Broadband low-inductance ohmic-capacitive voltage divider for a partial discharge measurement

Abstract

The invention relates to a broadband low-inductance ohmic-capacitive voltage divider (1) for a partial discharge measurement, having at least one first part (T1) and at least one second part (T2), wherein the first part (T1) and the second part (T2) are connected in series in order to serve as a voltage divider (1), an inductively based partial discharge measuring device (TEL) i. is integrated into the first part (T1) or the second part (T2) or ii. is provided between the first part (T1) and the second part (T2), and the ohmic elements as well as the capacitive elements of the first part (T1) and of the second part (T2) are adapted to one another such that a low-impedance current flow through the partial discharge measuring device at a frequency which differs from the grid frequency and which is higher than 150 KHz is made possible.

Description

[0001] Low-inductance and broadband resistive-capacitive voltage divider for

[0002] Partial discharge measurement

[0003] The invention relates to a low-inductance and broadband resistive-capacitive voltage divider for partial discharge measurement.

[0004] background

[0005] In power transmission networks, voltage dividers and transformers are used in switchgear to measure the nominal values ​​of current and voltage; these are typically separate devices for AC and DC voltage. Partial discharge sensors may also be installed elsewhere in the switchgear to monitor the equipment for faults and aging.

[0006] The integration of electrically controlled systems such as car charging stations, PV systems, etc., makes monitoring the voltage quality particularly necessary to ensure grid security.

[0007] Monitoring partial discharges and voltage quality contributes to ensuring power supply quality.

[0008] Current voltage dividers are manufactured using thin wound wires, discrete high-voltage resistant elements, or woven resistive elements, and while they exhibit some good parasitic properties, their manufacturing is complex.

[0009] Due to their inherent complexity, only a few manufacturers are able to offer such voltage dividers. This, in turn, results in limited production volumes while demand is constantly increasing. Although the applicant has made efforts in the past to offer alternatives, these have not yet been commercialized.

[0010] Similar problems and solutions exist in other areas of technology. However, these solutions are very specific and not universally applicable, which hinders their wider dissemination and use.

[0011] For example, a resistive-capacitive divider for measuring high voltage is described in the article "Development of Broadband Resistive-Capacitive Parallel-Connection Voltage Divider for Transient Voltage Monitoring" by Shijun Xie et al., published in Energies 2022, 15, 451. https: / / doi.org / 10.3390 / enl5020451. However, due to its RCR design (i.e., resistors are also connected in series in the capacitive path), the divider shown there is unable to provide a low-frequency path for partial discharge measurement, as the divider exhibits a high overall impedance even at high frequencies.

[0012] Task

[0013] Based on this, it would be advantageous to be able to offer solutions that allow for the cost-effective and easily scalable voltage dividers suitable for partial discharge measurement.

[0014] Brief description of the invention

[0015] The problem is solved by a device according to claim 1. Advantageous uses are also specified in the further claims. Further advantageous embodiments are the subject of the description and the figures.

[0016] Brief description of the figures: The invention will be described in more detail below using the figures. These show

[0017] Fig. aa shows the basic measurement setup according to embodiments of the invention,

[0018] Fig. 1b shows the basic measurement setup according to embodiments of the invention, taking into account parasitic elements.

[0019] Fig. 2 shows a schematic impedance curve of voltage dividers and a partial discharge measuring device according to embodiments of the invention,

[0020] Fig. 3 shows an exemplary embodiment of a voltage divider,

[0021] Fig. 4 shows a side view of part of an exemplary embodiment,

[0022] Fig. 5 shows a perspective view of part of an exemplary embodiment, and

[0023] Fig. 6 shows a frontal view of part of an exemplary embodiment.

[0024] Detailed presentation

[0025] The invention will now be described in more detail with reference to the figures. It should be noted that different aspects are described, each of which can be used individually or in combination. That is, each aspect can be used with different embodiments of the invention, unless explicitly presented as a pure alternative.

[0026] Furthermore, for the sake of simplicity, reference will generally be made to only one entity at a time. Unless explicitly stated otherwise, the invention may also include several of the entities concerned. Therefore, the use of the words "a", "an", and "one" should only be understood as an indication that at least one entity is used in a simple embodiment.

[0027] The following description refers to the illustrations. As a rule, identical or similar elements will be designated with the same or similar reference symbols. In embodiments of the invention, a low-inductance, broadband resistive-capacitive voltage divider 1 is provided for partial discharge measurement.

[0028] This voltage divider 1 has – as shown in Figure 1a – at least a first part TI and at least a second part T2. The first part TI and the second part T2 are connected in series to serve as voltage divider 1. Furthermore, the voltage divider 1 includes an inductively based partial discharge measuring device TEL.

[0029] The inductively based partial discharge measuring device TEL can be positioned in different ways. For example, it is possible that the partial discharge measuring device TEL is integrated into the first part TI or the second part T2. It is also possible – as indicated in Figure 1 – that the partial discharge measuring device TEL is arranged between the first part TI and the second part T2 – essentially in series within the voltage divider itself.

[0030] The ohmic element(s) R1 T I, R2 T I as well as the capacitive element(s) C Ti of the first part TI and the ohmic element(s) R1 T 2, R2 T 2 as well as the capacitive element(s) C TThe two components of the second part T2 are coordinated in such a way that a low-impedance current flow through the partial discharge measuring device TEL is enabled at a frequency different from the mains frequency, which is higher than 150 kHz.

[0031] Technically speaking, the voltage divider therefore has an ohmic part (left dashed frame in Fig. 1a) and a parcel-capacitive part (right dashed frame in Fig. 1a).

[0032] The voltage divider constructed in this way generally also exhibits parasitic inductances and / or parasitic resistances, which are taken into account in the equivalent electrical circuit diagram of Figure 1b. Alternatively or additionally, specific inductances and / or parasitic resistances, e.g., as SMB components, can also be provided. A corresponding exemplary impedance curve is shown in Figure 2. As can be seen, the transfer impedance curve of the partial discharge measuring device TEL shows an exemplary high value at the mains frequency, while it drops to a low value at a significantly higher frequency. The transfer impedance results, for example, from the output voltage relative to the input current. That is, for low frequencies, the transfer impedance is low, meaning that an input current will only induce a very small output voltage. In Figure 2, at approximately...At 2 MHz, the transfer impedance of the TEL is higher, and therefore the same input current will result in a higher output voltage.

[0033] This means that the partial discharge measuring device (TEL) can be designed as a high-frequency current transformer (HFCT). Such partial discharge measuring devices (TEL) can have one or more highly permeable cores with associated electrical windings.

[0034] In other words, the partial discharge measurement device (TEL) can be integrated into the voltage divider. Partial discharge measurement can be achieved by coupling high-frequency current pulses using magnetic fields. Within the overall system, the parasitic properties resulting from resonance phenomena in the broadband voltage sensor can be exploited and tuned using discrete circuit boards, so that the divider becomes a low-impedance coupling path in the case of resonance, while the high impedance is used for DC and AC voltages.

[0035] The low impedance in the resonance case leads to an increase in the measurement sensitivity of the partial discharge measurement.

[0036] In one embodiment of the invention, the first part TI of the voltage divider 1 is provided on a circuit board. Likewise, in one embodiment of the invention, the second part T2 of the voltage divider 1 can be provided on a circuit board.

[0037] This allows for cost-effective production even in high volumes, while maintaining good quality and low variation in properties. According to a further embodiment of the invention, at least some of the ohmic element(s) R1 exhibit T I, R2 T I as well as the capacitive elements C Ti of the first part TI and the ohmic element(s) R1 T 2, R2 T 2 as well as the capacitive element(s) C T 2 of the second part T2 has a low temperature coefficient.

[0038] In a further embodiment of the invention, at least a part of the ohmic element(s) RITI, R2 T I as well as the capacitive elements C Ti of the first part TI and the ohmic element(s) R1T2, R2T2 as well as the capacitive element(s) C T 2 of the second part T2 are provided as concentrated SMD components.

[0039] According to yet another embodiment of the invention, the voltage divider 1 provides a low-pass or band-pass characteristic.

[0040] In yet another embodiment of the invention, the partial discharge measuring device TEL is suitable for detecting currents at a frequency of more than 150 kHz.

[0041] Furthermore, in an embodiment of the invention, the bandpass characteristic of the voltage divider 1 can be matched to the frequency characteristic of the inductively based partial discharge measuring device TEL.

[0042] Likewise, in an embodiment of the invention - as indicated in Figure 3 - a plurality of first parts TI and second parts T2 can be provided alternately in a series circuit.

[0043] For example, the multitude of first parts TI and second parts T2 can be arranged helically around a support TR.

[0044] Without limiting the generality, a voltage divider 1 according to the invention can be designed for an applied voltage of 1 kV and more. Likewise, a voltage divider 1 according to the invention can be designed such that the current flow is limited for very high frequencies.

[0045] It should be noted that a remaining (parasitic) residual inductance L T I, L T This can result in a limited current flow for very high frequencies. However, even then, a frequency window for low-impedance current measurement is established.

[0046] In embodiments of the invention, the transfer characteristic of the voltage divider can be adapted to the transfer characteristic of the (integrated) partial discharge measuring device TEL, so that the partial discharge measurement occurs in the resonance case of the voltage divider 1. This design allows for improved sensitivity in the partial discharge measurement, while the voltage signal (DC voltage signal, AC voltage signal with mains frequency) and harmonics are not affected.

[0047] A partial discharge measuring device TEL arranged in the voltage divider 1 thus enables the detection of partial discharges in the voltage divider 1 itself and adjacent equipment.

[0048] The advantage is that currents through the voltage divider 1 in the frequency range below 1 MHz, i.e. especially in the range of the mains frequency, are very low, and in addition, a partial discharge measuring device TEL can be designed so that it is not sensitive at low frequencies, so that the mains frequency currents are not detected.

[0049] Partial discharges generally result in broadband and high-frequency equalizing currents, which can be detected very sensitively due to the transmission characteristics of voltage divider 1 and partial discharge measuring device TEL.

[0050] Without limiting the generality of the invention, it can be used in both DC and AC networks. It should be noted that the frequency at which the partial discharge measuring device (TEL) becomes sensitive can be adjusted by selecting a suitable core material and a suitable number of windings. For example, the partial discharge measuring device (TEL) can have a (ring) core made of ferrite (e.g., a mixed material, manganese-zinc, or nickel-zinc) or a nanocrystalline material with a corresponding number of primary and / or secondary windings, which can be used to adjust the frequency in the high-voltage circuit and / or the voltage transfer ratio.For example, it may be sufficient to simply pass a connecting cable between a first part TI and a second part T2 through a toroidal core, while on the secondary side one or a few turns are sufficient to tap off a partial discharge voltage (for a measurement).

[0051] For example, the partial discharge measuring device TEL can be set so that the resonant frequency of the voltage divider 1 and the sensitive frequency range overlap.

[0052] Advantageously, the voltage divider 1 has low inductance and high precision.

[0053] For example, the first part TI and / or the second part of the voltage divider 1 can be manufactured using circuit boards on which SMD components for the inductive elements L are mounted. T I, L T 2. capacitive elements C T i, C T 2 and / or resistive elements R1 T I, R2 TI, R1T2, R2T2 are applied.

[0054] The use of circuit boards allows for the routing of conductive traces in such a way that parasitic effects can be minimized. At the same time, SMD components exhibit a low temperature coefficient. This is particularly true for NPO capacitors (as an example of capacitive elements). T i, C T 2) are fully temperature compensated.

[0055] The circuit boards can be designed in suitable quantities with nominal capacitance and resistance such that a series resonant circuit is created by the connecting elements. This allows for the precise and cost-effective production of large quantities of the first TI and second T2 components. In the resonance case, a low-impedance measurement path for high-frequency currents is created, which is advantageous for partial discharge measurements. To achieve the highest possible resonant frequency, the nominal capacitance and voltage divider ratio can be appropriately selected, and the divider can be designed with low inductance.

[0056] Furthermore, stray capacitances can be taken into account for high voltage levels, which could otherwise have a negative impact on the resonant circuit and the measurement accuracy of the sensors.

[0057] In this regard, a design of the internal structure can be used in which the electric field direction of the circuit boards is specifically played off against each other (PCB field grating) in order to homogenize the stray capacitance of the equipment.

[0058] Due to the planar design of circuit boards, a preferred orientation is given in particular, which cannot be achieved with conventional components.

[0059] The nested design in the form of a helix structure with horizontal arrangement of the circuit boards corresponding to the first part TI and the second T2 - as shown in Figure 3 - results in a directed field (e.g. towards earth), which reduces the susceptibility to earth scattering capacitances.

[0060] For example, a first part TI and / or a second part T2 – as shown in different perspectives in Figures 4-6 – can have a fastening element B with which the first part TI and / or the second part T2 can be attached to a support TR, e.g., by means of a screw connection. Furthermore, each part can in turn consist of two circuit boards, with a first circuit board PI containing the resistive component R1. T I, R2 T I, R1T2, R2 T 2 and a second circuit board P2 the capacitive component C T i, C T 2

[0061] Advantageously, the voltage divider 1 according to the invention can be designed to be broadband. With a broadband design of the device, partial discharges can be recorded relative to ripple voltages, harmonic oscillations, or even transients. It should be noted that, simultaneously with a voltage measurement for power quality / voltage

[0062] Due to the different frequency components at which these are measured, partial discharge measurement is also possible.

Claims

Claims 1. Low-inductance and broadband resistive-capacitive voltage divider (1) for partial discharge measurement, comprising • At least a first part (TI) and • At least a second part (T2), • Where the first part (TI) and the second part (T2) are connected in series to serve as a voltage divider (1), • wherein an inductively based partial discharge measuring device (TEL) is i. integrated into the first part (TI) or the second part (T2), or ii. arranged between the first part (TI) and the second part (T2), • wherein the ohmic elements as well as the capacitive elements of the first part (TI) and the second part (T2) are matched to each other in such a way that a low-impedance current flow through the partial discharge measuring device (TEL) is enabled at a frequency other than the mains frequency which is higher than 150 kHz.

2. Voltage divider (1) according to claim 1, characterized in that the first part (TI) of the voltage divider (1) is printed on a circuit board.

3. Voltage divider (1) according to claim 1 or 2, characterized in that the second part (T2) of the voltage divider (1) is printed on a circuit board.

4. Voltage divider (1) according to one of the preceding claims, characterized in that at least a part of the ohmic or capacitive elements of the first part (TI) and / or the second part (T2) have a low temperature coefficient.

5. Voltage divider (1) according to one of the preceding claims, characterized in that at least a part of the ohmic or capacitive elements of the first part (TI) and / or the second part (T2) are provided as lumped SMD components.

6. Voltage divider (1) according to one of the preceding claims, characterized in that the voltage divider (1) provides a low-pass or band-pass characteristic.

7. Voltage divider (1) according to one of the preceding claims, characterized in that the partial discharge measuring device (TEL) is suitable for detecting currents at a frequency of more than 150 kHz.

8. Voltage divider (1) according to one of the preceding claims, characterized in that the bandpass characteristic of the voltage divider (1) is matched to the frequency characteristic of the inductively based partial discharge measuring device (TQL).

9. Voltage divider (1) according to one of the preceding claims, characterized in that a plurality of first parts (TI) and second parts (T2) are provided alternately in a series circuit.

10. Voltage divider according to claim 8, characterized in that the plurality of first parts (TI) and second parts (T2) are arranged helically around a support (TR).

11. Voltage divider (1) according to one of the preceding claims, characterized in that the applied voltage is 1 kV or more.

12. Voltage divider (1) according to one of the preceding claims, characterized in that the current flow is limited for very high frequencies.

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