Partial discharge measuring device for AC rotating electric machines, method for determining partial discharge of AC rotating electric machines
The partial discharge measuring device for AC rotating electric machines uses a metal foil electrode and detection resistor with a high-pass filter to measure voltage signals, addressing the costs and risks of existing methods, and accurately calculates Qmax using cumulative relative frequency, ensuring safe and efficient diagnosis.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- JFE PLANT ENG CO LTD
- Filing Date
- 2024-11-13
- Publication Date
- 2026-05-25
AI Technical Summary
Existing partial discharge measurement methods for AC rotating electric machines are costly, require equipment modification, and pose a risk of ground faults, while existing methods for power cables do not accurately measure partial discharges in rotating electric machines and require complex noise reduction techniques.
A partial discharge measuring device using a metal foil electrode attached to the power cable near the lead wire end, connected to a detection resistor and grounded, with a high-pass filter to measure voltage signals, eliminating the need for coupling capacitors and allowing for easy installation without modification, and calculating maximum discharge charge (Qmax) using cumulative relative frequency.
Enables cost-effective partial discharge measurement in AC rotating electric machines without equipment retrofitting, reduces the risk of ground faults, and accurately determines maximum discharge charge (Qmax) even when frequency information is unclear, using a simple and efficient method.
Smart Images
Figure 2026085323000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a partial discharge measuring device for measuring partial discharge occurring in an AC rotating electrical machine, and a partial discharge determination method for determining partial discharge based on the measurement results of the partial discharge measuring device.
Background Art
[0002] As one method for detecting partial discharge generated due to insulation deterioration of an AC motor or an AC generator (hereinafter referred to as "AC rotating electrical machine"), for example, there is a coupling capacitor method for measuring partial discharge by a coupling capacitor connected in parallel to the main circuit of the rotating electrical machine as in Patent Document 1.
[0003] In Patent Document 1, a circuit configuration in which a coupling capacitor is connected in parallel to the main circuit of the rotating electrical machine and connected to the ground is used to detect partial discharge signals by a plurality of sensors. Further, as another detection means using a coupling capacitor, a circuit configuration in which a coupling capacitor is connected in parallel to the main circuit of the rotating electrical machine and connected to the ground via a detection resistor R may be used. In this case, since the partial discharge signal passing through the coupling capacitor passes through the known detection resistor R and flows to the ground, a voltage proportional to the magnitude of the partial discharge signal is generated at both ends of the detection resistor R. By measuring this voltage with a partial discharge measuring instrument, the partial discharge signal is measured.
[0004] The coupling capacitor method, which is one method for detecting partial discharge generated due to insulation deterioration of a rotating electrical machine, allows the capacitance of the coupling capacitor C to be arbitrarily selected. The reactance of the coupling capacitor can be calculated by Xc = 1 / (2πfC). For example, when using a coupling capacitor with a capacitance of 80 pF, a signal with a commercial frequency f = 60 Hz of the rotating electrical machine has a high reactance of Xc ≒ 33 MΩ. Therefore, the coupling capacitor serves as a high-pass filter that hardly passes signals of the commercial frequency. Also, the frequency of the partial discharge signal generated in the rotating electrical machine is a high-frequency signal in the kHz to MHz band. Therefore, the partial discharge signal can be detected by passing through the coupling capacitor.
[0005] Furthermore, in the field of measuring partial discharge in power cables, for example, there is the disclosure of a "partial discharge detection device" in Patent Document 2. The invention disclosed in Patent Document 2 is described as follows: "A partial discharge detection device comprising: a detection means provided on an insulating coating layer of a power cable, which receives high-frequency components of a signal generated inside the power cable by a partial discharge pulse and propagating through the outer conductive layer of the power cable via the coating layer; and a signal processing means for processing the output of the detection means, wherein the detection means includes an electrode mounted on the coating layer of the power cable and an inductance element coupled in series with the coupling capacitance of the electrode to the outer conductive layer to exhibit resonant characteristics." (See Claim (1) of Patent Document 2)
[0006] Furthermore, the maximum discharge charge amount (Qmax), which can be managed as an absolute value in terms of trend, is used as an evaluation index for partial discharge associated with insulation degradation in rotating electrical machines. The maximum discharge charge amount (Qmax) is determined by measuring the frequency of partial discharge occurrence or partial discharge pulses within a unit time, as described in Patent Document 1, and treating the amount of discharge charge that occurs a predetermined number of times within a certain period of time (for example, 1 second or 1 cycle) as the maximum discharge charge amount (Qmax). The maximum discharge charge (Qmax) is defined, for example, in the international standard (IEC60270), as the discharge charge amount that occurs at a frequency of 10 pulses / second (10 pps).
[0007] Other evaluation indicators include the PRPD (Phase Resolved Partial Discharge) pattern (Φ-qn pattern), where the x-axis represents the phase angle (0-360°), the y-axis represents the discharge charge amount (discharge magnitude), and the z-axis represents the discharge frequency (hue). This pattern makes it easy to intuitively understand the characteristics of partial discharge, and allows for the estimation of the discharge location based on the characteristics of the partial discharge. Relatively inexpensive diagnostic devices using this pattern are becoming more common. [Prior art documents] [Patent Documents]
[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-138168 [Patent Document 2] Japanese Patent Application Publication No. 4-181177 [Overview of the project] [Problems that the invention aims to solve]
[0009] While the coupling capacitor method disclosed in Patent Document 1 offers high detection accuracy, the coupling capacitor itself is expensive. Furthermore, for example, when diagnosing a rotating electric machine in operation, equipment such as the coupling capacitor must be permanently installed beforehand, requiring costly modification work on existing equipment. Furthermore, because the coupling capacitor is connected to the main circuit, there is a non-zero risk of a ground fault occurring due to a failure of the coupling capacitor.
[0010] Furthermore, in partial discharge measurements during operation, for example, noise signal removal is crucial. Patent document 1, for instance, discriminates noise by detecting and comparing the signals for each phase with a common signal for all three phases. However, implementing this method requires a diagnostic device with multiple channels or multiple single-channel diagnostic devices, resulting in high-cost diagnostic equipment.
[0011] The method disclosed in Patent Document 2 is specifically for measuring partial discharges occurring in power cables and does not mention the measurement of partial discharges in rotating electric machines, etc. Furthermore, the partial discharge signals generated in power cables are minute compared to those of rotating electric machines, making it essential to select and connect an appropriate inductance L (coil) for noise reduction and improved sensitivity.
[0012] Furthermore, in order to calculate the aforementioned maximum discharge charge (Qmax), information such as the frequency and magnitude of partial discharges within a unit time is required, as described in Patent Document 1. However, while inexpensive commercially available diagnostic devices that emphasize evaluation using PRPD patterns (Φ-qn patterns) make it easy to intuitively understand the occurrence of partial discharges, they may not be able to calculate the maximum discharge charge amount (Qmax) because the frequency of partial discharges [pulses / second] is unclear.
[0013] This invention was made to solve the aforementioned problems, and aims to provide a partial discharge measuring device for AC rotating electric machines that is inexpensive, does not require modification work on existing equipment, and has a low risk of accidents. Furthermore, the aim is to provide a partial discharge detection method for determining partial discharge in an AC rotating electric machine by determining the maximum discharge charge amount (Qmax) when information on the partial discharge frequency [pulses / second] cannot be correctly obtained. [Means for solving the problem]
[0014] (1) The partial discharge measuring device according to the present invention measures partial discharge generated in an AC rotating electric machine, The present invention is characterized by comprising: a metal foil electrode of a predetermined area attached to the outer surface of the power main cable within 1 m from the lead wire end of the power main cable connected to the lead wire end of the AC rotating electric machine; a circuit with one end connected to the metal foil electrode and grounded via a detection resistor; and a partial discharge measuring instrument that measures a voltage signal caused by partial discharge occurring across the detection resistor by inputting it via a high-pass filter.
[0015] (2) A method for determining partial discharge of an AC rotating electric machine, which determines the degree of partial discharge by calculating the maximum discharge charge amount (Qmax) based on the measurement results measured by the partial discharge measuring device for the AC rotating electric machine described in (1) above, This method is characterized by calculating the maximum discharge charge (Qmax) using the cumulative relative frequency when the partial discharge frequency [pulses / second] is unclear. [Effects of the Invention]
[0016] According to the partial discharge measuring device of the present invention, a metal foil electrode with a predetermined area, a circuit having one end connected to the metal foil electrode and grounded through a detection resistor, and a voltage signal caused by partial discharge generated at both ends of the detection resistor are input through a high-pass filter and measured by a partial discharge measuring instrument. By having these components, unlike the conventional coupling capacitor method, it is not necessary to purchase a coupling capacitor or perform renovation work on existing equipment, and it is possible to easily measure existing equipment. In addition, it is not necessary to retrofit a coupling capacitor to a rotating electrical machine, and it is possible to diagnose the presence or absence of partial discharge without taking the risk of a ground fault accident due to a coupling capacitor failure, that is, with the risk being zero. Furthermore, an inductance L (coil) for noise removal and sensitivity improvement, which was essential in Patent Document 2, becomes unnecessary.
Brief Description of the Drawings
[0017] [Figure 1] It is an explanatory diagram of a partial discharge measuring device according to an embodiment of the present invention. [Figure 2] It is an explanatory diagram showing the main cable shown in FIG. 1 as an electric circuit.
Embodiments for Carrying Out the Invention
[0018] [Embodiment 1] The partial discharge measuring device 1 according to the present embodiment measures partial discharge generated in the AC rotating electrical machine 3, and includes a metal foil electrode 5, a circuit 7, and a partial discharge measuring instrument 9, as shown in FIGS. 1 and 2. Hereinafter, each component will be described in detail.
[0019] <Metal Foil Electrode> The metal foil electrode 5 is attached to the outer surface of the power main cable 13 within 1 m from the end of the lead wire 11 in the power main cable 13 connected to the end of the lead wire 11 (3-phase) in the AC rotating electrical machine 3. As shown in Figure 2, the main power cable 13 is composed of a main cable conductor 15, a main cable insulator 17, a main cable shielding layer 19, and a main cable outer sheath 21. By attaching metal foil electrodes 5 to the outer surface of the main power cable 13, the capacitance of the main cable outer sheath 21 can be used as a coupling capacitor to measure partial discharge.
[0020] As the metal foil electrode 5, a tape-shaped copper foil, lead foil, gold foil, or other material with excellent conductivity is preferred.
[0021] The metal foil electrode 5 was defined as having a "predetermined area" because the capacitance of the main cable outer sheath 21 can be adjusted by adjusting the area of the metal foil electrode 5. Therefore, the area adjusted to achieve the optimal capacitance was defined as the predetermined area.
[0022] Increasing the area to which the metal foil electrode 5 is attached improves sensitivity, but conversely, it becomes easier to pick up noise. Therefore, the area of the metal foil electrode 5 should be set to an optimal value based on the relationship between sensitivity and noise, depending on the AC rotating electric machine 3 being measured.
[0023] The reason for placing the metal foil electrode 5 within 1m of the end of the lead wire 11 is as follows: First, the ends of the lead wires 11 of the AC rotating electric machine 3 are normally housed in a terminal box and connected to the main power cable 13 in the terminal box 23 (see Figure 1). Therefore, the main power cable 13 connected thereto is used instead of the lead wires 11. Furthermore, the reason for setting the measurement point within 1m of the end of the lead wires 11 in the main power cable 13 is that the partial discharge signal attenuates as the distance from the partial discharge source to the metal foil electrode 5 increases. Since the purpose is to measure the partial discharge in the AC rotating electric machine 3, it is preferable to be close to the AC rotating electric machine 3, and it was confirmed that measurement is possible within 1m.
[0024] <Circuit> Circuit 7 has one end connected to the metal foil electrode 5 and is grounded via the detection resistor 25. The partial discharge signal generated in the AC rotating electric machine 3 passes through the metal foil electrode 5 and the known detection resistor 25, and flows to ground. As a result, a voltage proportional to the magnitude of the partial discharge signal is generated across the detection resistor 25.
[0025] <Partial discharge measuring device> The partial discharge measuring instrument 9 measures the voltage caused by the partial discharge occurring across the detection resistor 25 by inputting it through the high-pass filter 27.
[0026] In determining partial discharge based on measurement results from the partial discharge measuring instrument 9, the maximum discharge charge amount (Qmax) is generally used as an absolute value evaluation index for trend management. For example, the international standard (IEC60270) recommends treating the discharge charge amount that occurs at a frequency of 10 partial discharges per second (10pps: 10 pulses / second) as the maximum discharge charge amount (Qmax).
[0027] Therefore, in actual diagnosis, information such as the frequency of partial discharge [pulses / second] and the intensity of partial discharge (magnitude of discharge) is acquired, and the maximum discharge charge amount (Qmax) is calculated by the diagnostic device.
[0028] Furthermore, since the partial discharge signals generated by rotating electric machines (hundreds of pC to tens of thousands of pC) are relatively larger than those generated by power cables (several pC to several hundred pC), partial discharges can be detected without basically using inductance L (coil) for noise reduction or sensitivity improvement, as described in Patent Document 2.
[0029] The partial discharge measuring device 1 of the present invention comprises a metal foil electrode 5 of a predetermined area, a circuit 7 with one end connected to the metal foil electrode 5 and grounded via a detection resistor 25, and a partial discharge measuring instrument 9 that measures the voltage signal caused by the partial discharge occurring across the detection resistor 25 by inputting it via a high-pass filter 27. This eliminates the need to purchase coupling capacitors or modify existing equipment, as in the conventional coupling capacitor method, and allows for easy measurement of existing equipment. Furthermore, it eliminates the need to retrofit coupling capacitors to rotating electric machines, allowing for diagnosis of partial discharge without the risk of ground fault accidents caused by coupling capacitor failure, meaning the risk is zero. Furthermore, the inductance L (coil) required for noise reduction and sensitivity improvement, which was deemed essential in Patent Document 2, becomes unnecessary.
[0030] As described above, in actual diagnosis, information such as the frequency of partial discharge [pulses / second] and partial discharge intensity (magnitude of discharge) obtained from the partial discharge measuring instrument 9 is acquired, and the maximum discharge charge amount (Qmax) is calculated by the diagnostic device. However, some partial discharge measuring instruments prioritize judging by the partial discharge waveform (visual appearance) rather than absolute value evaluation indicators such as the maximum discharge charge (Qmax). In particular, relatively inexpensive partial discharge measuring instruments do not accurately provide information on the partial discharge frequency [pulses / second], and only provide information such as "the higher the partial discharge frequency (darker hue), the greater the number of occurrences." Therefore, it was not possible to calculate the maximum discharge charge (Qmax) using conventional calculation methods.
[0031] Therefore, in this invention, we have diligently investigated whether it is possible to calculate the maximum discharge charge amount (Qmax) even when information on the frequency of partial discharge [pulses / second] cannot be correctly obtained. As a result, we have found that by using the calculation of cumulative relative frequency, it is possible to calculate the maximum discharge charge amount (Qmax) in a manner similar to the conventional calculation method. For partial discharges, information data (such as discharge charge amount, phase angle, and numerical values corresponding to the hue and intensity of partial discharge frequency) obtained from a partial discharge measuring instrument that cannot correctly obtain information on the partial discharge frequency [pulses / second] can be organized using a calculation program to determine how often a predetermined amount of discharge charge occurs per second. From this data, the cumulative relative frequency can be calculated, and the discharge charge amount at which the relative frequency reaches a predetermined value can be defined as the maximum discharge charge amount (Qmax). [Explanation of Symbols]
[0032] 1 Partial discharge measuring device 3 AC Rotating Electric Machines 5 Metal foil electrode 7 circuits 9 Partial discharge meter 11 Lead wires 13. Main power cable 15 Main cable conductor 17 Main cable insulator 19 Main cable shielding layer 21 Main cable outer sheath 23 Terminal box 25 detection resistor 27 High-pass filter
Claims
1. A partial discharge measuring device for measuring partial discharges occurring in AC rotating electric machines, A partial discharge measuring device for an AC rotating electric machine, characterized by comprising: a metal foil electrode of a predetermined area attached to the outer surface of a main power cable connected to the lead wire end of the main power cable within 1 m from the lead wire end of the main power cable; a circuit with one end connected to the metal foil electrode and grounded via a detection resistor; and a partial discharge measuring device that measures a voltage signal caused by partial discharge occurring across the detection resistor by inputting it via a high-pass filter.
2. A method for determining partial discharge of an AC rotating electric machine, comprising calculating the maximum discharge charge amount (Qmax) based on the measurement results obtained by the partial discharge measuring device for the AC rotating electric machine described in claim 1, and determining the degree of partial discharge, A method for determining partial discharge in an AC rotating electric machine, characterized by calculating the maximum discharge charge amount (Qmax) using the cumulative relative frequency when the partial discharge frequency [pulses / second] is unclear.