DE102010060333B4 - Decentralized generation plant, in particular wind energy plant, test circuit and test method - Google Patents

Abstract

A decentralized electrical generating system connected to a grid (N), characterized by a test circuit (P) for testing the reaction of the generating plant to an overvoltage with an inductive resistor switchable between the generating plant (DEA) and the grid (N) (L) and a capacitive resistor (C) for providing a test overvoltage, wherein the capacitive resistor (C) via a switch (S2) is switchable.

Description

The invention relates to a decentralized electrical generation plant, in particular a wind turbine, which is connected to a network, and a test circuit for testing the response of such a generating plant to an overvoltage and a method for testing the response of such a generating plant to an overvoltage.

The invention can be used in particular in wind turbines. Wind turbines are usually connected to electrical supply networks. To ensure the stability of such electrical supply networks, the grid operators issue connection guidelines for the decentralized generation plants connected to the grid. These connection guidelines prescribe the behavior of the generation systems during a fault in the network. Generating plants that do not comply with the corresponding connection directive may only be connected to the grid to a limited extent. This applies not only to wind turbines but also to other decentralized generation systems of the supply network.

Disruptions in the supply network can z. B. be short-term overvoltages, which are caused for example by a load shedding. Furthermore, short-term voltage dips can occur, which can be caused for example by short circuits in the transmission network.

The decentralized generation plants should advantageously be able to pass through these fault conditions without disconnecting from the grid. In addition, the generating plant should particularly preferably support the mains voltage by supplying reactive power or by drawing on reactive power.

The connection directives generally stipulate that the conformity of the production plants with the connection guidelines is verified by means of a certification process, whereby the corresponding test usually takes place directly in the corresponding supply network.

The invention can now be used on a test circuit that can simulate the fault conditions, thus on the one hand to give the manufacturers of decentralized generation facilities the opportunity to adapt the systems according to the guidelines. On the other hand, the test circuit can also be used during the certification process.

In the DE 31 09 465 A1 a noise signal generator is described which injects high-energy signals to the power lines of electrical equipment for testing purposes via a series resonant circuit with a capacitive and an inductive resistance, without causing a high energy loss of the test signal or the mains voltage occurs.

The invention has for its object to provide a test circuit and a test method by which the reaction of a generating plant to a test overvoltage can be tested while the generating plant is connected to the grid.

A generation system according to the invention for solving the problem is part of claim 1, a test circuit according to the invention for solving the problem is part of claim 14 and an inventive test method for solving the problem is part of claim 16. Advantageous developments are part of the dependent claims.

The object is achieved by a test circuit for testing the reaction of the generating plant to an overvoltage, with a switchable between the generating plant and the network resonant circuit, in particular a series resonant circuit, with an inductive resistor and a capacitive resistor to provide a test overvoltage, wherein the capacitive resistance (C) via a switch (S ₂ ) is switchable, and by a generating plant with such a test circuit.

By means of the test circuit according to the invention, it is possible for the generating plant to simulate mains overvoltage. At the same time, the generating plant can continue to be connected to the grid and fed into the grid. As a result, a test situation that is as realistic as possible can also be produced.

The resonant circuit preferably has a series branch in which the inductive resistor is arranged, and a parallel branch in which the capacitive resistor is arranged. In this case, the inductive resistor may be connected in series with the usually predominantly inductive network impedance.

The test circuit has only a small influence on the line voltage at the input side of the test circuit during the test. It is therefore possible to test the reaction of the generating plant without unnecessarily influencing the network.

In this case, the voltage across the parallel branch can represent the test overvoltage provided to the energy system. The mains voltage can represent the input voltage of the test circuit. The test circuit increases the voltage and provides it to the generating plant as test overvoltage.

Due to the properties of the resonant circuit, the mains voltage can be increased with suitable dimensioning of the inductive and the capacitive resistance. In addition, the behavior of the test circuit can be further improved by further components:
Particularly preferably, a damping resistor is arranged in the parallel branch. By this damping resistor, which may be arranged in particular in series with the capacitive resistance, the switching behavior when switching on the test circuit can be influenced. In particular, transient oscillations of the resonant circuit can be damped by the damping resistor.

Further preferably, a discharge resistor is arranged in the parallel branch. By this particular switchable discharge resistor, the capacitive resistance can be discharged defined defined after completion of the test. In this respect, the discharge resistor should be arranged parallel to the capacitive resistor. Due to the discharge resistor, a defined output state of the test circuit can be restored after each test attempt. Furthermore, a risk to the operator is reduced by a charged capacity.

In a further possible embodiment, an unloading throttle is arranged in the discharge circuit of the capacitive resistor. About the discharge choke, the capacitive resistance can be discharged independently, so that preferably a switch can be saved. In addition, there is no longer the danger that discharge will no longer take place if the discharge switch is defective.

In addition to overvoltages, voltage dips can also be a power failure. Particularly preferably, the test circuit should be able to simulate such voltage dips of the network of decentralized generation plant in order to check the reaction of the generating plant to such a voltage dip can.

In order to provide a test voltage which is lower than the mains voltage, the test circuit can have a switchable inductive resistor parallel to the parallel branch. This second inductive resistor thus forms an inductive voltage divider with the inductive resistor of the series branch. The voltage across the shunt is reduced from the voltage at the input of the test circuit and may represent the input voltage of the generator.

In a preferred embodiment, the test circuit has a surge arrester at the input and / or at the output of the test circuit. Another surge arrester may be provided, for example, to secure the parallel branch. Overvoltages can occur, for example, during switching operations.

The test circuit can be connected between the grid and the generating plant. For this purpose, in particular circuit breakers can be used. The following switches can preferably be used:
In an advantageous embodiment, the resonant circuit can be bridged via a bypass switch. Furthermore, the test circuit on the network side and / or generating plant side can be separated by means of a switch from the network or the generating plant. Through the bypass switch, however, the generating plant can continue to feed into the network when z. For example, there are breaks, maintenance or interruptions between tests.

The capacitive resistance is switched on via a switch. In one possible embodiment, the inductive resistor can be bridged via a bypass switch. By opening this bypass switch, the inductive resistor can be switched on. During the test, the bypass switch of the inductive resistor can thus be opened first, in which case the capacitive resistor is subsequently connected in order to provide the test overvoltage.

The inductive resistance and the capacitive resistance must be sufficiently dimensioned for use, in particular in medium-voltage networks. The capacitive resistance can be for example consist of several parallel and / or series-connected capacitors. The inductive resistor may consist, for example, of a plurality of coils connected in series and / or in parallel. The individual capacitors or the individual coils can preferably be switched on individually. Preferably, the capacitive resistance and / or the inductive resistance is adjustable. As a result, the test voltage can be adjusted.

In order to carry out the test at the site of the generating plant, it is advantageous if the test circuit is suitable for transport. The test circuit is preferably arranged in one or more mobile containers, in particular insulated containers. These containers can be brought by conventional means of transport to the place of production. Preferably, the containers are designed weatherproof, so that the test is independent of external environmental conditions.

The test circuit is preferably designed such that in the case of a three-phase structure, the test voltage in each of the three phases can be increased at the same time. Furthermore, the test voltage could also be increased individually in each individual phase.

The invention is not limited to wind turbines. Rather, it can also be used in other decentralized generation plants such as photovoltaic systems, combined heat and power plants or gas and diesel generators. In addition to this use in the decentralized power supply, the invention can also be found in devices of electric mobility, especially in batteries of electric cars, use. The grid can be a medium voltage network or a low voltage network.

The test method according to the invention for testing the power generation plant is carried out while the generating plant is connected to the grid. The power plant can feed energy into the grid during the test.

During the test, electrical characteristics of the generating plant can be measured. The measuring devices used for this purpose may be part of the generating plant or the switchable test circuit. The same applies to the evaluation of the test and the evaluation equipment used for this purpose.

The embodiments and developments described in connection with the test circuit according to the invention can also be used in the test method according to the invention.

Advantageous embodiments of the invention will be described with reference to the following figures. Show it:

1 a schematic equivalent circuit diagram of a network connected to a generation system with intermediate test circuit;

2 a second embodiment of a test circuit;

3 a third embodiment of a test circuit;

4 a fourth embodiment of a test circuit;

5 a fifth embodiment of a test circuit;

6 a sixth embodiment of a test circuit;

7 a seventh embodiment of a test circuit;

8th an eighth embodiment of a test circuit arranged in three containers; and

9 A ninth embodiment of a test circuit.

The 1 shows the inventive principle of the test circuit, which can be used to test the response of a decentralized generation plant DEA, such as a wind turbine, to an overvoltage.

The generating plant DEA is connected to a grid N with a schematically illustrated grid impedance Z _N. The test circuit can be connected between the grid N and the generating plant DEA.

The test circuit comprises a series resonant circuit having an inductive resistor L and a capacitive resistance C. The inductive resistor L is here in a series branch of the resonant circuit. The inductive resistance L is thus in series with the network impedance Z _{N of} the network N. About the inductance of the inductive resistor L, the repercussions on the network N can be reduced to a required level. In the series branch, the ohmic resistance should also be kept low.

The resonant circuit further has a parallel branch, in which the capacitive resistor C is arranged. In the parallel branch, a damping resistor R _D is also arranged, which can affect the transient response of the resonant circuit in a favorable manner.

The mains voltage represents the input voltage of the test circuit. The output voltage of the test circuit, which is provided to the generating plant, corresponds to the voltage across the parallel branch.

The inductive resistor L can be bridged via a power switch S ₁ . The capacitive resistor can be connected via a circuit breaker S ₂ . When the bypass switch S _{1 is closed} and the switch S ₂ is open, the generating plant is connected directly to the grid N without any further influence.

To test the reaction of the generating plant DEA to an overvoltage, the switch S ₁ is first opened. Subsequently, the switch S _{1 is} closed, so that the generating plant DEA is now connected via the resonant circuit to the network N. Due to the selected dimensioning of the inductance of the inductive resistor L and the capacitance of the capacitance C, a comparison with the mains voltage U _NETZ increased test overvoltage U _{DEA can be provided} at the output of the test circuit. This can be specified in the steady state as follows:

The 1 shows a single-phase equivalent circuit of the test circuit. In an analogous manner, the test circuit can also be constructed in three phases.

The capacitive resistor C may consist of a parallel and / or series connection of a plurality of capacitors. The capacitance of the capacitive resistor C may be, for example, in the range of 1 to 100 μF. The inductance of the inductive resistor L may be in the range of 10 to 1000 mH. The inductive resistor L may be constructed from a plurality of coils connected in series and / or in parallel.

The test circuit enables the behavior of the DEA generating plant to be checked for short-time overvoltage and thus optimized. Thus, the risk can be reduced that in the event of an actual grid overvoltage due to uncontrolled behavior of different generation plants, the network N is additionally destabilized.

The 2 shows a second embodiment of a test circuit P. At the input and the output of the test circuit P is a surge arrester ÜA arranged against earth. As a result, the test circuit can be protected against overvoltages of the network N and against overvoltages of the DEA generation plant. Furthermore, starting from the test circuit P, no overvoltages are fed into the grid N and the generating plant DEA. Surge arresters may also be present between the phases.

Another surge arrester ÜA is arranged parallel to the parallel branch, so that this is also protected against overvoltages.

Parallel to the parallel branch, a discharge resistor R _E is also arranged, which can be connected via a switch S ₃ . The discharge switch S ₃ can after opening a test at open Switch S _{2 are} closed, so that the capacitive resistance C via the discharge resistor R _E and the damping resistor R _D can be discharged.

The parallel branch ends at a star point SP. The star point is earthed in particular in the case where the voltage is to be increased even in a single phase. However, the star point can also be executed in isolation. In a three-phase application, the capacitive parallel branches of all three phases can end in the neutral point.

The 3 shows a third embodiment of a test circuit P. The difference compared to the test circuit after 2 is that the switch S _{2 has been} omitted, the switch S _{4 has been} added.

The 4 shows a fourth embodiment of a test circuit P. The difference from the embodiment according to 2 is that in addition a power switch S _{5 has been} added on the network side, with which the test circuit P can be disconnected from the network N. Furthermore, a circuit breaker S _{6 has been} added on the generating side, by means of which the test circuit P can be disconnected from the generating plant DEA. By the two switches S ₅ and S ₆ , the test circuit P can thus be switched dead.

The 5 shows a fifth embodiment of a test circuit C. In this embodiment is compared to the embodiment according to 4 In addition, a bypass switch S ₇ provided by which the power generation plant DEA with open switches S ₅ and S ₆ and thus voltage-free resonant circuit can continue to be operated on the network N. Thus, for example, maintenance work on the test circuit can be carried out without the generation system DEA has to be taken from the network N. During the test, the switch S _{7 is} open. Air-insulated switches can be used as test switches.

The 6 shows a sixth embodiment of a test circuit P. In contrast to the embodiment according to 5 this test circuit P is no longer the power switch S ₁ . Particularly preferably, this circuit is used in encapsulated switchgear.

The 7 shows a seventh embodiment of a test circuit P, the opposite to the circuit according to 2 is changed so that instead of the discharge switch S _3, a discharge choke L _{E is arranged} in series with the discharge resistor R _E. The discharge throttle can be designed such that it blocks at 50/60 Hz. As soon as the power switch S ₂ opens, the remaining DC voltage can discharge via the discharge choke L _E and the discharge resistor R _E. The advantage of this embodiment is that the discharge is done independently and also the switch S ₃ can be saved. Furthermore, it is advantageous that there is no longer the danger that if the discharge switch S _{3 is} defective, no rapid discharge would take place.

The 8th shows an eighth embodiment of a test circuit. The test circuit is arranged in three ISO sea containers CT ₁ , CT ₂ and CT ₃ . The individual containers CT ₁ , CT ₂ and CT ₃ are independent of each other, for example by means of trucks can be loaded. The test circuit can thus be easily brought to the location of the decentralized generation plant DEA.

The electrical connection of the test circuit between the CT ₁ , CT ₂ and CT _{3 containers} is made with short lengths of MS cable. The test voltages are provided to a transformer T of the generating plant DEA.

In the first container CT ₁ a switchgear with circuit breakers including test switches is arranged. The switchgear of the container CT ₁ includes the switches S ₁ , S ₅ , S ₆ , S ₇ , S ₈ and S ₉ .

Furthermore, measuring devices M _E such as current transformers and voltage transformers are provided in the container CT _{1 on the} input side. On the output side, measuring devices M _A such as current transformers and voltage transformers are also arranged. Other measuring devices, not shown, such as current transformers can also be arranged in parallel branch. The measuring devices M _E and M _A can be used for measuring the reaction of the generating plant DEA, wherein the result of the measurement of a not shown computer-based evaluation in the container CT ₁ can be supplied. In the container CT ₁ surge arresters and a control system are also arranged.

In the second container CT ₂ , the parallel branch of the series resonant circuit is arranged. The parallel branch consists of the capacitive resistor C, the damping resistor R _D , the parallel connected discharge resistor R _E and the discharge throttle L _E. In the container CT ₂ switches S ₂ and S ₁₀ are further arranged.

In the third container CT ₃ , the series branch of the resonant circuit is arranged. The serial branch includes the inductive resistor L.

In addition, a further inductive resistor L _{P is} arranged in the container CT ₃ , which is arranged parallel to the parallel branch of the resonant circuit. This parallel inductive resistor L _P can be used together with the inductive resistor L in the series branch in the sense of an inductive divider to provide a reduced compared to the mains voltage test voltage. This operating mode of the test circuit is possible even without the presence of the container CT ₂ .

In the case of using the inductive voltage divider can be adjusted by the ratio of the two adjustable Teilerimpedanzen L and L _P desired for the generating system residual voltage.

After switching on the resonant circuit or the inductive voltage divider, the electrical properties of the decentralized generation system DEA are measured, so that the reaction of the DEA generating system can be checked for an overvoltage or a voltage dip.

If the voltage is to be increased in only one or two phases, the connection of the parallel branch with capacitor C and resistor R can be effected in one or two phases. The star point of the parallel branch should be identical to that at the transformer of the network, so that the phase position of the current in the parallel branch is about 90 ° leading to the corresponding phase-earth voltage. If this is not the case, the addition of the voltage drop across the inductance L is no longer in phase with the phase-earth voltage and the voltage increase is uneven in the two phases involved.

The use of compensation coils between transformer star point and ground, isolated star points and possibly high earth resistances can not always guarantee that the two star points are at the same potential. To circumvent this, it is possible to carry out the test in general three-phase and only through those affected branches II to the generating unit DEA, which are needed. For this purpose, it makes sense in two of three phases in each case two single-pole circuit breaker S ₁₁ according to the 9 insert. The circuit breaker S ₁₁ , are arranged between parallel branch and generating DEA. Branch I is thus unaffected.

Reference numerals:

• C

  capacitive resistance

  DEA

  decentralized generation plant

  I

  uninfluenced branch

  II

  affected branch

  L

  inductive resistance

  L _E

  discharge reactor

  L _P

  inductive resistance in parallel branch

  M _A

  Measuring device (output side)

  M _E

  Measuring device (input side)

  N

  network

  P

  test circuit

  R _D

  damping resistor

  R _E

  discharge

  S ₁ -S ₁₁

  switch

  SP

  star point

  T

  transformer

  Prob

  Surge arresters

  Z _N

  Line impedance

Claims (17)

A decentralized electrical generating system connected to a grid (N), characterized by a test circuit (P) for testing the reaction of the generating plant to an overvoltage with an inductive resistor switchable between the generating plant (DEA) and the grid (N) (L) and a capacitive resistor (C) for providing a test overvoltage, wherein the capacitive resistor (C) via a switch (S ₂ ) is switchable. Decentralized electrical generation plant according to claim 1, characterized in that the resonant circuit is a series branch, in which the inductive resistor (L) is arranged and connected in series with the impedance of the network (N), and a parallel branch, in which the capacitive resistance (C) is arranged, wherein the voltage across the parallel branch represents the power plant (DEA) provided test overvoltage. Decentralized electrical generating plant according to claim 2, characterized in that in the parallel branch, a damping resistor (R _D ) is arranged, which is arranged in particular in series with the capacitive resistor (C). Decentralized electrical generation plant according to one of claims 2 to 3, characterized in that in the parallel branch a, in particular switchable, discharge resistor (R _E ) is arranged, which is arranged in particular parallel to the capacitive resistor (C). Decentralized electrical generating plant according to one of claims 2 to 4, characterized in that parallel to the parallel branch, in particular adjustable, switchable inductive resistor (L _P ) is arranged, by means of the generating plant (DEA) compared to the mains voltage reduced test voltage can be provided , Decentralized electrical generating installation according to one of the preceding claims, characterized in that the resonant circuit can be bypassed via a bypass switch (S ₇ ). Decentralized electrical generating installation according to one of the preceding claims, characterized in that the inductive resistor (L) can be bridged via a bypass switch (S ₁ ). Decentralized electrical generating installation according to one of the preceding claims, characterized by a surge arrester (ÜA) at the input and / or at the output of the test circuit (P). Decentralized electrical generating installation according to one of the preceding claims, characterized in that the capacitive resistor (C) and / or the inductive resistor (L) are adjustable. Decentralized electrical generation plant according to one of the preceding claims, characterized in that the capacitive resistor (C) consists of a plurality of parallel and / or series-connected capacitors and / or that the inductive resistor (L) of a plurality of series and / or parallel-connected coils consists. Decentralized electrical generating installation according to one of the preceding claims, characterized in that the mains voltage is the input voltage of the test circuit (P). Decentralized electrical generating plant according to one of the preceding claims, characterized in that the test circuit (P) in one or more mobile containers (CT1, CT2, CT3) is arranged. Decentralized electrical generation plant according to one of the preceding claims, characterized in that it is designed as a wind energy plant. Test circuit for testing the response of a decentralized electrical generation plant (DEA) connected to a grid (N) to an overvoltage, characterized by a resonant circuit with an inductive resistor (L) and a switchable circuit between the generating plant (DEA) and the grid (N) capacitive resistor (C) for providing a test overvoltage, wherein the capacitive resistor (C) via a switch (S ₂ ) is switchable. Test circuit according to claim 14, characterized by a surge arrester (UA) arranged at the input and / or the output. Method for testing the response of a decentralized electrical generating installation (DEA) connected to a grid (N) to an overvoltage, characterized in that by means of an oscillating circuit connected between the generating station (DEA) and the grid (N) with an inductive resistor (L ) and a capacitive resistor (C) a test overvoltage is generated, wherein the capacitive resistor (C) via a switch (S ₂ ) is switched on. A method according to claim 16, characterized in that after connecting the resonant circuit electrical properties of the generating plant (DEA) are measured.

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