Patent Application
20240159816
This application claims the benefit of priority from French Patent Application No. 22 11411, filed on Nov. 2, 2022, the entirety of which is incorporated by reference.
The present invention relates to a device and to a method for applying and measuring a transient overvoltage in an electrical cable.
The invention belongs to the field of electrical cables intended to transport energy and/or to transmit data. It is particularly applicable to the field of analysing the behaviour of the electrical insulation of high-voltage direct current cables in the event of transient overvoltage (TOV).
In the field of HVDC (high-voltage direct current) cables, validation tests are required not only under DC power, but also to check the behaviour of the electrical insulation system of the cable in the event of unconventional waveforms occurring, such as temporary overvoltages with a very slow rising edge.
Currently, these validation tests are generally carried out on real insulation systems and on real cables. The process takes time and is expensive.
It is necessary to be able to carry out these tests in the laboratory on insulating plate specimens and/or cables of reduced dimension that are representative of real insulation systems and cables in order to study, more rapidly and at low cost, the electrical properties of the insulation system when it is subjected to an uncommon waveform of this kind.
The present invention aims to rectify the abovementioned drawbacks of the prior art.
For this purpose, the present invention proposes a device for applying and measuring a transient overvoltage in an electrical cable, comprising:
Therefore, by virtue of a simple and inexpensive electrical circuit, the present invention makes it possible to perform validation tests in the laboratory on insulation system specimens and/or on mini-cables more rapidly and more economically than in the field.
In one particular embodiment, the device also comprises at least one protective resistor.
This makes it possible not to damage the test specimen while studying its behaviour upon the occurrence of the overvoltage.
In one particular embodiment, the high-voltage switch comprises at least one high-voltage fast transistor.
This makes it possible to quickly create an overvoltage and, in combination with the control resistor and the decoupling capacitor, to easily adjust the characteristics of the waveform associated with the overvoltage for the purposes of the validation test of the specimen.
In one particular embodiment, the test specimen is an electrically insulating plate having a thickness between 500 μm and 1.5 mm.
This makes it possible to reconstruct, at low cost, and on the small scale of the test laboratory, the electrical properties of an insulation system that are equivalent to those of a real electrical insulation system of a cable.
As a variant, the test specimen is a high-voltage direct current mini-cable having an insulation with a thickness of 1.5 mm.
This thickness of 1.5 mm should be compared with a thickness of 20 mm of insulation for a real cable, which shows the saving made by using a specimen and not a real cable.
For the same purpose as that indicated above, the present invention also proposes a method for measuring a transient overvoltage in an electrical cable by way of a device, as described succinctly above, noteworthy in that it comprises steps of:
In one particular embodiment, the overvoltage is equal to 0.7 U0, where U0 denotes the predetermined DC voltage.
Since the particular features and the advantages of the method are similar to those of the device, they are not repeated here.
Other aspects and advantages of the invention will become apparent on reading the detailed description below of particular embodiments, which are given by way of entirely non-limiting examples, with reference to the appended drawings, in which:
The circuit diagram in
The device 10 comprises a test specimen, which is illustrated by dashes in the drawing and representative of the electrical cable.
By way of non-limiting example, this test specimen may be an electrically insulating plate having a thickness between 500 μm and 1.5 mm, or else a high-voltage direct current mini-cable having an insulation with a length of 1.5 mm.
The device 10 also comprises a first DC voltage generator DCS designed to generate a predetermined DC voltage U0. One terminal of the first DC voltage generator DCS is connected to earth and the other terminal thereof is connected to the test specimen, which is, moreover, also connected to earth. The first DC voltage generator DCS is therefore designed to apply the voltage U0 to the test specimen.
The device 10 also comprises a second DC voltage generator DC2 designed to generate a predetermined overvoltage. In the particular embodiment of
In order for the overvoltage to be applied only temporarily, the device 10 also comprises a high-voltage switch 12. One terminal of the high-voltage switch 12 is connected to earth and the other terminal thereof is connected to the second DC voltage generator DC2. The high-voltage switch 12 is designed to convert the overvoltage into a voltage, the waveform of which is a square wave, with a view to applying it to the test specimen.
By way of entirely non-limiting example, the high-voltage switch 12 can be closed for 130 ms, that is to say that, during this time interval, the + and − terminals of the high-voltage switch 12 are connected to one another. The overvoltage 0.7 U0 is then applied to the test specimen for 130 ms.
By way of entirely non-limiting example, the high-voltage switch 12 can comprise at least one high-voltage fast transistor. In the particular embodiment shown, the high-voltage switch 12 is a high-voltage fast transistor.
In order to monitor the voltage rise time of the test specimen when the overvoltage is applied thereto, that is to say to measure this voltage rise time, the device 10 also comprises a control resistor R2, of which one terminal is connected to the second DC voltage generator DC2 and to the high-voltage switch 12 and the other terminal is connected to the test specimen and to earth.
Moreover, in order to monitor the overvoltage fall time in the test specimen, that is to say to measure this time when the overvoltage is no longer applied, the device 10 also comprises a decoupling capacitor C1, of which one terminal is connected to the second DC voltage generator DC2 and to the high-voltage switch 12 and the other terminal is connected to the test specimen and to earth.
Optionally, the device 10 can also comprise one or more protective resistors. In the particular embodiment shown, the device 10 comprises a first protective resistor R1 connected between the second DC voltage generator DC2 and the high-voltage switch 12 and a second protective resistor R3, of which one terminal is connected to the first DC voltage generator DCS and the other terminal is connected between, on the one hand, the test specimen and, on the other hand, the second DC voltage generator DC2 and the high-voltage switch 12.
The graph in
The voltage at the start of the test is U0. Then, when the overvoltage 0.7 U0 is applied to the test specimen, the voltage reaches a peak U1, the value of which therefore being 1.7 U0.
The control resistor R2 makes it possible to measure the time interval T1 between the start of the voltage rise and the voltage peak U1. Typically, it is found that T1 is between 1 and 3 ms.
The decoupling capacitor C1 makes it possible to measure the time interval T2 during which the voltage exceeds 90% of its maximum value (namely 0.9. (U1-U0), as shown on the graph). Typically, it is found that T2 is between 10 and 150 ms.
Therefore, the method, according to the present invention, for measuring a transient overvoltage of an electrical cable by way of the device 10 comprises the following steps.
The first DC voltage generator DCS applies the predetermined DC voltage U0 to the test specimen.
Then, the second DC voltage generator DC2 applies the predetermined overvoltage, 0.7 U0 in the non-limiting example given here, in the form of a square wave provided by the high-voltage switch 12, to the test specimen.
The control resistor R2 then monitors, i.e. measures, the voltage rise time T1 of the test specimen and the decoupling capacitor C1 monitors, i.e. measures, the overvoltage fall time T2.
Therefore, the device 10 and the method according to the invention make it possible to monitor the waveform associated with the applied overvoltage, in particular the voltage rise time T1 and the overvoltage fall time T2, precisely, rapidly and at low cost.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2211411 | Nov 2022 | FR | national |
