beginning.
Such as shown in Figure No. 9 2x3 transformer of the invention has an inverted V- delta series Δ configuration. In said transformer of the invention, each secondary winding group has three separated portions of coils arranged into two different columns of the three-phase core (three (3) columns) .
Figure No. 10 (B) shows how, on each column of the transformer of the invention there are three sections of coil in secondary windings as follows: 41S-1, 41S-2 y 41S- 3, in column 1, 42S-1, 42S-2 y 42S-3 for column 2 and 43S-1, 43S-2 y 43S-3 for column 3.
To achieve the delta series A connection, the end of section 41S-1 is connected to the beginning of section 41S- 2; the end of section 41S-2 is connected to the beginning of section 43S-1, which end is connected to the beginning of section 43S-2. Also, the end of section 43S-2 is connected to the beginning of section 42S-1 and the end of this section 42S-1 is connected to the beginning of section 42S-2, which end is connected to the beginning of section 41S-1 (Figures 9 and 10(B)).
From the beginnings of each section 41S-1, 42S-1 and 43S-1 there are respectively connected conductors or terminals x, y, z of the transformer.
Additionally, common point of sections 41S-1 & 41S-2 is connected to the beginning of section 43S-3 which end is connected to the ends of sections 42S-3 y 41S-3, to form the neutral reference of the transformer. These bridges are connected to the Pn output of the transformer. In other hand, common point of sections 42S-1 & 42S-2 is connected to the beginning of section 41S-3, and common point of sections 43S-1 & 43S-2 is connected to the beginning of section 42S-3.
As shown in Figure No. 10 (B) , windings are mounted on the three columns of the core; therefore, main branch identified as x-Pn locates portions of windings 41S-1 and 41S-2 on column 1 and section 43S-3 on column 3. Also, branch identified as y-Pn locates portions of winding 42S-1 and 42S-2 on column 2 and section 41S-3 on column 1, and, finally, the branch identified as z-Pn locates portions of winding 43S-1 and 43S-2 on column 3 and portion 42S-3 on column 2.
Figures No. 9 and 10 (B) show how sections 41S-3, 42S-3 and 43S-3 support a tension drop equal to sections 41S-2, 42S-2 and 43S-2, because they have the same number of turns per section. As mentioned before, connection of ends of section 3 of each column (41S-3, 42S-3 and 43S-3) defines the neutral reference of the transformer which makes possible to connect loads requiring neutral (single-phase loads) .
Such as observed in the phase diagram in Figure No. 11, as a consequence that sections 41S-1, 42S-1 y 43S-1 are connected in delta and each portion is located in a column of the core, each output tension of the transformer is 120°out of phase with one another (x-y, y-z, and z-y) , and in a V3 ratio between phase-phase and phase-neutral tensions of the transformer (x-y, y-z, z-x: x-Pn, y-Pn, z- Pn) .
Additionally, turns ratio between sections Sl, and S2 or S3 of each column (for example 41S-1 vs. 41S-2 and/or 41S-3, and also for the other columns) is 2 to 1.
In other hand, regarding the primary side of the transformer object of the invention, to assure necessary flow Φ in the column which does not have winding, and guarantee induction of tension in the set of concentric windings of the same column, an inverted V (incomplete Y) configuration is required (Figure No. 9, Figure No. 10(A)), as follows:
U terminal of the transformer is connected to the end of coil IP; in other hand beginning of coil IP is connected to the beginning of coil 3P, which end is connected to the W terminal of the transformer. Inverted V connection guarantees said flow in the column without primary winding, no matter which of medium tension phases is used as power input.
Such as observed in Figure No. 6, primary windings of the transformer of the invention have different taps allowing adjust output tension of the transformer.
The transformer thus constructed provides effectively a three-phase system with tensions which are 120°out of phase with one another, and with a phase-phase and phase-neutral ratio equal to V3, from two medium tension phases.
2x3 transformer object of the invention may be configured to work as elevator or reducer, to have in general any type of construction and type of magnetic sheet, (core of column, shielded, amorphous type) , with or without forced ventilation, counting on any type of insulating and cooling means, and with any material of high, medium and/or low tension coils (copper and/or aluminum)
In general, said transformer of the invention may have any power, and rated voltage; preferred powers and voltages for 2x3 transformers of the invention are:
Nominal power (kVA) : 5, 10, 15, 30, 45, 75, 112.5, 150, 225, 300, 400, 500, 630, 750, 800, 1 000, 1 250, 1 600, 2 000, 2 500, 3 000, 3 750, 5 000, 30 000, 90 000 Rated Voltage (series): HT <= 15 kV, LT <= 1.2 kV; HT <= 46 kV, LT <= 15 kV, HT <= 220 kV, LT <= 46 kV
Delta series Δ connection, developed in the present invention may be achieved by using some connections different from those described before for the 2x3 transformer, and continue providing a three-phase and neutral output with a tension ratio between phases and neutral of V3 and being said tension 120° out of phase with each other. Figure No. 12 illustrates another preferred embodiment of the 2x3 transformer of the invention wherein the connection of secondary windings has a different order for delta series configuration.
Advantageously, winding connection and 2x3 transformer object of the present invention may supply a three-phase system from a feeding of only two phases, either in an elevator or reducer system, in performance with any rated voltage or nominal power. The present invention allows satisfy superior demands of load in regions only having two distribution lines, and avoiding thus the need or reconfiguring the distribution system, which implies among others: high costs, excessive time, acquirement of permissions for grid installation, etc.
The invention is also versatile because it allows the simultaneous supply of a single-phase and three-phase system from a two-phase grid, having three output phases and a neutral .
The invention may also be used in current urban-type medium voltage three-phase distribution systems.
EXAMPLES
To illustrate the invention a 2x3 transformer was built according to a preferred embodiment of the invention with the following specifications:
Sn = 45 [kVA] Un = 13200/214 [V]
In order to prove the performance of said transformer of the invention in the supply of a three-phase system, following testing were carried out:
a. Previous Routine tests:
1. Measurement of insulating resistance
2. Transformation ratio
3. Determination of no load losses and current
4. Determination of the short circuit tension and load losses
5. Measurement of winding resistance
b. Short circuit test 1 (NTC 2
1. An assay lasting 250 ms in the maximum voltage position
2. Three assays lasting 250 ms in the position of rated voltage
3. An assay lasting 250 ms in minimum voltage position
4. A long lasting assay, 1448,8 ms in minimum voltage position .
c. Subsequent routine tests. (Equal to those described in letter a., carried out after short circuit).
1 Testing made in the High Tension Laboratory, in Universidad del VaIIe, CaIi, Colombia, laboratory credited to carry out these assays by Office Action 3979 on February 21 , 2003, issued by Superintendence of Industry and Commerce.
2 NTC: COLOMBIAN TECHNICAL STANDARD. Results
4. ROUTINE TESTS
4.1 Insulating resistance
Before - 25,0 0 C After - 26,5 0 C
HT-ground LT-ground HT-LT HT-ground LT-ground HT-LT
100 M 500 M 600 M 1500 M 900 M 4,5 G Uncertainty of measurement 2,9%
4.2 Transformation ratio
Before After Variation [%]
Tap
U V W U V W U V W
1 55,96 55,40 - 56,69 55,79 - 1,31 0,71
2 54,59 54,05 - 55,23 54,44 - 1,16 0,71
3 53,23 52,71 - 53,80 53,11 - 1,06 0,77
4 51,87 51,37 - 52,31 51,87 - 0,84 0,97
5 50,51 50,02 - 50,92 50,41 - 0,81 0,77
Uncertainty of measurement 0,1%
4.3 Determination of no load losses and current
Variables Before After
TAP POSITION 2
TEMPERATURE (°C) 25,50 30,90
PHASE U V W U V W
PHASE-PHASE 214,25 213,91 211,83 212,87 212,35
VOLTAGE (V)
AVERAGE PHASE- 213,33 212,29
PHASE VOLTAGE (V)
LOSSES (W) 193,10 191,90
CURRENT (A) 2,953 3,170 2,761 2,918 3,115 2,732
AVERAGE CURRENT 2, 961 2,922
(A) LOSSES REFERRED AT 194,31 193 , 89 20 °C (W)
Uncertainty of measurement 1,8%
4.4 Determination of load losses and short circuit voltage
Variables Before After
PHASE U V W U V W
TAP POSITION TEMPERATURE (°C) 27,10 30, 70 PHASE-PHASE VOLTAGE 428,30 432, .50 (V)
AVERAGE PHASE-PHASE 428,30 432,50 VOLTAGE (V) LOSSES (W) 412, 20 418 ,90
CURRENT (A) 74,40 75, 40 135, 00 75, 30 75, 10 137, 40
SECONDARY
CURRENT (A) PRIMARY 1,908 1, 925 LOSSES REFERRED AT 470, 50 467 ,93 85 °C (W)
TEMPERATURE (°C) 27,10 30,70 PHASE-PHASE VOLTAGE 424,30 424,40 (V)
AVERAGE PHASE-PHASE 424,30 424,40 VOLTAGE (V) LOSSES (W) 427,20 424,90
CURRENT (A) 80 75,50 135, 50 74, 60 74,90 136, 80
SECONDARY
CURRENT (A) PRIMARY 1,981 1, 971 LOSSES REFERRED AT 475,80 477,10 85 °C (W)
TEMPERATURE ( C) 27,10 30,70 PHASE-PHASE VOLTAGE 408,00 391,40 (V) AVERAGE PHASE-PHASE 408 , 00 391,40
VOLTAGE (V)
LOSSES (W) 480,20 440,70
CURRENT (A) 78,10 79,30 142,30 74,70 74,50 136,20
SECONDARY
CURRENT (A) PRIMARY 2,222 2,121
LOSSES REFERRED AT 504,30 499,72
85 °C (W)
Uncertainty of measurement 0,7%
4.5 Winding Resistance
Variables Before After
PHASE x-y y-z Z -x x-y y-z z-x
TAP POSITION 2
TEMPERATURE (°C) 25,10 31,10
LT WINDING RESISTANCE 3,83 3,82 3, 93 3,91 3,93 4,05
(m ) AVERAGE LT RESISTANCE 3,86 3,96
(m )
AVERAGE RESISTANCE AT 4,75 4,77 85 °C (m )
Uncertainty of measurement 0,5 £
Variables Before After
PHASE U V U V
TAP POSITION 1
TEMPERATURE (°C) 25,00 31,00
HT WINDING 27,80 27,60 28,60 28,30
RESISTANCE ( )
AVERAGE HT WINDING 27,70 28,45
AVERAGE RESISTANCE 34,10 34,24 AT 85 °C ( )
TEMPERATURE (°C) 25,10 31 , 10
HT WINDING 27,00 26,90 27 , 80 27 , 60 RESISTANCE ( ) AVERAGE HT WINDING 26,95 27,70 ( )
AVERAGE RESISTANCE 33,17 33,32 AT 85 °C ( )
TEMPERATURE (°C) 25,20 31,00
HT WINDING 25,00 24,90 25,70 25,50 RESISTANCE ( )
AVERAGE HT WINDING 24,95 25, 60
AVERAGE RESISTANCE 30,70 30,81
AT 85 °C ( )
Uncertainty of measurement 0,5%
5. SHORT CIRCUIT ASSAY
5.1 Asymmetrical current
Peak current (first Peak) (A)
Number Tap
Ia Ib Ic
1 1 88,50 -90,31 2 2 90,56 -92,41 3 2 90,56 -92,41 4 2 90,56 -92,41 5 5 94,69 -94,50
-39,31 37,75
5.2 Variation of short circuit symmetrical rms current
Number Tap Ia (A) (RMS) Ib (A) (RMS) Ic (A) (RMS) B* F* Var B* F* Var %* B* F* Var
%* %*
1 56,2 56,1 -0,11 55,80 56,5 1,13
1 5 2
2 57,6 58,3 1,17 56,56 57,9 2,52
7 5 8
2 58,4 58,3 -0,11 57,29 57,9 1,21 1 5 8
4 2 57,6 58,3 1,17 57,29 58,7 2,51
7 5 2
5 5 66,3 67,1 1,20 67,46 66,8 -0,98
5 2 0
6 5 67,0 64,1 -4,22 68,14 63,8 -6,27
2 9 6
*B = Beginning, F= Final, Var% = Variation %
5.3 Duration of assays
Number Tap Voltage Current Duration (ms) Cycle
(V) (A)
1 1 12889,50 56,19 257,04 15,4
2 2 12560,69 57, 64 259,04 15,5
3 2 12560,68 58,01 259,40 15, 6
4 2 12726,28 58,01 250,16 15,0
5 5 12231,67 66, 93 259,00 15,5
6 5 12397,46 65,80 1448,80 86,9
Summary of results obtained
Insulating Resistance:
Data obtained are comparable to transformers of the same series, HT < 15 kV and LT series <= 1.2 kV, having a normal variation of the results before and alter short circuit test.
Transformation Ratio:
Results agree with the design turns ratio, having a normal variation of results before and alter the short circuit test. Table below summarizes the results obtained from no load loses, load losses and total losses.
No load losses:
An increase in no load losses is obtained referred at 20 0 C of 7.2%, compared to a transformer designed under NTC 819 (180 / 193.89 W respectively), with normal variation of results before and alter short circuit test. Load losses:
As observed in previous table, with 2x3 transformer of the invention, a significant decrease in load losses is surprisingly obtained referred at 85 0 C of 32.8%, compared to a transformer designed under NTC 819 (710 / 477.1 W respectively) . This represents a significant advantage by allowing technical losses reduction for any electricity company, in relation to the use of conventional construction and connections. Also, a reduction in total loses was obtained with the transformer of the invention of 24,7% compared to a conventional NTC transformer.
A normal variation of results before and after short circuit test was also obtained.
Winding Resistance:
Values obtained are within expected ranges obtaining a normal variation of results before and after short circuit test.
Short Circuit Tests
The transformer withstood properly the assay; subsequently, a visual inspection inside thereof was carried out wihtout finding any significant abnormality.
FRA analysis
Additionally, an analysis known as FRA (Frequency Response Analysis) was carried out, in the High Tension Laboratory of the Universidad del Valle, CaIi, Colombia. This is an efficient method, widely known in the art allowing assess easily mechanical integrity of internal components of the transformer, namely: core structures, windings and fastening system, since it measures electric transfer functions in a wide range of frequencies after injecting a sinusoidal tension wave. Upon analysis of the results, there can be induced geometric insignificant changes produced by internal or external failures which modify its mechanical and/or electric integrity. The technique used for the 2x3 transformer uses the principle known as SFRA (sweep frequency response analysis), measuring method in the frequency domains. It is a comparative method, that is, SFRA results of one phase are compared to the results of other phases in the same transformer .
In the technical field, SFRA method is widely used in scientific research to verify the state of the transformer after the short circuit test or transport thereof. Also, it is very useful to determine its state after operating associated electric or mechanical protections, or significant variation in variables measured on the transformer (such as, for example, DGA results, dissolved gas analysis) .
Figures No. 13, 14 and 15 show graphs obtained from different SFRA assays with the 2x3 transformer according to the present invention. Said graphs clearly evidence that no significant changes exist in the performance of the transformer before and after short circuit test (Magnitude, dB vs. Frequency, Hz, HO = central point of the HT input, without supply) .
These results imply the 2x3 distribution transformer to be designed and constructed to withstand common short circuit stresses present in the day to day operation.
Electric tests prove that winding connections and the 2x3 transformer of the invention are suitable for the three- phase power supply from a two-phase feeding.
Despite a particular embodiment of the invention has been disclosed for illustration purposes, it is recognized that variations and modifications to the embodiment are in the scope of the application of the present invention.