JPH0554913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for diagnosing the state of insulation deterioration of electrical equipment, such as rubber-plastic insulated power cables.

[Prior Art and Problems to be Solved by the Invention] As a means of knowing the state of insulation deterioration of rubber/plastic insulated power cables, etc., it is possible to measure the current flowing through the insulated portion of the cable and analyze the contents. There is a way to know, but with regard to deterioration caused by moisture absorption, which is one type of insulation deterioration, it has been confirmed that the minute DC component and low frequency component flowing in the AC charging current are the signals related to the deterioration. Based on this knowledge, a new method for diagnosing insulation deterioration has been developed.

However, when implementing the above method, it is necessary to install a measuring device between the low pressure side of the specimen and the ground.
Furthermore, it is necessary to remove all grounding from the specimen and at the same time provide appropriate insulation between the low-voltage side of the specimen and the ground, but in the case of electrical equipment installed on site, these requirements are not necessarily met. This is not always the case, and in fact, it is rarely satisfied. Therefore, in order to be able to measure the DC component while the low voltage side of the specimen is grounded, it is necessary to connect the high voltage power supply of the specimen to the A method of measuring between the ground is being considered. However, in this case, it is necessary to change a part of the commercial circuit (the high-voltage power supply side circuit of the DUT), and there is a risk that erroneous signals may be emitted and the commercial circuit itself may be damaged. A possible method is to install a high-voltage power supply for measurement separately from the power supply, connect it to the specimen, and install a measuring device between the high-voltage power supply for measurement and the ground to detect the DC component, etc.
However, in this case, it is necessary to select a power supply according to the capacitance of the specimen, and therefore, a large capacity power supply must be installed for a specimen with a large capacitance. This method not only necessitates larger and more expensive equipment, but also has drawbacks such as increased risk during testing. For this reason, these methods are currently hardly applied to practical lines, and only when the low-voltage side of the specimen can be completely insulated from the ground.
A measuring device is installed between the low-voltage side of this test object and the ground, and the direct current component is detected by this measuring device.

In this way, although all conventional methods of this type are known to be good in principle, they lack versatility and have not been put into practical use. .

[Means for Solving the Problems] An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a versatile method for diagnosing insulation deterioration of electrical equipment. A variable reactor, an excitation transformer, and a DC component measuring device that can resonate at commercial frequencies with the capacitance of the insulated part of the electrical equipment are connected in series to the high voltage side of the electrical equipment. The purpose is to detect the direct current component of the current flowing through the insulated parts.

[Function] The principle of diagnosing insulation deterioration by measuring DC components, etc. is that when the test object is a power cable, the first
The purpose is to detect minute direct current components in alternating current charging current in a closed loop consisting of a power transformer 1, high voltage lead cable 2, specimen 3, and ground 4 as shown in the figure. Here, only one of the three phases is shown, and corresponds to a state in which the neutral point of the transformer 1 is grounded directly or via an arbitrary impedance.
If the neutral point of the transformer 1 is ungrounded, a closed loop will not be formed, so in such a case, a ground voltage detection transformer (GPT) 5 is installed in parallel with the transformer 1, and By grounding the gender point, a closed loop is formed between the GPT 5 and the specimen 3. Therefore, the purpose can be achieved by inserting a DC component measuring device including a low-pass filter between the external shielding layer of the specimen 3 and the ground 4, ie, at point A in the figure. However, if the specimen 3 is a power cable and its outer shielding layer is entirely grounded, or even if the outer shielding layer is initially insulated from the ground with an anticorrosion layer, damage to the anticorrosion layer may occur. If the ground insulation is poor due to aging or the like, it is actually difficult to detect the DC component at the point A.

On the other hand, in view of this, it is conceivable to detect at point B or point C, but in this case, the risk increases because it involves changing the commercial power supply circuit. Also,
It is possible to detect it at point D between the neutral point of GPT5 and the ground 4, but GPT5 is an important element for system control, and if its circuit is changed, an erroneous signal will cause a serious problem in system control. There is a risk of giving. In addition, the neutral point of the power transformer 1, GPT
In the case of 5 installation, since DC components etc. flow in parallel to both, it is necessary to measure both or remove the grounding of one, which only makes detection less convenient. Otherwise, it may lead to the increased risk mentioned above.

Due to these points, it has conventionally been considered practically difficult to detect DC components on the commercial power source side.

To solve this problem, a measuring transformer can be used, but this requires a transformer capacity equal to the charging capacity, and in reality, it is not only difficult to transport such a device to the site. , which requires a large power supply and can only be applied to limited locations.

Therefore, in order to make this type of insulation deterioration diagnosis method by detecting DC components widely available, it was necessary to develop a new method including the development of the power supply unit.

The present invention satisfies the above-mentioned need by newly using a series resonant high voltage power supply as a power supply.

According to the present invention, the following new advantages arise.

(1) In other words, in the case of a transformer that uses normal primary and secondary windings, the voltage on the primary side is directly converted to the secondary side (the conversion multiple differs somewhat depending on the frequency), so it is simply a commercial Not only frequency voltages but also all voltages from low frequencies to high frequencies are generated on the secondary side.

When seeking a power source to obtain high voltage at the installation site, as is the purpose of this invention, general distribution lines are used, but recently the loads on distribution lines are subject to complicated control operations. Because
For example, voltage control using thyristors causes voltage changes in power distribution systems from low frequencies to high frequencies.

Therefore, when this is used to operate a so-called high-voltage transformer, low-frequency to high-frequency voltages are generated on the high voltage side, and the corresponding low-frequency components are also generated in the insulated parts of the specimen and the DC component measurement circuit. Since the contained current flows, the measurement results will include unknown errors, making it impossible to properly diagnose deterioration.
Therefore, in the present invention, an excitation transformer 8 is connected in series to the high voltage side of the specimen 3 via a variable reactor 7, as shown in FIG. A circuit is constructed by installing a measuring device 6 through a low-pass filter. In this way, the impedance [j(ωL-1/ωC)] of the disturbance voltage from the power source that falls outside of the resonance condition increases, so the current becomes small, and therefore the DC and low frequency components become smaller. The error experienced by the circuit that measures this will be reduced.

(2) If the insulation part of the specimen is extremely deteriorated and the voltage used during diagnosis causes dielectric breakdown, in conventional circuits, a large current will flow in and concentrated energy will be generated at the point of dielectric breakdown. However, when a series resonant circuit is used, the capacitance C of the specimen 3 is short-circuited at the same time as the insulation breaks down, and the circuit is automatically closed to the reactor 7. The current source voltage is the low output voltage of the excitation transformer 8 (generally 1/10 to 1/50 of the voltage applied to the specimen), so The energy generated is extremely small and there is no danger of fire or the like.

Points (1) and (2) above are extremely important elements in carrying out accurate insulation diagnosis in modern power facilities, which are overcrowded and cannot tolerate power outages due to accidents.

Next, when performing insulation diagnosis using these devices, the test object is normally completely disconnected from the commercial voltage system, but because it involves a lot of work, it is difficult to do so. If you try to diagnose the specimen without using it, the high voltage of the commercial system and the voltage from the measurement system will be superimposed on the specimen, and depending on the phase timing, the voltage will be too high, causing damage to the insulated parts of the specimen or the DC component. etc. will damage the measurement circuit. Damage to the DUT due to diagnostic activities is the best thing to avoid, and in order to prevent this, it is necessary to confirm in advance that no other voltage is applied to the DUT, and If other voltages are applied, measures must be taken such as not generating voltage from the measurement system and protecting the measurement circuit.

A basic circuit for this purpose is shown in FIG.

Here, a capacitance type voltage divider 9 is provided between the high voltage side of the specimen 3 and the ground 4 in parallel with the variable reactor 7, the excitation transformer 8, and the low-pass filter 6, and the excitation transformer 8 and the low-pass filter A switch 10 is provided to short-circuit the switch 6, and the switch 10 is connected via a relay based on the output voltage.
Add a circuit to operate the voltage 1 to the specimen 3.
1 is applied or not, the switch 10 is closed or opened.

Furthermore, when carrying out the present invention, it is necessary to lead a high voltage to the specimen 3 through a crowded arrangement of various equipment. At this time, a high voltage insulated lead cable 2 is used between the high voltage generator section and the specimen 3. In this case, by adjusting the variable reactor of the high voltage generator in advance so as to satisfy the resonance condition with the capacitance of the lead cable, voltage divider 9, etc., the following advantages occur.

In other words, if by some chance the high voltage lead cable 2 comes into contact with the terminal of the DUT 3 while another voltage is being applied to the DUT 3, at that moment the connection will be made from the other voltage side to the measurement system side. An inrush current may flow into the system, causing disturbance to other voltages, or abnormal voltage may enter the measurement system.
There is a risk of damaging the equipment used there. However, if the reactor 7 that resonates the measurement system with the commercial frequency including the lead cable 2 is adjusted in advance, the impedance seen from the other voltage side will be in a parallel resonance state of L and C, resulting in a very high impedance. (theoretically infinite),
Even if the lead cable 2 is connected in this state, the inrush current is extremely small, and disturbance to other voltage sides and damage to the device can be prevented.

It should be noted that the grounding of the external shielding circuit of the lead cable, the grounding of the specimen, and the grounding of various devices in the measurement system may be individually or commonly connected. Moreover, there is no problem in measurement even if the common connection is grounded at one or two points. However, if the lead cable or various equipment in the measurement system itself deteriorates and a DC component is generated at the deteriorated point, check the current component in advance or make sure that the DC component does not flow into the measurement system. Needless to say, it is necessary to connect the wires.

In addition, as a method for diagnosing insulation deterioration, there is a method of detecting the DC component or low frequency component included in the charging current component by commercial frequency AC voltage, and a method of detecting the DC component or low frequency component by superimposing a minute DC voltage on the AC voltage. There is also a method of detecting this by increasing the low frequency part, but in this case, a circuit that superimposes a minute DC voltage is added to the low voltage side of the measurement system, that is, to a part of the circuit that measures the DC component, etc. There is a need to.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 4, taking as an example a case where the specimen is a power cable.

First, the measurement system 12 of the present invention is installed near the specimen 3. The variable reactor 7 is adjusted in advance so that it resonates with the capacitance of the high-voltage lead cable 2, capacitive voltage divider 9, etc. at the commercial frequency.

At this time, the switch 10 is kept in the closed state. Connect the high voltage lead cable 2 to the specimen 3. At this time, even if the switch 14 is closed and voltage is applied to the DUT 3, the impedance of the measurement system 12 seen from the voltage side is almost infinite, so the inrush current There is almost no flow. Further, since the voltage divider 9 detects the voltage and closes the switch 10, the excitation transformer 8 and the measuring device 6 for direct current and low frequency components are not disturbed at all. If no voltage is applied to the specimen 3, the switch 10 is opened. Therefore, the excitation transformer 8 is connected to a distribution power source (not shown) via a voltage regulator 13. Thereafter, the variable reactor 7 and the voltage regulator 13 are adjusted to create a new resonance state, and then a predetermined high voltage is applied to the specimen 3. In this state, a signal current is detected by a DC component or low frequency part measuring device 6 including a low-pass filter, and the insulation deterioration state of the specimen 3 is diagnosed based on its characteristics.

After collecting the data, the connection to the power distribution system power source is cut off, and the connection between the lead cable 2 and the specimen 3 is cut off. At this time, if the reactor 7 is set manually or automatically so that it resonates with the capacitance of the lead cable 2, voltage divider 9, etc.,
The next measurement will be convenient and safe.

[Effects of the Invention] Due to recent social conditions, there is a strong desire to improve the reliability of power equipment, and it is also required to strictly prevent spillover accidents such as fires due to failure of electrode equipment.

To this end, it is necessary to take measures to maintain the integrity of the insulators of high-voltage power equipment, and in the event that the insulators deteriorate, it must be detected quickly and measures such as repairs must be taken.

However, the number of target devices is enormous, and the development of a simpler and more reliable diagnostic method has been awaited. It has been found that detecting the direct current component or low frequency component is extremely effective for detecting aging deterioration of insulators, especially the relatively frequent deterioration due to moisture absorption. There has been a strong need for a general-purpose diagnostic method for power equipment, especially equipment with different grounding conditions. The present invention provides a variable reactor, an excitation transformer, and
By connecting a DC component measuring device in series to the high-voltage side of the electrical equipment and detecting the DC component, etc. from the current flowing through the electrical equipment, the drawbacks of the conventional technology described above can be overcome and versatility achieved. The present invention provides a method for diagnosing insulation deterioration of certain electrical equipment.

In this way, the present invention meets the above-mentioned desire, and will greatly contribute to further stabilizing the power supply in the future.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional method for diagnosing insulation deterioration of electrical equipment, FIGS. 2 and 3 are diagrams each illustrating the principle of the method of diagnosing insulation deterioration of electrical equipment of the present invention, and FIG. 4 is an explanatory diagram of the method of diagnosing insulation deterioration of electrical equipment of the present invention. FIG. 2 is an explanatory diagram of an embodiment of the insulation deterioration diagnosis method. 1... Power transformer, 2... Lead cable, 3... Test object (power cable), 4... Earth,
5... Voltage transformer, 6... DC component measuring device, 7...
Variable reactor, 8...Excitation transformer, 9...
Capacitance type voltage divider, 10... switch, 11...
Other power supplies, 12...Measurement system, 13...Voltage regulator, 14...Switch.

Claims (1)

[Claims] 1. The low voltage side of the electrical equipment 3 whose insulation deterioration is to be diagnosed is grounded, and the excitation transformer 8 is connected in series to the high voltage side via the lead cable 2 and the variable reactor 7, and the low voltage of the excitation transformer 8 is Insert a low pass filter 6 between the side and the ground 4,
Furthermore, a switch 10 for short-circuiting the voltage measuring device 9, the excitation transformer 8, and the low-pass filter 6 is provided between the high voltage side of the electrical equipment 3 and the ground 4 in parallel with the variable reactor 7, the excitation transformer 8, and the low-pass filter 6. When diagnosing insulation deterioration of the electrical equipment 3 using a circuit that short-circuits and releases the excitation transformer 8 and the low-pass filter 6 as appropriate, first connect the lead cable 2 between the electrical equipment 3 and the variable reactor 7. Prior to connection, the variable reactor 7 is set so that, with the switch 10 closed, the reactance of the variable reactor 7 and the capacitance of the lead cable 2 are in a resonant state with respect to the commercial frequency at which the electrical equipment 3 is operated.
After that, connect the lead cable 2 to the electric device 3, make sure that no voltage is applied to the electric device 3, open the switch 10, and then turn on the variable reactor 7 again. Adjustment is made to create a new resonance state, and then a predetermined voltage is applied to the electrical equipment 3 through the excitation transformer 8, and at this time, out of the current flowing through the low-pass filter 6 to the insulated part of the electrical equipment 3, A method for diagnosing insulation deterioration of electrical equipment, characterized by diagnosing insulation deterioration of the electrical equipment 3 by detecting DC components and checking the contents thereof.