CN112710931B - Method and system for detecting earth leakage current of secondary side long-distance cable pair of alternating current system - Google Patents
Method and system for detecting earth leakage current of secondary side long-distance cable pair of alternating current system Download PDFInfo
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- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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Abstract
The method and the system for detecting the earth leakage current by the long-distance cable on the secondary side of the alternating current system establish a leakage current composite detection criterion after compensation of inherent residual current and inherent leakage current, and realize detection of asymmetric leakage current and three-phase leakage current of the long-distance cable on the secondary side of the alternating current system through discrimination of a logic circuit; the insulation condition of the long cable is monitored on line, so that whether the potential hazard exists in the alternating current system is judged, and an alarm signal is sent out, so that the potential hazard of the ground fault caused by the abnormal insulation can be found in time, and the occurrence of fire accidents is effectively avoided; the composite criterion of current detection is introduced, and the inherent residual current is compensated, so that the protection dead zone is greatly reduced, the leakage alarm constant value is further reduced, and the discrimination sensitivity is improved.
Description
Technical Field
The invention belongs to the technical field of on-line monitoring of electrical equipment and loops of transformer substations, and particularly relates to a method and a system for detecting a ground leakage current of a secondary side long-distance cable of an alternating current system.
Background
The transformer substation with 220kV or below unattended operation and 500kV less attended operation gradually becomes normal, and higher requirements are provided for daily operation and maintenance of the transformer substation. The transformer substation electrical fire accident is the key point of transformer substation operation and maintenance work attention. In general, an in-station electrical fire is classified into a fire caused by a short circuit of a cable or a load and a fire caused by insulation breakdown, and the former has a large short-circuit current, and a fault current can be cut off by the operation of an air switch, a fuse, and a protection device. The latter generally has a small fault current, and is often discovered when an electric shock accident or a fire occurs, which has a great fire protection pressure on a substation alternating current system with a large number of cables. Leakage current caused by insulation damage occurs between the ABCN four lines and the ground wire, the insulation condition of a secondary circuit of the alternating current system of the transformer substation can be evaluated by monitoring, calculating and analyzing the contrast leakage current of a feeder cable and a load of the alternating current system, fault hidden dangers can be found in time, and fire accidents are effectively avoided.
In a transformer substation, long-distance cables of an alternating current chamber and a switching field are crossed in a secondary side loop of an alternating current system, for example, long-distance cables of an alternating current secondary loop of a high-voltage circuit breaker and long-distance cables of an air cooling loop of a transformer, the cable laying length is long, and insulation hidden trouble links are multiple. In the prior art, monitoring and protecting measures of a secondary side long-distance cable of a transformer substation alternating current system are mainly used for monitoring an air switch and residual current. The long-distance cables on the secondary side of the alternating current system of most transformer substations are provided with air switches, and when faults such as interphase short circuit and the like occur, the air switches can remove the faults; however, when the insulation between the two electrodes is damaged, the air switch cannot operate due to a small leakage current, and the leakage current is present for a long time, which may cause a fire in an unfavorable case. In recent years, due to the attention on fire caused by insulation damage, part of transformer substations are provided with total-station residual current monitoring devices, and part of key transformer substations are also provided with branch residual current monitoring devices, so that the insulation level of a long-distance cable branch can be monitored by means of a residual current transformer, but the residual current monitoring devices can only reflect single-phase leakage faults and have larger protection dead zones; especially, when a three-phase leakage current fault occurs, the offset effect between the leakage currents of all phases causes that the residual current monitoring device cannot reflect the three-phase leakage current fault. Therefore, the monitoring of the secondary side long-distance cable of the alternating current system is urgent, and leakage faults can be found in time.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide a method and a system for detecting the earth leakage current of the secondary side long-distance cable of the alternating current system, establish a leakage current composite detection criterion after inherent residual current compensation, and realize the detection of the asymmetric leakage current and the three-phase leakage current of the secondary side long-distance cable of the alternating current system through the discrimination of a logic circuit; the insulation condition of the long cable is monitored on line, so that whether the potential hazard exists in the alternating current system is judged, and an alarm signal is sent out, so that the potential hazard of the ground fault caused by the abnormal insulation can be found in time, and the occurrence of fire accidents is effectively avoided; the composite criterion of current detection is introduced, and the inherent residual current is compensated, so that the protection dead zone is greatly reduced, the leakage alarm constant value is further reduced, and the discrimination sensitivity is improved.
The invention adopts the following technical scheme.
The method for detecting the earth leakage current of the secondary side long-distance cable of the alternating current system comprises the following steps:
step 3, establishing a leakage current composite detection criterion based on the current data acquired in the step 2; compensating intrinsic residual current and intrinsic leakage current in the leakage current composite detection criterion based on the current data acquired in the step 1;
and 4, detecting asymmetric leakage current and three-phase leakage current of the secondary side long-distance cable of the alternating current system by judging a logic circuit according to the compensated leakage current composite detection criterion.
Preferably, the first and second liquid crystal display panels are,
the step 3 comprises the following steps:
step 3.1, establishing a detection criterion of the steady-state residual current based on the head end residual current; on the basis of the inherent residual current of the head end, the inherent residual current in the detection criterion of the steady-state residual current is compensated;
step 3.2, establishing a detection criterion of residual current increment based on a vector difference between the residual current of the head end at the moment t and the residual current of the head end at the moment t + delta t; compensating the inherent residual current in the detection criterion of the residual current increment based on the inherent residual current of the head end;
3.3, establishing a detection criterion of the steady-state residual current differential motion based on the head end residual current and the tail end residual current; compensating the inherent residual current in the detection criterion of the steady-state residual current differential motion based on the inherent residual current of the head end and the inherent residual current of the tail end;
step 3.4, establishing a detection criterion of the single-phase current difference flow based on the head end leakage current and the tail end leakage current; and compensating the inherent leakage current in the detection criterion of the single-phase current difference current based on the inherent leakage current at the head end and the inherent leakage current at the tail end.
Preferably, the first and second electrodes are formed of a metal,
in step 3.1, the detection criterion of the steady-state residual current after the inherent residual current compensation meets the following relational expression:
in the formula (I), the compound is shown in the specification,
I M the head-end residual current is represented,
I′ M the residual current inherent in the head end is represented,
I MA representing the head end a-phase load current,
I w1 an alarm set value indicative of a steady state residual current overflow,
I w2 an alarm constant value representing the steady-state residual current under heavy load and satisfying I w2 ＝k 1 I w1 ，
I e And the rated current of the long-distance cable on the secondary side of the alternating current system is shown.
Preferably, the first and second electrodes are formed of a metal,
in step 3.2, the detection criterion of the residual current increment after the inherent residual current compensation meets the following relational expression:
|I M (t)-I M (t+Δt)|>ΔI z1
in the formula (I), the compound is shown in the specification,
I M (t) represents the head end residual current at time t,
I M (t + Δ t) represents the head end residual current at time t + Δ t, where Δ t represents a fixed time interval,
ΔI z1 representing a constant value of the residual current increment.
Preferably, the first and second liquid crystal display panels are,
in step 3.3, the detection criterion of the steady-state residual current differential after the inherent residual current compensation meets the following relational expression:
in the formula (I), the compound is shown in the specification,
I d representing the difference between the head-end steady state residual current and the tail-end steady state residual current,
I′ d representing the difference current of the head end steady state intrinsic residual current and the tail end steady state intrinsic residual current,
I wd1 an alarm constant value indicative of a steady state residual current differential current flowing,
I wd2 and the alarm constant value represents the steady state residual current difference current under heavy load.
Preferably, the first and second electrodes are formed of a metal,
in step 3.4, the detection criterion of the single-phase current difference current after the compensation of the inherent leakage current meets the following relational expression:
|I MA -I NA -I′ Ad |>I w1A
in the formula (I), the compound is shown in the specification,
I NA showing the load current of the end a phase,
I′ Ad representing the difference flow of the head end intrinsic leakage current and the tail end intrinsic leakage current,
I w1A alarm set values representing phase a current difference flow.
Preferably, the first and second electrodes are formed of a metal,
in the step 4, the process is carried out,
the detection of the asymmetric leakage current of the long-distance cable on the secondary side of the alternating current system is realized through the judgment of a logic circuit by using a detection criterion of the steady-state residual current after the compensation of the inherent residual current, a detection criterion of the residual current increment and a detection criterion of the steady-state residual current differential motion;
the detection criterion of the steady-state residual current after the inherent residual current compensation, the detection criterion of the residual current increment, the detection criterion of the steady-state residual current differential motion and the detection criterion of the single-phase current difference after the inherent leakage current compensation are distinguished by a logic circuit, so that the detection of the three-phase leakage current of the long-distance cable on the secondary side of the alternating current system is realized.
The system for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system comprises: the device comprises a current acquisition module, an electric leakage detection module and an electric leakage fault diagnosis display module;
the current acquisition module comprises N head end current acquisition modules and N tail end current acquisition modules; the current acquisition module is used for acquiring the inherent residual current of the head end, the inherent residual current of the tail end, the inherent leakage current of the head end and the inherent leakage current of the tail end of the secondary side long-distance cable of the alternating current system at the construction acceptance stage of the secondary side long-distance cable of the alternating current system; the method is also used for acquiring head end residual current, tail end residual current, head end leakage current and tail end leakage current of the secondary side long-distance cable of the alternating current system at the state detection stage of the secondary side long-distance cable of the alternating current system;
the leakage detection module comprises a leakage current composite detection unit and a logic circuit; the leakage current composite detection unit is internally provided with a leakage current composite detection criterion compensated by inherent residual current and inherent leakage current; the logic circuit comprises a NOR gate and an AND gate; the leakage detection module utilizes leakage current composite detection criteria to realize detection of asymmetric leakage current and three-phase leakage current of the long-distance cable on the secondary side of the alternating current system through discrimination of the logic circuit;
and the electric leakage fault display module is used for displaying the detected electric leakage fault in real time.
Preferably, the first and second electrodes are formed of a metal,
head end current acquisition module includes: residual current transformers integrally arranged on the A-phase, B-phase, C-phase and N-phase wires on the side, close to the bus, of the cable and a single-phase current transformer arranged on any phase of the side, close to the bus, of the cable;
a terminal current collection module comprising: the residual current transformers are integrally arranged on the A phase, the B phase, the C phase and the N line of the cable close to the load side, and the single-phase current transformer is arranged on any phase of the cable close to the load side.
Compared with the prior art, the invention has the beneficial effects that:
1. the insulation condition of the long cable is monitored on line, whether hidden danger exists in an alternating current system is judged, and an alarm signal is sent out, so that the hidden danger of ground fault caused by insulation abnormity can be found in time, and the occurrence of fire accidents is effectively avoided.
2. The composite criterion of current detection is introduced, and the inherent residual current is compensated, so that the protection dead zone is greatly reduced, the leakage alarm constant value is further reduced, and the discrimination sensitivity is improved.
Drawings
FIG. 1 is a flow chart of a method for detecting a ground leakage current of a secondary side long-distance cable of an AC system according to the present invention;
FIG. 2 is a schematic diagram illustrating a leakage current composite detection criterion in the method for detecting a leakage current of a secondary side long-distance cable pair of an AC system according to the present invention;
FIG. 3 is a graph showing the action of the steady-state residual current differential in the method for detecting the earth leakage current by using the secondary side long-distance cable pair of the AC system according to the present invention;
FIG. 4 is a comparison graph of the changes of the protection dead zone and the criterion sensitivity before and after the compensation of the inherent residual current in the method for detecting the earth leakage current by using the secondary side long-distance cable pair of the AC system according to the present invention;
FIG. 5 is a schematic diagram of a logic circuit in the method for detecting the earth leakage current of the secondary side long-distance cable pair of the AC system according to the present invention;
fig. 6 is a schematic diagram of a system for detecting a secondary side long-distance cable to ground leakage current of an ac system according to the present invention.
Detailed Description
The present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.
Referring to fig. 1, the method for detecting the earth leakage current of the secondary side long-distance cable of the alternating current system comprises the following steps:
And 2, as shown in fig. 2, in the state detection stage of the secondary side long-distance cable of the alternating current system, respectively acquiring the head end residual current and the tail end residual current of the secondary side long-distance cable of the alternating current system by using the residual current transformer, and respectively acquiring the head end leakage current and the tail end leakage current of the secondary side long-distance cable of the alternating current system by using the single-phase current transformer.
In the preferred embodiment, the A phase, the B phase, the C phase and the N line at the head end and the tail end of the cable are integrally provided with residual current transformers, and residual current data of the long-distance cable on the secondary side of the alternating current system are acquired respectively in the construction acceptance stage and the state detection stage; and installing single-phase current transformers on A phases at the head end and the tail end of the cable, and respectively collecting the secondary side long-distance cable leakage current of the alternating current system in a construction acceptance stage and a state detection stage.
It should be noted that, a person skilled in the art may select the phase line on which the single-phase current transformer is installed according to actual application needs, and in the preferred embodiment, various leakage alarms including the B-phase, the C-phase and the three-phase can be implemented by monitoring the leakage current of the a-phase and the residual current of the three-phase, so that the preferred embodiment of the present invention selects to install the single-phase current transformer on the a-phase, which is a non-limiting preferred option.
Step 3, establishing a leakage current composite detection criterion based on the current data acquired in the step 2; and (2) compensating the inherent residual current and the inherent leakage current in the leakage current composite detection criterion based on the current data acquired in the step (1).
In the preferred embodiment, the collected current data at the head end of the cable is used as the basis for establishing the detection criteria, and a person skilled in the art can select the current data at the head end or the tail end to establish the detection basis according to the actual application situation of the engineering. The preferred embodiment of the present invention uses head-end current data as a non-limiting preferred choice.
In particular, the amount of the solvent to be used,
the step 3 comprises the following steps:
step 3.1, establishing a detection criterion of the steady-state residual current based on the head end residual current; and compensating the inherent residual current in the detection criterion of the steady-state residual current based on the inherent residual current of the head end.
In particular, the amount of the solvent to be used,
in step 3.1, the detection criterion of the steady-state residual current after the inherent residual current compensation meets the following relational expression:
in the formula (I), the compound is shown in the specification,
I M the head-end residual current is represented,
I′ M the residual current inherent in the head end is represented,
I MA representing the head end a-phase load current,
I w1 an alarm constant value indicative of a steady state residual current overflow,
I w2 the alarm constant value of the steady-state residual current under the heavy load is represented and meets I w2 ＝k 1 I w1 In the preferred embodiment, k 1 ＝1.5，
I e And the rated current of the long-distance cable on the secondary side of the alternating current system is shown.
Step 3.2, establishing a detection criterion of residual current increment based on a vector difference between the residual current of the head end at the moment t and the residual current of the head end at the moment t + delta t; and compensating the inherent residual current in the detection criterion of the residual current increment based on the inherent residual current of the head end.
In particular, the amount of the solvent to be used,
in step 3.2, the detection criterion of the residual current increment after the inherent residual current compensation meets the following relational expression:
|I M (t)-I M (t+Δt)|>ΔI z1
in the formula (I), the compound is shown in the specification,
I M (t) represents the head end residual current at time t,
I M (t + Δ t) represents the head end residual current at time t + Δ t, where Δ t represents a fixed time interval,
ΔI z1 representing a constant value of the residual current increment.
3.3, establishing a detection criterion of the steady-state residual current differential motion based on the head end residual current and the tail end residual current; and compensating the inherent residual current in the detection criterion of the steady-state residual current differential motion based on the inherent residual current of the head end and the inherent residual current of the tail end.
In particular, the amount of the solvent to be used,
in step 3.3, as shown in fig. 3, the detection criterion of the steady-state residual current differential compensated by the inherent residual current satisfies the following relation:
in the formula (I), the compound is shown in the specification,
I d representing the difference between the head-end steady state residual current and the tail-end steady state residual current,
I′ d representing the difference current of the head end steady state intrinsic residual current and the tail end steady state intrinsic residual current,
I wd1 an alarm constant value representing a steady state residual current differential current over-current,
I wd2 and the alarm constant value represents the steady state residual current difference current under heavy load.
Step 3.4, establishing a detection criterion of the single-phase current difference flow based on the head end leakage current and the tail end leakage current; and compensating the inherent leakage current in the detection criterion of the single-phase current difference current based on the inherent leakage current at the head end and the inherent leakage current at the tail end.
In particular, the amount of the solvent to be used,
in step 3.4, the detection criterion of the single-phase current difference current after the compensation of the inherent leakage current meets the following relational expression:
|I MA -I NA -I′ Ad |>I w1A
in the formula (I), the compound is shown in the specification,
I NA which represents the leakage current at the end of the line,
I′ Ad representing the difference flow of the head end intrinsic leakage current and the tail end intrinsic leakage current,
I w1A alarm set values representing phase a current difference flow.
The change of the protection dead zone before and after the compensation of the inherent residual current and the inherent leakage current is compared with that of the left graph in figure 4, and the protection dead zone is greatly reduced after the inherent residual current and the inherent leakage current are compensated by adopting the detection method provided by the invention.
The change of the discrimination sensitivity before and after the compensation of the inherent residual current and the inherent leakage current is compared with the graph on the right side of the graph in FIG. 4, and after the inherent residual current and the inherent leakage current are compensated by adopting the detection method provided by the invention, the electric leakage alarm fixed value is further reduced, and the discrimination sensitivity is improved.
And 4, detecting asymmetric leakage current and three-phase leakage current of the secondary side long-distance cable of the alternating current system by judging a logic circuit according to the compensated leakage current composite detection criterion.
In particular, the amount of the solvent to be used,
in the step 4, the process is carried out,
as shown in fig. 5, the detection criterion of the steady-state residual current, the detection criterion of the residual current increment and the detection criterion of the steady-state residual current differential after the inherent residual current compensation are distinguished by the logic circuit, so as to realize the detection of the asymmetric leakage current of the secondary side long-distance cable of the alternating current system;
as shown in fig. 5, the detection criteria of the steady-state residual current after the inherent residual current compensation, the detection criteria of the residual current increment, the detection criteria of the steady-state residual current differential, and the detection criteria of the single-phase current difference after the inherent leakage current compensation are distinguished by the logic circuit, so that the detection of the three-phase leakage current of the long-distance cable on the secondary side of the alternating current system is realized.
In the preferred embodiment, the logic circuit is shown in fig. 5 and includes a nor gate, a first and gate, and a second and gate. It should be noted that, those skilled in the art can design and develop logic circuits using different digital processor modules according to actual requirements, so as to implement detection of asymmetric leakage and three-phase leakage according to multiple detection criteria. The logic circuitry in the preferred embodiment of the present invention is only for the non-limiting preferred choice of implementing leakage current detection based on composite detection criteria.
As shown in fig. 6, the system for detecting the earth leakage current of the secondary side long-distance cable of the ac system includes: the device comprises a current acquisition module, an electric leakage detection module and an electric leakage fault diagnosis display module.
The current acquisition module comprises N head end current acquisition modules and N tail end current acquisition modules; the current acquisition module is used for acquiring the inherent residual current of the head end, the inherent residual current of the tail end, the inherent leakage current of the head end and the inherent leakage current of the tail end of the secondary side long-distance cable of the alternating current system at the construction acceptance stage of the secondary side long-distance cable of the alternating current system; the method is also used for collecting the head end residual current, the tail end residual current, the head end leakage current and the tail end leakage current of the secondary side long-distance cable of the alternating current system in the state detection stage of the secondary side long-distance cable of the alternating current system.
The leakage detection module comprises a leakage current composite detection unit and a logic circuit; the leakage current composite detection unit is internally provided with a leakage current composite detection criterion compensated by inherent residual current and inherent leakage current; the logic circuit comprises a NOR gate and an AND gate; the leakage detection module utilizes leakage current composite detection criteria to realize detection of asymmetric leakage current and three-phase leakage current of the secondary side long-distance cable of the alternating current system through discrimination of the logic circuit.
And the electric leakage fault display module is used for displaying the detected electric leakage fault in real time.
In particular, the amount of the solvent to be used,
head end current acquisition module includes: the residual current transformers are integrally arranged on the A phase, the B phase, the C phase and the N phase of the cable close to the bus side, and the single-phase current transformer is arranged on any phase of the cable close to the bus side.
A terminal current collection module comprising: the residual current transformers are integrally arranged on the A phase, the B phase, the C phase and the N line of the cable close to the load side, and the single-phase current transformer is arranged on any phase of the cable close to the load side.
Compared with the prior art, the invention has the beneficial effects that:
1. the insulation condition of the long cable is monitored on line, whether hidden danger exists in an alternating current system is judged, and an alarm signal is sent out, so that the hidden danger of ground fault caused by insulation abnormity can be found in time, and the occurrence of fire accidents is effectively avoided.
2. The composite criterion of current detection is introduced, and the inherent residual current is compensated, so that the protection dead zone is greatly reduced, the leakage alarm constant value is further reduced, and the discrimination sensitivity is improved.
The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.
Claims (9)
1. A method for detecting the earth leakage current of a long-distance cable on the secondary side of an alternating current system is characterized in that,
the method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system comprises the following steps:
step 1, in the construction acceptance stage of the secondary side long-distance cable of the alternating current system, respectively acquiring the inherent residual current of the head end and the inherent residual current of the tail end of the secondary side long-distance cable of the alternating current system by using a residual current transformer, and respectively acquiring the inherent leakage current of the head end and the inherent leakage current of the tail end of the secondary side long-distance cable of the alternating current system by using a single-phase current transformer;
step 2, in the state detection stage of the long-distance cable on the secondary side of the alternating current system, respectively collecting the head end residual current and the tail end residual current of the long-distance cable on the secondary side of the alternating current system by using a residual current transformer, and respectively collecting the head end leakage current and the tail end leakage current of the long-distance cable on the secondary side of the alternating current system by using a single-phase current transformer;
step 3, establishing a leakage current composite detection criterion based on the current data acquired in the step 2; compensating intrinsic residual current and intrinsic leakage current in the leakage current composite detection criterion based on the current data acquired in the step 1;
the step 3 comprises the following steps:
step 3.1, establishing a detection criterion of the steady-state residual current based on the head end residual current; compensating inherent residual current in the detection criterion of the steady-state residual current based on the inherent residual current of the head end;
step 3.2, establishing a detection criterion of residual current increment based on a vector difference between the residual current of the head end at the moment t and the residual current of the head end at the moment t + delta t; compensating the inherent residual current in the detection criterion of the residual current increment based on the inherent residual current of the head end;
3.3, establishing a detection criterion of the steady-state residual current differential motion based on the head-end residual current and the tail-end residual current; compensating the inherent residual current in the detection criterion of the steady-state residual current differential motion based on the inherent residual current of the head end and the inherent residual current of the tail end;
step 3.4, establishing a detection criterion of the single-phase current difference flow based on the head end leakage current and the tail end leakage current; compensating the inherent leakage current in the detection criterion of the single-phase current difference current based on the inherent leakage current at the head end and the inherent leakage current at the tail end;
and 4, detecting asymmetric leakage current and three-phase leakage current of the secondary side long-distance cable of the alternating current system by judging a logic circuit according to the compensated leakage current composite detection criterion.
2. The method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system as claimed in claim 1,
in step 3.1, the detection criterion of the steady-state residual current after the inherent residual current compensation meets the following relational expression:
in the formula (I), the compound is shown in the specification,
I M the head-end residual current is represented,
I′ M the residual current inherent in the head end is represented,
I MA to representThe head end of the A-phase load current,
I w1 an alarm set value indicative of a steady state residual current overflow,
I w2 an alarm constant value representing the steady-state residual current under heavy load and satisfying I w2 ＝k 1 I w1 ，k 1 In order to be the load factor,
I e and the rated current of the long-distance cable on the secondary side of the alternating current system is shown.
3. The method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system as claimed in claim 1,
in step 3.2, the detection criterion of the residual current increment after the inherent residual current compensation meets the following relational expression:
|I M (t)-I M (t+Δt)|＞ΔI z1
in the formula (I), the compound is shown in the specification,
I M (t) represents the head end residual current at time t,
I M (t + Δ t) represents the head end residual current at time t + Δ t, where Δ t represents a fixed time interval,
ΔI z1 representing a constant value of the residual current increment.
4. The method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system as claimed in claim 1,
in step 3.3, the detection criterion of the steady-state residual current differential after the inherent residual current compensation meets the following relational expression:
in the formula (I), the compound is shown in the specification,
I d representing the difference between the head-end steady state residual current and the tail-end steady state residual current,
I′ d representing head-end and tail-end steady-state intrinsic residual currentsThe difference stream is then fed back to the first stage,
I MA the load current of the A phase at the head end is shown,
I wd1 an alarm constant value indicative of a steady state residual current differential current flowing,
I wd2 an alarm constant value representing a steady state residual current differential current under heavy load,
I e and the rated current of the long-distance cable on the secondary side of the alternating current system is shown.
5. The method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system as claimed in claim 1,
in step 3.4, the detection criterion of the single-phase current difference current after the compensation of the inherent leakage current meets the following relational expression:
|I MA -I NA -I′ Ad |＞I w1A
in the formula (I), the compound is shown in the specification,
I NA showing the load current of the end a phase,
I MA representing the head end a-phase load current,
I′ Ad representing the difference flow of the head end intrinsic leakage current and the tail end intrinsic leakage current,
I w1A an alarm set value representing the phase a current differential flow.
6. The method for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system as claimed in claim 1,
in the step 4, the process is carried out,
the detection of the asymmetric leakage current of the long-distance cable on the secondary side of the alternating current system is realized through the judgment of a logic circuit by using a detection criterion of the steady-state residual current after the compensation of the inherent residual current, a detection criterion of the residual current increment and a detection criterion of the steady-state residual current differential motion;
the detection of the three-phase leakage current of the long-distance cable on the secondary side of the alternating current system is realized through the discrimination of a logic circuit by the detection criterion of the steady-state residual current after the inherent residual current compensation, the detection criterion of the residual current increment, the detection criterion of the steady-state residual current differential motion and the detection criterion of the single-phase current difference after the inherent leakage current compensation.
7. The system for detecting the earth leakage current of the secondary side long-distance cable of the alternating current system according to any one of claims 1 to 6,
the system for detecting the earth leakage current of the secondary side long-distance cable pair of the alternating current system comprises: the device comprises a current acquisition module, an electric leakage detection module and an electric leakage fault diagnosis display module;
the current acquisition module comprises N head end current acquisition modules and N tail end current acquisition modules; the current acquisition module is used for acquiring the inherent residual current of the head end, the inherent residual current of the tail end, the inherent leakage current of the head end and the inherent leakage current of the tail end of the secondary side long-distance cable of the alternating current system at the construction acceptance stage of the secondary side long-distance cable of the alternating current system; the method is also used for acquiring head end residual current, tail end residual current, head end leakage current and tail end leakage current of the secondary side long-distance cable of the alternating current system at the state detection stage of the secondary side long-distance cable of the alternating current system;
the leakage detection module comprises a leakage current composite detection unit and a logic circuit; the leakage current composite detection unit is internally provided with a leakage current composite detection criterion compensated by inherent residual current and inherent leakage current; the logic circuit comprises a NOR gate and an AND gate; the leakage current detection module utilizes leakage current composite detection criteria to realize detection of asymmetric leakage current and three-phase leakage current of the long-distance cable on the secondary side of the alternating current system through discrimination of the logic circuit;
and the electric leakage fault display module is used for displaying the detected electric leakage fault in real time.
8. The system for detecting the secondary side long-distance cable-to-earth leakage current of the alternating current system as claimed in claim 7,
the head end current acquisition module includes: the residual current transformers are integrally arranged on the A phase, the B phase, the C phase and the N phase of the cable close to the bus side, and the single-phase current transformer is arranged on any phase of the cable close to the bus side.
9. The system for detecting the secondary side long-distance cable-to-earth leakage current of the alternating current system as claimed in claim 8,
the terminal current collection module includes: the residual current transformers are integrally arranged on the A phase, the B phase, the C phase and the N line of the cable close to the load side, and the single-phase current transformer is arranged on any phase of the cable close to the load side.
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