CN104111370A - Method for measuring zero-sequence current in three-phase ungrounded system - Google Patents
Method for measuring zero-sequence current in three-phase ungrounded system Download PDFInfo
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- CN104111370A CN104111370A CN201410302314.7A CN201410302314A CN104111370A CN 104111370 A CN104111370 A CN 104111370A CN 201410302314 A CN201410302314 A CN 201410302314A CN 104111370 A CN104111370 A CN 104111370A
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Abstract
The invention discloses a method for measuring zero-sequence current in a three-phase ungrounded system. The method includes the following steps: step one, using current transformers with large transformation ratios to measure primary side three-phase current; step two, using the abovementioned current transformers to perform secondary side current three-phase synthesis; step three, using a micro current transformer with a small transformation ratio to measure the synthetic secondary side current to output small current; and step four, after connecting the output small current in the step three with a resistor, converting the output small current to output voltage which is converted to digital signals through an AD converter and sent to a detection device. According to the invention, the method for measuring a primary part of zero-sequence current adopts a large transformation ratio method, production is convenient, measuring accuracy is high, and small current can be measured; the resolution ratio of zero-sequence current measurement of a bus can be improved, and when a ground fault occurs in the bus, ground current of the ground fault can be precisely judged according to the method, thereby reducing power failure time caused by ground connection of the bus.
Description
Technical field
The invention belongs to power measurement field, relate to a kind of in three-phase isolated neutral system the measuring method of zero-sequence current.
Background technology
During the electric system single phase ground fault of power transformer isolated neutral, there is no short-circuit loop, can not produce short-circuit current, relay protection of power system can trip, and electric system allows to continue operation a period of time.But single-phase earthing is also harmful to electric system.Therefore, during this system single phase ground fault, relay protection must be sent alerting signal, by operator, makes respective handling, finally faulty line is carried out to interruption maintenance.
For faulty line is carried out to interruption maintenance, relay protection should be sent alerting signal and be pointed out faulty line.Relay protection judges whether single phase ground fault is easy to realize.But capacity current during isolated neutral system single phase ground fault is less, judge which bar line failure just very difficult.So far the performance factor of one-phase grounding wire-selective device is very low both at home and abroad.
Summary of the invention
The technical problem to be solved in the present invention be to provide a kind of in three-phase isolated neutral system the measuring method of zero-sequence current, the measuring method that has solved traditional bus zero-sequence current all adopts the little no-load voltage ratio mode of current transformer to measure, and has that measuring accuracy is low, bus zero-sequence current measures inaccurate shortcoming when very little;
Zero sequence current measurement method of the present invention, adopts large velocity ratio mode, has measuring accuracy high, can measure the feature of existing current signal when bus zero-sequence current is very little.
For achieving the above object, technical scheme of the present invention is as follows:
A measuring method for zero-sequence current in three-phase isolated neutral system, comprises the following steps:
Step 1, utilize the current transformer of large velocity ratio to measure primary side three-phase current;
Step 2, above-mentioned current transformer carry out secondary side, and to carry out current three-phase synthetic;
Step 3, synthetic secondary side current are measured the little electric current of output by miniature little transformation ratio current transformer;
Step 4, step 3 is exported after little current-series resistance, be converted to output voltage, this output voltage is converted to digital signal by AD converter and delivers to pick-up unit.
In a preferred embodiment of the invention, the large velocity ratio numerical value in described step 1 is 300-600.
In a preferred embodiment of the invention, the miniature little no-load voltage ratio numerical value in described step 3 is 2.
By above technical scheme, the invention has the beneficial effects as follows:
Zero sequence current measurement method of the present invention adopts large velocity ratio mode, has measuring accuracy high, can survey little electric current; Can improve the resolution to bus zero sequence current measurement, when earth fault appears in bus, can accurately judge according to the method type and the distance of earth fault, reduce the power off time causing due to busbar grounding.
Accompanying drawing explanation
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.
Fig. 1 is step schematic diagram of the present invention.
Fig. 2 measurement result schematic diagram of the present invention.
Embodiment
For technological means, creation characteristic that the present invention is realized, reach object and effect is easy to understand, below in conjunction with concrete diagram, further set forth the present invention.
With reference to Fig. 1, a kind of in three-phase isolated neutral system the measuring method of zero-sequence current, comprise the following steps:
Step 1 S01, utilize the current transformer of three large velocity ratios to measure a three-phase current, wherein large velocity ratio numerical value is 300-600;
It is synthetic that step 2 S02, above-mentioned current transformer carry out secondary side three-phase current, and the synthetic way of concrete electric current adopts three-phase input end is connected together, and three-phase output end is connected together, as the input and output of zero-sequence current);
Step 3 S03, synthetic secondary side current are measured the little electric current of output by miniature little transformation ratio current transformer, and the miniature little no-load voltage ratio numerical value in step 3 is 2;
Step 4 S04, step 3 is exported after little current-series resistance, be converted to output voltage, this output voltage is converted to digital signal by AD converter and delivers to pick-up unit.
Primary current mutual inductor in above-mentioned steps one is selected, half value to maximum current of option means maximum current.
Secondary instrument in above-mentioned steps three is measured the value of mutual inductor, according to a no-load voltage ratio, chooses the value of full scale at the maximum current of secondary generation.
Embodiment 1:
For example primary side circuit zero-sequence current has 1A, with the current transformer of 600:1 no-load voltage ratio, measures, and secondary current is 1/600=1.667mA;
Secondary side micro-transformer of current 5:2.5mA, output current is 0.833mA;
Micro-transformer of current output is 0.1667V with 200 Ohmage serial conversion voltages, is easy to be converted to digital signal by AD converter.
Experimental result is measured:
Selecting large velocity ratio is three of 600:1 current transformers, measures the curve map of 0.1-10A zero-sequence current, and as Fig. 2, wherein transverse axis represents the point of measuring, such as the 1st be 0.3A, 2 0.6A .... the longitudinal axis represents current values.
As can be seen from Fig., we use current mutual inductor with high transforming ratio, and while measuring primary current 0.1A-10A, result precision is high, and the linearity is good.
More than show and described ultimate principle of the present invention and principal character and advantage of the present invention.The technician of the industry should understand; the present invention is not restricted to the described embodiments; that in above-described embodiment and instructions, describes just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.The claimed scope of the present invention is defined by appending claims and equivalent thereof.
Claims (3)
1. a measuring method for zero-sequence current in three-phase isolated neutral system, is characterized in that, comprises the following steps:
Step 1, utilize the current transformer of large velocity ratio to measure primary side three-phase current;
Step 2, above-mentioned current transformer carry out secondary side, and to carry out current three-phase synthetic;
Step 3, synthetic secondary side current are measured the little electric current of output by miniature little transformation ratio current transformer;
Step 4, step 3 is exported after little current-series resistance, be converted to output voltage, this output voltage is converted to digital signal by AD converter and delivers to pick-up unit.
According to claim 1 a kind of in three-phase isolated neutral system the measuring method of zero-sequence current, it is characterized in that, the large velocity ratio numerical value in described step 1 is 300-600.
According to claim 1 a kind of in three-phase isolated neutral system the measuring method of zero-sequence current, it is characterized in that, the miniature little no-load voltage ratio numerical value in described step 3 is 2.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201410302314.7A CN104111370A (en) | 2014-06-30 | 2014-06-30 | Method for measuring zero-sequence current in three-phase ungrounded system |
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| CN201410302314.7A CN104111370A (en) | 2014-06-30 | 2014-06-30 | Method for measuring zero-sequence current in three-phase ungrounded system |
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| CN104111370A true CN104111370A (en) | 2014-10-22 |
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| CN201410302314.7A Pending CN104111370A (en) | 2014-06-30 | 2014-06-30 | Method for measuring zero-sequence current in three-phase ungrounded system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104391170A (en) * | 2014-12-19 | 2015-03-04 | 国家电网公司 | Detection and calculation method for zero-sequence current |
| CN116500328A (en) * | 2023-06-06 | 2023-07-28 | 无锡市锡山湖光电器有限公司 | High-precision three-phase current sensor |
Citations (5)
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| JPH10243548A (en) * | 1997-02-24 | 1998-09-11 | Toko Electric Co Ltd | Line-to-ground fault detector for high-voltage distribution line |
| CN201408227Y (en) * | 2009-02-24 | 2010-02-17 | 上海宝钢化工有限公司 | Portable 380V power system zero sequence current detection device |
| CN102135561A (en) * | 2011-02-23 | 2011-07-27 | 山东大学 | Measuring device and method for zero-sequence current of non-effectively neutral grounded system |
| CN203326558U (en) * | 2013-07-10 | 2013-12-04 | 王小华 | Low-voltage leakage protection equipment for non-grounding neutral point system |
| CN103513154A (en) * | 2013-10-12 | 2014-01-15 | 河南开启电力实业有限公司 | Power distribution network electric leakage signal on-line detection device |
-
2014
- 2014-06-30 CN CN201410302314.7A patent/CN104111370A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10243548A (en) * | 1997-02-24 | 1998-09-11 | Toko Electric Co Ltd | Line-to-ground fault detector for high-voltage distribution line |
| CN201408227Y (en) * | 2009-02-24 | 2010-02-17 | 上海宝钢化工有限公司 | Portable 380V power system zero sequence current detection device |
| CN102135561A (en) * | 2011-02-23 | 2011-07-27 | 山东大学 | Measuring device and method for zero-sequence current of non-effectively neutral grounded system |
| CN203326558U (en) * | 2013-07-10 | 2013-12-04 | 王小华 | Low-voltage leakage protection equipment for non-grounding neutral point system |
| CN103513154A (en) * | 2013-10-12 | 2014-01-15 | 河南开启电力实业有限公司 | Power distribution network electric leakage signal on-line detection device |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104391170A (en) * | 2014-12-19 | 2015-03-04 | 国家电网公司 | Detection and calculation method for zero-sequence current |
| CN116500328A (en) * | 2023-06-06 | 2023-07-28 | 无锡市锡山湖光电器有限公司 | High-precision three-phase current sensor |
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Application publication date: 20141022 |
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