JP4751789B2 - Non-grounded circuit insulation monitoring method and apparatus - Google Patents

Description

  The present invention relates to a circuit insulation monitoring technique for monitoring the insulation state of a non-grounded circuit, and more particularly to a monitoring method and apparatus suitable for insulation monitoring of a non-grounded circuit used in a hospital operating room, an intensive care unit, and the like.

  Electrical circuits such as operating rooms and intensive care units in hospitals are not used to protect patients by minimizing leakage current in the event of a ground fault, or to prevent secondary disasters caused by electric shocks of doctors and nurses. A grounding type electric circuit is used.

  In recent years, many medical devices have been installed in operating rooms and the like, and the wiring distance tends to be long. When the length is long, the capacitance to the ground of the wiring increases. The probability increases and the risk of electric shock increases.

  Therefore, an insulation monitoring / warning device is used for an ungrounded electric circuit used in a hospital operating room or an intensive care unit.

  This alarm device is stipulated by JIS to operate when any one of the ungrounded electrical circuits is connected to the ground with a low impedance conductor and the value of the ground fault current flowing becomes 2 mA. ing.

Conventionally, the following method has been used as an insulation monitoring device for such an ungrounded electric circuit.
(1) Resistive grounding method: Connect a resistor to the electric circuit, create a neutral point, ground the neutral point to the ground via a current detector, and leak current flowing from the ground to the neutral point in the event of a one-line ground fault Method to detect.
(2) DC superposition method: A method in which a DC current detector and a DC power source are connected between one line of the electric circuit and the ground, and a DC current that changes as the insulation resistance of the electric circuit changes is detected.
(3) Low frequency superposition method: A low frequency current detector and an AC power source having a frequency sufficiently lower than the system frequency are connected between the line of the circuit and the ground, and the low frequency current that changes with the change in the insulation resistance of the circuit (For example, patent document 1).
(4) Line sequential switching monitoring method: Connect one end of the current detector to the ground, and insert the other end alternately between each line of the circuit and the ground with a semiconductor or mechanical alternating switch, and the insulation resistance of the circuit A method of detecting current that changes with changes.

  However, the above methods (1) to (4) have the following problems.

  That is, in the method of (1), when the insulation resistance of the electric circuit is lowered at the same time, or when the capacitance to the ground is increased, the capacitance with respect to the ground of each line increases almost equally. No voltage is generated between them, and a decrease in impedance cannot be detected.

  In the method (2), since the detection signal is a direct current, it is impossible to detect a decrease in impedance with respect to an increase in the ground capacitance of the electric circuit.

  In addition, since the insulation resistance value for each line cannot be detected, the value when one line is deteriorated in insulation and the detection value when both lines are deteriorated are the same. Will end up.

  In addition, since the method (3) also has a low frequency, when the ground capacitance of the electric circuit increases, unlike the impedance value at the system frequency, the decrease in impedance cannot be accurately detected as it is.

  In addition, since the insulation resistance value for each line cannot be detected, the value when one line is deteriorated in insulation and the detection value when both lines are deteriorated are the same. Will end up.

  The method (4) can detect both one-line and both-line ground faults and can also detect a decrease in impedance due to an increase in the ground capacitance, but noise is generated due to a sudden change in the ground voltage of the circuit, and the electrocardiogram Damage to medical equipment such as meters.

  Therefore, the applicant of the present application has developed a line sequential switching monitoring method using a frequency superposition slightly different from the system frequency as a result of various experimental investigations in order to solve the problems of each of the above methods, and has put them into practical use (for example, Patent Document 2).

The previously proposed invention will be described as a prior art with reference to FIGS. FIG. 3 is an explanatory diagram, P1 and P2 are ungrounded electric circuits for monitoring insulation, 1 is an insulating transformer, 2 is a signal power source, 3 is a current detector, and the signal power source 2 and the current detector 3 are insulating transformers 1 Is connected in series between the neutral point and ground (earth) E. Reference numerals 4 and 5 denote the impedance between the current paths P ₁ and P ₂ .

  The signal power source 2 outputs an alternating current signal having a frequency slightly different from the system frequency and ½ of the system circuit voltage. When the frequency of the system is 50 Hz (or 60 Hz) and the voltage is 100 V, an AC signal of 50 V at 55 Hz, for example, slightly different from this frequency is generated.

Then, the 55 Hz, 50 V AC signal is applied between the neutral point of the insulating transformer 1 and the ground. As shown in FIGS. 4A and 4B, 50 Hz and 55 Hz are synthesized between the electric circuit P ₁ and the ground E and between the electric circuit P ₂ and the ground E by the application of the AC signal, respectively. The combined voltage repeats a gentle increase and decrease with a maximum amplitude of 100 V, a minimum amplitude of 0 V, and a cycle number of 5 Hz. When the voltage between the electric circuit P ₁ and the ground E is maximum, the voltage between the electric circuit P ₂ and the ground is minimum, and when the voltage between the electric circuit P ₁ and the ground is minimum, the voltage between the electric circuit P ₂ and the ground is Maximum.

A current proportional to this voltage is a path of an electric circuit P ₁ -ground impedance 4 -ground E -current detector 3 -signal power source 2 -neutral point, and the electric circuit P ₂ side has an electric circuit P ₂ -ground impedance 5- It flows in the path of earth E-current detector 3-signal power source 2-neutral point.

Since this current increases as the insulation resistance of the electric circuits P ₁ and P ₂ decreases and the ground impedances 4 and 5 decrease due to the increase in capacitance between the electric circuit and ground, this current is detected by the current detector 3. Thus, the insulation state can be monitored.

Further, when the human body touches the electric paths P ₁ and P ₂ , a current flows through the human body. However, it is necessary to limit the current to such a level that there is no danger to the human body (2 mA). The current limiter 6 is provided in series with the voltage limiter 3 to limit the current.
JP-A-7-209366 Japanese Patent Publication No. 1-160888.

  In the above-mentioned prior proposal invention, when the voltage between one line and the ground becomes maximum, the voltage between the other line and ground becomes minimum. Even if the insulation resistance of the two wires decreases in a balanced manner, there is an advantage that the deterioration of the insulation resistance of the electric circuit can be detected.

  In addition, since insulation monitoring is performed with an alternating voltage that gradually increases and decreases, there is an advantage that a decrease in ground impedance accompanying an increase in capacitance between the electric circuit and the ground can be detected.

  Moreover, the switching of the electric circuit to be monitored is not performed using a mechanical or electrical switch as in the conventional example, and when the voltage between one line and the ground becomes maximum, the voltage between the other line and the ground is Since it is performed by using the minimum, there is no noise at the time of switching the electric circuit to be monitored, and therefore there is an advantage that no noise disturbance is given to a precise medical measuring instrument. It is something that has been used for practical use.

  However, in recent years, with the advancement of medical technology, computer control has been introduced in the medical device field, and the medical device itself has been required to have high precision.

  For example, an electrocardiograph is processed to capture a slight change in the electrocardiogram waveform by using a steep digital filter to remove the hum noise of the system frequency as much as possible and to obtain an electrocardiogram waveform faithful to the source waveform. It is becoming. At this time, the applied signal for detection is slightly different from the system frequency, and since the voltage of the applied signal is high, a steep filter cannot be removed, and it has become an obstacle as hum noise.

  Therefore, the present invention has an object to provide an insulation monitoring method and a monitoring device that can take advantage of the above-described prior invention and can monitor insulation even when the voltage of a detection signal is low.

Means for solving the above-described problems in the present invention include a signal power source for generating a voltage detection signal having a frequency different from the frequency of the electric circuit between the neutral point of the transformer having the ungrounded electric circuits P ₁ and P ₂ and the ground. A detection circuit is formed by connecting high resistance resistors in series, current detection means for detecting a current flowing through the detection circuit is provided in the detection circuit, and a detection signal detected by the current detection means is passed through a filter. The signal power supply frequency and the current of the circuit frequency are taken out, respectively, and the total impedance between the circuit and the earth is measured by the detection signal from the signal power supply taken out. The zero-phase voltage between the sex point and the ground, and the zero-phase voltage and the electric circuit P ₁ . From path voltage obtained by the path voltage signal input circuit which detects the voltage of the P _2, obtains the earth voltage of each path P _1, P _2, the impedance with frequency of the total impedance path due to the frequency of the signal power obtained by the measurement The impedance between the electric circuits P ₁ and P ₂ and the earth is obtained using the converted impedance, and the electric current P ₁ and the earth and the current between the electric circuit P ₁ and the earth and P ₂ and the earth are obtained by dividing the voltage between the electric circuits by this impedance. The insulation resistance between them is monitored.

  In this way, by measuring the impedance between the electric circuit and the ground from the current of the detection signal, and converting to the impedance according to the frequency of the electric circuit (system) using this measured impedance, the voltage of the signal power supply is monitored. Even if it is low, the insulation of the electric circuit can be monitored regardless of the frequency of the signal power source.

  Further, by providing a high resistance in the detection circuit, safety can be improved without a current limiter.

Then, the impedance between each of the electric circuits P ₁ and P ₂ and the ground is obtained by using the impedance according to the frequency of the electric circuit converted as described above, and the current flows when one line is grounded by the conductor from the impedance and the voltage between the grounds of the electric circuit. The current value that will be calculated is calculated, and when the current value exceeds a preset current value, an alarm signal is output to issue an alarm.

As an insulation monitoring device, a high and low antibody and a signal power source that generates a voltage detection signal having a frequency different from the frequency of the electric circuit are connected in series between the neutral point of the transformer having the ungrounded electric circuits P ₁ and P ₂ and the ground. A detection circuit formed, a current detection unit provided in the detection circuit for detecting a current flowing through the detection circuit, and a current detected by the current detection unit using a filter to detect a frequency of a detection signal and a current based on a frequency of an electric circuit, respectively. An arithmetic unit input means for separating the detection signal input circuit and the electric circuit signal input circuit and inputting them to the arithmetic means; and an electric circuit voltage signal provided in the electric circuit for detecting the electric circuit voltages of the electric circuits P ₁ and P ₂ and a path voltage detection circuit for input to the arithmetic means, said arithmetic means calculates a total impedance between the electric path and the earth by the frequency of the detected signal at the input from the detection signal input circuit signal, circumference of path The zero-phase voltage between the neutral point and the ground obtained from the signal by the wave number is detected, the ground-to-ground voltage of each circuit is obtained from the zero-phase voltage and the circuit voltage, and the total impedance according to the frequency of the calculated detection signal is calculated as the circuit. The impedance is converted into the total impedance according to the frequency of the current, and the impedance between each electric circuit P ₁ and the ground, and between P ₂ and the earth is obtained using the converted impedance , and _one line is grounded by the conductor from this impedance and the voltage between the electric circuits . A current value that will flow at times is calculated, and an alarm signal is output when the current value exceeds a preset current value .

  Since this invention is comprised as mentioned above, there exists the following effect.

  (1) Since a low voltage that does not affect the medical device can be used as a detection signal, it is possible to select a frequency that does not affect the measurement result of the medical device and that is not affected by the harmonics of the commercial frequency. A device suitable for insulation monitoring of the electric circuit of a medical device can be obtained.

  (2) The non-grounded circuit is connected to the ground with a high resistance (1 MΩ or more), a detection signal source and a signal current detection resistor, and the insulation resistance between the circuit and the ground and the impedance due to the increase in ground capacitance Therefore, a circuit for limiting the current is not necessary and the safety is improved.

(3) At the same time as the detection signal is extracted, the commercial frequency signal is extracted, and the voltage (V ₁ , V ₂ ) between each line and ground is obtained from this zero-phase voltage and circuit voltage. The impedance between the electric circuit and the ground can be kept high.

(4) An alarm output is issued when either of the current values obtained by dividing the circuit voltage at each impedance is above a predetermined level, thereby indicating which insulation failure of the circuit P ₁ or P ₂ is displayed. It becomes possible.

  (5) Since the calculation is performed separately for the resistance component and the capacitor component, if the insulation is deteriorated due to the resistance component, it is determined that the degree of danger is higher and a warning can be issued with high sensitivity.

(6) Although described with single-phase two-wire, detection with the above method is also possible with single-phase three-wire.
In addition, even three-phase three-wire calculation is complicated, but detection is possible.

  Hereinafter, embodiments of the present application will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of the present invention. In the figure, reference numeral 1 is an insulating transformer, P ₁ and P ₂ are non-grounded electric circuits (hereinafter abbreviated as electric circuits) for monitoring the insulation on the secondary side of the transformer 1, 10 is a high resistance body having a high resistance value, 11 Is a signal power source for generating a detection signal, and the high resistor 10 and the signal power source 11 are connected in series between the neutral point of the transformer 1 and the ground E to form a detection circuit.

  A signal current detection resistor 12 is formed of a resistor connected in series with a detection circuit.

  An arithmetic unit input means 20 includes a detection signal input circuit 20A and an electric circuit signal input circuit 20B. The signal input circuits 20A and 20B are filters 21A and 21B, amplifiers 22A and 22B, and A / D conversion circuits 23A and 23B, respectively. The detection signal input circuit 20A takes out the signal at the frequency of the detection signal from both ends of the signal detection resistor 12 by the filter 21A, performs A / D conversion, and outputs it to the arithmetic means 30.

  Similarly, the electric circuit signal input circuit 20 </ b> B takes out the signal of the electric circuit frequency by the filter 21 </ b> B, performs A / D conversion, and outputs it to the calculation means 30.

  An electric circuit voltage signal input circuit 31 includes a transformer 31a, a power supply circuit 31b, and an A / D conversion circuit 31C, and detects voltages and frequencies of the electric circuits P1 and P2 and inputs them to the calculation means 30. A warning means 40 is a means for allowing a human to quickly detect by means of sound or light when a warning output signal is issued by the calculation means 30.

Reference numerals 51 and 52 denote ground impedances between the electric circuits P ₁ and P ₂ and the ground E.

  As the generation frequency of the signal power source 11 that generates the detection signal, a frequency that is not affected by the harmonics of the electric circuit is selected. For example, the frequency of the electric circuit is generally 50 Hz (or 60 Hz) of the commercial power supply, and the third harmonic contained in the commercial power supply is 150 Hz (180 Hz), and therefore the frequencies that do not affect these frequencies. For example, 166 Hz is selected, and the voltage is set to a low voltage such as about 12.5 V so as not to affect the medical device.

Insulation monitoring of the ungrounded circuit is performed by applying a detection signal of 166 Hz, 12.5 V between the circuit P ₁ and the ground E and between the circuit P ₂ and the ground E by the signal power source 11 according to the above example, and the current flowing at this time is detected as a signal current Detected by the resistor 12, and the detection signal input circuit 20A sends a detection signal at a detection signal of 166 Hz to the calculation means 30, and the calculation means 30 measures the insulation resistance between the electric circuit and the ground and the ground capacitance.

In this measurement, assuming that the resistance of the high-resistance element 10 is Z ₀ and the impedances at 166 Hz between the electric circuits P ₁ and P ₂ and the ground are Z ₁ ′ and Z ₂ ′, respectively, the total at 166 Hz between the electric circuit and the ground. The impedance Z ₃ ′ is
Z ₃ ′ = 1 / {(1 / Z ₁ ′) + (1 / Z ₂ ′)} (1)
It becomes.

  The current i flowing through the detection circuit is detected by the detection resistor of the signal current detection resistor 12.

When the voltage of the signal source 11 and V _{11,
i = V 11 / (Z 3} '+ Z 0) ......... (2)
Z ₃ ′ = (V ₁₁ / i) −Z ₀ (3)
In can therefore be found a total impedance at 166Hz.

Next, the calculating means 30 takes in the signal of the electric circuit frequency (commercial frequency) via the electric circuit signal input circuit 20B. This commercial frequency signal corresponds to a zero-phase voltage (V ₀ ) between the neutral point and the ground, and each electric circuit P ₁ , P is determined from this zero-phase voltage and the line voltage of the electric circuit measured by the electric circuit voltage signal input circuit 31. ₂ and the ground voltages V ₁ and V ₂ are obtained, the measured value is converted into the impedance of the commercial frequency, and the impedance between the electric circuits P ₁ and P ₂ and the ground is obtained using the converted impedance. Then, from this impedance and the circuit voltage, a current that will flow when one line is grounded by a conductor is obtained, and when a preset current value is exceeded, an alarm signal is output to the alarm means 40 to issue an alarm.

Next, calculation of impedance at commercial frequencies between the electric circuits P ₁ and P ₂ and the ground will be described.

FIG. 2 is an equivalent circuit of a commercial frequency signal detection part, and the impedances of the electric circuits P ₁ and P ₂ are obtained by the following equation.

Since the sum of the currents flowing into the points of interest is zero according to Kirchhoff's law, if the currents flowing into the points G in FIG. 2 are i ₀ , i ₁ , i ₂ ,
i ₀ + i ₁ + i ₂ = 0 (4)
I ₀ = V ₀ / Z ₀ , i ₁ = V ₁ / Z ₁ , i ₂ = V ₂ / Z ₂
If 1 / Z ₀ , 1 / Z ₁ , 1 / Z ₂ are replaced with admittances Y ₀ , Y ₁ , Y ₂ , the total admittance Y ₃ between the electric circuit and the ground is Y ₃ = Y ₁ + Y ₂ .

Here, Z ₀ is a known value for the high resistor inserted in the detection circuit, and therefore Y ₀ is also known. Y ₃ is the reciprocal of the impedance converted from the impedance Z ₃ ′ obtained by the expression (3) into the impedance of the commercial frequency, and this value is also known.
Rewriting equation (4)
(V ₀ · Y ₀ ) + (V ₁ · Y ₁ ) + (V ₂ · Y ₂ ) = 0
V ₁ · Y ₁ = − (V ₀ · Y ₀ + V ₂ · Y ₂ ) (5)
Since Y ₂ = Y ₃ −Y ₁ , the equation (5) is V ₁ · Y ₁ = − (V ₀ · Y ₀ + V ₂ · Y ₃ −V ₂ · Y ₁ )
_{V 1 · Y 1 -V 2 ·} Y 1 = - (V 0 · Y 0 + Y 2 · Y 3)
When Y ₁ is calculated,
Y ₁ = − (V ₀ · Y ₀ + V ₂ · Y ₃ ) / (V ₁ −V ₂ )
The impedance of _one electric circuit P ₁ is obtained when Z ₁ = 1 / Y ₁ .

Similarly, the impedance of the other electric circuit P ₂ is obtained.

That is, Y ₂ = − (V ₀ · Y ₀ + V ₁ · Y ₃ ) / (V ₂ −V ₁ )
Z ₂ = 1 / Y ₂
This calculation is performed by the calculation circuit 30, and an alarm is issued from the alarm means 40 when either of the current values obtained by dividing the circuit voltage by the obtained impedances is equal to or higher than a preset set level.

  In the above description, an example in which the frequency of the signal power source is 166 Hz has been described. However, any frequency may be used as long as the frequency is different from the frequency of the electric circuit.

The block diagram of embodiment of this invention. The equivalent circuit diagram of a commercial frequency signal detection part. Explanatory drawing of the conventional non-grounded electric circuit insulation monitoring apparatus. Explanatory drawing of the detection signal of the conventional non-grounding circuit insulation monitoring apparatus.

DESCRIPTION OF SYMBOLS 10 ... High resistor 11 ... Signal power supply 12 ... Signal current detection resistor 20 ... Operation part input means 20A ... Detection signal input circuit 20B ... Electric circuit signal input circuit 21A, 21B ... Filter 22A, 22B ... Amplifier 23A, 23B ... A / D conversion circuit 30 ... arithmetic means 31 ... electric circuit voltage signal input circuit 40 ... alarm means 51, 52 ... impedance to ground

Claims (3)

A detection circuit in which a signal power source for generating a voltage detection signal having a frequency different from the frequency of the electric circuit and a high-resistance resistor are connected in series between the neutral point and the ground of the transformer having the ungrounded electric circuits P ₁ and P ₂ The detection circuit is provided with current detection means for detecting the current flowing through the detection circuit, and the current based on the frequency of the signal power supply and the frequency of the electric circuit is extracted from the detection signal detected by the current detection means through a filter. Then, the total impedance between the electric circuit and the ground is measured by the detection signal from the extracted signal power supply, and then the zero-phase voltage between the neutral point and the ground obtained from the signal current according to the frequency of the extracted electric circuit, and the zero-phase Voltage and circuit P ₁ . From path voltage obtained by the path voltage signal input circuit which detects the voltage of the P _2, obtains the earth voltage of each path P _1, P _2, the impedance with frequency of the total impedance path due to the frequency of the signal power obtained by the measurement The impedance between the electric circuits P ₁ and P ₂ and the earth is obtained using the converted impedance, and the electric current P ₁ and the earth and the current between the electric circuit P ₁ and the earth and P ₂ and the earth are obtained by dividing the voltage between the electric circuits by this impedance. insulation monitoring method for ungrounded path, characterized in that the insulation resistance between the so as to respectively monitor. The impedance between each of the electric circuits P ₁ and P ₂ and the ground is obtained by using the impedance according to the frequency of the electric circuit converted in claim 1, and the current flows when one line of the electric circuit is grounded by a conductor from the impedance and the voltage between the electric circuits. Aro will calculate the current value, the insulation monitoring method for ungrounded path according to claim 1, characterized in that outputs a warning signal when it exceeds a current value current value is set in advance. A detection circuit formed by serially connecting a high and low antibody and a signal power source that generates a voltage detection signal having a frequency different from the frequency of the electric circuit between the neutral point and the ground of the transformer having the non-grounded electric circuits P ₁ and P ₂ ; Current detection means provided in the detection circuit for detecting a current flowing in the detection circuit, and a detection signal input circuit and an electric circuit, respectively, for a detection signal frequency and an electric circuit frequency by a filter from the current detected by the current detection means. An arithmetic unit input means for classifying and inputting to the arithmetic means by a signal input circuit, and an electric circuit for detecting an electric circuit voltage of the electric circuits P ₁ and P ₂ by inputting an electric circuit voltage signal provided in the electric circuit and inputting the electric circuit voltage to the calculating means A voltage detection circuit, and the calculation means calculates a total impedance between the electric circuit and the ground according to the frequency of the detection signal from the signal input from the detection signal input circuit, and is obtained from the signal based on the frequency of the electric circuit . The zero-phase voltage between the neutral point and the ground is detected, the ground-to-ground voltage of each circuit is obtained from the zero-phase voltage and the circuit voltage, and the total impedance based on the frequency of the calculated detection signal is calculated as the total impedance based on the frequency of the circuit. Using the converted impedance, the impedance between each electric circuit P ₁ and the earth and between the P ₂ and the earth is obtained, and the current will flow when one line is grounded by a conductor from the impedance and the voltage between the earth of the electric circuit . An insulation monitoring device for an ungrounded electrical circuit, wherein a current value is calculated and an alarm signal is output when the current value exceeds a preset current value .

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