Detection device and method for detecting faults in a transformer of a wind turbine

Abstract

A detection device and method for detecting a fault in a transformer (10) of a wind turbine (1) is described, wherein the transformer (10) transforms a lower voltage output from a generator (5) of the wind turbine (1) to a low voltage side of the transformer (10) into a higher voltage output from the transformer (10) at a high voltage side, the detection device comprising: a voltage detection device (11) configured to detect a voltage at a first node (12) at the low voltage side of the transformer (10); a current detection device (11) configured to detect a current at a second node (13) at the high voltage side of the transformer (10). The detection device is configured to detect a fault in the transformer (10) based on the detected voltage and the detected current.

Description

Technical Field

[0001] The present invention relates to the field of wind turbines. Conventional wind turbines include multiple elements, including a tower, a nacelle mounted to the tower, and a rotor with a plurality of rotatable blades mounted to the nacelle. The wind turbine also includes a generator, which generates an AC voltage through the rotational motion of the rotor. The transformer transforms the voltage from one level to another, such as a low voltage generated by the generator to a higher voltage. The higher voltage is also called "medium voltage". "Medium voltage" is a voltage between 1 kV and 36 kV that is generally known.

[0002] In particular, the invention relates to a detection device and a method for detecting faults in a transformer of a wind turbine. Summary of the invention

[0003] There may be a need for a low-cost detection device which enables reliable detection of faults occurring in a transformer. This need may be met by the subject matter according to the independent claims. The invention is further developed as stated in the dependent claims.

[0004] According to a first aspect of the invention, there is provided a detection device for detecting a fault in a transformer of a wind turbine, wherein the transformer transforms a voltage from one level to another level, from a lower voltage outputted from a generator of the wind turbine at a low voltage side of the transformer, for example, to a higher voltage outputted from the transformer at a high voltage side. The detection device comprises a voltage detection device configured to detect a voltage at a first node at the low voltage side of the transformer; and a current detection device configured to detect a current at a second node at the high voltage side of the transformer. The detection device is configured to detect a fault in the transformer based on the detected voltage and the detected current. The control device comprises a logic circuit, wherein the control device is configured to disconnect the line switch if the logic circuit detects at least one of the following conditions: an open phase at the low voltage side if the voltage detection device detects a zero-sequence voltage or a zero-sequence voltage exceeding a certain threshold and a voltage unbalance; and an open phase at the high voltage side if the voltage detection device detects no zero-sequence voltage or a zero-sequence voltage falling below a certain threshold and a voltage unbalance.

[0005] There may be a voltage difference between the neutral points, which is known by the technical terminus technicalus as zero sequence voltage. Its amount depends on the inequality of the impedances in the network.

[0006] In a balanced multiphase system, the phase voltages are substantially equal. The inequality of the phase voltages results in voltage imbalance as known in the technical term, ie voltage imbalance is a measure of the voltage difference between the phases.

[0007] Advantageously, the invention is valid for any wind turbine technology, regardless of the wind turbine size, the grid frequency and the voltage to which it is connected, with the following requisites: the wind turbine comprises a power transformer thereon, so that the power generation and the output to the grid are done in different voltage levels. Furthermore, the system cannot be a system with a neutral isolated from the earth, both at the low voltage side and at the high voltage side to which the transformer is connected. A third requisite is that the wind turbine has a line switch capable of interrupting the output line of the transformer with the possibility of being controlled by an external signal.

[0008] The term "high voltage" does not necessarily mean a voltage greater than a certain value, and the term "low voltage" does not necessarily mean a voltage less than a certain value. Instead, the terms "high voltage" and "low voltage" should be understood as the high voltage being greater than the low voltage. The low voltage may have a value of about 690 V, while the high voltage may have a value of several kV, for example, between 1 kV and 36 kV. The high voltage is sometimes also designated as "medium voltage".

[0009] Preferably, the detection device further comprises a control device configured to open the line switch based on the detected voltage and the detected current, thereby interrupting the output line of the transformer.

[0010] Preferably, the control device is configured to disconnect the line switch if at least one of the following conditions occurs: an overvoltage is detected by the voltage detection device, an overcurrent is detected by the current detection device, and a difference between the frequency at the low voltage side or at the high voltage side and the corresponding target frequency exceeds a threshold. In this regard, the voltage detection device also detects the frequency of the voltage at the first node at the low voltage side of the transformer, and / or the current detection device also detects the frequency of the current at the second node at the high voltage side of the transformer.

[0011] Preferably, the control device is configured to open the line switch if the current sensing device detects at least one of a phase overcurrent, a zero sequence overcurrent and a negative sequence overcurrent.

[0012] Preferably, the control device is configured to open the line switch if the voltage detection device detects at least one of a total harmonic distortion (THDv), a zero sequence or neutral voltage and an undervoltage above a defined level.

[0013] Preferably, the control device is configured to open the line switch if an external trip signal is input into the control device.The external trip signal may come from a control device of the same wind turbine, from another protection device installed in the wind turbine or from manual tripping.

[0014] Preferably, the detection device further includes a line switch arranged in an output line of the transformer after the second node at the high voltage side.

[0015] According to a second aspect of the invention, a wind turbine comprises a detection device according to the invention.

[0016] According to a third aspect of the present invention, there is provided a method for detecting a fault in a transformer of a wind turbine, wherein the transformer transforms a lower voltage outputted from a generator of the wind turbine at a low voltage side of the transformer to a higher voltage outputted from the transformer at a high voltage side. The method comprises the following steps: a voltage detection step to detect a voltage at a first node at the low voltage side of the transformer; and a current detection step to detect a current at a second node at the high voltage side of the transformer. The method detects a fault in the transformer based on the detected voltage and the detected current. The control step disconnects the line switch under at least one of the following conditions: a phase failure at the low voltage side if the voltage detection step detects a zero sequence voltage or a zero sequence voltage exceeding a certain threshold and a voltage unbalance; and a phase failure at the high voltage side if the voltage detection step detects no zero sequence voltage or a zero sequence voltage falling below a certain threshold and a voltage unbalance.

[0017] Preferably, the method further comprises a control step to open the line switch based on the detected voltage and the detected current, thereby interrupting the output line of the transformer behind the second node.

[0018] Preferably, the control step disconnects the line switch if at least one of the following conditions occurs: overvoltage is detected in the voltage detection step, overcurrent is detected in the current detection step, and the difference between the frequency at the low voltage side or the high voltage side and the corresponding target frequency exceeds a threshold.

[0019] Preferably, the controlling step opens the line switch if at least one of a phase overcurrent, a zero-sequence or neutral overcurrent, and a negative-sequence overcurrent is detected in the current detecting step.

[0020] Preferably, the controlling step opens the line switch if at least one of a total harmonic distortion (THDv) above a defined level, a zero sequence or neutral voltage, and an undervoltage is detected in the voltage detecting step.

[0021] Preferably, if an external trip signal is input, the controlling step opens the line switch.

[0022] The main components used to implement the present invention are commercially available, so that the solution according to the present invention can be implemented at low cost.

[0023] It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims.

[0024] However, a person skilled in the art will gather from the above and following description that, unless otherwise stated, in addition to any combination of features belonging to one type of subject matter, any combination between features relating to different subject matters, in particular any combination between features of apparatus type claims and features of method type claims, is also considered to be disclosed by the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment described hereinafter and are explained with reference to the examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

[0026] Figure 1 A wind turbine and its various elements are shown;

[0027] Figure 2 shows a schematic circuit diagram of a detection device according to an embodiment of the present invention;

[0028] Figure 3 shows a schematic logic circuit for controlling a line switch according to an embodiment of the present invention; and

[0029] Figure 4 FIG. 4 shows a schematic logic circuit for controlling a line switch according to another embodiment of the present invention. DETAILED DESCRIPTION

[0030] The illustrations in the drawings are schematically. It is noted that in different figures, similar or identical elements are provided with the same reference signs.

[0031] Figure 1 A wind turbine 1 is shown. The wind turbine 1 comprises a nacelle 3 and a tower 2. The nacelle 3 is mounted on top of the tower 2. The nacelle 3 is rotatably mounted relative to the tower 2 by means of a yaw bearing. The axis of rotation of the nacelle 3 relative to the tower 2 is called the yaw axis.

[0032] The wind turbine 1 further comprises a rotor having three rotor blades 6 ( Figure 1 3 , a hub 4 is depicted with two rotor blades 6 therein. The hub 4 is rotatably mounted relative to the nacelle 3 by means of a main bearing 7 . The hub 4 is rotatably mounted around a rotor rotation axis 8 .

[0033] The wind turbine 1 further comprises a generator 5. The generator 5 in turn comprises a rotor connecting the generator 5 with the hub 4. The hub 4 is directly connected to the generator 5, so that the wind turbine 1 is called a gearless direct drive wind turbine. Such a generator 5 is called a direct drive generator 5. As an alternative, the hub 4 can also be connected to the generator 5 via a gearbox. This type of wind turbine 1 is called a geared wind turbine. The present invention is suitable for both types of wind turbines 1.

[0034] A generator 5 is housed within the nacelle 3. The generator 5 is arranged and prepared for converting the rotational energy from the hub 4 into electrical energy in the shape of AC power.

[0035] Figure 2 A schematic circuit diagram comprising a detection device according to an embodiment of the present invention is shown. The detection device is typically arranged in a tower 2 and is configured to detect a fault in a transformer 10 of a wind turbine 1. The transformer 10 is arranged in a nacelle 3. The present invention is also applicable to a wind turbine in which the transformer 10 is not arranged in the nacelle 3 but is arranged in the tower 2 or even on or in a base outside the wind turbine 1. The transformer 10 transforms a lower voltage output from a generator 5 of the wind turbine 1 at a low voltage side of the transformer 10 into a higher voltage output from the transformer 10 at a high voltage side.

[0036] The detection device is arranged to detect a fault in the transformer 10 of the wind turbine 1. Such a fault may be a phase break at the low voltage side and / or at the high voltage side. The term "phase break" means an open circuit. Such a fault may also include a short circuit, such as a so-called turn-to-turn fault at the low voltage side and / or at the high voltage side. A fault may also include a short circuit between a phase and ground or a phase-to-phase short circuit at the low voltage side and / or at the high voltage side.

[0037] If a fault is detected, a trip signal is output via the trip signal line 19, thereby triggering the line switch 14. The line switch 14 interrupts the output line 15 of the transformer 10. The line switch 14 may be an independent switch or a backup switch in addition to the existing switch.

[0038] The detection device includes a voltage detection device 11 configured to detect a voltage at a first node 12 at a low voltage side of the transformer 10, a current detection device 11 configured to detect a current at a second node 13 at a high voltage side of the transformer 10, and a line switch 14 arranged in an output line 15 of the transformer 10 behind the second node 13 at the high voltage side.

[0039] The detection device further comprises a control device 11 configured to open the line switch 14 based on the detected voltage and the detected current, thereby interrupting the output line 15 of the transformer 10. Interruption of the output line 15 is performed if certain conditions are met as follows, which are discussed below.

[0040] The control device 11 is configured to disconnect the line switch 14 if at least one of the following conditions occurs: the voltage detection device 11 detects an overvoltage, the current detection device 11 detects an overcurrent, and the difference between the frequency at the low voltage side or at the high voltage side and the corresponding target frequency exceeds a threshold. If the voltage at the low voltage side exceeds a first threshold, an overvoltage may be detected. If the current at the high voltage side exceeds a second threshold, an overcurrent may be detected.

[0041] If frequency detection is required, the voltage detection device 11 detects not only the amplitude of the voltage, but also the frequency of the voltage at the first node 12 at the low voltage side of the transformer 10, and / or the current detection device 11 detects not only the amplitude of the current, but also the frequency of the current at the second node 13 at the high voltage side of the transformer 10.

[0042] In addition, the control device 11 is configured to disconnect the line switch 14 if at least one of a phase overcurrent, a zero sequence or neutral overcurrent, and a negative sequence overcurrent is detected by the current detection device 11. These overcurrents can be detected if at least one of a phase current, a zero sequence or neutral current, and a negative sequence current at the high voltage side exceeds a certain threshold value.

[0043] The zero sequence or neutral current as a differential current can be calculated from the sum of the currents of all phases other than the protective phase introduced into the electrical system, or it can be measured at a point in the electrical system as the vectorial sum of the currents of all active phases at that point. For example, such a current can occur due to an insulation fault.

[0044] Negative sequence overcurrent is an indicator of an asymmetrical fault, for example in a three-phase electrical system. An asymmetrical fault may result in unequal currents with unequal phase shifts in a three-phase system. An asymmetrical fault may occur due to the presence of an open circuit or a short circuit within a transformer. Open circuits and short circuits may result in an asymmetrical fault in a transformer.

[0045] Furthermore, the control device 11 is configured to disconnect the line switch 14 if the voltage detection device 11 detects at least one of a total harmonic distortion (THDv) above a defined level, a zero sequence or neutral voltage, and an undervoltage. If the voltage at the low voltage side drops below a third threshold, an undervoltage may be detected. If the value of the zero sequence or neutral voltage exceeds a fourth threshold, a zero sequence or neutral voltage may be detected.

[0046] Total harmonic distortion (THDv) above a defined level can be detected, and if its value exceeds a fifth threshold, protection is triggered. Total harmonic distortion (THDv) is an indicator of harmonic distortion in a signal. Total harmonic distortion (THDv) is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.

[0047] Furthermore, the control device 11 is configured to open the line switch 14 if an external trip signal is input into the control device 11 via the external trip signal line 17. The external trip signal is generated by an external control device (not shown).

[0048] The control device 11 is powered by a power line 16. The power line 16 may be fed by an uninterruptible power supply (UPS). The control device 11 is connected to a data output line 18. The data output line 18 may include a communication bus and a digital output interface. Remote access may be achieved to obtain information from the detection device, and diagnostic and forensic capabilities may be improved. In addition, the control device 11 is connected to a human-machine interface so that the control device 11 and the interruption conditions may be configured to meet user or customer requirements.

[0049] Figure 3 A schematic logic circuit included in a control device 11 for controlling a line switch 14 according to an embodiment of the present invention is shown. In this embodiment, a phase failure at the low voltage side is detected. The logic circuit includes a voltage unbalance detection block 21, a zero sequence or neutral voltage detection block 20 and an AND gate 22. The control device 11 is configured to disconnect the line switch 14 if the logic circuit detects a phase failure at the low voltage side. This detection is performed if the voltage detection device 11 detects that the zero sequence voltage exceeds a certain threshold value through the zero sequence or neutral voltage detection block 20 and that the voltage imbalance exceeds a certain threshold value through the voltage unbalance detection block 21.

[0050] Figure 4A schematic logic circuit for controlling a line switch according to another embodiment of the present invention is shown. In this embodiment, a phase failure at the high voltage side is detected. The logic circuit includes a voltage imbalance detection block 24, a zero-sequence voltage detection block 23 and an AND gate 25. The control device 11 is configured to disconnect the line switch 14 if the logic circuit detects a phase failure at the high voltage side. This detection is performed if the voltage detection device 11 detects that the zero-sequence voltage drops below a specific threshold through the zero-sequence voltage detection block 23 and detects that the voltage imbalance exceeds a specific threshold through the voltage imbalance detection block 24.

[0051] The definitions and settings for tripping the line switch can be learned by modeling the wind turbine. The behavior of the wind turbine can be simulated using a specific simulation model. For some protections, settings can be defined, considering some safety factors on the envelope of the most restrictive (in time and level) transition and operating conditions for the wind turbine. A similar approach can be done for high THDv protection.

[0052] Other logical protection algorithms may depend on transformer characteristics: connection group, earthing system, etc.

[0053] The verification process for your setup can include the following steps:

[0054] -Simulation of the system based on leakage reactance under special conditions using a recently developed model for transformers with advanced electrical simulation software;

[0055] - Comparison based on finite element (FE) simulations with the transformer manufacturer’s detailed design model;

[0056] - Evaluation by small-scale tests performed at the manufacturer's tests bench;

[0057] - Actual scale testing and final validation in field operation.

[0058] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. In addition, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A detection device for detecting a fault in a transformer (10) of a wind turbine (1), wherein: The transformer (10) transforms a lower voltage output from a generator (5) of the wind turbine (1) at a low voltage side of the transformer (10) into a higher voltage output from the transformer (10) at a high voltage side, wherein the detection device comprises: a voltage detection device (11) configured to detect a voltage at a first node (12) at the low voltage side of the transformer (10); A current detection device (11) is configured to detect a current at a second node (13) at the high voltage side of the transformer (10); wherein, The detection device is configured to detect a fault in the transformer (10) based on the detected voltage and the detected current; wherein, The detection device comprises a logic circuit, wherein the detection device is configured to detect a fault in the transformer (10) if the logic circuit detects at least one of the following conditions: If the voltage detection device (11) detects that the zero-sequence voltage exceeds a certain threshold and the voltage unbalance exceeds a certain threshold, a phase is disconnected at the low voltage side; and If the voltage detection device (11) detects that the zero-sequence voltage drops below a certain threshold and the voltage unbalance exceeds a certain threshold, a phase is disconnected at the high voltage side.

2. The detection device according to claim 1, further comprising a control device (11) configured to open a line switch (14) based on the detected voltage and the detected current so as to interrupt the output line (15) of the transformer (10).

3. A detection device for detecting a fault in a transformer (10) of a wind turbine (1) according to claim 1 or 2, in, The detection device is configured to detect a fault in the transformer (10) if at least one of the following conditions occurs: the voltage detection device (11) detects an overvoltage, the current detection device (11) detects an overcurrent, and a difference between a frequency at the low voltage side or at the high voltage side and a corresponding target frequency exceeds a threshold.

4. A detection device for detecting a fault in a transformer (10) of a wind turbine (1) according to claim 1 or 2, in, The detection device is configured to detect a fault in the transformer (10) if the current detection device (11) detects at least one of a phase overcurrent, a zero-sequence or neutral overcurrent and a negative-sequence overcurrent.

5. A detection device for detecting a fault in a transformer (10) of a wind turbine (1) according to claim 1 or 2, in, The detection device is configured to detect a fault in the transformer (10) if the voltage detection device (11) detects at least one of a total harmonic distortion THDv above a defined level, a zero sequence or neutral voltage, and an undervoltage.

6. The detection device for detecting a fault in a transformer (10) of a wind turbine (1) according to claim 2, wherein: The detection device is configured to detect a fault in the transformer (10) if an external trip signal is input into the control device (11).

7. The detection device for detecting a fault in a transformer (10) of a wind turbine (1) according to claim 2, wherein: The detection device further includes the line switch (14), which is arranged in an output line (15) of the transformer (10) after the second node (13) at the high voltage side.

8. A wind turbine (1) comprising a detection device according to any one of claims 1-7.

9. A method for detecting a fault in a transformer (10) of a wind turbine (1), wherein: The transformer (10) transforms a lower voltage output from a generator (5) of the wind turbine (1) at a low voltage side of the transformer (10) into a higher voltage output from the transformer (10) at a high voltage side, the method comprising the following steps: a voltage detection step of detecting a voltage at a first node (12) at the low voltage side of the transformer (10); a current detection step of detecting a current at a second node (13) at the high voltage side of the transformer (10); and A detection step of detecting a fault in the transformer (10) based on the detected voltage and the detected current; wherein: The detecting step detects a fault in the transformer (10) in at least one of the following conditions: If the voltage detection step detects that the zero-sequence voltage exceeds a certain threshold and the voltage unbalance exceeds a certain threshold, disconnecting a phase at the low voltage side; and If the voltage detection step detects that the zero-sequence voltage drops below a certain threshold and the voltage unbalance exceeds a certain threshold, a phase is disconnected at the high voltage side.

10. The method according to claim 9, further comprising A control step, based on the detected voltage and the detected current, opens a line switch (14) to interrupt an output line (15) of the transformer (10) behind the second node (13).

11. The method according to claim 9 or 10, in, The detection step detects a fault in the transformer (10) if at least one of the following conditions occurs: an overvoltage is detected in the voltage detection step, an overcurrent is detected in the current detection step, and a difference between a frequency at the low voltage side or at the high voltage side and a corresponding target frequency exceeds a threshold.

12. The method according to claim 9 or 10, in, If at least one of a phase overcurrent, a zero-sequence or neutral overcurrent, and a negative-sequence overcurrent is detected in the current detecting step, the detecting step detects a fault in the transformer (10).

13. The method according to claim 9 or 10, in, If at least one of a total harmonic distortion (THDv) above a defined level, a zero sequence or neutral voltage, and an undervoltage is detected in the voltage detection step, the detection step detects a fault in the transformer (10).

14. The method according to claim 10, in, If an external trip signal is input, the control step opens the line switch (14).

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