JP2007298330A - Method and device for measuring insulation resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously measure insulation resistance without performing troublesome measurement operations and without being affected by variation in a power supply. <P>SOLUTION: Two sets made of resistors having a high resistance value and resistors having a low resistance value, namely a positive pole side set (R11, R12) and a negative pole side (R21, R22) are connected in series between a positive pole P and a negative pole N. A resistor R3 having a low resistance value is connected to a neutral point M of the two sets of resistors. When respective resistance values of the positive pole side, negative pole side R12, R22, R3 are made into the same value by a T-type detection circuit having one end grounded, the detection voltages VR12, VR22, VR3 generated at both ends of respective resistors are detected. A voltage ratio VR12/VR3 or VR22/VR3 is obtained, and the ratio is multiplied by a constant K value the same as the resistors R11, R21. Accordingly, the insulation resistance value is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a measuring method and apparatus for measuring an insulation resistance of a circuit in an operating state of a system, that is, in a live line state. For example, in an electric propulsion ship using a DC power supply, from the viewpoint of safety confirmation during operation, the power supply circuit is required to be always in a live state and continuously monitor the insulation resistance. It is suitable for use in such applications.

As a method for measuring the insulation resistance, a method using an insulation resistance meter as shown in FIG. Further, a method for measuring the insulation resistance in the operating state of the system is called a so-called live line Meg, and a method using the bridge principle shown in FIG. 5 is known.
The former insulation resistance meter is a method in which the insulation resistance is indirectly measured from the ammeter indicated value of the current i flowing through the insulation resistance RPX by a constant power source S (500 V or 1000 V is generally used) in the insulation resistance meter. Therefore, it is necessary to measure the insulation resistance when the power is stopped. For this reason, there is a problem that the insulation resistance cannot be measured during the operation of the system.

On the other hand, the latter live wire Meg is indirectly insulated from the VR resistance value when the ammeter instruction becomes zero by adjusting the variable resistor VR so that the instruction of the ammeter M in the bridge circuit becomes zero. Since this method measures the resistance RPX, a complicated measurement operation (adjustment operation) is required, but there is a problem that continuous measurement cannot be performed.
Therefore, a device that does not require such a complicated measurement operation is disclosed in Patent Document 1, for example.

Japanese Patent Laid-Open No. 01-165773

However, the device described in Patent Document 1 has a problem that it is easily affected by power supply fluctuations because no consideration is given to power supply fluctuations.
Therefore, an object of the present invention is to make it possible to measure insulation resistance continuously without complicated measurement operations and stably without being subject to power supply fluctuations.

In order to solve such a problem, in the invention of claim 1, two sets of a first resistor having a high resistance value and a second resistor having a low resistance value are connected in series between the positive electrode and the negative electrode. A T-type detection circuit is formed by connecting a third resistor having a low resistance value to the neutral point of these two sets of detection resistors, and grounding one end thereof,
Voltages generated at both ends of the positive and negative second resistors and at both ends of the third resistor when the resistance values of the positive and negative second and third resistors are the same. And the voltage ratio of the second resistor on the positive electrode side to the voltage ratio of the third resistor or the voltage ratio of the second resistor on the negative electrode side to the voltage on the third resistor is calculated. Is multiplied by a constant K value equal to that of the first resistor to obtain an insulation resistance value.

  In the invention of claim 2, two sets of a first resistor having a high resistance value and a second resistor having a low resistance value are connected in series between the positive electrode and the negative electrode, and these two sets of detection resistors A third resistor having a low resistance value is connected to the neutral point of the capacitor, one end of which is grounded, and the resistances of the positive and negative second resistors and the third resistor Voltage detection means for detecting voltages generated at both ends of the positive and negative second resistors and the third resistor when the values are the same, and the voltage of the positive second resistor A first computing means for computing the voltage ratio of the three resistors, a second computing means for computing the voltage ratio of the negative second resistor to the third resistor, and a voltage ratio from the first computing means. Third calculation means for multiplying a constant K value that is the same value as that of the first positive-side first resistor, and a voltage ratio from the second calculation means to the negative-side first resistance. And having a fourth computing means for multiplying a constant K value equal to the vessels, and display means for displaying either one of the output of the third or fourth calculation means as the insulation resistance.

  In the second aspect of the present invention, there is provided a polarity discriminating means for discriminating the polarity of the voltage generated in the third resistor. When it is negative, the calculation and display on the negative electrode side can be performed and the calculation and display on the positive electrode side can be locked (invention of claim 3). In the invention of claim 2 or 3, the insulation resistance Alarm means for issuing an alarm upon determining that the value has fallen below a preset value can be provided (invention of claim 4).

  According to the present invention, since the insulation resistance can be continuously measured during operation of the system, it is possible to always check the safety of the system. Further, not only a complicated measurement operation is unnecessary, but also devised so as not to be affected by fluctuations in the power supply, there is an advantage that stable measurement is possible.

FIG. 1 is a block diagram showing an embodiment of the present invention.
The detection resistors 1 (R11) to 5 (R3) constitute a T-type detection circuit, and signals 6 (voltage VR12) and 8 (voltage VR22) from the resistors 2 (R12), 4 (R22) and 5 (R3), respectively. And 7 (voltage VR3) are obtained, respectively. These signals 6 to 8 are input to the primary side of the isolation converters 9 (IAP), 10 (IAM), and 11 (IAN), and are isolated and converted to secondary signals 12 to 14, respectively.

  The secondary signals 12 to 14 have their harmonic components removed by the low-pass filters 15 (LPP) to 18 (LPN) to become signals 19 to 21, of which the signals 19 and 20 are sent to the positive divider 25 (DP). The signals 20 and 21 are input to the negative divider 26 (DN), and division is performed. The polarity discriminator 22 (PC) discriminates the polarity of the signal 20 and outputs a signal 23 (ON) when the signal 20 is in the (+) direction, that is, when the voltage VR3 is in the (+) direction, (− ) Direction 24, the signal 24 (ON) is output.

When the polarity discriminator 22 (PC) outputs a signal 23 in the (+) direction, the calculators 25 and 31 on the positive electrode side, the display device (IND) 35 and the alarm device (AL) 36 are operated, and the negative electrode side is connected. Lock it. Similarly, when the polarity discriminator 22 (PC) outputs the signal 24 in the (−) direction, the negative side calculators 26 and 32, the display device 35, and the alarm device 36 are operated to lock the positive side.
Hereinafter, the case where the polarity discriminator 22 (PC) outputs the signal 23 in the (+) direction and measures the positive-side insulation resistance will be described.

Fig.2 (a) is explanatory drawing in the case of measuring a positive electrode side insulation resistance.
Here, the ratio of the resistance R11 to R12 on the positive electrode side or the resistance R21 to R22 on the negative electrode side is about 1: 1/100 to 1: 1/25, which is the circuit voltage value to be measured, Or, select the optimum value according to the range of the insulation resistance value to be measured. Details will be described later.

  For example, when measuring the insulation resistance of a DC voltage 500 V circuit, when the detection resistance value is selected as R11, R21 = 1 MΩ, R12, R22 = 10 KΩ, RPX = ∞ when the insulation resistance is infinite. The current IRX shown in FIG. As a result, the voltages VR12, VR22 across the detection resistors R12, R22 are VR12 = VR22, the current IP flowing through the detection resistance values R11, R12, R21, R22 is IP≈V ÷ (R11 + R12 + R21 + R22), and the M potential is VP. = VN = 250V, and a resistance ratio of 1: 1/100 between the resistors R11 and R12, a voltage of 250V / 100≈2.5V is generated in the resistors R12 and R22.

  Assuming that the positive-side insulation resistance RPX of the power supply circuit is reduced, a ground current IRX = V ÷ (RPX + R3 + R21 + R22) flows in the ground circuit, and a voltage of VR3 = IRX × R3 is generated at both ends of the detection resistor R3. At this time, the voltage VR12 across the detection resistor R12 is determined by the current IP, and the voltage VR3 across the detection resistor R3 is determined by the current IRX. That is, when R11 and RPX are sufficiently larger than R12 and R3, respectively, if R12 = R3, the ratio of the voltage values of VR12 and VR3 is considered to be the reciprocal of the ratio of the resistance values of R11 and RPX. The voltage ratio n (VR12 / VR3) of VR3 is obtained, and the insulation resistance value can be obtained by multiplying the ratio n by the detection resistance R11, that is, n × R11 = RPX.

The above is performed as follows in the circuit of FIG.
That is, the signal 6 of the voltage VR12 across the detection resistor R12 becomes the signal 19 via the isolation converter 9 → the signal 12 → the low pass filter 15 and is input to one of the dividers 25. Further, the signal 7 of the voltage VR3 across the detection resistor R3 generated by the current IRX becomes the signal 20 via the insulation converter 10 → the signal 13 → the low pass filter 16, and is input to the other of the divider 25, and the polarity is discriminated. Is input to the device 22.

  At this time, since the signal 20 is in the positive (+) direction, the polarity discriminator 22 discriminates the (+) direction and outputs a signal 23 (ON), and the divider 25 and the multiplier 31 are put in the calculation state. The display device 35 and the alarm device 36 are switched to the positive electrode side. Further, the signal 24 (OFF) causes the divider 26 and the multiplier 32 to be in a non-computation state, and the operations on the negative side of the display device 35 and the alarm device 36 are locked.

  By the above switching, the divider 25 outputs a signal 27 indicating VR12 / VR3 which is the ratio of the signal 19 and the signal 20, and inputs the signal 27 to one of the multipliers 31. The constant setter 29 (F) outputs a signal 30 that makes the set value K the same as that of the detection resistors R11 and R21 and inputs the signal 30 to the other of the multiplier 31. Therefore, the multiplier 31 multiplies the output signal 27 from the divider 25 and the signal 30 indicating the constant K from the constant setter 29 and outputs a signal 33.

  The signal 33 indicates an insulation resistance value RPX = (VR12 / VR3) × K (resistance value of R11) to be obtained. This is given to the display device 35 and displayed on the alarm device 36 in advance. When it falls below the insulation resistance value, an alarm is issued and a process for safety management is performed such as recording the insulation resistance value that changes in time series with the output signal 37. As shown in FIG. 1, a measurement power source 38 (S) and a power switch 39 (SW) are provided, and by using these, a circuit, device or apparatus in a non-energized state, that is, not in a live line state Insulation resistance can be measured.

FIG. 2B is an explanatory diagram for measuring the negative electrode side insulation resistance.
In this case, the insulation resistance to be measured is RNx, and the current IRX flows through this, so that the resistance R12 is replaced with the resistor R22, and the insulation resistance value RNX to be obtained from the same relationship as described above is
RNX = (VR22 / VR3) × K (resistance value of R21)
Can be obtained as

  In the circuit of FIG. 1, the signals 6, 12, 19, 27 and 33 are converted to signals 8, 14, 21, 28 and 34, the arithmetic circuits 25 and 31 are switched to the arithmetic circuits 26 and 32, the signal 23 is turned OFF and the signal 24 is switched off. By replacing each with ON, the negative electrode side insulation resistance can be measured in exactly the same manner as when the positive electrode side insulation resistance is measured.

FIG. 3 shows a calculation example of the voltage detection characteristic and the voltage magnification n.
Assuming that the resistance value RPX = 1MΩ of the insulation resistance is R11 = RPX = 1MΩ and R12 = R3 = 1OKΩ, it can be determined that VR12 = VR3≈1.65 from FIG. 3A, and the voltage ratio n = VR12 / VR3 Since 1.65 / 1.65 = 1, RPX = K (R11 = 1MΩ) × 1 = 1MΩ is obtained.

Similarly, when the voltage ratio n = VR12 / VR3 = 10, RPX = K (1MΩ) × 10 = 10MΩ, and when the voltage ratio n = VR12 / VR3 = 100, RPX = K (1MΩ) × 100 = 100MΩ, the voltage ratio n = 0.1 can be obtained as 0.1 MΩ (see FIG. 3B).
When the voltage of the power supply circuit fluctuates, the currents IP and IRX fluctuate in proportion to this and the VR12 and VR3 also fluctuate, but the voltage ratio n = VR12 / VR3 does not change. Therefore, according to the present invention, even if the circuit voltage to be measured fluctuates, the measurement value is not affected by this, so that it is possible to obtain a stable measurement of insulation resistance.

Next, selection of the resistors R11 to R22 will be described.
In the above, the case where a circuit with a voltage of 500 V is measured as the resistors R11, R21 = 1 MΩ and the resistors R12, R22 = 10 KΩ has been described. At this time, when the insulation resistances RPX and RNX are infinite, the potential at the neutral point M is 250V, and the detection voltage VR12 = VR22≈2.5V.

  Here, when the voltage of 500 V fluctuates in the range of 600 V (+ 20%) to 400 (−20%), if the insulation resistances RPX and RNX are infinite, the detection voltage VR12 = VR22≈3 V to 2.5 V to 2 V It fluctuates in the range. However, since the detection voltage ratio n does not change, there is no influence on the measured value. Also, when measuring the insulation resistance of a circuit with a voltage of 1000 V, the potential of M is 500 V and the detection voltage VR12 = VR22 = 500 / 100≈5 V, but in this case also the detection voltage ratio n does not change, so the measured value There is no impact on

  Further, if each resistance value is R11, R21 = 1 MΩ, and the resistance ratio 1: 1/100 of the resistors R12, R22 = 10 KΩ is 1: 1/50, that is, the resistors R12, R22 = 20 KΩ, VR12, VR22 is 2 .5V to 5V, resistance ratio is 1: 1/25, resistance R12, R22 = 40KΩ, VR12 and VR22 change detection voltage from 2.5V to 10V, but the voltage ratio is unchanged. There is no impact on

  In the above, the resistance values of the resistors R11 and R21 are fixed and the resistance values of the resistors R12 and R22 are changed. However, the resistance values of the resistors R12 and R22 may be fixed and the resistance values of the resistors R11 and R21 may be changed. Needless to say. That is, the resistance values of R11, R21 and R12, R22 can be selected as optimum values in order to obtain the voltage of the measurement circuit and the optimum detection voltage.

  The present invention is intended for a non-grounded circuit, and is not applicable because the insulation resistance to be measured is short-circuited in a one-wire grounded circuit, and both the positive-side insulation resistance and the negative-side insulation resistance are comparable. Is not applicable because the current does not flow through the ground circuit (resistor R3).

Configuration diagram showing an embodiment of the present invention Explanatory diagram of measuring operation of positive side and negative side insulation resistance in Fig. 1 Explanatory drawing of the voltage detection characteristic and voltage detection magnification of FIG. Illustration of megger Illustration of hot wire Meg

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1-5 ... Resistor, 6-8, 12-14, 19-21, 23, 24, 27, 28, 30, 33, 34, 37 ... Signal, 9-11 ... Insulation converter, 15-18 ... Low pass Filter, 22 ... Polarity discriminator, 25, 26 ... Divider, 29 ... Constant setter, 31, 32 ... Multiplier, 35 ... Display device, 36 ... Alarm device, 38 ... Power supply for measurement, 39 ... Power switch

Claims (4)

Two pairs of a first resistor having a high resistance value and a second resistor having a low resistance value are connected in series between the positive electrode and the negative electrode, and the neutral point of these two detection resistors is low. A T-type detection circuit comprising a third resistor having a resistance value and having one end grounded,
Voltages generated at both ends of the positive and negative second resistors and at both ends of the third resistor when the resistance values of the positive and negative second and third resistors are the same. And the voltage ratio of the second resistor on the positive electrode side to the voltage ratio of the third resistor or the voltage ratio of the second resistor on the negative electrode side to the voltage on the third resistor is calculated. Is multiplied by a constant K value equal to that of the first resistor to obtain an insulation resistance value.   Two pairs of a first resistor having a high resistance value and a second resistor having a low resistance value are connected in series between the positive electrode and the negative electrode, and the neutral point of these two detection resistors is low. When a third resistor having a resistance value is connected and one end thereof is grounded, and the resistance values of the positive and negative second resistors and the third resistor are set to the same value Voltage detecting means for detecting voltages generated at both ends of the positive and negative second resistors and the third resistor, respectively, and a voltage ratio of the positive second resistor to the third resistor. A first computing means for computing, a second computing means for computing a voltage ratio of the voltage of the negative second resistor to the third resistor, a positive first resistor on the voltage ratio from the first computing means, The third arithmetic means for multiplying the constant K value having the same value, and the constant K having the same value as that of the negative first resistor in the voltage ratio from the second arithmetic means. A fourth computing means for multiplying the insulation resistance measuring apparatus characterized by having a display means for displaying either one of the output of the third or fourth calculation means as the insulation resistance.   Polarity discrimination means for discriminating the polarity of the voltage generated in the third resistor is provided. When the polarity is positive, the calculation and display on the positive side can be performed and the calculation and display on the negative side are locked. When the polarity is negative, the polarity is negative. 3. The insulation resistance measuring device according to claim 2, wherein the calculation and display on the positive side are enabled and the calculation and display on the positive electrode side are locked.   4. The insulation resistance measuring apparatus according to claim 2, further comprising alarm means for issuing an alarm upon determining that the insulation resistance value has fallen below a preset value.

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