METHOD FOR SHOCK TESTING OF AN ELECTRICAL SYSTEM

Description

[0001] The present invention relates to a method for impulse voltage testing of an electrical system according to the preamble of claim 1.

[0002] Such methods are known from the prior art. They are used to detect short circuits and insulation faults within a winding of electrical systems with coils, such as electric motors or generators. For this purpose, a charged capacitor is connected in parallel to the winding under test relatively quickly. This generates a relatively high voltage in the winding for a relatively short time. The energy stored in the capacitor discharges into the inductor. The energy then stored in the inductor discharges back into the capacitor. Due to damping losses, this process can be measured at the winding terminals as a damped oscillation. When the amplitude has fallen below a certain threshold or is no longer measurable, the process can be considered complete. Conclusions about the quality of the winding can be drawn from the course of the damped oscillation.In a properly functioning winding, the oscillation has a typical frequency and a characteristic amplitude profile. If there are significant deviations from this frequency and amplitude profile, the winding can be detected as faulty.

[0003] From US 3,869,664 A, an impulse voltage tester is known that simultaneously applies oppositely polarized impulse voltage pulses to a test winding and a standard winding. If the electrical properties of the two windings are asymmetrical, a differential voltage corresponding to the difference in voltages developed across the windings is applied to a fault detection circuit. If the asymmetry is sufficiently large, a fault is indicated.

[0004] In contrast, the present invention is based on the objective of increasing the repetition rate for multiple executions of the process.

[0005] This problem is solved by a method according to claim 1 and by a device according to claim 11. Embodiments of the invention are specified in the dependent claims.

[0006] First, an electrical voltage pulse is applied to the electrical system under test, for example, a winding of an electric motor or generator, via at least two electrical contacts of the system. The voltage pulse can be applied, for example, by connecting a capacitor in parallel with the winding. The amplitude of the voltage pulse can be reached within 50 ns to 1 µs after the capacitor is switched on. This is therefore a relatively high voltage that is reached very quickly when the capacitor is switched on.

[0007] The voltage pulse is triggered by connecting semiconductor elements to a first state. These semiconductor elements can, for example, be cascaded. This is advantageous for generating a voltage pulse with a particularly high voltage. In the first state, the semiconductor elements connect an electrical energy storage device, such as a capacitor, to the electrical system. It is particularly possible for the energy storage device to be connected in parallel to the electrical system in the first state of the semiconductor elements.

[0008] The semiconductor elements can be, for example, transistors, in particular bipolar transistors, insulated-gate bipolar transistors (IGBTs), field-effect transistors, metal-oxide-semiconductor field-effect transistors, junction field-effect transistors, and / or silicon carbide field-effect transistors. Each semiconductor element has a gate terminal. When the semiconductor elements are switched to the first state, a capacitance is charged at the gate terminal.

[0009] A voltage waveform is measured between the two electrical contacts immediately after the voltage pulse is applied. It is particularly possible to measure the voltage waveform during and immediately after the voltage pulse is applied. The voltage waveform comprises a damped oscillation. The oscillation can, for example, be sinusoidal. The voltage waveform can consist primarily of this damped oscillation.

[0010] The measured voltage profile is analyzed to detect partial discharges in the electrical system. The detection of such partial discharges also allows conclusions to be drawn about the quality of the electrical system.

[0011] The damped oscillation is actively terminated. In this context, active termination means, in particular, that the process causing the oscillation is interrupted. This could, for example, mean disconnecting the electrical connection between the electrical system and an energy storage device. The energy storage device could be, for instance, a capacitor connected in parallel to the electrical system to deliver the voltage pulse. Active termination explicitly does not mean waiting until the amplitude of the oscillation has been damped to such an extent that it is no longer measurable.

[0012] In addition to actively terminating the damped oscillation, the capacitances at the gate terminals can be actively discharged. This is advantageous for quickly switching the semiconductor elements back to a second state in which the electrical energy storage device is disconnected from the electrical system. If the semiconductor elements are transistors, for example, they can only be switched to the second state if the capacitances at the gate terminals are discharged. Only then is it possible to prepare the energy storage device to deliver another voltage pulse.

[0013] In this context, active discharge refers specifically to the discharge of the gate terminals via one or more components that are not used to charge the capacitors. These components could, for example, be a discharge resistor.

[0014] Unlike some other applications of semiconductor devices, active discharge cannot be achieved through simple grounding because the semiconductor devices are galvanically isolated from other components. Grounding would eliminate this galvanic isolation, which is necessary due to the high voltages involved.

[0015] Actively terminating the damped oscillation allows the process to be repeated particularly quickly. As long as the oscillation is ongoing, the energy storage device used to deliver the voltage pulse cannot be recharged to deliver the next pulse. Therefore, the faster the damped oscillation is terminated, the sooner the process can be repeated, since the energy storage device can be recharged after the oscillation is stopped. Actively discharging the capacitors also has the advantage that the energy storage device can be quickly recharged, and the semiconductor elements can then be switched back to their initial state to deliver the next electrical voltage pulse. In the production processes of electric motors or generators, pulse voltage tests are typically performed several times.The specific number of required impulse voltage tests is recommended in the relevant standards. If, for example, the oscillation is interrupted after less than 1 millisecond and normally lasts several milliseconds, the repetition rate for the impulse voltage tests can be increased accordingly. Thus, for example, 300 impulse voltage tests can be performed in less than 10 seconds. It is even possible to perform 100 impulse voltage tests in just one second. If the damped oscillation is not interrupted and lasts, for example, 20 milliseconds, several minutes are required for the same number of impulse voltage tests. This represents an enormous time saving, particularly in the industrial production of electric motors and generators.

[0016] Terminating the oscillation is possible without any disadvantages, since for the impulse voltage test with simultaneous partial discharge test, the voltage profile is only relevant immediately after the voltage surge. The subsequent course of the voltage does not need to be evaluated to reliably detect faults in the electrical system.

[0017] According to one embodiment of the invention, the damped oscillation can be terminated after one oscillation period or after half an oscillation period. Often, one oscillation period or even just half an oscillation period is sufficient for the impulse voltage test with partial discharge test.

[0018] It is also possible that the damped oscillation is terminated before an amplitude of less than 100 volts is measured in the damped oscillation.

[0019] It is also possible that the damped oscillation is terminated after less than 10 milliseconds, preferably after less than 1 millisecond.

[0020] It is possible for the semiconductor elements to electrically connect a single energy storage device to the electrical system. It is also possible for the semiconductor elements to electrically connect multiple energy storage devices to the electrical system.

[0021] According to one embodiment of the invention, the semiconductor elements can be galvanically isolated from one another. In particular, it is possible to switch the semiconductor elements galvanically isolated from one another, for example, to the first state. Galvanic isolation is advantageous when the semiconductor elements are cascaded and designed for switching very high voltages.

[0022] According to one embodiment of the invention, the damped oscillation can be terminated by switching the semiconductor elements to the second state. When the semiconductor elements are in the second state, the electrical connection between the electrical energy storage device and the electrical system is broken. This allows the energy storage device to be prepared for the next surge voltage test by recharging it with electrical energy.

[0023] According to one embodiment of the invention, the semiconductor elements can be switched to the second state by electrically discharging the capacitance of the gate terminal.

[0024] According to one embodiment of the invention, the capacitance of the gate terminal can be discharged via a thyristor or a transistor and a discharge resistor. As soon as the discharge of the gate terminal capacitance is to take place, the thyristor or the transistor is switched to conducting, so that the discharge of the gate terminal capacitance occurs via the discharge resistor.

[0025] According to one embodiment of the invention, the damped oscillation can be terminated after a certain period of time. This period can be defined by the discharge of a delay element. For the purposes of this description, a delay element is understood to be, in particular, a combination of a resistor and a capacitor, which may be connected in parallel. For example, after the period of time has elapsed, the delay element can switch on a discharge transistor, which in turn switches on the thyristor or the transistor.

[0026] According to one embodiment of the invention, the energy storage device can be recharged while the voltage pulse is being delivered. The delay element can also be recharged during this process. This ensures that the capacitance of the gate terminal is not discharged as long as the energy storage device is being recharged. Thus, the transistors remain in their initial state while the energy storage device is being recharged.

[0027] According to one embodiment of the invention, after the damped oscillation has ceased, a further electrical voltage pulse can be delivered to the electrical system via the two electrical contacts of the electrical system. This can be done in the same manner as the first voltage pulse. The repeated delivery of voltage pulses is advantageous for a particularly thorough testing of the electrical system. For example, standards may specify how often a particular electrical system must be tested.

[0028] According to one embodiment of the invention, the voltage pulse can have a voltage of more than 500 volts. The 500 volts can be achieved, for example, by discharging the energy storage device within less than 1 microsecond.

[0029] The device according to claim 12 comprises several, preferably cascaded, semiconductor elements, an energy storage device, terminals for an electrical connection of the device to the electrical system, first means for switching the semiconductor elements into a first state, and second means for switching the semiconductor elements into a second state. The energy storage device can, for example, be configured as a capacitor. In the first state of the semiconductor elements, the energy storage device is electrically connected to the terminals. In particular, it is possible that in the first state of the semiconductor elements, the energy storage device is connected in parallel to the electrical system if the electrical system is connected to the terminals. In the second state of the semiconductor elements, the energy storage device is disconnected from at least one of the terminals. The device is configured to carry out a method according to an embodiment of the invention.

[0030] According to one embodiment of the invention, the semiconductor elements can be configured as transistors having a gate terminal. The first means and the second means can each be electrically connected to the gate terminal of the transistors. Depending on how the gate terminal is controlled, a voltage pulse can be generated or the electrical connection between the energy storage device and the electrical system can be broken.

[0031] According to one embodiment of the invention, the second means can be configured to electrically discharge the capacitance of the gate terminal of the transistors. This allows the transistors to be switched into the second state.

[0032] Features described in relation to embodiments of the method may also be provided in embodiments of the device.

[0033] Further features and advantages of the present invention will become clear with reference to the following description of preferred embodiments and the accompanying figures. The same reference numerals are used for identical or similar components and for components with identical or similar functions. This shows Fig. 1 a schematic block diagram of a section of a device according to an embodiment of the invention.

[0034] The device comprises a control energy storage device 1. This can be, for example, a capacitor. The device also comprises a trigger detection device 2, a gate control device 3, transistors 4, a galvanic isolation device 5, and a shutdown electronics device 6.

[0035] The control energy storage device 1 serves to control the transistors 4. The transistors 4 are electrically connected to terminals (in Fig. 1 (not shown) connected to which an electrical system can be connected for impulse voltage testing. Furthermore, transistors 4 are electrically connected to an energy storage device (in Fig. 1 (not shown). When transistors 4 are switched to conduct using the control energy storage device 1 and the electrical system is connected to the terminals, the energy storage device is connected in parallel to the electrical system. This can also be referred to as the first state of transistors 4.

[0036] The trigger detection unit 2 is configured to detect a trigger signal. When the trigger signal is detected, the trigger detection unit 2 causes the gate drive 3 to drive the gates of the transistors 4, switching the transistors 4 into their first state using energy from the control energy storage unit 1. The energy from the storage unit is then discharged into the electrical system, triggering the damped oscillation. The frequency and amplitude of the damped oscillation are analyzed by measuring instruments (not shown), allowing faults or deviations in the electrical system from a norm to be detected.

[0037] After one oscillation period, or even after only half a period, the damped oscillation is actively terminated by the shutdown electronics 6, which switches the transistors 4 to a second state in which they are non-conducting. This disconnects the energy storage device from the electrical system. This can be achieved, for example, by discharging the capacitances of the gate terminals of the transistors 4. This discharge causes the transistors 4 to switch to the second state more quickly than would be the case without the shutdown electronics. Thus, the energy storage device can be recharged very soon after the voltage pulse is delivered, making it available for delivering another voltage pulse relatively quickly.

[0038] The shutdown electronics 6 include a thyristor and a discharge resistor for discharging the capacitances of the gate terminals of transistors 4. The thyristor is electrically connected to the gate terminals of transistors 4. After a certain period of time, the thyristor discharges the gate terminals via the discharge resistor. This period is defined by the discharge of a delay element. Once the delay element is discharged, the time period has elapsed. After the time period has expired, the delay element switches on a discharge transistor, which in turn switches the thyristor on, thus discharging the capacitances of the gate terminals 4.

[0039] If the energy storage device is recharged during the voltage pulse or during the damped oscillation, the delay element is also prevented from discharging, so that no discharge of the gate terminal capacitances occurs and the transistors 4 remain in the second state.

[0040] The energy storage device is then recharged, and another voltage pulse is delivered to the electrical system in the same or a similar manner. Because the damped oscillations generated by the voltage pulses are interrupted and the gate terminal capacitances are actively discharged, numerous pulse voltage tests can be performed in a very short time. In the industrial production of electric motors or generators, this reduces the time required for pulse voltage testing from several minutes to just a few seconds.

Claims

1. Method for surge voltage testing of an electrical system, comprising the following steps: - delivering an electrical voltage surge to the electrical system via at least two electrical contacts of the electrical system, wherein the delivery of the voltage surge is triggered by a switching of semiconductor elements (4) into a first state, wherein the semiconductor elements (4) in the first state electrically connect an electrical energy store to the electrical system, wherein the semiconductor elements (4) each have a gate connection, wherein in each case a capacitance at the gate connection is charged when the semiconductor elements (4) are switched into the first state; - measuring a voltage profile between the two electrical contacts directly after the delivery of the voltage surge, wherein the voltage profile comprises a damped oscillation; - analyzing the measured voltage profile in order to detect partial discharges in the electrical system; characterized in that - the damped oscillation is actively aborted.

2. Method according to Claim 1, characterized in that the capacitances at the gate connections are actively discharged, wherein the gate connections are discharged via one or more components which are not used for charging the capacitances.

3. Method according to Claim 1 or 2, characterized in that the damped oscillation is aborted after one oscillation period or after half an oscillation period.

4. Method according to either of the two preceding claims, characterized in that the damped oscillation is aborted by the semiconductor elements (4) being switched into a second state, wherein the electrical connection between the electrical energy store and the electrical system is disconnected when the semiconductor elements (4) are in the second state.

5. Method according to the preceding claim, characterized in that the semiconductor elements (4) are switched into the second state by the capacitance of the gate connection of the semiconductor elements (4) being electrically discharged in each case.

6. Method according to the preceding claim, characterized in that the capacitance of the gate connection is discharged via in each case a thyristor or a transistor and a discharge resistor.

7. Method according to one of the preceding claims, characterized in that the damped oscillation is aborted after a time period has elapsed, wherein the time period is defined by a discharge of a delay element.

8. Method according to the preceding claim, characterized in that the energy storage is recharged during the delivery of the voltage surge, and wherein the delay element is likewise recharged during a recharging of the energy storage.

9. Method according to one of the preceding claims, characterized in that, after the damped oscillation has been aborted and / or after the capacitances of the gate connections have been discharged, a further electrical voltage surge is delivered to the electrical system via the two electrical contacts of the electrical system.

10. Method according to one of the preceding claims, characterized in that the voltage surge has a voltage of more than 500 V.

11. Device for surge voltage testing of an electrical system, comprising a plurality of semiconductor elements (4), an energy storage, connections for an electrical connection of the device to the electrical system, first means (3) for switching the semiconductor elements (4) into a first state and second means (6) for switching the semiconductor elements (4) into a second state, wherein the energy storage is electrically connected to the connections in the first state of the semiconductor elements (4), wherein the energy storage is separated from at least one of the connections in the second state of the semiconductor elements (4), characterized in that the device is designed to carry out a method according to one of the preceding claims.

12. Device according to the preceding claim, characterized in that the semiconductor elements (4) are designed as transistors (4), wherein the transistors (4) each have a gate connection, wherein the first means (3) and the second means (6) are each electrically connected to the respective gate connection of the transistors (4).

13. Device according to the preceding claim, characterized in that the second means (6) are designed to electrically discharge the capacitance of the gate connection of the transistors (4) in each case.