Background technique
Currently, the power cable of 35kV, 66kV, 110kV and 110kV above is single-core cable, cable goldBelong to shielded layer (being also referred to as cable shield below) one end three-phase to interconnect and be grounded, the other end is earth-free, when in lightning wave or cableWhen portion's overvoltage is flowed along cable core, the ungrounded end of cable shield will appear higher impulse overvoltage；Or when system is shortWhen road fault current flows through cable core, the earth-free end of shielded layer also will appear very high line-frequency induction overvoltage；Or in electricityIn the case that cable power supply distance is longer and cable shield aging, cable shield is ungrounded under system normal running (operation) conditionsEnd also will appear higher line-frequency induction voltage, persistently generate damage to cable external shielding layer.
The protection of high-voltage cable shielding layers generallys use resistor valve sheet protector.Under normal working voltage, protector is inExisting high resistance, it is extremely small by the operating current of protector, it is substantially at off state.Between cable shield and the earth notAccess is formed, no electric current passes through cable shield.When existing in cable due to lightning stroke or the propagation of Operating Over Voltage Surge wave,The metal screen layer of cable can sense the impulse overvoltage of generation.The overvoltage occurred on cable shield reaches protectorOrigination action voltage when, the resistance value of protector declines quickly, make to be linked to be access between cable shield and the earth, generationHigh current flows into the earth through protector by cable shield.At this moment the origination action voltage of the voltage on cable sheath and protectorMore much lower than impulse overvoltage, high current flows into the earth from protector, rather than flows into the earth by breakdown sheath, to protectDestruction of the cable shield from arriving overvoltage.After having served as loss of voltage, resistor valve sheet restores its high-resistance characteristic again, protectionDevice and cable run are restored to the state normally disconnected with the earth again.
High-tension cable generally uses cross-linked polyethylene insulated cable, the insulation performance of the cable shield after long-playIt is deteriorated, resistance to voltage levels decline, and the origination action voltage of the protector of resistance to pressure ratio of shielded layer is low.When there is overvoltage impact, protectionDevice not yet acts, and shielded layer insulate weakness will be first breakdown, and high current flows into the earth in the weakness, can be to cable sheathVery big damage is caused, so, the origination action overtension of general cable protective layer protector can not be to decreasing insulatingCable shield afterwards plays a protective role.
Conventional cable protective layer protector can only inhibit Lightning Over-voltage and switching overvoltage, cannot pass through electric current for a long time,Therefore the overvoltage generated in operation cannot be inhibited.And the cable protective layer protector of novel cable sheath protector cooperation is onlyCable shield protection problem after considering shielded layer decreasing insulating, for some cables containing higher harmonic currentIn, for example, the cable of steel mill, in the oscillation overvoltage problem that causes of higher harmonic current can not then solve.
Summary of the invention
In view of this, it is an object of the invention to propose a kind of cable shield electric current bleeder.
According to an aspect of the invention, there is provided a kind of cable shield electric current bleeder, comprising: the electric current is let outThe one end for putting device is connected with the ungrounded end of the cable shield, the other end and the cable of the electric current bleederThe ground terminal of shielded layer is connected, and the electric current bleeder includes first-grade protection circuit, and the first-grade protection circuit includes series connectionCapacitor and resistance, the first end of the capacitor is connected with the ungrounded end, the first end of the resistance with it is describedGround terminal is connected.
Optionally, the first-grade protection circuit further include: voltage-limiting element, the first end of the voltage-limiting element and the capacitorThe first end of device is connected, and the second end of the voltage-limiting element is connected with the first end of the resistance.
Optionally, the voltage-limiting element is zinc oxide voltage-limiting element.
Optionally, the electric current bleeder further include: insulation crust, the first-grade protection circuit are set to the insulationIn shell.
Optionally, the impedance of the capacitor is less than the equivalent impedance of the cable shield.
Optionally, the resistance value of the resistance is less than the equivalent impedance of the cable shield.
Optionally, the cable is multi-phase cable, and ground connection after one end multiphase of the multi-phase cable is cross interconnected forms instituteState ground terminal.
Optionally, the ungrounded end of the ground terminal and each phase cable shield in the multi-phase cable passes through one respectivelyA first-grade protection circuit constitutes circuit.
Optionally, the electric current bleeder further include: high-voltage terminal, the first-grade protection circuit pass through the high pressureTerminals are connected with the cable shield.
Optionally, the resistance is noninductive resistance.
From the above it can be seen that the cable shield electric current bleeder of the embodiment of the present invention can be according to cable shieldThe mechanism that the induced voltage and fault overvoltage that layer occurs generate absorbs overvoltage energy using first-grade protection circuit, so as toInduced voltage and the failure over-voltage for inhibiting cable shield, can play a protective role to cable shield.
Specific embodiment
To make the objectives, technical solutions, and advantages of the present invention clearer, below in conjunction with specific embodiment, and referenceAttached drawing, the present invention is described in more detail.
It should be noted that all statements for using " first " and " second " are for differentiation two in the embodiment of the present inventionThe non-equal entity of a same names or non-equal parameter, it is seen that " first " " second " only for the convenience of statement, does not answerIt is interpreted as the restriction to the embodiment of the present invention, subsequent embodiment no longer illustrates this one by one.
Fig. 1 is a kind of schematic diagram of cable shield electric current bleeder shown according to an exemplary embodiment, such as Fig. 1Shown, one end of the electric current bleeder is connected with the ungrounded end N of the cable shield, the electric current bleederThe other end is connected with the ground terminal GND of the cable shield, and the electric current bleeder includes first-grade protection circuit, the electricityFlowing leadage circuit includes concatenated capacitor C1 and resistance Ra, the first end of the capacitor Ca and the ungrounded end N phaseEven, the first end of the resistance is connected with the ground terminal GND.
The cable shield electric current bleeder of the embodiment of the present invention can according to cable shield occur induced voltage andThe mechanism that fault overvoltage generates absorbs overvoltage energy using first-grade protection circuit, to can inhibit induced voltage and failureOver-voltage can play a protective role to cable shield.
Fig. 2 is a kind of schematic diagram of cable shield electric current bleeder shown according to an exemplary embodiment, describedFirst-grade protection circuit may also include that voltage-limiting element Ma, the first end of the first end of the voltage-limiting element Ma and the capacitor CaIt is connected, the second end of the voltage-limiting element is connected with the first end of the resistance Ra.
In a kind of achievable mode, the voltage-limiting element can be zinc oxide voltage-limiting element.Zinc oxide voltage-limiting element can be withIt avoids cable shield from generating overvoltage due to being struck by lightning, can play a protective role to cable shield.
In a kind of achievable mode, the electric current bleeder may also include that insulation crust, the first-grade protection circuitIt is set in the insulation crust, which is used to play the circuit of its inside the protection such as waterproof, insulation and isolationEffect.
In a kind of achievable mode, the impedance of the capacitor is less than the equivalent impedance of the cable shield, for example,Much smaller than the equivalent impedance of cable shield, (equivalent impedance can be obtained according to Dai Weinan equivalent theorem for the impedance of the capacitor), as the voltage class of cable is different, cable making material is different and the length of transmission line of electricity is different, cable shieldThe equivalent impedance of layer is different, and the value of capacitor employed in first-grade protection circuit and resistance also has difference.For example, forThe capacitor of 470 μ F can be used in the crosslinked polyetylene insulated polyvinyl chloride boot power cable of 35KV, and 10 Ω resistance can be used.It lets outThe high-frequency energy in circuit can be absorbed in capacitor in electric discharge road, induced voltage is reduced, for example, can inhibit 48Hz-1000KHzInduced voltage and fault overvoltage in range, and reduce the ungrounded end line-frequency induction voltage of sheath under system normal running (operation) conditionsSize, normal cable shielded layer protector can be overcome just for the protection defect of break over voltage height and Lightning Over-voltage.
In a kind of achievable mode, the resistance value of the resistance is less than the equivalent impedance of the cable shield, such as canUsing the resistance of 1~20 Ω, play the role of being divided with the equivalent resistance of cable shield, which can break LC and returnThe condition of resonance on road can avoid that resonance occurs, to avoid generating excessively high resonance potential.
In a kind of achievable mode, the cable is multi-phase cable, such as can be threephase cable, the multi-phase cableOne end multiphase it is cross interconnected after ground connection, form the ground terminal.
In a kind of achievable mode, the ground terminal is ungrounded with each phase cable shield in the multi-phase cableEnd constitutes circuit by a first-grade protection circuit respectively.Fig. 3 is a kind of cable shown according to an exemplary embodimentThe schematic diagram of shielded layer first-grade protection circuit, in electric current bleeder shown in fig. 3, which is with threephase cableExample is illustrated, which includes A phase, B phase and C phase, which connects end H1, H2 and H3 difference non-lyCircuit is constituted by a first-grade protection circuit and the common ground terminal of the shielded layer of each phase cable.
In a kind of achievable mode, the electric current bleeder may also include that high-voltage terminal, the electric current vent dischargeRoad is connected by the high-voltage terminal with the cable shield.
In a kind of achievable mode, the resistance is noninductive resistance, for example, to can be configured to thermal capacity big, scattered for the resistanceThe preferable noninductive resistance of hot property.
In a kind of achievable mode, the electric current bleeder may also include earthing pole, which is used for will be describedElectric current bleeder is connected with the earth, so that the electric current bleeder can release to electric current.
The beneficial effect of the cable shield electric current bleeder of the embodiment of the present invention is illustrated below.
The conducting wire of single-core cable and the relationship of metallic shield be seen as a transformer armature winding and it is secondary aroundGroup.When passing through alternating current in cable core, around a part of magnetic line of force for generating will intersect with shielded layer, make cable screensIt covers layer and generates induced voltage, the size of induced voltage and the length of cable run and the electric current flowed through in core are directly proportional.OnlineWhen road occurs short trouble, impacts by switching overvoltage or lightning stroke, very high induced voltage will form on cable shield, veryTo the jacket insulation layer that may puncture cable.Since cable shield distribution parameter is inductance and capacitor, in a certain specific frequencyUnder resonance can also occur so that the voltage of cable shield is very big, insulating layer can be damaged.The cable of the embodiment of the present inventionZinc oxide voltage-limiting element in shielded layer electric current bleeder can generate to avoid cable shield since cable is struck by lightningOvervoltage can also be used as the back-up protection of cable shield, and high-frequency energy can be absorbed in the capacitor of RC branch, reduce induced electricityPressure, series resistance can break LC loop resonance condition, avoid that resonance occurs and generate excessively high resonance potential.
Below by way of to the cable that above-mentioned electric current bleeder is not used and having used the electricity of above-mentioned electric current bleederThe result that cable is tested respectively is compared, to be illustrated to the beneficial effect of above-mentioned electric current bleeder:
By establishing shielding of the digital simulation model of cable shield to the cable for being not connected with above-mentioned electric current bleederLayer is tested, and following test result can be obtained:
Cable shield exists over the ground compared with high induction voltage, and load current is bigger, and induced voltage is bigger；Cable shield pairThere are more serious higher-order of oscillation components for ground voltage and electric current；There are biggish distribution capacity between threephase cable shielded layer,It is easy to cause high frequency resonant voltage.
The cable for having used above-mentioned electric current bleeder is tested, following test result can be obtained:
The damping circuit electric current through the above test results, we can know that cable shield electric current bleeder can release, effectivelyOpen-circuit over-voltage is avoided, meanwhile, it is capable to the energy for high frequency of releasing and prevent resonance.
It should be understood by those ordinary skilled in the art that: the discussion of any of the above embodiment is exemplary only, notIt is intended to imply that the scope of the present disclosure (including claim) is limited to these examples；Under thinking of the invention, above embodimentsOr can also be combined between the technical characteristic in different embodiments, step can be realized with random order, and be existed such asMany other variations of the upper different aspect of the invention, for simplicity, they are not provided in details.
In addition, to simplify explanation and discussing, and in order not to obscure the invention, it can in provided attached drawingIt is connect with showing or can not show with the well known power ground of integrated circuit (IC) chip and other components.Furthermore, it is possible toDevice is shown in block diagram form, to avoid obscuring the invention, and this has also contemplated following facts, i.e., about thisThe details of the embodiment of a little block diagram arrangements be height depend on will implementing platform of the invention (that is, these details shouldIt is completely within the scope of the understanding of those skilled in the art).Elaborating that detail (for example, circuit) is of the invention to describeIn the case where exemplary embodiment, it will be apparent to those skilled in the art that can be in these no detailsIn the case where or implement the present invention in the case that these details change.Therefore, these descriptions should be considered as explanationProperty rather than it is restrictive.
Although having been incorporated with specific embodiments of the present invention, invention has been described, according to retouching for frontIt states, many replacements of these embodiments, modifications and variations will be apparent for those of ordinary skills.ExampleSuch as, discussed embodiment can be used in other memory architectures (for example, dynamic ram (DRAM)).
The embodiment of the present invention be intended to cover fall into all such replacements within the broad range of appended claims,Modifications and variations.Therefore, all within the spirits and principles of the present invention, any omission, modification, equivalent replacement, the improvement madeDeng should all be included in the protection scope of the present invention.