WO2006049521A1 - Voltage transformer with improved metrological qualities - Google Patents

Voltage transformer with improved metrological qualities Download PDF

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Publication number
WO2006049521A1
WO2006049521A1 PCT/PL2005/000069 PL2005000069W WO2006049521A1 WO 2006049521 A1 WO2006049521 A1 WO 2006049521A1 PL 2005000069 W PL2005000069 W PL 2005000069W WO 2006049521 A1 WO2006049521 A1 WO 2006049521A1
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WO
WIPO (PCT)
Prior art keywords
gap
voltage
transformer
voltage transformer
air
Prior art date
Application number
PCT/PL2005/000069
Other languages
French (fr)
Inventor
Wojciech Piasecki
Pentti Mahonen
Mariusz Luto
Original Assignee
Abb Sp. Z O. O.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Sp. Z O. O. filed Critical Abb Sp. Z O. O.
Publication of WO2006049521A1 publication Critical patent/WO2006049521A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F38/00—Adaptations of transformers or inductances for specific applications or functions
    • H01F38/20—Instruments transformers
    • H01F38/22—Instruments transformers for single phase ac
    • H01F38/24—Voltage transformers
    • H01F38/26—Constructions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/40—Structural association with built-in electric component, e.g. fuse
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F3/00—Cores, Yokes, or armatures
    • H01F3/10—Composite arrangements of magnetic circuits
    • H01F3/14—Constrictions; Gaps, e.g. air-gaps

Definitions

  • the subject of the invention is a voltage transformer with improved metrological qualities, applicable especially in medium voltage networks.
  • Known voltage transformers have magnetic cores of high magnetic permeability and low magnetic loss.
  • the cores of voltage transformers do not have air-gaps because they adversely effect the metrological parameters of transformers, in particular their phase angle error.
  • air-gaps in magnetic cores of transformers and reactors are commonly used to prevent saturation of cores in the presence of voltage direct component. Air-gaps are also made in the cores of voltage transformers to obtain transformers which can measure transient states during which current direct component occurs.
  • Polish patent application P-363815 presents an example of a design solution for such core.
  • the magnetic insert is used to suppress ferroresonance states of the ferromagnetic core.
  • ThTe magnetic insert is made of a soft magnetic material whose magnetic parameters are different from the magnetic parameters of the ferromagnetic body of the core.
  • Voltage transformers containing gapless cores of high permeability allow the construction of compact, high-accuracy class transformers.
  • the cores of such transformers become saturated at small values of the current.
  • the presence of even a small value of the direct component in voltage results in a significant shift of the working point of the transformer and a possibility of saturation of the core even if the varying component of voltage does not exceed the rating.
  • the fact that in case of disturbances in the power network the transformer can easily be put into the state of saturation causes a danger of ferroresonance state excitation, especially in networks with an isolated star point.
  • An air-gap made in the magnetic core will allow to avoid the problem of current overload of the primary winding of the voltage transformer, but the presence of the gap will result in the phase angle error, which will make it practically impossible to meet the requirements relating to the metering class, especially class 0.5 and 0.2.
  • the essence of the voltage transformer comprising a magnetic core with primary winding and at least one secondary windings in which the primary winding is fitted with at least two terminals to which the leads of the power network are connected, while at least of the secondary winding is fitted with at least two terminals for connecting the inputs of the measuring system, is that the magnetic core has an air-gap, and a phase compensation circuit is connected parallel with the secondary winding of the magnetic core.
  • the parameters of the phase compensation system are selected so that the phase compensation circuit causes a phase displacement of the voltage from the secondary winding of the transformer by an angle opposite to the phase angle error of the transformer with the magnetic core with the air-gap but without the phase compensation circuit
  • phase compensation system contains a capacitor.
  • the air-gap has a thickness smaller than 1 mm.
  • the air-gap is situated transversal to the direction of the magnetic flux in the magnetic core.
  • the advantage of the inventive transformer is an increased resistance of the voltage transformer to the presence, temporary or permanent, of the direct component in the voltage on the transformer primary winding terminals, which is achieved by increasing the reluctance of the core.
  • the increase in the reluctance of the magnetic core is achieved by using an air-gap, while maintaining high metrological parameters by using a system of phase correction. This makes it possible to build a transformer meeting the requirements for class 0.5 and 0.2 of a reduced, compared to the traditional design, failure rate caused by thermal damage to the primary winding.
  • fig.1 shows schematically the structure of the voltage transformer as a view
  • fig. 2 the current-voltage characteristic of the transformer
  • fig.3 - a diagram of the phase angle error.
  • the voltage transformer 1 contains a ferromagnetic core 2 of a rectangular shape and a primary 3 and secondary 4 windings, which are concentrically wound on one of the core 2 arms.
  • a transverse air-gap 5 is formed in the core 2.
  • the first of the primary winding 3 terminals is connected to the phase lead of the power network, and the second terminal of the primary winding 3 is connected to the ground potential.
  • phase compensation system 6 The circuit of a phase compensation system 6 is connected in parallel to the circuit of the secondary winding 4, while the inputs of a measuring system 7 are connected to the outputs of the phase compensation system 6.
  • the phase compensation system 6 has its operating parameters selected in such way that during the operation of the voltage transformer there is a displacement of the phase of the voltage from the secondary winding 4 of the transformer 1 by an angle equal in value to the phase angle error of the transformer 1, but having an opposite sign.
  • a capacitor is used in the phase compensation system 6.
  • the air-gap made in the ferromagnetic core 1 is less than 1 mm thick.
  • fig. 2 shows two curves CJ. and C2, serving as examples of current-voltage characteristicse (I - current intensity, LJ - current voltage) for transformers having the same number of turns, the curve CJ_ relating to a transformer with a core without an air-gap, and the curve C2 relating to a transformer with a core with a gap.
  • I - current intensity, LJ - current voltage current-voltage characteristicse
  • Fig. 3 illustrates, for an example of a voltage transformer, the effects of a 0.6 mm-thick air-gap and a phase compensation system, depending on the load for the gap, where line 1 shows the value of the phase angle error of a transformer without a gap, line 2 shows the value of the phase angle error of a transformer with a gap but without a phase compensation system, and line 3 shows the value of the phase angle error of a transformer with a gap and with a phase compensation system.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Transformers For Measuring Instruments (AREA)

Abstract

The subject of the invention is a voltage transformer with improved metrological qualities applicable especially in medium voltage networks. The voltage transformer according to the invention has an air-gap (5) in the magnetic core (2) and a phase compensation circuit (6) connected in parallel to the terminals of the secondary winding (4) of the transformer which are used for connecting the inputs of a voltage measuring system (7).

Description

Voltage transformer with improved metrological qualities
The subject of the invention is a voltage transformer with improved metrological qualities, applicable especially in medium voltage networks.
Known voltage transformers have magnetic cores of high magnetic permeability and low magnetic loss. The cores of voltage transformers do not have air-gaps because they adversely effect the metrological parameters of transformers, in particular their phase angle error.
Nevertheless, air-gaps in magnetic cores of transformers and reactors are commonly used to prevent saturation of cores in the presence of voltage direct component. Air-gaps are also made in the cores of voltage transformers to obtain transformers which can measure transient states during which current direct component occurs.
There are also known magnetic cores with a gap in the magnetic material, but in the case of cores for voltage transformers this gap is filled with a magnetic insert.
Polish patent application P-363815 presents an example of a design solution for such core. In this case, the magnetic insert is used to suppress ferroresonance states of the ferromagnetic core. ThTe magnetic insert is made of a soft magnetic material whose magnetic parameters are different from the magnetic parameters of the ferromagnetic body of the core.
Voltage transformers containing gapless cores of high permeability allow the construction of compact, high-accuracy class transformers. However, the cores of such transformers become saturated at small values of the current. The presence of even a small value of the direct component in voltage results in a significant shift of the working point of the transformer and a possibility of saturation of the core even if the varying component of voltage does not exceed the rating. This results in the occurrence of large measuring errors and an increase in the root-mean-square current of the transformer, which in consequence can lead to thermal damage to the winding. In addition, the fact that in case of disturbances in the power network the transformer can easily be put into the state of saturation causes a danger of ferroresonance state excitation, especially in networks with an isolated star point. An air-gap made in the magnetic core will allow to avoid the problem of current overload of the primary winding of the voltage transformer, but the presence of the gap will result in the phase angle error, which will make it practically impossible to meet the requirements relating to the metering class, especially class 0.5 and 0.2.
The essence of the voltage transformer, comprising a magnetic core with primary winding and at least one secondary windings in which the primary winding is fitted with at least two terminals to which the leads of the power network are connected, while at least of the secondary winding is fitted with at least two terminals for connecting the inputs of the measuring system, is that the magnetic core has an air-gap, and a phase compensation circuit is connected parallel with the secondary winding of the magnetic core.
Preferably the parameters of the phase compensation system are selected so that the phase compensation circuit causes a phase displacement of the voltage from the secondary winding of the transformer by an angle opposite to the phase angle error of the transformer with the magnetic core with the air-gap but without the phase compensation circuit
Preferably the phase compensation system contains a capacitor.
Preferably the air-gap has a thickness smaller than 1 mm.
Preferably the air-gap is situated transversal to the direction of the magnetic flux in the magnetic core.
The advantage of the inventive transformer is an increased resistance of the voltage transformer to the presence, temporary or permanent, of the direct component in the voltage on the transformer primary winding terminals, which is achieved by increasing the reluctance of the core. The increase in the reluctance of the magnetic core is achieved by using an air-gap, while maintaining high metrological parameters by using a system of phase correction. This makes it possible to build a transformer meeting the requirements for class 0.5 and 0.2 of a reduced, compared to the traditional design, failure rate caused by thermal damage to the primary winding.
The subject of the invention is presented as an embodiment in the drawing, where fig.1 shows schematically the structure of the voltage transformer as a view, fig. 2 - the current-voltage characteristic of the transformer, and fig.3 - a diagram of the phase angle error. The voltage transformer 1 contains a ferromagnetic core 2 of a rectangular shape and a primary 3 and secondary 4 windings, which are concentrically wound on one of the core 2 arms. A transverse air-gap 5 is formed in the core 2. The first of the primary winding 3 terminals is connected to the phase lead of the power network, and the second terminal of the primary winding 3 is connected to the ground potential. The circuit of a phase compensation system 6 is connected in parallel to the circuit of the secondary winding 4, while the inputs of a measuring system 7 are connected to the outputs of the phase compensation system 6. The phase compensation system 6 has its operating parameters selected in such way that during the operation of the voltage transformer there is a displacement of the phase of the voltage from the secondary winding 4 of the transformer 1 by an angle equal in value to the phase angle error of the transformer 1, but having an opposite sign. In the phase compensation system 6, as one of the possible embodiments, a capacitor is used. For voltage transformers of measuring classes 0.5 and 0.2 the air-gap made in the ferromagnetic core 1 is less than 1 mm thick.
The effect of the air-gap 4 on the resultant core 1 magnetization characteristic is presented in fig. 2 which shows two curves CJ. and C2, serving as examples of current-voltage characteristicse (I - current intensity, LJ - current voltage) for transformers having the same number of turns, the curve CJ_ relating to a transformer with a core without an air-gap, and the curve C2 relating to a transformer with a core with a gap. It can be seen from the figures that the use of the gap 5 results in a change in the shape of the transformer characteristic consisting in a considerable decrease of the steepness of the characteristic when an air-gap is used.
Fig. 3 illustrates, for an example of a voltage transformer, the effects of a 0.6 mm-thick air-gap and a phase compensation system, depending on the load for the gap, where line 1 shows the value of the phase angle error of a transformer without a gap, line 2 shows the value of the phase angle error of a transformer with a gap but without a phase compensation system, and line 3 shows the value of the phase angle error of a transformer with a gap and with a phase compensation system.
Connection of the phase compensation system 6 to the secondary winding 4 of the voltage transformer prevents the occurrence of the phase angle error resulting from the presented change in the characteristic.

Claims

Claims
1. A voltage transformer, comprising a magnetic core with a primary winding and at least one secondary winding, in which the primary winding is fitted with at least two terminals to which the leads of a power network are connected, while at least one of the secondary windings is fitted with at least two terminals for connecting the inputs of a measuring system, characterized in that the magnetic core (2) has an air-gap (5) and a phase compensation circuit (6) is connected in parallel to the terminals of the secondary winding (4).
2. A voltage transformer according to claim 1 , characterized in that the parameters of the phase compensation circuit (6) are selected so that the phase compensation circuit (6) causes a phase displacement of the voltage from the secondary winding (4) of the transformer by an angle opposite to the phase angle error of the transformer with the magnetic core (2) with the air-gap (5) but without the phase compensation circuit (6).
3. A voltage transformer according to claim 1 , characterized in that the phase compensation circuit (6) comprises a capacitor.
4. A voltage transformer according to claim 1 , characterized in that the air-gap
(5) has a thickness smaller than 1 mm.
5. A voltage transformer according to claim 1 , characterized in that the air- gap (5) is situated transversal to the direction of the magnetic flux in the magnetic core (2).
PCT/PL2005/000069 2004-11-08 2005-11-04 Voltage transformer with improved metrological qualities WO2006049521A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
PLP-371072 2004-11-08
PL371072A PL205002B1 (en) 2004-11-08 2004-11-08 Voltage transformer with improved metrological properties

Publications (1)

Publication Number Publication Date
WO2006049521A1 true WO2006049521A1 (en) 2006-05-11

Family

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Family Applications (1)

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Country Status (2)

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PL (1) PL205002B1 (en)
WO (1) WO2006049521A1 (en)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH240528A (en) * 1944-01-05 1945-12-31 Isaak Dr Goldstein Transformer, especially voltage converter, with an open iron core.
DE913445C (en) * 1943-12-16 1954-06-14 Savoisienne De Const Electr Sa Arrangement for voltage correction in voltage transformers
GB895629A (en) * 1959-08-15 1962-05-02 Asea Ab Measuring device for measuring electrical power and power factor or loss angle at low power factor
US3781667A (en) * 1972-03-17 1973-12-25 Gen Electric High voltage resonant testing circuit
GB2319345A (en) * 1996-11-12 1998-05-20 Gec Meters Ltd Electricity consumption metering with transformer phase angle error compensation

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE913445C (en) * 1943-12-16 1954-06-14 Savoisienne De Const Electr Sa Arrangement for voltage correction in voltage transformers
CH240528A (en) * 1944-01-05 1945-12-31 Isaak Dr Goldstein Transformer, especially voltage converter, with an open iron core.
GB895629A (en) * 1959-08-15 1962-05-02 Asea Ab Measuring device for measuring electrical power and power factor or loss angle at low power factor
US3781667A (en) * 1972-03-17 1973-12-25 Gen Electric High voltage resonant testing circuit
GB2319345A (en) * 1996-11-12 1998-05-20 Gec Meters Ltd Electricity consumption metering with transformer phase angle error compensation

Also Published As

Publication number Publication date
PL205002B1 (en) 2010-03-31
PL371072A1 (en) 2006-05-15

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