CN109358310B - Device and method for detecting broken zero line of three-phase four-wire electric energy meter - Google Patents
Device and method for detecting broken zero line of three-phase four-wire electric energy meter Download PDFInfo
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- CN109358310B CN109358310B CN201811462638.1A CN201811462638A CN109358310B CN 109358310 B CN109358310 B CN 109358310B CN 201811462638 A CN201811462638 A CN 201811462638A CN 109358310 B CN109358310 B CN 109358310B
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- 238000000034 method Methods 0.000 title claims description 8
- 238000005070 sampling Methods 0.000 claims abstract description 70
- 239000003990 capacitor Substances 0.000 claims abstract description 26
- 238000001514 detection method Methods 0.000 claims abstract description 21
- 238000010586 diagram Methods 0.000 description 2
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- 238000012986 modification Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/04—Testing or calibrating of apparatus covered by the other groups of this subclass of instruments for measuring time integral of power or current
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
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- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
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Abstract
The invention discloses a zero line breakage detection device and a detection method for a three-phase four-wire electric energy meter. The detection device comprises three groups of voltage sampling circuits which are in one-to-one correspondence with the three-phase circuits; the voltage sampling circuit comprises a collection end, an input end, a first zero line end, a second zero line end, a first sampling resistor, a sampling capacitor and a second sampling resistor, wherein the input end is used for being connected with a sampled live wire, the first zero line end and the second zero line end are used for being connected with a zero line, the first sampling resistor is connected between the collection end and the input end, the sampling capacitor is connected between the collection end and the first zero line end, and the second sampling resistor is connected between the input end and the second zero line end; the capacitance values of the sampling capacitors of the three groups of voltage sampling circuits are equal, and the capacitance value of the other group of sampling capacitors is unequal to the capacitance value of the other two groups of sampling capacitors. The invention has simple structure, judges the zero line breaking event through the phase difference between the phase voltages, and avoids the misjudgment possibly caused by working conditions such as overvoltage, undervoltage and the like.
Description
Technical Field
The invention relates to a low-cost broken zero line detection device suitable for a three-phase four-wire electric energy meter, and also relates to a broken zero line detection method.
Background
In a three-phase four-wire power supply system, under the working condition of unbalanced load operation, namely unbalanced load of three phases, if a zero line is disconnected, neutral points can be caused to deviate, and the danger of electric shock is easy to occur. Therefore, more and more users require the electric energy meter to have a zero line breakage detection function.
At present, the common method for detecting broken zero line is as follows: when the A, B, C phase voltage sampling loop uses sampling resistors with different resistance values and the zero line is disconnected, the sampling value of the A, B, C phase voltage sampling loop changes due to the offset of the neutral point, so that the measured A, B, C phase voltage value changes. According to the empirical value, the variation range of the voltages of each phase under the condition of zero line breakage can be obtained. And finally, the electric energy meter program judges whether the current working condition is zero line breakage or not by comparing the voltage values. However, the method is only suitable for the condition that the ammeter works at rated voltage, and the on-site working condition often generates overvoltage and undervoltage, so that misjudgment is very easy to occur under the condition.
Disclosure of Invention
The invention provides a zero line breakage detection device and a detection method for a three-phase four-wire electric energy meter, and aims at: and misjudgment of zero line breakage is avoided, and reliability of detection judgment is improved.
The technical scheme of the invention is as follows:
a broken zero line detection device of a three-phase four-wire electric energy meter comprises three groups of voltage sampling circuits which are in one-to-one correspondence with three-phase lines;
the voltage sampling circuit comprises a collection end, an input end, a first zero line end, a second zero line end, a first sampling resistor, a sampling capacitor and a second sampling resistor, wherein the input end is used for being connected with a sampled live wire, the first zero line end and the second zero line end are used for being connected with a zero line, the first sampling resistor is connected between the collection end and the input end, the sampling capacitor is connected between the collection end and the first zero line end, and the second sampling resistor is connected between the input end and the second zero line end;
the capacitance values of the sampling capacitors of the three groups of voltage sampling circuits are equal, and the capacitance value of the other group of sampling capacitors is unequal to the capacitance value of the other two groups of sampling capacitors.
As a further improvement of the invention: maximum acquisition end is setThe collectable voltage value is U', the maximum input voltage of the input end is U, and the resistance value of the first sampling resistor is R i The resistance value of the second sampling resistor is R ii The relation of the sampled resistance values is:
as a further improvement of the invention: the first sampling resistor is formed by connecting a plurality of resistors in series.
As a further improvement of the invention: in each voltage sampling circuit, the first sampling resistor is formed by connecting eight resistors with equal resistance in series.
As a further improvement of the invention: the resistance values of the second sampling resistors in the three groups of voltage sampling circuits are equal.
The broken zero line detection method based on the broken zero line detection device of the three-phase four-wire electric energy meter comprises the following steps:
step 1, setting a zero line breaking event marking bit; the method comprises the steps that (1) an electric energy meter is electrified and initialized, zero line breakage event marking positions are cleared, and the electric energy meter respectively collects voltages of A phase, B phase and C phase through each collecting end;
step 2, reading the phase difference between the voltages of the A phase, the B phase and the C phase at intervals, and setting the phase difference between the A phase and the B phase asThe phase difference between the B phase and the C phase is +.>The phase difference between A and C phases is->And (3) making:
and 3, judging according to the following criteria:
criterion a: the voltage values of the phase A, the phase B and the phase C are all larger than a preset critical voltage;
criterion b:and->At least one of which is larger than a preset phase difference threshold value;
if the two criteria are met, setting the marking position of the zero line breaking event, and executing the step 4, otherwise, resetting the marking position of the zero line breaking event, and returning to executing the step 2;
and step 4, if the zero line breaking event marking bit is kept in a set state all the time within a preset duration, judging that the zero line breaking event occurs, otherwise, returning to the step 2.
Further: the phase difference threshold is 20 degrees.
Further: the duration is 10 seconds.
Compared with the prior art, the invention has the following positive effects: (1) The structure is simple, the change to the existing design is small, and the cost is low; (2) By using the difference between capacitance values, the phase difference between three-phase voltages after the zero line is broken is changed, so that the zero line breaking event criterion can be changed from the original voltage value to the phase difference between the phase voltages, and misjudgment possibly caused by working conditions such as overvoltage and undervoltage is avoided.
Drawings
Fig. 1 is a circuit schematic diagram of a voltage sampling circuit.
Fig. 2 is a schematic circuit diagram of three voltage sampling circuits in an embodiment.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings:
a broken zero line detection device of a three-phase four-wire electric energy meter comprises three groups of voltage sampling circuits which are shown in figure 1 and correspond to three-phase lines one by one.
The voltage sampling circuit comprises a collection end 1, an input end 3 used for being connected with a sampled live wire, a first zero line end 6 and a second zero line end 7 used for being connected with a zero line, a first sampling resistor 2 connected between the collection end 1 and the input end 3, a sampling capacitor 4 connected between the collection end 1 and the first zero line end 6, and a second sampling resistor 5 connected between the input end 3 and the second zero line end 7;
since the resistance withstand voltage of a large resistance is insufficient, the first sampling resistor 2 is typically composed of a plurality of resistors connected in series.
Thus, as in fig. 2: the resistors R1-R9 and the capacitor C1 form an A-phase voltage sampling circuit, the resistors R10-R18 and the capacitor C2 form a B-phase voltage sampling circuit, and the resistors R19-R27 and the capacitor C3 form a C-phase voltage sampling circuit.
Further, R1-R8 are equal in resistance, R10-R17 are equal in resistance, and R19-R26 are equal in resistance. The resistance values of R9, R18 and R27 are equal.
The capacitance values of the capacitors C2 and C3 are equal, the capacitance value of the capacitor C1 is not equal to the capacitance value of the capacitor C2 and the capacitor C3, and the capacitors C2 and C3 have larger difference, so that when the working condition of zero line breakage occurs, the phase difference between A, B, C phase voltages can change due to the difference of the capacitance values of the capacitors C1, C2 and C3, and whether the zero line breakage occurs can be judged through the change of the phase difference.
In general, the capacitance ratio of C2 to C1 is greater than 5 and less than 15, and a typical value is: c1 0.01uf,C2 0.1uf,C3 0.1uf.
The resistance values of the resistors R1-R27 can be freely configured according to actual needs, and the selection of the resistance values is determined by the maximum voltage input range allowed by the sampling loop. Let the maximum collectable voltage value of the collection terminal 1 be U', the maximum input voltage of the input terminal 3 be U, and the resistance value of the first sampling resistor 2 be R i Second sampling resistor5 has a resistance value of R ii The sampling resistance should satisfy the following conditions:
the broken zero line detection method based on the broken zero line detection device of the three-phase four-wire electric energy meter comprises the following steps:
step 1, setting a zero line breaking event marking bit; the method comprises the steps that (1) an electric energy meter is electrified and initialized, zero line breakage event marking bits are cleared, and the electric energy meter respectively collects voltages of A phase, B phase and C phase through each collecting end 1;
step 2, reading the phase difference between the voltages of the A phase, the B phase and the C phase at intervals, and setting the phase difference between the A phase and the B phase asThe phase difference between the B phase and the C phase is +.>The phase difference between A and C phases is->And (3) making:
and 3, judging according to the following criteria:
criterion a: the voltage values of the phase A, the phase B and the phase C are all larger than a preset critical voltage;
criterion b：And->At least one of which is larger than a preset phase difference threshold value, wherein the phase difference threshold value is preferably 20 degrees;
if the two criteria are met, setting the marking position of the zero line breaking event, and executing the step 4, otherwise, resetting the marking position of the zero line breaking event, and returning to executing the step 2;
and 4, if the zero line breaking event mark bit is kept in a set state all the time within a preset time period (generally 10 seconds), judging that the zero line breaking event occurs, otherwise, returning to the step 2.
According to the voltage sampling circuit, when the working condition of zero line breakage occurs, the phase difference between A, B, C phase voltages can change due to different capacitance values of the capacitors C1, C2 and C3, and the 120-degree phase difference deviating from the standard is combined with the software judgment logic, so that the detection of the zero line breakage event is realized.
It is obvious that the phase difference change at the time of the zero line break is caused by the structure of the sampling circuit, particularly the relation between the capacitance values, and the method of judging the zero line break event by the phase difference is not limited to the above-mentioned one.
The scope of the present invention includes, but is not limited to, the above embodiments, and any conceivable alternatives, modifications, and improvements made to the present technology fall within the scope of the present invention.
Claims (4)
1. A broken zero line detection device of a three-phase four-wire electric energy meter is characterized in that: the voltage sampling circuit comprises three groups of voltage sampling circuits which are in one-to-one correspondence with the three-phase circuits;
the voltage sampling circuit comprises a collection end (1), an input end (3) used for being connected with a sampled live wire, a first zero line end (6) and a second zero line end (7) used for being connected with the zero line, a first sampling resistor (2) connected between the collection end (1) and the input end (3), a sampling capacitor (4) connected between the collection end (1) and the first zero line end (6) and a second sampling resistor (5) connected between the input end (3) and the second zero line end (7);
the sampling capacitors (4) of the three groups of voltage sampling circuits, wherein the capacitance values of two groups of sampling capacitors (4) are equal, and the capacitance value of the other group of sampling capacitors (4) is unequal to the capacitance value of the other two groups of sampling capacitors (4);
the maximum collectable voltage value of the collecting end (1) is set as U', the maximum input voltage of the input end (3) is set as U, and the resistance value of the first sampling resistor (2) is set as R i The resistance value of the second sampling resistor (5) is R ii The relation of the sampled resistance values is:
the detection steps are as follows:
step 1, setting a zero line breaking event marking bit; the method comprises the steps of powering on and initializing an electric energy meter, resetting a zero line breaking event marking bit, and respectively acquiring voltages of a phase A, a phase B and a phase C through each acquisition end (1) of the electric energy meter;
step 2, reading the phase difference between the voltages of the A phase, the B phase and the C phase at intervals, and setting the phase difference between the A phase and the B phase asThe phase difference between the B phase and the C phase is +.>The phase difference between A and C phases is->And (3) making:
and 3, judging according to the following criteria:
criterion a: the voltage values of the phase A, the phase B and the phase C are all larger than a preset critical voltage;
criterion b:and->At least one of which is larger than a preset phase difference threshold value; the phase difference threshold is 20 degrees;
if the two criteria are met, setting the marking position of the zero line breaking event, and executing the step 4, otherwise, resetting the marking position of the zero line breaking event, and returning to executing the step 2;
step 4, if the zero line breaking event mark position is kept in a set state all the time within a preset duration, judging that the zero line breaking event occurs, otherwise, returning to the step 2; the duration is 10 seconds.
2. The three-phase four-wire electric energy meter zero line breakage detection device according to claim 1, wherein: the first sampling resistor (2) is formed by connecting a plurality of resistors in series.
3. The three-phase four-wire electric energy meter zero line breakage detection device according to claim 2, wherein: in each voltage sampling circuit, the first sampling resistor (2) is formed by connecting eight resistors with equal resistance values in series.
4. The three-phase four-wire electric energy meter zero line breakage detection device according to claim 1, wherein: the resistance values of the second sampling resistors (5) in the three groups of voltage sampling circuits are equal.
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| CN111999554A (en) * | 2020-08-25 | 2020-11-27 | 成都长城开发科技有限公司 | Zero line detection circuit, ammeter and zero line detection method |
| CN112596019A (en) * | 2020-12-22 | 2021-04-02 | 杭州海兴电力科技股份有限公司 | Three-phase four-wire electric energy meter zero line lack detection method based on voltage difference |
| CN113009380B (en) * | 2020-12-31 | 2022-11-04 | 宁波三星医疗电气股份有限公司 | Neutral line disconnection fault detection method based on electric energy meter and readable storage medium |
| CN113777532B (en) * | 2021-11-10 | 2022-02-18 | 武汉中电国为技术有限公司 | System, method and device for recognizing zero-line and phase-loss of power secondary equipment side |
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