transformer

Abstract

The present disclosure relates to a transformer comprising a primary winding and a secondary winding and at least one additional winding electrically connected to a tap changer. The tap changer is connected to a power supply. The power supply is connected between a low and a high potential of the at least one additional winding.

Description

[0001] TRANSFORMER

[0002] The present disclosure relates to a transformer and in particular to a transformer having a power supply connected thereto.

[0003] Transformers are central components of alternating current (AC) electric systems, enabling the power transfer between all different voltage levels, from HVAC to MVAC and LVAC (high- voltage AC, medium voltage AC and low voltage AC). Often, transformers are electrically passive magnetic components.

[0004] The development of power electronics (PE) devices allowing to deliver new functionalities required due to, e.g., an increasing number of local power generation sources as well as development of sensors that enable collecting processing information about a transformer's condition, increase a requirement for stable and cost-effective power supply for control circuits and sensors.

[0005] However, actively controlled transformers are also needed in the grid for voltage and power flow regulation, on-load-tap-changers (OLTC) and Phase-Shift Transformer (PST), respectively. These use actively controlled elements that require a local LV auxiliary power supply, often within the transformer tank.

[0006] With increasing complexity and installed power of actively controlled (PE converter interfaced) modern electric applications, the needs of the modern electric systems are constantly evolving, requiring more and more flexibility - enabled by actively controlled nodes.

[0007] This can be achieved using actively controlled transformers, on-load-tap-changers (OLTC) and Phase-Shift Transformer (PST). The transformers may use specially constructed windings with multiple terminals, called taps, and a moving contactor that can slide over these taps to regulate the output voltage by regulating the total numberof windings turns. Depending on the type of tap changer, this may require a servo motor that drives the slide contactor to the required position.

[0008] A solution without moveable components such as motors controls a tap position with a PE switch. The switching operation can be done with PE modules. A device that can discreetly regulate a turns ratio may be called power electronic tap changer (PETAC).

[0009] A more modern realisation of an on-load-tap-changer and phase-shifting functionality can be provided with a, so called, power-electronics tap-changer (PETAC). Instead of multiple taps, PETAC uses a single section of the winding and a power electronics converter with pulse- width-modulation (PWM) to provide the same functionality of the OLTC, but with dynamic control and without any moving parts - only using solid-state devices (switches). Alternatively, the same windings used for a traditional OLTC may be used but switched from one position to another by power electronic devices such as thyristors or other solid state devices, avoiding mechanical switching. In general, tap changers can be classified into mechanical or PE-based tap changers, wherein the present disclosure can be applied to both variants, but mainly focuses on PE-based tap changers.

[0010] Whether it is an OLTC or PETAC based actively controlled transformer, an auxiliary power supply is needed, to power the sliding contactor drive system of the OLTC, to power the DC bus pre charging and control and gate-driver circuits of the PETAC, and to provide reliable triggering of thyristor switches independently of the load current.

[0011] Providing the LV auxiliary supply in the tank is not a trivial task. Generally, it is necessary to route the cables from the nearest LV grid access point in the installation to the transformer and inside the tank. However, sometimes, the place of instalment of the transformer can be rather remote, and an access point to the LVAC grid may not be available or not easily accessible. For this reason, some transformers have a special tertiary winding to provide local LVAC access in case this is needed for various local equipment.

[0012] Further, even if the access to LVAC is available, for the above applications it is still needed to route it inside the tank. Extra perforations of the tank and bushings are needed for this purpose. This is increasing the part-count, complexity and cost. Moreover, each bushing is significantly contributing to, and possible adversely affecting, the reliability of the transformer - e.g., possibility of oil leak etc.

[0013] The present disclosure provides a solution forthe above mentioned problems and deficiencies of the prior art.

[0014] The invention is specified by the independent claims. Preferred embodiments are defined in the dependent claims. In the following description, although numerous features may be designated as optional, it is nevertheless acknowledged that all features comprised in the independent claims are not to be read as optional.

[0015] The present disclosure relates to a transformer comprising a primary winding and a secondary winding and at least one additional winding electrically connected to a tap changer. The tap changer is connected to a power supply. The power supply is connected between a low and a high potential of the at least one additional winding.

[0016] Various embodiments may preferably implement the following features.

[0017] Preferably, each additional winding comprises a first connection point and a second connection point. Preferably, the tap changer and the power supply are connected between the first and the second connection points.

[0018] Preferably, the at least one additional winding is electrically connected in series to the primary winding or the secondary winding.

[0019] Preferably, the power supply comprises a rectifier, more preferably a low power rectifier.

[0020] Preferably, the rectifier is one of a diode rectifier, a full bridge converter, or a half bridge converter.

[0021] Preferably, the power supply is not galvanically insulated.

[0022] Preferably, the power supply is connected to a floating potential.

[0023] Preferably, the power supply is galvanically insulated. Preferably, the transformer is a liquid filled transformer, preferably an oil-immersed or ester- immersed transformer.

[0024] Preferably, the power supply is provided within a transformer tank.

[0025] Preferably, the power supply is configured to power at least one of a sensor, power electronics, power electronic valves, or local electronics of the transformer.

[0026] Preferably, the tap changer is one of an on load tap changer, OLTC, a power electronics tap changer, PETAC, or a phase-shift transformer, PST.

[0027] Preferably, the transformer comprises a plurality of additional windings and each additional winding is connected to a respective tap changer comprising a respective power supply.

[0028] Preferably, the transformer is a three-phase transformer.

[0029] In view of the above, the present disclosure provides a solution for how to provide an auxiliary power supply, in particular a low voltage auxiliary power supply, within the transformer tank that is very simple, cost-effective and features high reliability.

[0030] In particular, the present disclosure proposes a solution that directly uses the extra winding portions of the OLTC or PETAC windings to provide the LV power supply needed inside of the transformer tank.

[0031] To decrease conductive losses, the PE devices may be positioned on MV or HV circuit of the transformers and power supply located in the same circuit allows to decrease electrical stress between mentioned components and allows high integration inside of the transformer tank. This advantage refers also to the power supply for various sensors that need to be installed inside of the tank.

[0032] Other aspects, features, and advantages will be apparent from the summary above, as well as from the description that follows, including the figures and the claims.

[0033] Fig. 1 shows an auxiliary power supply connection according to an embodiment of the present disclosure. Fig. 2A shows an auxiliary power supply without galvanic insulation according to an embodiment of the present disclosure.

[0034] Figs. 2B to 2D show rectifiers according to embodiments of the present disclosure.

[0035] In the figures, the same or similar elements are denoted by the same reference signs. Unless indicated otherwise, the embodiments shown in the figures are fully compatible with each other.

[0036] Non-isolated power supply for power electronic devices and sensors utilising power from transformer windings generally receive their power either from taps of a tapping zone, if existing, or from dedicated internal tap or taps.

[0037] Fig. 1 shows an illustration of a connection of an auxiliary powersupply 3 connection according to an embodiment. In Fig. 1, only one phase A is depicted but the disclosure is not limited thereto. Similarly, the additional windings / connections / taps al, a21, a22 are shown on a secondary side 2 but may also be installed at a primary side 1 of the transformer.

[0038] The transformer according to an embodiment comprises a primary winding 1 and a secondary winding 2. Moreover, at least one additional winding 3 is electrically connected to a tap changer 4. As outlined above, the tap changer 4 may be any one of an OLTC, PETC, PST or the like. The tap changer 4 is connected to a power supply 6, in particular an auxiliary power supply 6. The power supply 6 is connected between a low and a high potential of the at least one additional winding 3.

[0039] In an embodiment, each additional winding 3 comprises a first connection point and a second connection point. The tap changer 4 and the power supply 6 may be connected between the first and the second connection points.

[0040] In Fig. 1, the secondary side is sub-divided into three sections, i.e., the secondary winding 2 and two additional windings 3 but the present disclosure is not limited thereto.

[0041] Moreover, the at least one additional winding 3 is electrically connected in series to the primary winding 1 or the secondary winding 2 (in Fig. 1, a connection to the secondary winding is depicted). In the embodiment of Fig. 1, at the secondary winding output al, a first additional winding 3 is electrically connected in series. In particular, the additional winding 3 is formed between the secondary winding output al and a first tap connection point a22. The first tap connection point a22 has a higher potential than the secondary winding output al. That is, a first tap is formed between the secondary winding output al and the first tap connection point a22. In other words, the first tap is formed by a first additional winding 3 or a part of the additional winding 3.

[0042] Moreover, the transformer of Fig. 1 comprises a second tap connection point a21 having a higher potential than the first tap connection point a22. That is, a second tap is formed between the first tap connection point a22 and the second tap connection point a21. In other words, the second tap is formed by a second additional winding 3 or a part of the additional winding 3.

[0043] In the shown embodiment of Fig. 1, the first connection point of the first additional winding 3 (first tap) is the secondary winding output al and the second connection point is the second tap connection point a22. Analogously, the first connection point of the second additional winding 3 (second tap) is the first tap connection point a22 and the second connection point is the second tap connection point a21.

[0044] In order to change the taps of the transformer, three tap changers 4 are provided in the embodiment of Fig. 1 which are connected to the secondary winding 2 and each additional winding 3, respectively. That is, a tap changer 4 is electrically connected to the secondary winding output al, to the first tap connection point a22 and to the second tap connection point a21, respectively. The outputs of the tap changers 4 are connected and an output voltage is provided at an output a3.

[0045] Each tap changer 4 has a dedicated (auxiliary) power supply (APS) 6 which is connected at a floating potential as shown in Fig. 1. In particular, an APS 6 is connected between the secondary winding output al and the first tap connection point a22, and two APSs 6 are connected between the first tap connection point a22 and the second tap connection point a21. In an embodiment, one APS 6 may supply power to a plurality of tap changers 4.

[0046] In an embodiment as shown in Fig. 2A, the power supply 6 is not galvanically insulated. In an embodiment, the power supply 6 comprises a rectifier 5.

[0047] As shown in Figs. 2B to 2D, the rectifier 5 may be one of a diode rectifier (Fig. 2B), a full bridge converter (Fig. 2C), or a half bridge converter (Fig. 2D).

[0048] The power supply 6 may be connected to a floating potential. Moreover, the power supply 6 may be galvanically insulated.

[0049] The transformer may be a liquid filled transformer. In an embodiment, the transformer may be an oil-immersed or ester-immersed transformer. In an embodiment, the power supply is provided within a transformer tank.

[0050] The power supply 6 may be configured to, i.e., utilised to, power at least one of a sensor, power electronics, power electronic valves, or local electronics of the transformer.

[0051] The tap changer 4 may be one of an on load tap changer, OLTC, a power electronics tap changer, PETAC, or a phase-shift transformer, PST.

[0052] The transformer may comprise a plurality of additional windings 3 and each additional winding 3 may be connected to a respective tap changer 4 comprising a respective power supply 6.

[0053] The transformer may be a three-phase transformer.

[0054] As outlined above, an Auxiliary Power Supply (APS) 6 according to the present disclosure may convert AC voltage available from a transformer winding 1, 2 ,3, since the potential difference between taps (additional windings 3) is typically small in transformers. Such a connection can be used for feeding an APS 6. In case the voltage distance (potential difference) between available taps (additional windings 3) is high and high voltage APS 6 is required, the dedicated taps (additional windings 3) can be created. In that manner, a transformer may be adapted to the specific needs of the APS 6 and / or the tap changer(s) 4.

[0055] In many cases, a low voltage APS 6 can be used. The APS 6 may power PE valves or sensors and the control signals are delivered with fibre glass wiring that provides an insulation distance and allows to save the space required for installation. In addition, in the case of oil filled transformers, the required path through the tank is limited to only the optical path which may be positioned in any convenient position on or in the tank. Since in that case, the APS 6 is / are connected within the tank, no additional wiring from the outside is necessary, and therefore installation space is saved and there is no requirement of sealing any additional openings in the tank.

[0056] The electrical distance between powering circuit and PE valves or sensors may also be reduced and an electrical distance between PEs is maintained.

[0057] In case of liquid filled transformers, APS 6 and PE (tap changer 4) located on the floating potential may use the transformer liquid as the insulation and cooling media and therefore further increase compactness of the design. The described topology due to compactness of design can be utilised in case only limited space for installation is available or additional space cost is high like in compact substations typical for distribution transformers

[0058] The present disclosure presents a cost-effective way of supplying the APS 6 without modification or with a minor modification of transformer windings 1, 2, 3.

[0059] The presented power supply design solves the problem of isolation between MV / HV and ground as well as continuous power delivery.

[0060] The location of the tap changer 4, e.g., the PE, on MV / HV transformer windings reduce conductive losses, provides the required functionality without drawbacks while providing insulation as well as a compact size.

[0061] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below.

[0062] Furthermore, in the claims the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single unit may fulfil the functions of several features recited in the claims. The terms "essentially", "about", "approximately" and the like in connection with an attribute or a value particularly also define exactly the attribute or exactly the value, respectively. Any reference signs in the claims should not be construed as limiting the scope.

[0063] List of reference signs

[0064] 1 Primary winding

[0065] 2 Secondary winding

[0066] 3 Additional winding 4 Tap changer / OLTC / PETC / PST

[0067] 5 Rectifier

[0068] 6 (Auxiliary) Power Supply / APS

[0069] A First phase al Secondary winding output a21 Second tap connection point a22 First tap connection point a3 Output

Claims

CLAIMS1. Transformer, comprising a primary winding and a secondary winding, at least one additional winding electrically connected to a tap changer, wherein the tap changer is connected to a power supply, and wherein the power supply is connected between a low and a high potential of the at least one additional winding.

2. Transformer according to claim 1, wherein each additional winding comprises a first connection point and a second connection point, and wherein the tap changer and the power supply are connected between the first and the second connection points.

3. Transformer according to claim 1 or 2, wherein the at least one additional winding is electrically connected in series to the primary winding or the secondary winding.

4. Transformer according to any one of claims 1 to 3, wherein the power supply comprises a rectifier, preferably a low power rectifier.

5. Transformer according to claim 4, wherein the rectifier is one of a diode rectifier, a full bridge converter, or a half bridge converter.

6. Transformer according to any one of claims 1 to 5, wherein the power supply is connected to a floating potential.

7. Transformer according to any one of claims 1 to 6, wherein the power supply is galvanically insulated, orwherein the power supply is not galvanically insulated.

8. Transformer according to any one of claims 1 to 7, wherein the transformer is a liquid filled transformer, preferably an oil-immersed or ester-immersed transformer, wherein preferably, the power supply is provided within a transformer tank.

9. Transformer according to any one of claims 1 to 8, wherein the power supply is configured to power at least one of a sensor, power electronics, power electronic valves, or local electronics of the transformer.

10. Transformer according to any one of claims 1 to 9, wherein the tap changer is one of an on load tap changer, OLTC, a power electronics tap changer, PETAC, or a phase-shift transformer, PST.

11. Transformer according to any one of claims 1 to 10, wherein the transformer comprises a plurality of additional windings and each additional winding is connected to a respective tap changer comprising a respective power supply.

12. Transformer according to any one of claims 1 to 11, wherein the transformer is a three- phase transformer.

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