Earth impedance measuring circuit and earth impedance measuring method
阅读说明：本技术 对地阻抗测量电路、对地阻抗测量方法 (Earth impedance measuring circuit and earth impedance measuring method ) 是由 李修连 江世军 于 2021-10-11 设计创作，主要内容包括：本发明公开了一种对地阻抗测量电路、对地阻抗测量方法,所述对地阻抗测量电路通过在隔离交流电源侧的火线和零线之间设置电源电压检测电路来检测隔离交流电源的电源电压,并在隔离交流电源侧的火线和零线之间、电气设备用电线路侧的火线和零线之间形成交流电正半周检测支路和交流电负半周检测支路,可以准确地检测出火线的对地阻抗值和零线的对地阻抗值,从而可以快速地判别出具体是哪条输出线路出现对地阻抗异常,并且实现了定量检测,对于用电安全保障、线路检测和维护具有积极作用。(The invention discloses an earth impedance measuring circuit and an earth impedance measuring method, wherein the earth impedance measuring circuit is used for detecting the power supply voltage of an isolated alternating current power supply by arranging a power supply voltage detecting circuit between a live wire and a zero line at the side of the isolated alternating current power supply, and an alternating current positive half-cycle detecting branch circuit and an alternating current negative half-cycle detecting branch circuit are formed between the live wire and the zero line at the side of the isolated alternating current power supply and between the live wire and the zero line at the side of a line for electrical equipment, so that the earth impedance value of the live wire and the earth impedance value of the zero line can be accurately detected, and the specific output line with earth impedance abnormality can be rapidly judged, quantitative detection is realized, and positive effects on electricity safety guarantee, line detection and maintenance are achieved.)
1. An impedance to ground measurement circuit for detecting whether an impedance to ground of an isolated ac power output line is abnormal, comprising:
the power supply voltage detection circuit is arranged at the isolated alternating current power supply side, connected between the live line and the zero line and used for detecting the power supply voltage of the isolated alternating current power supply;
the earth impedance detection circuit is arranged on the side of an isolated alternating current power supply and the side of a circuit for electrical equipment, is connected between a live wire and a zero line, and forms an alternating current positive half-cycle detection branch and an alternating current negative half-cycle detection branch between the live wire and the zero line for detecting earth impedance values of the live wire and the zero line of the isolated alternating current power supply.
2. The impedance to ground measurement circuit according to claim 1, wherein the power supply voltage detection circuit includes a resistor R1, a resistor R2, and a first current detection device, the resistor R1 and the resistor R2 being connected in series between the zero lines of the live line isolated from the ac power supply side, the first current detection device being configured to detect a value of current flowing through the resistor R1 and the resistor R2, resistance values of the resistor R1 and the resistor R2 being known.
3. The impedance to ground measurement circuit of claim 2, wherein the supply voltage detection circuit further comprises a diode D1, a diode D2, a resistor R3, and a resistor R4, the resistor R3 and the resistor R4 are connected in series between the zero lines of the live wire on the side of isolating the alternating current power supply, and forms a parallel branch with the branch of the resistor R1 and the resistor R2, the diode D1 is arranged on the branch of the resistor R1 and the resistor R2, the cathode of the diode D1 is connected with the live wire, the anode is connected with the resistor R1, the diode D2 is arranged on the branch circuit of the resistor R3 and the resistor R4, the cathode of the diode D2 is connected with the zero line, the anode is connected with the resistor R3, the voltage drop of the diode D1 and the diode D2 and the resistance values of the resistor R3 and the resistor R4 are known, the first current detection device is used for detecting the current value of the branch in which the resistor R1 and the resistor R2 are positioned in the negative half cycle of the alternating current and detecting the current value of the branch in which the resistor R3 and the resistor R4 are positioned in the positive half cycle of the alternating current.
4. The impedance to ground measurement circuit of claim 1, wherein the impedance to ground detection circuit comprises a diode DNResistance RN1Resistance RN2Resistance RL1Resistance RL2Diode DLA second current detecting device, the diode DNResistance RN1Resistance RN2Connected in series between the live wire and the ground wire, and a diode DNThe negative pole of the resistor is connected with the live wire, and the positive pole of the resistor is connected with the resistor RN1Connected, the diode DLResistance RL1Resistance RL2A diode D connected in series between the zero line and the ground lineLThe negative pole of the resistor is connected with the zero line, the positive pole of the resistor is connected with the resistor RL1Connecting the live wire and the zero wire of the electric circuit side for the electrical equipment with the ground wire respectively, wherein the impedance between the live wire and the ground wire forms an equivalent resistance RLThe impedance between the zero line and the ground line forms an equivalent resistance RNThe equivalent resistance RLDiode DLResistance RL1Resistance RL2Equivalent resistance RNForming an alternating current positive half-cycle detection branch, and the equivalent resistance RLEquivalent resistance RNDiode DNResistance RN1Resistance RN2Forming an AC negative half-cycle detection branch, wherein a diode DNAnd a diode DLIs known, resistor RN1Resistance RN2Resistance RL1And a resistance RL2Is known, and the second current sensing device is used for sensing the diode D in the positive half cycle of the alternating currentLResistance RL1Resistance RL2The current value of the branch and the detection diode D at the negative half cycle of the alternating currentNResistance RN1Resistance RN2The current value of the branch in which the current is flowing.
5. The impedance to ground measurement circuit of claim 1, wherein the isolated ac power source is a single-phase ac isolated power source or a three-phase ac isolated power source.
6. An impedance measurement method using the impedance measurement circuit according to any one of claims 1 to 5, comprising:
detecting a power supply voltage value of an isolated alternating current power supply;
respectively detecting the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch;
and calculating the earth impedance values of the live wire and the zero wire based on the detected power supply voltage value, the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch.
7. The method of impedance measurement according to claim 6, further comprising:
and comparing the earth impedance values of the live wire and the zero wire with a preset safety threshold, and sending out an alarm prompt if the earth impedance value of the live wire or the earth impedance value of the zero wire is smaller than the preset safety threshold.
8. The method of measuring earth impedance of claim 6, wherein the process of detecting a supply voltage value of the isolated AC power supply comprises:
detecting the peak voltage U at two ends of the resistor R1 through a voltmeter in the negative half cycle of the alternating currentNSince the resistance values of the resistor R1 and the resistor R2 and the voltage drop of the diode D1 are known, the voltage drop is based on the formula UNL＝UN*(R1+R2)÷R1+UDCalculating to obtain a voltage value between the zero line and the live line, wherein UNLIs the peak voltage of the zero line relative to the live line, UDIs the voltage drop of diode D1;
detecting the peak voltage U at two ends of a resistor R3 through a voltmeter at the positive half cycle of the alternating currentLSince the resistance values of the resistor R3 and the resistor R4 and the voltage drop of the diode D2 are known, the voltage drop is based on the formula ULN＝UL*(R3+R4)÷R3+UDCalculating to obtain a voltage value between the zero line and the live line, wherein ULNIs the peak voltage of the live line relative to the zero line, UDIs the voltage drop of diode D2.
9. The method for measuring earth impedance according to claim 8, wherein the process of separately detecting the current value in the ac positive half-cycle detection branch and the current value in the ac negative half-cycle detection branch specifically includes the following steps:
the resistance R is detected by a voltmeter in the negative half cycle of the alternating currentN1Peak voltage U acrossN1Due to the resistance RN1And a resistance RN2Resistance value of, diode DNIs known based on formula IN1＝UN1/RN1The resistance R is obtained by calculationN1The current value of the branch is based on the formula UEL＝UN1*(RN1+RN2)÷RN1+UDCalculating to obtain the voltage value between the ground wire and the live wire, wherein UELIs the peak voltage of the ground line relative to the live line, UDIs a diode DNPressure drop of (d);
the resistance R is detected by a voltmeter in the positive half cycle of the alternating currentL1Peak voltage U acrossL1Due to the resistance RL1And a resistance RL2Resistance value of, diode DLAre known, based on the equationFormula IL1＝UL1/RL1The resistance R is obtained by calculationL1The current value of the branch is based on the formula UEN＝UL1*(RL1+RL2)÷RL1+UDCalculating to obtain a voltage value between the ground wire and the zero line, wherein UENIs the peak voltage of the earth wire relative to the zero line, UDIs a diode DLPressure drop of (d).
10. The method for measuring earth impedance according to claim 9, wherein the process of calculating the earth impedance values of the live wire and the neutral wire based on the detected power voltage value, the current value in the ac positive half-cycle detection branch and the current value in the ac negative half-cycle detection branch specifically includes the following steps:
in the negative half cycle of the alternating current, IN＝IN0+IN1Wherein, INTo measure the total current in the loop, IN＝(UNL-UEL)/RN，IN0The value of the current between live and ground, IN0＝UEL/RL；
In the positive half cycle of the alternating current, IL＝IL0+IL1Wherein, ILTo measure the total current in the loop, IL＝(ULN-UEL)/RL，IL0Is the current value between the zero line and the ground line, IL0＝UEN/RN；
Will UNL、ULN、UEN、UEL、IN、IN0Substituting into a formula to jointly solve to obtain:
RL＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IN1*UEN+IL1(UNL-UEL)]
RN＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IL1*UEL+IN1(ULN-UEN)]。
Technical Field
The invention relates to the technical field of ground impedance detection of a power circuit for an isolated power supply, in particular to a ground impedance measuring circuit, and further particularly relates to a ground impedance measuring method adopting the ground impedance measuring circuit.
Background
The isolated power supply is widely used in many occasions due to its unique power supply characteristics. However, when the output line of the isolated power supply is abnormal to the ground, the safety characteristics of the isolated power supply are lost, and even potential safety hazards exist. For example: the live wire for isolating the output of the single-phase alternating current power supply has relatively low impedance to the ground, and when a human body touches the zero line output by the power supply, an electric shock accident can occur; similarly, any power line isolating the three-phase ac power output has a relatively small impedance to ground, and when a human body touches other output power lines, an electric shock accident may occur. The conventional detection method at present can not distinguish which output power line is specifically the line with abnormal impedance to ground, and can not detect in real time, and when the impedance of a plurality of power lines to the ground is small, the detection result is inaccurate, and even the electric shock risk is caused without alarming. In addition, the conventional detection method can only realize qualitative detection, namely, only can detect the impedance abnormality of the power output line to the ground, but cannot detect an accurate impedance value.
Disclosure of Invention
The invention provides an impedance to ground measuring circuit and an impedance to ground measuring method, which aim to solve the defects of the conventional detection method.
According to an aspect of the present invention, there is provided an impedance to ground measurement circuit for detecting whether an impedance to ground of an isolated ac power supply output line is abnormal, comprising:
the power supply voltage detection circuit is arranged at the isolated alternating current power supply side, connected between the live line and the zero line and used for detecting the power supply voltage of the isolated alternating current power supply;
the earth impedance detection circuit is arranged on the side of an isolated alternating current power supply and the side of a circuit for electrical equipment, is connected between a live wire and a zero line, and forms an alternating current positive half-cycle detection branch and an alternating current negative half-cycle detection branch between the live wire and the zero line for detecting earth impedance values of the live wire and the zero line of the isolated alternating current power supply.
Further, the power supply voltage detection circuit comprises a resistor R1, a resistor R2 and a first current detection device, wherein the resistor R1 and the resistor R2 are connected in series between the zero lines of the live wire isolated from the alternating current power supply side, the first current detection device is used for detecting the current value flowing through the resistor R1 and the resistor R2, and the resistance values of the resistor R1 and the resistor R2 are known.
Further, the power supply voltage detection circuit also comprises a diode D1, a diode D2, a resistor R3 and a resistor R4, the resistor R3 and the resistor R4 are connected in series between the zero lines of the live wire on the side of isolating the alternating current power supply, and forms a parallel branch with the branch of the resistor R1 and the resistor R2, the diode D1 is arranged on the branch of the resistor R1 and the resistor R2, the cathode of the diode D1 is connected with the live wire, the anode is connected with the resistor R1, the diode D2 is arranged on the branch circuit of the resistor R3 and the resistor R4, the cathode of the diode D2 is connected with the zero line, the anode is connected with the resistor R3, the voltage drop of the diode D1 and the diode D2 and the resistance values of the resistor R3 and the resistor R4 are known, the first current detection device is used for detecting the current value of the branch in which the resistor R1 and the resistor R2 are positioned in the negative half cycle of the alternating current and detecting the current value of the branch in which the resistor R3 and the resistor R4 are positioned in the positive half cycle of the alternating current.
Further, the impedance to ground detection circuit includes a diode DNResistance RN1Resistance RN2Resistance RL1Resistance RL2Diode DLA second current detecting device, the diode DNResistance RN1Resistance RN2Connected in series between the live wire and the ground wire, and a diode DNThe negative pole of the resistor is connected with the live wire, and the positive pole of the resistor is connected with the resistor RN1Connected, the diode DLResistance RL1Resistance RL2A diode D connected in series between the zero line and the ground lineLThe negative pole of the resistor is connected with the zero line, the positive pole of the resistor is connected with the resistor RL1Connecting the live wire and the zero wire of the electric circuit side for the electrical equipment with the ground wire respectively, wherein the impedance between the live wire and the ground wire forms an equivalent resistance RLThe impedance between the zero line and the ground line forms an equivalent resistance RNThe equivalent resistance RLDiode DLResistance RL1Resistance RL2Equivalent resistance RNForming an alternating current positive half-cycle detection branch, and the equivalent resistance RLEquivalent resistance RNDiode DNResistance RN1Resistance RN2Forming an AC negative half-cycle detection branch, wherein a diode DNAnd a diode DLIs known, resistor RN1Resistance RN2Resistance RL1And a resistance RL2Is known, and the second current sensing device is used for sensing the diode D in the positive half cycle of the alternating currentLResistance RL1Resistance RL2The current value of the branch and the current value of the branch are negativeHalf-cycle detection diode DNResistance RN1Resistance RN2The current value of the branch in which the current is flowing.
Further, the isolation alternating current power supply is a single-phase alternating current isolation power supply or a three-phase alternating current isolation power supply.
In addition, the invention also provides an impedance to ground measuring method, which adopts the impedance to ground measuring circuit, and comprises the following contents:
detecting a power supply voltage value of an isolated alternating current power supply;
respectively detecting the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch;
and calculating the earth impedance values of the live wire and the zero wire based on the detected power supply voltage value, the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch.
Further, the following contents are also included:
and comparing the earth impedance values of the live wire and the zero wire with a preset safety threshold, and sending out an alarm prompt if the earth impedance value of the live wire or the earth impedance value of the zero wire is smaller than the preset safety threshold.
Further, the process of detecting the power supply voltage value of the isolated ac power supply includes the following steps:
detecting the peak voltage U at two ends of the resistor R1 through a voltmeter in the negative half cycle of the alternating currentNSince the resistance values of the resistor R1 and the resistor R2 and the voltage drop of the diode D1 are known, the voltage drop is based on the formula UNL＝UN*(R1+R2)÷R1+UDCalculating to obtain a voltage value between the zero line and the live line, wherein UNLIs the peak voltage of the zero line relative to the live line, UDIs the voltage drop of diode D1;
detecting the peak voltage U at two ends of a resistor R3 through a voltmeter at the positive half cycle of the alternating currentLSince the resistance values of the resistor R3 and the resistor R4 and the voltage drop of the diode D2 are known, the voltage drop is based on the formula ULN＝UL*(R3+R4)÷R3+UDCalculating to obtain a voltage value between the zero line and the live line, wherein ULNPeak power of live wire relative to zero linePress UDIs the voltage drop of diode D2.
Further, the process of respectively detecting the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch specifically includes the following steps:
the resistance R is detected by a voltmeter in the negative half cycle of the alternating currentN1Peak voltage U acrossN1Due to the resistance RN1And a resistance RN2Resistance value of, diode DNIs known based on formula IN1＝UN1/RN1The resistance R is obtained by calculationN1The current value of the branch is based on the formula UEL＝UN1*(RN1+RN2)÷RN1+UDCalculating to obtain the voltage value between the ground wire and the live wire, wherein UELIs the peak voltage of the ground line relative to the live line, UDIs a diode DNPressure drop of (d);
the resistance R is detected by a voltmeter in the positive half cycle of the alternating currentL1Peak voltage U acrossL1Due to the resistance RL1And a resistance RL2Resistance value of, diode DLIs known based on formula IL1＝UL1/RL1The resistance R is obtained by calculationL1The current value of the branch is based on the formula UEN＝UL1*(RL1+RL2)÷RL1+UDCalculating to obtain a voltage value between the ground wire and the zero line, wherein UENIs the peak voltage of the earth wire relative to the zero line, UDIs a diode DLPressure drop of (d).
Further, the process of calculating the ground impedance values of the live line and the zero line based on the detected power voltage value, the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch specifically includes the following steps:
in the negative half cycle of the alternating current, IN＝IN0+IN1Wherein, INTo measure the total current in the loop, IN＝(UNL-UEL)/RN，IN0Is the value of the current between the live and ground lines,IN0＝UEL/RL；
in the positive half cycle of the alternating current, IL＝IL0+IL1Wherein, ILTo measure the total current in the loop, IL＝(ULN-UEL)/RL，IL0Is the current value between the zero line and the ground line, IL0＝UEN/RN；
Will UNL、ULN、UEN、UEL、IN、IN0Substituting into a formula to jointly solve to obtain:
RL＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IN1*UEN+IL1(UNL-UEL)]
RN＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IL1*UEL+IN1(ULN-UEN)]。
the invention has the following effects:
according to the earth impedance measuring circuit, the power supply voltage of the isolated alternating current power supply is detected by arranging the power supply voltage detecting circuit between the live wire and the zero wire at the side of the isolated alternating current power supply, and the alternating current positive half-cycle detecting branch and the alternating current negative half-cycle detecting branch are formed between the live wire and the zero wire at the side of the isolated alternating current power supply and between the live wire and the zero wire at the side of the electric line for electrical equipment, so that the earth impedance value of the live wire and the earth impedance value of the zero wire can be accurately detected, and specific output lines with earth impedance abnormality can be rapidly judged, quantitative detection is realized, and positive effects on electricity safety guarantee, line detection and maintenance are achieved.
In addition, the impedance to ground measurement method of the present invention also has the above-described advantages.
In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a schematic circuit diagram of an impedance to ground measurement circuit according to a preferred embodiment of the present invention.
Fig. 2 is a schematic circuit diagram of an impedance to ground measurement circuit according to another embodiment of the present invention.
Fig. 3 is a schematic circuit diagram of the ac positive half cycle detection branch according to the preferred embodiment of the present invention.
Fig. 4 is a schematic circuit diagram of the ac negative half cycle detection branch according to the preferred embodiment of the present invention.
Detailed Description
The embodiments of the invention will be described in detail below with reference to the accompanying drawings, but the invention can be embodied in many different forms, which are defined and covered by the following description.
As shown in fig. 1, a preferred embodiment of the present invention provides an impedance to ground measurement circuit for detecting whether an impedance to ground of an isolated ac power output line is abnormal, including:
the power supply voltage detection circuit is arranged at the isolated alternating current power supply side, connected between the live line and the zero line and used for detecting the power supply voltage of the isolated alternating current power supply;
the earth impedance detection circuit is arranged on the side of an isolated alternating current power supply and the side of a circuit for electrical equipment, is connected between a live wire and a zero line, and forms an alternating current positive half-cycle detection branch and an alternating current negative half-cycle detection branch between the live wire and the zero line for detecting earth impedance values of the live wire and the zero line of the isolated alternating current power supply.
It can be understood that the circuit for measuring the impedance to ground of the embodiment detects the power supply voltage of the isolated alternating current power supply by arranging the power supply voltage detection circuit between the live wire and the zero wire of the isolated alternating current power supply side, and forms an alternating current positive half-cycle detection branch and an alternating current negative half-cycle detection branch between the live wire and the zero wire of the isolated alternating current power supply side and between the live wire and the zero wire of the circuit side for the electrical equipment, so that the impedance to ground of the live wire and the impedance to ground of the zero wire can be accurately detected, and the specific output line which has the impedance to ground abnormality can be rapidly judged, and quantitative detection is realized, and the circuit has positive effects on electricity safety guarantee, line detection and maintenance.
Specifically, the power supply voltage detection circuit includes a resistor R1, a resistor R2, and a first current detection device, the resistor R1 and the resistor R2 are connected in series between the zero lines of the live line on the isolated ac power supply side, the first current detection device is used for detecting the value of current flowing through the resistor R1 and the resistor R2, and the resistance values of the resistor R1 and the resistor R2 are known. The first current detection device can adopt an ammeter, the ammeter is directly connected in series in a branch where the resistor R1 and the resistor R2 are located, and the voltage value between the live wire and the zero wire on the side of the isolated alternating current power supply can be calculated by combining detected current values in the branch due to the fact that the resistance values of the resistor R1 and the resistor R2 are known. The first current detection device can also adopt a voltmeter, the voltmeter is connected with the resistor R1 or the resistor R2 in parallel, the current value flowing through the resistor R2 can be measured, and the voltage value between the live wire and the zero wire on the side of the isolated alternating current power supply is calculated.
Preferably, as shown in fig. 2, in another embodiment of the present invention, the power supply voltage detection circuit further includes a diode D1, a diode D2, a resistor R3, and a resistor R4, the resistor R3 and the resistor R4 are connected in series between the zero lines of the live line on the ac power supply side, and form a parallel branch with the branch where the resistor R1 and the resistor R2 are located, the diode D1 is disposed on the branch where the resistor R1 and the resistor R2 are located, the cathode of the diode D1 is connected to the live line, the anode is connected to the resistor R1, the diode D2 is disposed on the branch where the resistor R3 and the resistor R4 are located, the cathode of the diode D2 is connected to the zero line, the anode is connected to the resistor R3, and the voltage drop of the diode D1 and the diode D2, and the resistances of the resistor R3 and the resistor R4 are known. The first current detection device is used for detecting the current value of the branch in which the resistor R1 and the resistor R2 are positioned in the negative half cycle of the alternating current and detecting the current value of the branch in which the resistor R3 and the resistor R4 are positioned in the positive half cycle of the alternating current. When the alternating current is in a negative half cycle, the potential of the zero line is higher than that of the live line, the branch where the resistor R1, the resistor R2 and the diode D1 are located is conducted, the branch where the resistor R3, the resistor R4 and the diode D2 are located is not conducted, and the power supply voltage of the negative half cycle of the alternating current can be calculated by measuring the current values in the branch where the resistor R1, the resistor R2 and the diode D1 are located. And when the alternating current is in the positive half cycle, the potential of the live wire is higher than that of the zero line, the branch where the resistor R1, the resistor R2 and the diode D1 are located is not conducted, the branch where the resistor R3, the resistor R4 and the diode D2 are located is conducted, and the power supply voltage of the positive half cycle of the alternating current can be obtained by measuring the current values in the branch where the resistor R3, the resistor R4 and the diode D2 are located. The number of the first current detection devices is two, and one current detection device is arranged in each of the two parallel branches.
For example, during the negative half cycle of the alternating current, the peak voltage value at the two ends of the measuring resistor R1 is UNAnd the peak voltage U between the zero line and the live line at the moment can be calculatedNLThe calculation formula is as follows:
UNL＝UN*(R1+R2)÷R1+UDequation 1
Wherein, UNLIs the peak voltage of the zero line relative to the live line, UDFor the voltage drop of the diode D1, R1 is the resistance of the resistor R1, R2 is the resistance of the resistor R2, because R1, R2 and U are connectedDAre all known, by measuring UNThen U can be obtained by calculationNL。
Similarly, in the positive half cycle of the alternating current, the voltage peak value at the two ends of the measuring resistor R3 is ULAnd the peak voltage U between the zero line and the live line at the moment can be calculatedLNThe calculation formula is as follows:
ULN＝UL*(R3+R4)÷R3+UDequation 2
Wherein, UNLIs the peak voltage of the live line relative to the zero line, UDIs the voltage drop of the diode D2 due to R3, R4 and UDAre all known, by measuring ULThen U can be obtained by calculationLN。
It can be understood that by arranging two parallel detection branches and arranging a diode in each detection branch to conduct forward conduction and reverse cut-off, the interference between the positive half cycle and the negative half cycle of the alternating current can be effectively reduced, and the detection result of the power supply voltage is more accurate.
It will be appreciated that, as shown in connection with figures 2, 3 and 4, the impedance to ground detection circuit comprises a diode DNResistance RN1Resistance RN2Resistance RL1Resistance RL2Diode DLA second current detecting device, the diode DNResistance RN1Resistance RN2Connected in series between the live wire and the ground wire, and a diode DNThe negative pole of the resistor is connected with the live wire, and the positive pole of the resistor is connected with the resistor RN1Connected, the diode DLResistance RL1Resistance RL2A diode D connected in series between the zero line and the ground lineLThe negative pole of the resistor is connected with the zero line, the positive pole of the resistor is connected with the resistor RL1Connecting the live wire and the zero wire of the electric circuit side for the electrical equipment with the ground wire respectively, wherein the impedance between the live wire and the ground wire forms an equivalent resistance RLThe impedance between the zero line and the ground line forms an equivalent resistance RN. The equivalent resistance RLDiode DLResistance RL1Resistance RL2Equivalent resistance RNAn alternating current positive half cycle detection branch is formed, as shown in fig. 3. The equivalent resistance RLEquivalent resistance RNDiode DNResistance RN1Resistance RN2Forming an alternating current negative half cycle detection branch as shown in fig. 4. Wherein, the diode DNAnd a diode DLIs known, resistor RN1Resistance RN2Resistance RL1And a resistance RL2Is known, and the second current sensing device is used for sensing the diode D in the positive half cycle of the alternating currentLResistance RL1Resistance RL2The current value of the branch and the detection diode D at the negative half cycle of the alternating currentNResistance RN1Resistance RN2The current value of the branch in which the current is flowing. It is to be understood that the second current detection device is the same as the first current detection device, and preferably employs a voltmeter.
In particular, the voltage meter is passed through in the negative half cycle of the alternating currentDetecting resistance RN1Peak voltage U acrossN1Due to the resistance RN1And a resistance RN2Resistance value of, diode DNThe voltage drop is known, the peak voltage between the ground line E and the live line L can be obtained by calculation, and the calculation formula is as follows:
UEL＝UN1*(RN1+RN2)÷RN1+UDequation 3
Wherein, UELIs the peak voltage of the ground line relative to the live line, UDIs a diode DNPressure drop of RN1Is a resistance RN1Resistance value of RN2Is a resistance RN2The resistance value of (c).
Similarly, the resistor R is detected through a voltmeter at the positive half cycle of the alternating currentL1Peak voltage U acrossL1Due to the resistance RL1And a resistance RL2Resistance value of, diode DLThe voltage drop is known, the peak voltage between the ground wire E and the zero line N can be obtained through calculation, and the calculation formula is as follows:
UEN＝UL1*(RL1+RL2)÷RL1+UDequation 4
Wherein, UENIs the peak voltage of the earth wire relative to the zero line, UDIs a diode DLPressure drop of RN3Is a resistance RN3Resistance value of RN4Is a resistance RN4The resistance value of (c).
Meanwhile, the following can be calculated:
IN1＝UN1/RN1equation 5
IL1＝UL1/RL1Equation 6
Wherein, IN1For making resistance R in negative half-cycle of alternating currentN1Current value of the branch in which I is locatedL1For making resistance R in positive half-cycle of alternating currentL1The current value of the branch in which the current is flowing.
And in the negative half cycle of the alternating current, UNL＝RN*IN+UELThen, then
IN＝(UNL-UEL)/RNEquation 7
Wherein, INTo measure the total current in the loop at negative half cycles of the alternating current.
Similarly, in the positive half cycle of the alternating current, ULN＝RL*IL+UENThen, then
IL＝(ULN-UEN)/RLEquation 8
Wherein, ILTo measure the total current in the loop at positive half cycles of the alternating current.
At the same time, the user can select the desired position,
IN0＝UEL/RLequation 9
IL0＝UEN/RNEquation 10
Wherein, IN0For the value of the current between live and earth during the negative half-cycle of the current, IL0Is the value of the current between the zero line and the ground line at the positive half cycle of the current.
While
IN＝IN0+IN1Equation 11
IL＝IL0+IL1Equation 12
Substituting equation 7 and equation 9 into equation 11 yields:
(UNL-UEL)/RN＝UEL/RL+IN1equation 13
Substituting equation 8 and equation 10 into equation 12 yields:
(ULN-UEN)/RL＝UEN/RN+IL1equation 14
Solving equations 13 and 14 yields:
RL＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IN1*UEN+IL1(UNL-UEL)]
RN＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IL1*UEL+IN1(ULN-UEN)]。
in addition, the isolation alternating current power supply is a single-phase alternating current isolation power supply or a three-phase alternating current isolation power supply.
In addition, another embodiment of the present invention further provides an impedance measurement method, preferably using the impedance measurement circuit as described above, including the following:
detecting a power supply voltage value of an isolated alternating current power supply;
respectively detecting the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch;
and calculating the earth impedance values of the live wire and the zero wire based on the detected power supply voltage value, the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch.
It can be understood that, in the ground impedance measuring method of this embodiment, the power supply voltage for isolating the ac power supply is detected by the power supply voltage detecting circuit, then the ac positive half-cycle detecting branch and the ac negative half-cycle detecting branch detect the corresponding current values, and finally, the ground impedance values of the live wire and the zero wire are calculated based on the power supply voltage value, the current value in the ac positive half-cycle detecting branch and the current value in the ac negative half-cycle detecting branch, so that the ground impedance values of the live wire and the zero wire can be accurately detected, and thus which output line has the abnormal ground impedance can be rapidly determined, and quantitative detection is realized, which has positive effects on power safety guarantee, line detection and maintenance.
It is to be understood that in other embodiments of the present invention, the impedance to ground measurement method further includes the following:
and comparing the earth impedance values of the live wire and the zero wire with a preset safety threshold, and sending out an alarm prompt if the earth impedance value of the live wire or the earth impedance value of the zero wire is smaller than the preset safety threshold.
It is understood that the process of detecting the power supply voltage value of the isolated ac power supply includes the following:
detecting the peak voltage U at two ends of the resistor R1 through a voltmeter in the negative half cycle of the alternating currentNSince the resistance values of the resistor R1 and the resistor R2 and the voltage drop of the diode D1 are known, the voltage drop is based on the formula UNL＝UN*(R1+R2)÷R1+UDCalculating to obtain a voltage value between the zero line and the live line, wherein UNLIs the peak voltage of the zero line relative to the live line, UDIs the voltage drop of diode D1;
detecting the peak voltage U at two ends of a resistor R3 through a voltmeter at the positive half cycle of the alternating currentLSince the resistance values of the resistor R3 and the resistor R4 and the voltage drop of the diode D2 are known, the voltage drop is based on the formula ULN＝UL*(R3+R4)÷R3+UDCalculating to obtain a voltage value between the zero line and the live line, wherein ULNIs the peak voltage of the live line relative to the zero line, UDIs the voltage drop of diode D2.
It can be understood that the process of separately detecting the current value in the ac positive half-cycle detection branch and the current value in the ac negative half-cycle detection branch specifically includes the following steps:
the resistance R is detected by a voltmeter in the negative half cycle of the alternating currentN1Peak voltage U acrossN1Due to the resistance RN1And a resistance RN2Resistance value of, diode DNIs known based on formula IN1＝UN1/RN1The resistance R is obtained by calculationN1The current value of the branch is based on the formula UEL＝UN1*(RN1+RN2)÷RN1+UDCalculating to obtain the voltage value between the ground wire and the live wire, wherein UELIs the peak voltage of the ground line relative to the live line, UDIs a diode DNPressure drop of (d);
the resistance R is detected by a voltmeter in the positive half cycle of the alternating currentL1Peak voltage U acrossL1Due to the resistance RL1And a resistance RL2Resistance value of, diode DLIs known based on formula IL1＝UL1/RL1The resistance R is obtained by calculationL1The current value of the branch is based on the formula UEN＝UL1*(RL1+RL2)÷RL1+UDCalculating to obtain a voltage value between the ground wire and the zero line, wherein UENIs the peak voltage of the earth wire relative to the zero line, UDIs a diode DLPressure drop of (d).
It can be understood that the process of calculating the ground impedance values of the live wire and the zero wire based on the detected power voltage value, the current value in the alternating current positive half cycle detection branch and the current value in the alternating current negative half cycle detection branch specifically includes the following steps:
in the negative half cycle of the alternating current, IN＝IN0+IN1Wherein, INTo measure the total current in the loop, IN＝(UNL-UEL)/RN，IN0The value of the current between live and ground, IN0＝UEL/RL；
In the positive half cycle of the alternating current, IL＝IL0+IL1Wherein, ILTo measure the total current in the loop, IL＝(ULN-UEL)/RL，IL0Is the current value between the zero line and the ground line, IL0＝UEN/RN；
Will UNL、ULN、UEN、UEL、IN、IN0Substituting into a formula to jointly solve to obtain:
RL＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IN1*UEN+IL1(UNL-UEL)]
RN＝[(UNL-UEL)*(ULN-UEN)-(UEN*UEL)]÷[IL1*UEL+IN1(ULN-UEN)]。
in addition, because certain errors inevitably exist during measurement, some values close to the limit need to be pre-judged so as to avoid calculation errors. For example, when U is measuredL1When it is close to 0, R is considered to beLThe impedance value of the live wire to the ground is large; while measuringMeasure to UN1When it is close to 0, R is considered to beNThe large impedance value of the zero line to the ground is normal. In addition, when U is obtained by calculationENIs close to ULNWhen it is, R can be considered to beLVery small, i.e. abnormal values of the impedance of the live wire to ground; when U is obtained by calculationELIs close to UNLWhen it is, R can be considered to beNAnd the impedance value of the zero line to the ground is very small, namely abnormal. It will be appreciated that in the case of the above-mentioned limit values, it is difficult to detect an accurate impedance value to earth.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
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