CN109782106B - Direct current system ground fault searching device and method - Google Patents
Direct current system ground fault searching device and method Download PDFInfo
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- CN109782106B CN109782106B CN201910011949.4A CN201910011949A CN109782106B CN 109782106 B CN109782106 B CN 109782106B CN 201910011949 A CN201910011949 A CN 201910011949A CN 109782106 B CN109782106 B CN 109782106B
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Abstract
The invention discloses a direct current system ground fault finding method, which comprises the steps of identifying ground faults loop by loop, and identifying the ground faults branch by branch after determining a secondary loop with faults; the ground fault is found and immediately processed. The method for identifying the ground fault comprises the following steps: a shunt switch of a secondary circuit or an extremely short seal of a control fuse which is not in fault is used for connecting a universal meter in series at two ends of a fault one-pole switch or the control fuse; connecting one end of a test resistor with the resistance value R to the ungrounded one pole, and connecting the other end of the test resistor with the ground wire to form a loop with a ground fault point; disconnecting the switch or controlling the fuse, observing and recording the reading of the multimeter; and then disconnecting the grounded end of the test resistor, observing and recording the reading of the multimeter again, and if the difference value of the two readings of the multimeter is equivalent to the calculated current flowing through the test resistor, judging that the ground fault occurs. The invention can search the grounding point by adopting a segmented searching method under the condition of no shutdown, and search and eliminate the grounding fault; is simple and easy to operate.
Description
Technical Field
The invention relates to a ground fault finding device and method, in particular to a direct current system ground fault finding device and method, and belongs to the technical field of high-low voltage power distribution maintenance.
Background
The direct current control loop in the distribution room is wide in distribution, complex in path and multiple in exposed part. The direct current network is easily affected by external environmental factors, and under the action of adverse factors such as moisture, dust and the like, the insulation level of the direct current network is reduced, and even insulation damage can occur to ground. If the positive pole and the negative pole are grounded, the direct current loop short circuit fault occurs, the switch of the loop is tripped or the fuse wire is broken, the direct current system of the corresponding part is powered off, and the protection system loses the protection function. If one of the poles is grounded, the dc system continues to operate, which is a dangerous abnormal situation. If the protection circuit is grounded along with other points, the circuit breaker can be tripped mistakenly, and great economic loss is caused to production.
Disclosure of Invention
The invention aims to provide a device and a method for searching a direct current system ground fault.
In order to solve the technical problems, the invention adopts the technical scheme that:
a method for searching a ground fault of a direct current system comprises the following specific steps:
step 1: identifying the ground fault loop by loop: the method comprises the following specific steps:
step 1-1: judging the polarity of the occurrence of the ground fault: a shunt switch of a secondary circuit or an extremely short seal of a control fuse which is not in fault is used for connecting a universal meter in series at two ends of a fault one-pole switch or the control fuse;
step 1-2: connecting one end of a test resistor with the resistance value R to the ungrounded one pole, and connecting the other end of the test resistor with the ground wire to form a loop with a ground fault point;
step 1-3: calculate the current flowing through the test resistor: i = 220/R;
step 1-4: identifying a ground fault: disconnecting the switch or controlling the fuse, observing and recording the reading of the multimeter; disconnecting the grounded end of the test resistor, observing and recording the reading of the multimeter again, if the difference value of the two readings of the multimeter is equivalent to the current flowing through the test resistor calculated in the step 1-3, judging that a ground fault occurs, and turning to the step 2; otherwise, judging that no ground fault occurs.
Step 2: identifying the ground fault by branch: according to the sequence of the signal and indicator lamp part first and the operation part later and the outdoor part first and the indoor part later, the branch circuit terminal is gradually disconnected on the premise that the branch cannot be opened before the branch circuit terminal is disconnected, and whether the ground fault exists is identified by adopting the method in the step 1-4; if the grounding fault is found, turning to the step 3, otherwise, turning to the step 4;
and step 3: processing a ground fault;
and 4, step 4: and (4) closing the branch circuit terminal disconnected in the step (2).
Further, the resistance value of the test resistor is 44K Ω.
Further, the accuracy of the multimeter is 1/20000 of range.
The technical effect obtained by adopting the technical scheme is as follows:
1. the invention can search and eliminate the earth fault under the condition of no shutdown;
2. the invention adopts a method of sectional searching processing to search the grounding point, thereby eliminating the hidden trouble of equipment.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a flow chart of the present invention;
wherein: 1. multimeter 2, ground fault point 3, short seal 4, test resistance.
Detailed Description
Example 1:
a method for searching a ground fault of a direct current system comprises the following specific steps:
step 1: identifying the ground fault loop by loop: the method comprises the following specific steps:
step 1-1: judging the polarity of the occurrence of the ground fault: a shunt switch of a secondary circuit or an extremely short seal of a control fuse which is not in fault is used for connecting a universal meter in series at two ends of a fault one-pole switch or the control fuse;
step 1-2: connecting one end of a test resistor with the resistance value R to the ungrounded one pole, and connecting the other end of the test resistor with the ground wire to form a loop with a ground fault point;
step 1-3: calculate the current flowing through the test resistor: i = 220/R;
step 1-4: identifying a ground fault: disconnecting the switch or controlling the fuse, observing and recording the reading of the multimeter; disconnecting the grounded end of the test resistor, observing and recording the reading of the multimeter again, if the difference value of the two readings of the multimeter is equivalent to the current flowing through the test resistor calculated in the step 1-3, judging that a ground fault occurs, and turning to the step 2; otherwise, judging that no ground fault occurs.
Step 2: identifying the ground fault by branch: according to the sequence of the signal and indicator lamp part first and the operation part later and the outdoor part first and the indoor part later, the branch circuit terminal is gradually disconnected on the premise that the branch cannot be opened before the branch circuit terminal is disconnected, and whether the ground fault exists is identified by adopting the method in the step 1-4; if the grounding fault is found, turning to the step 3, otherwise, turning to the step 4;
and step 3: processing a ground fault;
and 4, step 4: and (4) closing the branch circuit terminal disconnected in the step (2).
Further, the resistance value of the test resistor is 44K Ω.
Further, the accuracy of the multimeter is 1/20000 of range.
A44K omega resistor, a 4-bit half-digital multimeter and a plurality of wired meter clamps were prepared. The shunt switch of the secondary circuit or the non-fault one-pole control fuse is short-sealed by an instrument clamp with a connecting wire, the gear of the multimeter is driven to 10A, and the multimeter is reliably and firmly connected in series to the two ends of the fault one-pole switch or the control fuse by an instrument pen wire or the instrument clamp with the connecting wire.
One end of the 44K omega resistor is connected to the ungrounded pole, the other end is connected with the ground wire (see the figure), and a ground fault point forms a loop, and the calculation can be carried out to obtain: i = U/R =220V/44K Ω =5 mA. That is, the current flowing through the resistor is 5mA, the resistance value of the coil of the relay is more than ten thousand at present, the action current is 21mA, and the current shortage of 5mA causes the malfunction. And (4) disconnecting the switch or controlling the fuse, observing the reading of the multimeter, and recording the reading. The 44K Ω resistor was then disconnected from the ground and the multimeter reading was observed for a 5mA change. The resistance grounding end is grounded repeatedly for several times, if the reading of the multimeter is unchanged, the secondary control loop is well insulated, and no grounding fault occurs. And searching the next secondary branch by the same short-sealing switch method, and if the reading of the multimeter changes in the range of 5mA, which indicates that the control loop has a grounding fault, reducing the range of searching the grounding point to the secondary control loop.
And (4) according to the schematic diagram of the loop, adopting a method of sectional searching processing, gradually disconnecting branch loop terminals (before the branch loop terminals are disconnected, branches cannot be opened) according to the content of the step four, and adopting the principle that the signal and indicator lamp part is firstly followed by the operation part, and the outdoor part is firstly followed by the indoor part. The cut-off time should be as short as possible, regardless of whether the circuit is grounded or not. When a certain branch circuit is grounded, the grounding point is found and processed in time.
Because the testing direct current grounding current is in milliampere level, a four-bit half-digital multimeter is adopted in actual searching for ensuring the testing precision. In the display panel of the digital instrument, three and a half mean 3 and 2 to 1 digital multimeter, the maximum display 1999, three and a half, three-digit represents that three digits are from 1 to 9, half means 2 to 1, four-digit half precision is higher than three and a half, and the principle is the same as three and a half; the three-position half precision can reach 1/2000, and the three-position half precision can reach 1/1000; the four-digit half maximum energy shows 19999 energy to 1/20000 and the four-digit half maximum energy shows 1/10000.
Claims (3)
1. A method for searching a ground fault of a direct current system is characterized by comprising the following steps: the method comprises the following specific steps:
step 1: identifying the ground fault loop by loop: the method comprises the following specific steps:
step 1-1: judging the polarity of the occurrence of the ground fault: the switch of the secondary loop or the one-pole short seal without fault of the control fuse is connected with the two ends of the fault one-pole switch or the control fuse in series;
step 1-2: connecting one end of a test resistor with the resistance value R to the ungrounded one pole, and connecting the other end of the test resistor with the ground wire to form a loop with a ground fault point;
step 1-3: calculate the current flowing through the test resistor: i = 220/R;
step 1-4: identifying a ground fault: disconnecting the switch or controlling the fuse, observing and recording the reading of the multimeter; disconnecting the grounded end of the test resistor, observing and recording the reading of the multimeter again, if the difference value of the two readings of the multimeter is equivalent to the current flowing through the test resistor calculated in the step 1-3, judging that a ground fault occurs, and turning to the step 2; otherwise, judging that no ground fault occurs;
step 2: identifying the ground fault by branch: according to the sequence of the signal and indicator lamp part first and then the operation part, the outdoor part first and then the indoor part, the branch circuit terminal is gradually disconnected on the premise that the branch cannot be opened before the branch circuit terminal is disconnected, and whether the ground fault exists is identified by adopting the method in the step 1-4; if the grounding fault is found, turning to the step 3, otherwise, turning to the step 4;
and step 3: processing a ground fault;
and 4, step 4: and (4) closing the branch circuit terminal disconnected in the step (2).
2. The dc system ground fault lookup method of claim 1, wherein: the resistance value of the test resistor is 44K omega.
3. The dc system ground fault lookup method of claim 1, wherein: further, the accuracy of the multimeter is 1/20000 of range.
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