CN108020763B - Method for monitoring early-stage electric tree defects of direct-current submarine cable - Google Patents

Abstract

The invention discloses a monitoring method for early electrical tree defects of a direct current submarine cable. The monitoring method comprises the following steps: inserting an alternating current of the same frequency as the specific frequency of the target direct current submarine cable when the electrical tree defect exists on the shielding layer of the target direct current submarine cable voltage source; obtain the armor layer voltage amplitude after the AC voltage source resonates with the voltage of the target DC submarine cable; match the armor layer voltage amplitude with the voltage amplitude in the pre-stored voltage set to determine the target DC submarine cable Whether the cable has electrical tree defects and the development stages of the electrical tree defects; the voltage set is the set of voltage amplitudes corresponding to the target DC submarine cables at different stages of the electrical tree defect development. The monitoring method provided by the invention can monitor the operation status of the DC submarine cable online, accurately diagnose the development stage of the electrical tree defect of the DC submarine cable, and avoid the breakdown of the insulating medium layer of the DC submarine cable.

Description

A monitoring method for early electrical tree defects of DC submarine cables

technical field

The invention relates to the field of on-line monitoring of high-voltage equipment, in particular to a monitoring method for early electrical tree defects of a direct current submarine cable.

Background technique

Compared with AC transmission technology, DC transmission technology has many advantages in the field of large-capacity, high-voltage, long-distance power transmission. With the rapid development of HVDC transmission technology, its application fields include: grid interconnection, urban power supply, island power supply, and wind power access, etc., especially in recent years, the construction of projects such as cross-sea DC transmission, offshore wind power generation and grid connection, etc. Extruded cross-linked polyethylene (XLPE) DC cables have been widely used for the problems of line corridors and urban aesthetics that need to be solved urgently for power supply in big cities.

Since extruded XLPE DC cables operate at the same voltage polarity for a long time, there may be a build-up of space charges. With the continuous accumulation of space charges, the local electric field in the cable insulating medium will be distorted, and the highest field strength in the medium will reach 8 times that of the applied electric field, which can easily lead to breakdown of the cable insulating medium, especially under the action of a strong electric field. The accumulation of sap will accelerate the development and aging process of electric tree branches. Therefore, the suppression of space charge and the on-line monitoring and diagnosis technology of extruded XLPE DC cable faults have become the key issues in the development of high-voltage DC cables. For the former, with the development of insulating materials and nanotechnology in recent years, adding nanomaterials to the insulating medium can effectively solve the space charge problem of extruded XLPE DC cables; for the latter, there is no effective method at home and abroad. , especially in the early monitoring and diagnosis of electrical tree defects in extruded XLPE DC cables.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a monitoring method for the early electrical tree defects of the DC submarine cable, which can monitor the operation status of the DC submarine cable online, accurately diagnose the development stage of the electrical tree defect of the DC submarine cable, and avoid the insulating medium layer of the DC submarine cable from being struck. Put on.

For achieving the above object, the present invention provides the following scheme:

A method for monitoring early electrical tree defects of a DC submarine cable, wherein the DC submarine cable is an extruded XLPE DC submarine cable; the DC submarine cable sequentially includes an armor layer, an inner lining layer, a shield layer, an insulation layer from outside to inside A dielectric layer and a wire core; both ends of the DC submarine cable are located at the converter station, and the middle part of the DC submarine cable is located on the seabed; the monitoring method includes:

An AC voltage source is connected to the shielding layer of the target DC submarine cable; the frequency of the AC voltage source is the same as the specific frequency when the target DC submarine cable has an electrical tree defect;

acquiring the armor layer voltage amplitude of the target DC submarine cable; the armor layer voltage amplitude is the voltage amplitude after resonance between the AC voltage source and the voltage of the target DC submarine cable;

Matching the voltage amplitude of the armor layer with the voltage amplitude in the pre-stored voltage set to determine whether the target DC submarine cable has electrical tree defects and the development stage of the electrical tree defects; the voltage set is: The target DC submarine cable is a collection of voltage amplitudes corresponding to different stages of electrical tree defect development.

Optionally, before connecting an AC voltage source to the shielding layer of the target DC submarine cable, the method further includes:

Determining the peculiar frequency when the DC submarine cables of different types have electrical tree defects;

Determine the voltage amplitudes corresponding to the different types of the DC submarine cables at different stages of the development of the electrical tree defect, and store the voltage amplitudes in the voltage sets corresponding to the different types of the DC submarine cables.

Optionally, before connecting an AC voltage source to the shielding layer of the target DC submarine cable, the method further includes:

determining the type of the target DC submarine cable;

According to the type of the target DC submarine cable, determine the unique frequency and voltage set when the target DC submarine cable has electrical tree defects.

Optionally, the determining of the unique frequency when the DC submarine cables of different models have electrical tree defects specifically includes:

The electrical tree defect is equivalent to a variable resistance in the insulating medium layer, and the cable module in the frequency phase domain model in the PSCAD software is used to establish different types of DC submarine cable models;

The resistance value of the variable resistor is adjusted, and according to the adjusted variable resistor, a simulation experiment is performed on the DC submarine cable models of different types, and it is determined that the DC submarine cables of different types have electrical tree defects unique frequency.

Optionally, the AC voltage source is a sinusoidal AC voltage source.

Optionally, the AC voltage source is a sinusoidal AC voltage source with a voltage amplitude of 0.01V.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The invention provides a method for monitoring early electrical tree defects of a direct current submarine cable. The direct current submarine cable is an extruded XLPE direct current submarine cable; the direct current submarine cable sequentially includes an armor layer, an inner lining layer, A shielding layer, an insulating medium layer and a wire core; both ends of the DC submarine cable are located at the converter station, and a middle part of the DC submarine cable is located on the ocean floor; the monitoring method includes: connecting the shielding layer of the target DC submarine cable input an AC voltage source; the frequency of the AC voltage source is the same as the specific frequency when the target DC submarine cable has electrical tree defects; obtain the armor layer voltage amplitude of the target DC submarine cable; the armor layer The voltage amplitude is the voltage amplitude after resonance occurs between the AC voltage source and the voltage of the target DC submarine cable; the armor layer voltage amplitude is matched with the voltage amplitude in the pre-stored voltage set to determine Whether the target DC submarine cable has an electrical tree defect and the development stage of the electrical tree defect; the voltage set is a set of voltage amplitudes corresponding to the target DC submarine cable in different stages of the electrical tree defect development. Therefore, the monitoring method provided by the present invention can monitor the operation status of the DC submarine cable online, accurately diagnose the development stage of the electrical tree defect of the DC submarine cable, and avoid the breakdown of the insulating medium layer of the DC submarine cable.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative labor.

1 is a schematic flowchart of a method for monitoring early electrical tree defects of a DC submarine cable according to an embodiment of the present invention;

Fig. 2 is the equivalent schematic diagram of the DC submarine cable structure and electrical tree defect of the present invention;

Fig. 3 is the simulation experiment schematic diagram of the direct current submarine cable of the present invention in PSCAD software;

4 is a schematic structural diagram of a DC submarine cable monitoring device according to an embodiment of the present invention;

FIG. 5 is a schematic diagram showing the comparison of voltage amplitudes at different stages of a DC submarine cable electrical tree defect according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a monitoring method for the early electrical tree defects of the DC submarine cable, which can monitor the operation status of the DC submarine cable online, accurately diagnose the development stage of the electrical tree defect of the DC submarine cable, and avoid the insulating medium layer of the DC submarine cable from being struck. Put on.

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic flowchart of a method for monitoring early electrical tree defects of a DC submarine cable according to an embodiment of the present invention. As shown in Figure 1, the monitoring method provided by the present invention includes:

Step 101: Connect an AC voltage source to the shielding layer of the target DC submarine cable; the frequency of the AC voltage source is the same as the specific frequency when the target DC submarine cable has electrical tree defects. In addition, due to the electrical tree defects of different development levels, the peculiar frequency of the target DC submarine cable is similar, so a specific value is chosen as the peculiar frequency.

Fig. 2 is the equivalent schematic diagram of the electrical tree defect of the DC submarine cable of the present invention. As shown in Fig. 2, the DC submarine cable is an extruded XLPE DC submarine cable; Inner lining layer, shielding layer, insulating medium layer and wire core.

Step 102: Obtain the armor layer voltage amplitude of the target DC submarine cable; the armor layer voltage amplitude is the voltage amplitude after resonance between the AC voltage source and the voltage of the target DC submarine cable.

Step 103: Match the voltage amplitude of the armor layer with the voltage amplitude in the pre-stored voltage set to determine whether the target DC submarine cable has an electrical tree defect and the development stage of the electrical tree defect; the The voltage set is a set composed of voltage amplitudes corresponding to the target DC submarine cable at different stages of development of the electrical tree defect.

Wherein, step 103 specifically includes:

When the electrical tree defect of the DC submarine cable is in the initial development stage, the voltage amplitude caused by the resonance will be very high. The greater the development of the electrical tree defect, the lower the voltage amplitude, so the development of the electrical tree defect is judged according to the voltage amplitude.

Preferably, the AC voltage source is a sinusoidal AC voltage source; the AC voltage source is a sinusoidal AC voltage source with a voltage amplitude of 0.01V.

Before executing step 101, the following preparations need to be done:

Step 1: Determine the unique frequency when the DC submarine cables of different types have electrical tree defects.

Step 2: Determine the voltage amplitudes corresponding to the different types of the DC submarine cables at different stages of the development of the electrical tree defect, and store the voltage amplitudes into the corresponding voltage sets.

The third step: determine the type of the target DC submarine cable;

Step 4: Determine the unique frequency and voltage set of the target DC submarine cable according to the model of the target DC submarine cable.

Wherein, the first step specifically includes: as shown in Figure 2, the electrical tree defect is equivalent to a variable resistance in the insulating medium layer, and the cable module in the frequency phase domain model in PSCAD software is used, Establish different types of DC submarine cable models; then adjust the resistance value of the variable resistor, and perform simulation experiments on the DC submarine cable models of different types according to the adjusted variable resistance to determine different models. The specific frequency of the DC submarine cable when there is an electrical tree defect.

Because the extruded XLPE DC submarine cable is in unipolar operation for a long time, there is the possibility of space charge accumulation, which is easy to cause and accelerate the electrical tree defect of the insulating medium layer of the extruded XLPE DC submarine cable. The present invention considers that the monitoring process of the entire extruded XLPE DC submarine cable is in a low frequency environment, and the second is that the monitoring object of the present invention is the early electrical tree defect, so in order to simplify the simulation process, the insulating medium layer of the extruded XLPE DC submarine cable is The electrical tree defect in is equivalent to a variable resistor R _tree .

Fig. 3 is a schematic diagram of the simulation experiment of the DC submarine cable of the present invention in PSCAD software, as shown in Fig. 3, the PSCAD simulation software adopts the cable module of the frequency-dependent phase domain model to simulate the working condition of the DC submarine cable in reality; Considering the early electric tree defect, the electric tree defect is equivalent to a variable resistance R _tree in the insulating dielectric layer to simulate the development of electric tree defect. In Figure 3, one end of the cable is connected to the DC voltage source, and its grounding method is different from that of the underground cable. The shielding layer of one end of the DC submarine cable is connected to the armored layer DC and adopts the ungrounded operation mode; the shielding layer of the other end is insulated from the armoring layer. , a resistor R ₁ with a resistance value of 1kΩ is set between the two, and a resistor R ₂ with a resistance value of 0.01Ω is set between the armor layer and the ground to indicate that it is directly grounded. The equivalent resistance R _tree of the electrical tree defect is set at a certain point in the DC submarine cable, and simulation experiments are carried out with R _tree = 10 ⁶ Ω, 10 ³ Ω, 10 ⁰ Ω, 10 ^-3 Ω respectively, so as to obtain the DC submarine cable's equivalent resistance R tree . Frequency characteristics specific to electrical tree defects in insulating dielectric layers.

In the implementation process, the simulation experiment part specifically includes: R _tree ≥10 ⁶ Ω, it is considered that the insulating medium layer of the DC submarine cable is good, and there is no partial discharge defect; 10 ⁶ Ω≥R _tree ≥10 ³ Ω, it is considered that the partial discharge defect is at the In the initial stage of development, only regular testing is required; 10 ³ Ω≥R _tree ≥10Ω, it is considered that the partial discharge defect is in the mid-term development stage, and regular monitoring is required, and the cycle is one week; 10Ω≥R _tree ≥10 ^-3 Ω, it is considered that the partial discharge defect is defective In the stage of rapid development, regular monitoring is required, and the periodic interval of each monitoring is shortened; 10 ^-3 Ω≥R _tree , it is believed that the partial discharge defect may break down the insulating dielectric layer, and its development should be monitored in real time. The effect is that the unique resonance frequency of the electrical tree defects of different types of DC cables can be obtained. In addition, it should be noted: 1. The above division of resistance values is only theoretical and only used for simulation research; 2. Because the development speed of partial discharge defects is different and has strong randomness, the monitoring period of each stage needs to be based on the actual situation. Depends.

FIG. 4 is a schematic structural diagram of a DC submarine cable monitoring device according to an embodiment of the present invention. As shown in FIG. 4 , the shielding layer of the DC submarine cable joint of the shore-based converter station is connected to an AC voltage source U _C with an amplitude of 0.01V, Its frequency is the same as the unique frequency when the insulating medium layer of the DC submarine cable obtained in the previous simulation study has electrical tree defects, which is used to cause resonance. In actual engineering monitoring, in order to enhance the effect of resonance and facilitate observation, a 15.9μF capacitor is often added between the AC voltage source U _C and the shielding layer. In addition, a wave recorder is connected to the joint of the armored layer at the same end to record the voltage waveform in the armored layer in real time, and transmit the information to the control center through the Beidou satellite system in real time. The control center estimates the insulation medium of the DC submarine cable through spectrum analysis. Development of electrical tree defects in layers.

FIG. 5 is a schematic diagram showing the comparison of voltage amplitudes at different stages of a DC submarine cable electrical tree defect according to an embodiment of the present invention. The voltage waveform in the armored layer will be recorded, and after spectrum transformation analysis, it can be seen that resonance is caused near 100Hz and there is an obvious voltage amplitude protrusion. As shown in FIG. 5 , it is preliminarily judged that there is an electrical tree defect in the DC submarine cable. In the follow-up monitoring, it was found that the electrical tree defects became more and more obvious with the extension of time, and the voltage amplitude around 100Hz dropped significantly, which also showed that the change of the voltage amplitude was related to the development of electrical tree defects, thus verifying Feasibility of the present invention.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

In this paper, specific examples are used to illustrate the principles and implementations of the present invention. The descriptions of the above embodiments are only used to help understand the methods and core ideas of the present invention; meanwhile, for those skilled in the art, according to the present invention There will be changes in the specific implementation and application scope. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims (4)

1. a monitoring method for the early stage electrical tree defect of a direct current submarine cable, is characterized in that, described direct current submarine cable is extruded type XLPE direct current submarine cable; Described direct current submarine cable comprises armor layer, inner lining successively from outside to inside layer, shielding layer, insulating medium layer and wire core; both ends of the DC submarine cable are located at the converter station, and the middle part of the DC submarine cable is located on the ocean floor; the monitoring method includes: An AC voltage source is connected to the shielding layer of the target DC submarine cable; the frequency of the AC voltage source is the same as the specific frequency when the target DC submarine cable has an electrical tree defect; the shielding layer of the target DC submarine cable is the same Before connecting an AC voltage source, the method further includes: determining the peculiar frequencies when the DC submarine cables of different types have electrical tree defects; value, and store the voltage amplitude in the voltage set corresponding to the DC submarine cables of different types; wherein, the determining the unique frequency when the DC submarine cables of different types have electrical tree defects specifically includes: The electrical tree defect is equivalent to a variable resistance in the insulating medium layer, and the cable module in the frequency phase domain model in the PSCAD software is used to establish different types of DC submarine cable models; for the variable resistance The resistance value is adjusted, and according to the adjusted variable resistance, simulation experiments are carried out on the DC submarine cable models of different types to determine the unique frequency when the DC submarine cables of different types have electrical tree defects; acquiring the armor layer voltage amplitude of the target DC submarine cable; the armor layer voltage amplitude is the voltage amplitude after resonance between the AC voltage source and the voltage of the target DC submarine cable; Matching the voltage amplitude of the armor layer with the voltage amplitude in the pre-stored voltage set to determine whether the target DC submarine cable has electrical tree defects and the development stage of the electrical tree defects; the voltage set is: The target DC submarine cable is a collection of voltage amplitudes corresponding to different stages of electrical tree defect development. 2. The monitoring method according to claim 1, wherein before connecting an AC voltage source on the shielding layer of the target DC submarine cable, the method further comprises: determining the type of the target DC submarine cable; According to the type of the target DC submarine cable, determine the unique frequency and voltage set when the target DC submarine cable has electrical tree defects. 3. The monitoring method according to claim 1, wherein the AC voltage source is a sinusoidal AC voltage source. 4 . The monitoring method according to claim 3 , wherein the AC voltage source is a sinusoidal AC voltage source with a voltage amplitude of 0.01V. 5 .

Images