JPH0783975A - Insulation monitor for electric circuit of non-grounded wiring system - Google Patents

Abstract

PURPOSE:To reduce a monitor current by stably monitoring a ground impedance. CONSTITUTION:A series circuit having a pair of resistors having high resistance values to obtain a neutral point is connected between secondary outputs of an insulation transformer 2, and a monitor power source 13 for alternately generating a DC voltage and an AC voltage of 110Hz is connected between the neutral point and the ground 15. A current detecting resistor R30 is connected in series with the power source 13, an output voltage of the resistor R30 is applied to first subtracting means 25 through a low-pass filter 24 to subtract a predetermined first voltage, and also applied from a high-pass filter 28 to second subtracting means 29 to subtract a predetermined second voltage. Thus, even if real number parts and imaginary parts of ground impedances Z1, Z2 are relatively smaller than resistance values of the pair of the resistors for obtaining the neutral point, the impedances Z1, Z2 can be accurately detected. Outputs of the first and second means 25, 29 are respectively held in sample and hold means 26, 30, applied to one adding means 27, and then level-discriminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-ground wiring type electric circuit insulation monitoring apparatus.

[0002]

2. Description of the Related Art Safety standards for hospital electrical equipment are stipulated in Japanese Industrial Standards JIS T 1022. If a ground fault current flows in an electric line and the power is cut off, there is a risk of seriously impairing medical care. It is stipulated that the outlet circuit in the medical room where the equipment is used is of the non-grounded wiring system, and an insulation monitoring device is provided on the power supply side of the non-grounded electric circuit. This insulation monitoring device is a method of measuring and monitoring the ground impedance of the electric circuit, and the alarm device installed in it is a ground fault that flows when one of the ungrounded electric circuits is connected to the ground with a low-impedance conductor. It is said that it must operate when the current value becomes 2 mA.

A typical prior art is Japanese Patent Publication No. 1-16088.
In this prior art, for example, 50 Hz
An auxiliary voltage source for applying an auxiliary voltage having a frequency, for example, 55 Hz, which is slightly separated from the frequency between the neutral point of the non-grounded electric path and the ground, and applying a voltage substantially equal to the earth voltage of the electric path. , A current detector for detecting a current flowing between the neutral point and the ground, and a current limiter for keeping the current flowing by the human body at 2 mA or less even if the human body contacts the non-grounded circuit in series. Connected and configured.

[0004]

In such a prior art, the current limiter keeps the current between the neutral point and the ground to be 2 mA or less for the purpose of monitoring. It is presumed that it is configured to constantly pass a certain amount of current, and therefore the monitored current is large, which impairs the insulation of the non-grounded circuit.

An object of the present invention is to provide an insulation monitoring device for an electric line of an ungrounded wiring system, which can monitor the impedance to ground stably and does not require a large monitoring current to flow in the ungrounded electric line. It is to be.

[0006]

According to the present invention, there are provided an insulating transformer having a primary input to which power source power is applied, and an insulating transformer.
A series circuit, which is connected between the next outputs and has a large resistance value so as to pass a current sufficiently smaller than the ground current value to be monitored, and the mutual connection of the pair of resistors in the series circuit. Detects a power supply for monitoring, which is interposed between a point and ground, and which alternately supplies a DC voltage and an AC voltage having a frequency different from that of the power supply, and DC and AC currents flowing through the power supply for monitoring. And a means for discriminating the detection output of the current detecting means at a predetermined level.

According to the present invention, the frequency of the power source for monitoring is in the vicinity of a harmonic frequency which is twice the frequency of the power source,
It is characterized in that it is set to a value different from the harmonic frequency.

According to the present invention, the current detecting means is provided with a current detecting resistor connected in series to the monitoring power source and a voltage between both ends of the current detecting resistor, and a cutoff frequency lower than the frequency of the power source. And a first low-pass filter for subtracting a predetermined first voltage from the output of the low-pass filter.
Second subtraction for subtracting a predetermined second voltage from the output of the subtracting means, the voltage across the current detecting resistor, the frequency of the AC voltage being filtered out, and the output of the AC voltage frequency filtering filter. Means and means for adding the respective outputs of the first and second subtraction means.

Further, the present invention is characterized by further comprising sample hold means for holding respective outputs of the first and second subtraction means.

Further, according to the present invention, the current detecting means is provided with a current detecting resistor connected in series to the monitoring power source and a voltage between both ends of the current detecting resistor, and a cutoff frequency lower than the frequency of the power source. And a first analog / digital conversion means for converting the output of the low-pass filter having a higher output level into a digital value with higher resolution, and a voltage across the current detection resistor.
A filter for filtering and extracting the frequency of the AC voltage; second analog / digital conversion means for converting the output of the AC voltage frequency filtering filter into a digital value with higher resolution as the output level is higher; And means for adding the respective outputs of the second analog / digital conversion means.

[0011]

According to the present invention, a series circuit composed of a pair of resistors is provided between the secondary outputs of the insulating transformers, and the neutral point, which is the connection point of the pair of resistors, and the ground, that is, the ground. In between, a DC power supply and an AC voltage are alternately switched, and a monitoring power supply is connected, and a current flowing through the monitoring power supply is detected by a current detecting means, and the detected current is level discriminated. Therefore, by selecting the resistance values of the pair of resistors to be sufficiently large values, the current flowing through the human body when the human body comes into contact with the non-grounded circuit which is the secondary output of the insulating transformer is set to, for example,
In addition to ensuring safety by setting A or less, such a current value is small so that the insulation of the non-grounded circuit is not deteriorated, and the above-mentioned 104 μA is less than the ground fault current value to be monitored, for example, 2 mA. It is a sufficiently small value.

According to the present invention, the monitoring power supply applies a DC voltage and an AC voltage between the neutral point and the ground, and therefore, the real component of the ground impedance between each of the two non-grounded circuits and the ground. Insulation monitoring can be performed by a certain resistance component and an imaginary component capacitance.

Further, according to the present invention, it is possible to monitor the respective ground impedances between the two respective non-grounded electric paths which are the secondary outputs of the insulating transformer and the ground,
That is, it is possible to monitor not only the insulation deterioration between one non-grounded circuit and the ground, but also the insulation deterioration between both ungrounded circuits and the ground.

The frequency of the power supply for monitoring is a harmonic frequency twice as high as the frequency of the system power supply, for example, 60 Hz or 50 Hz, that is, in the vicinity of 120 Hz or 100 Hz, and a value different from the harmonic frequency, for example, 110.
Defined in Hz. If the frequency of the AC voltage of the monitoring power supply is selected to be the same as or near the secondary output voltage of the isolation transformer, that is, the frequency of the system power supply,
The phase shift between the AC voltage of the monitoring power supply and the output of the system power supply becomes a problem, and the detection current may fluctuate due to the phase shift and the occurrence of beats. Therefore, the frequency of the AC voltage of the monitoring power supply and the system power supply It is necessary to separate it sufficiently from the frequency of. The secondary output voltage of the isolation transformer is configured to issue a warning by discriminating the level when the ground fault current value to be monitored, for example, the above-mentioned 2 mA less than the direct current resistance of 50 kΩ to the ground. In addition, the ground capacitance due to the stray capacitance due to the long installation of the electric path is such that the ground impedance is 50 kΩ at the system power supply frequency of 60 Hz or 50 Hz.
If it is 53μF or 0.063μF and the alarm is generated when the capacitance to ground is higher than this, when the monitoring power supply outputs an AC voltage, the capacitance to ground does not exceed the above-mentioned DC resistance of 50kΩ and is erroneously detected. In order to prevent this, the AC voltage frequency of the monitoring power supply must exceed the frequency of the system power supply.However, if the frequency is too high, the impedance at the aforementioned ground capacitance becomes small, and the The resistance becomes too small compared to the high resistance value of each pair of resistors, which makes detection difficult. Therefore, it is convenient to set the frequency of the AC voltage of the monitoring power supply as described above.

Further in accordance with the present invention, the current detecting means comprises:
Has a resistance for current detection connected in series to the power supply for monitoring,
The both-end voltage generated by the current flowing in the current detecting resistor is applied to the low-pass filter so that the voltage corresponding to the real part of the ground impedance is detected, and the first subtraction means further determines a predetermined first voltage from the output of the low-pass filter. By performing the subtraction, level discrimination can be easily performed even if the direct current resistance, which is the ground impedance, is relatively small compared to the high resistance value of each of the pair of resistors for obtaining the neutral point. In the same manner as above, the output from a high-pass filter or a band-pass filter, which is a filter for filtering out the frequency of the AC voltage, is subtracted by the second voltage determined in advance by the second subtraction means. It is possible to easily detect the capacitance to ground, which is the imaginary part of the impedance to ground.

Further, according to the present invention, by adding the outputs of the first and second subtracting means and then performing the level discrimination, it is possible to simplify the configuration by using a single adding means. .

Further in accordance with the present invention, there is further provided sample hold means for individually holding the respective outputs of the first and second subtraction means, and the outputs of these sample hold means are added by a subsequent adder circuit. This makes it possible to accurately discriminate the level of the ground impedance, which is the sum of the real part and the imaginary part.

Further, according to the present invention, when the current detecting means is realized by a processing means such as a microcomputer, the outputs of the low-pass filter and the AC voltage frequency filtering filter are increased in digital value by increasing the resolution as the output level increases. By using the first and second analog / digital conversion means for converting to the level, even if the ground impedance is relatively small compared to the high resistance value of the pair of resistance values for obtaining the neutral point, level discrimination Can be easily performed.

[0019]

1 is a block diagram showing the overall construction of an embodiment of the present invention. RMS value from commercial AC power supply 1
Electric power of 0V is given to the primary coil 3 of the isolation transformer 2. The frequencies f1 and f2 of the commercial AC power supply 1 are f1 = 50
Hz or f2 = 60 Hz. Isolation transformer 2 of 2
The output of the next coil 4 is supplied from electric lines 5 and 6 to electric equipment 7 such as hospitals and clinics. The electric paths 5 and 6 are of a non-grounded wiring system, and the electric impedances Z1 and Z2 between the electric paths 5 and 6 and the ground 8 are measured and monitored by the insulation monitoring device 9 according to the present invention. The output voltage of the secondary coil 4 of the insulating transformer 2 has an effective value of 100V.

As shown in a simplified form in FIG. 2, when the ground impedance of the electric path 5 is Z1, when the human body 10 contacts the other electric path 6 and the electric path 6 is grounded, the secondary of the insulating transformer 2 Reference numeral I1 from the coil 4 through the electric path 5, the ground impedance Z1, the ground, the human body 10 and the electric path 6.
The ground fault current shown by flows. When the value of this ground fault current is such that the value of the ground fault current flowing when one of the ungrounded electric circuits is connected to the ground by a low impedance conductor becomes 2 mA, the insulation monitoring device of the present case Reference numeral 9 gives an alarm by the alarm means 11. The ground impedance Z1 or Z2 at which such an alarm operation is performed is 50
It is kΩ (= 100V / 2mA). Referring again to FIG. 1, the series circuit 12 is connected between the electric paths 5 and 6 which are the outputs of the secondary coil 4 of the insulating transformer 2. This series circuit 12 is composed of a pair of resistors R1, R2 and R30, and has a large resistance value so as to pass only a current sufficiently smaller than the ground fault current value of 2 mA to be monitored, for example, 113 μA, and in this embodiment. R1 = R2 = 1MΩ, R30
= 47 kΩ.

The monitoring power supply 13 includes a connection point 14 which is a neutral point of the pair of resistors R1 and R2 of the series circuit 12 and the ground 1.
5 is interposed. The monitoring power supply 13 includes a DC power supply 16 that outputs a DC voltage, a commercial AC power supply 1 that is the system power supply, and thus a secondary coil 4 of an insulation transformer 2.
The AC power supply 17 that outputs an AC voltage having a frequency f3 different from the output of the above is output at different application timings. In this embodiment, in the monitoring power supply 13, the changeover switch 18 is equivalently shown to alternately switch and output the DC voltage and the AC voltage, and in the embodiments described later, the DC voltage and the AC voltage are equivalent. Are alternately repeated and output. The frequency f3 of the AC power supply 17 of the monitoring power supply 13 is twice the harmonic frequency 2 · f1 of the frequencies f1 and f2 of the commercial AC power supply 1.
It is set to a value near 2 · f2 and different from its harmonic frequency.

2 · f1 <f3 <2 · f2 (1) In this embodiment, f3 = 110 Hz.

The current detecting means 19 for detecting the current flowing through the monitoring power supply 13 includes a current detecting resistor R30 interposed in series between the monitoring power supply 13 and the ground 15. Resistance R
A noise removing capacitor C15 is connected in parallel to 30. In this specification, reference numerals of resistors and capacitors may represent their resistance values and capacitances. For example, R30 = 47 kΩ, C15 =
It is 0.01 μF.

In the current detecting means 19, the line 15 is connected to the ground 15, and the connection point 20 is connected to the line 23. In the current detecting means 19, the voltage across the current detecting resistor R30 is given to the low pass filter 24 and cutoff frequency f lower than the power supply frequencies f1 and f2.
c1, for example 7 Hz. Low pass filter 24
Is applied to the first subtraction means 25, where the output V1 of the low-pass filter 24 is used to determine a predetermined first voltage V
Subtract two. The output of the first subtraction means 25 is given to the sample hold means 26, held therein, and given to the addition means 27.

The voltage across the current detecting resistor R30 is also applied to the high pass filter 28. This high-pass filter 28 has a frequency f of the AC voltage of the monitoring power supply 13.
3 has a function of filtering and taking out 3 and its cutoff frequency fc2
Is chosen equal to the frequency f3 of the AC power supply 17, ie 110 Hz. The output of the high-pass filter 28 is given to the second subtraction means 29, and here the predetermined second voltage V4 is subtracted from the output V3 of the high-pass filter 28. The output of the second subtraction means 29 is the sample hold means 3
It is given to 0 and held, and is further given to the adding means 27, where the outputs of the sample and hold means 26, 30 are added. Thus, the current detecting means 19 includes the current detecting resistor R30 and the noise removing capacitor C15, and also includes the respective constituent elements 24 to 30.

The output from the adding means 27 of the current detecting means 19 is applied to the level discriminating means 31 to discriminate the level at a predetermined level. In this way, one of the ungrounded electric circuits 5 and 6 has a low impedance conductor. When the value of the ground fault current flowing when connected to the ground is 2 mA, the level discriminating output from the level discriminating means 31 is obtained, and the alarming means 11 generates an audible or visual display alarm. To be done.

FIG. 3 is an electric circuit diagram showing a specific configuration of the monitoring power supply 13 and the like. AC / DC in the electric circuits 5 and 6
The converter 32 is connected, positive and negative DC voltages are output to the lines 33 and 34, and the DC power supplies electric power to the electric circuit of the insulation monitoring device 9.

The monitoring power source 13 is basically a DC power source 1.
6, an AC power supply 17, and a buffer 18. The DC power supply 16 includes resistors R6 to R10 and capacitors C13 and C1.
4, including transistors TR1 and TR2, a photocoupler PC1 and a diode D3, and outputs a DC voltage to the line 36 when the timer signal from the line 35 is low level.

The AC power supply 17 has a structure for constantly generating a sine wave of frequency f3, and the sine wave output of the AC power supply 17 is led out to the line 37 and superposed on the DC voltage from the line 36 to form a buffer 18. Is given to and amplified. The output of buffer 18 is provided to connection point 14.

FIG. 4 is an electric circuit diagram showing a timer 38 for supplying a timer signal to the line 35. The timer 38
The period (T1 + T2) shown in FIG. 5 (1) on the line 35.
Derive the pulse of. For example, in this embodiment, T1 = T
2 = 5 sec. This timer signal 35 is the DC power supply 1
6 is applied to line 36 as shown in FIG.
The DC voltage shown in (2) is output. The AC voltage waveform derived from the AC power supply 17 on the line 37 is shown in FIG.
5 (3), the DC voltage of FIG. 5 (2) and the DC voltage of FIG. 5 (3) are added and superposed on the input end 39 of the buffer 18 as shown in FIG. 5 (4). Waveform is given. The buffer 18 has an input voltage of 12 on the line 39.
It has a characteristic of being saturated with V, and therefore, at the connection point 14, the DC voltage waveform 40 and the AC voltage waveform 4 shown in FIG.
A waveform in which 1 and 1 are periodically repeated is given.

The output of the timer 38 is also supplied to the timing generation circuit 42 shown in FIG. 4 described above, whereby the timing signal of FIG. 5 (6) is derived from the line 43 and the timing signal of FIG. The timing signal of 7) is derived. In FIGS. 5 (6) and 5 (7), T
3 = T5 = 4.5 sec, T4 = T6 = 0.5 sec. The times T3 and T4 are selected to be longer than the time required to stabilize the operation for insulation monitoring by the DC power supply 16 and the AC power supply 17.

FIG. 6 shows the low-pass filter 24 and the first
6 is an electric circuit diagram showing a specific configuration of subtraction means 25. FIG.
The voltage corresponding to the ground fault current of the current detection resistor R30 is applied to the buffer 45 of the low pass filter 24 and cut off by the resistors R32 and R33 and the capacitors C16 and C17 which are connected in association with the operational amplifier 46. It is filtered at the frequency fc1, and its output is half-wave rectified from the line 47 via the operational amplifier 48 and the diode D6, smoothed by the capacitor C18, and then from the buffer 49 to the line 50 via the resistor R38 to the output voltage V1 of the low-pass filter 24. Derived.

In the first subtracting means 25, the output of the low-pass filter 24 from the line 50 is given to one input of the subtracting circuit 52, and the voltage generating circuit 53 is provided to the other input.
A predetermined voltage V2 of, for example, 0.5 to 1 V is applied from the subtraction circuit 52 to the line 56 via the buffer 55 through the line 54 from the subtraction circuit 52.
Are amplified and derived. The buffer 55 has an amplifying function and outputs from the output voltage V1 of the low pass filter 24 to the voltage V2.
Is subtracted and amplified, the ground impedances Z1 and Z2 depend on the ground impedances Z1 and Z2 in the buffer 55 even if the ground impedances Z1 and Z2 are smaller than the resistance values of the resistors R1 and R2 of the series circuit 12. It is possible to easily amplify and detect the current flowing through the current detection resistor R30. The output of line 56 is diode D
It is smoothed and stabilized by the capacitor C19 via 7 and applied to the subsequent sample and hold means 26 via the line 57.

FIG. 7 is an electric circuit diagram showing a specific configuration of the high-pass filter 28 and the second subtraction means 29. The signal corresponding to the voltage across the resistor R30 for current detection from the buffer 45 shown in FIG. 6 is given from the line 58 to the high pass filter 28. The high-pass filter 28 has three operational amplifiers 59, 60, 61 connected in cascade, has a cut-off frequency fc2 equal to the oscillation frequency f3 of the AC power supply 17, as described above, and has a large Q value. The output of the operational amplifier 61 is the full-wave rectification circuit 62.
, And then the capacitor C36 and the operational amplifier 6
Smoothed by a smoothing circuit 93 composed of
4 to the second subtraction means 29.

The second subtraction means 29 is a high-pass filter 2
A subtraction circuit 66 for subtracting the output voltage V4 of the voltage generation circuit 65 from the voltage V3 derived from the line 64 of 8;
The output is amplified by the buffer 67, further smoothed and stabilized by the capacitor C37 via the diode D11, and is led to the line 68. Output voltage V4 of voltage generation circuit 65
Is set to, for example, 6.2 to 7.2V. By including the subtraction circuit 29, the ground impedance Z1,
Even when Z2 is smaller than the resistance values of the resistors R1 and R2 of the series circuit 12, the ground impedance Z1,
The current flowing in the current detection resistor R30 depending on Z2 is
The buffer 67 can be easily amplified and detected without causing saturation of the buffer 67.

The output from the first subtracting means 25 via the line 57 and the output from the second subtracting circuit 30 via the line 68 are given to the switching elements SW1 and SW2 of the sample and hold means 26 and 30 shown in FIG. The
It is held by capacitors C20 and C38, and these sample and hold means 26 and 30 are operational amplifiers 69 and 7.
Including 0. The switching elements SW1 and SW2 are connected from the timing signal generating circuit 42 shown in FIG.
When a high-level timing signal is applied via 44, it conducts and performs a sampling operation.

These sample and hold means 26, 30
The respective outputs of 1 are given to the adder circuit 73 via lines 71 and 72 and added. The adding circuit 73 is an operational amplifier 74.
, Whose output is stabilized by the capacitor C21. The output of the adding means 73 is given from the line 75 to one input of the operational amplifier 76 of the level discriminating means 31.
The other input of the operational amplifier 76 has resistors R96 and R97.
When the reference voltage set by the above is applied, level discrimination is performed, and the voltage level of the line 75 exceeds the discrimination level which is the reference voltage set by the resistors R96 and R97,
A high level signal is output to the line 77 to make the transistor TR5 conductive.

When the transistor TR5 is turned on, the relay coil 79 of the relay 78 is excited, the relay switch 80 is turned on, the alarm means 11 is operated, and sound and visual display are performed.

The output from the line 75 of the adding means 27 is
The current is applied to the ammeter 82 via the meter circuit 81, whereby the sum of the ground impedances Z1 and Z2 is applied to the ammeter 82.
Is displayed in.

During operation, the ground impedance Z1 has a value exceeding the DC resistance of 50 kΩ, and the ground impedance Z2.
Is infinite, a DC voltage is applied from the DC power supply 16 to the connection point 14 which is a neutral point in the period T1 of FIG. 5 (2), at which time the current flowing through the current detection resistor R30 is 104 μA. The voltage across the current detection resistor R30 is determined by the low-pass filter 24 and the first subtraction means 25.
After that, the sample hold means 26 performs time T in FIG.
The signal is sampled at 4, then held, and given to the adder circuit 27. In the next period T2, the AC voltage from the AC power supply 17 is applied to the connection point 14, and the voltage across the resistor R30 for current detection generated by the AC power supply 17 passes through the high-pass filter 28 and the second subtraction means 29, and the sample hold means 30. Is applied to the adder circuit 27, is sampled in the period T6, is then held, and is applied to the adder circuit 27. In this way, in the adding circuit 27, the voltage across the current detecting resistor R30 when the DC voltage of the DC power supply 16 is applied to the connection point 14 and when the AC voltage of the AC power supply 17 is applied is added by the adding means 27. The level is discriminated by the level discriminating means 31. As mentioned above, the ground impedance Z
1 exceeds DC resistance of 50 kΩ and impedance to ground Z2
Is infinite, the output of the addition means 27 is below the discrimination level of the level discrimination means 31, and the alarm means 11 is deactivated.

The ground impedance Z1 is a DC resistance of 50 k.
Assuming that the impedance is less than Ω and the ground impedance Z2 is infinite, then the output voltage of the adding means 27 becomes equal to or higher than the discrimination level, and therefore the alarm means 11 is activated and an alarm is generated. Such an operation is the same when the ground impedance Z2 is a DC resistance of 50 kΩ or less and the ground impedance Z1 is infinite.

Furthermore, the ground impedances Z1 and Z2
A similar alarm operation is performed even when the DC resistance, which is the sum of the above, is 50 kΩ or less.

Next, the ground impedance Z1 is a capacitance of 0.053 μF or 0.063 μF or more such as a stray capacitance which is 50 kΩ at the system frequencies f1 and f2,
Assume that the other ground impedance Z2 is infinite. During the period T1 in which the DC voltage of the DC power supply 16 is applied to the connection point 14, the voltage across the current detection resistor R30 is zero. When the AC voltage from the AC power supply 17 is applied to the connection point 14 in the next period T2, an AC current corresponding to the ground impedance Z1 = 27 kΩ at the frequency f3 flows through the current detection resistor R30, and the AC voltage is applied to the high-pass filter. 28 is filtered and held by sample hold means 30 via second subtraction means 29 and added means 27
The level discrimination circuit 31 discriminates the level in this way, and the alarm means 11 is activated.

As described above, when the ground impedance Z1 is, for example, 0.053 μF or more, the ground impedance Z2 is infinite, and when the frequency f3 of the AC power supply 17 is much higher than the system frequencies f1 and f2, for example, If f3 = 600 Hz, the ground impedance Z1 is about 5 kΩ, and the ground impedance Z1 = 5 kΩ is the resistance value of the resistor R1, for example, 1 MΩ.
Since it is too small to detect in comparison with the above, even if the subtraction operation in the second subtraction means 29 is performed, the amplification degree in the buffer 67 (see FIG. 7 described above) cannot help but be large. Influenced by temperature drift and the like, it becomes difficult to perform reliable detection.

On the contrary, when the frequency f3 of the AC power supply 17 is extremely lower than the system power supply frequencies f1 and f2, for example, f3 = 6 Hz, the ground impedance Z1 becomes 500 kΩ corresponding to 0.053 μF. At this time, assuming that the ground impedance Z2 is infinite, the level discrimination means 31 sets the discrimination level corresponding to the ground impedance Z1 = 500 kΩ in the voltage level given to the addition circuit 27 from the sample hold means 30 and derived. There must be. Then, when the ground impedance Z1 becomes equal to or lower than the DC resistance of 500 kΩ, the respective outputs from the respective sample hold means 26, 30 are added by the adding means 27, the level discriminating means 31 discriminates the level, and the alarm means 11 is operated. Will end up. That is, when a current smaller than the monitoring current 104 μA flows through the resistor R30, an alarm is issued. In order to prevent such a malfunction, the frequency f3 of the AC power supply 17 is set to the value shown by the equation 1 as described above.

FIG. 9 is a block diagram of a part of another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIGS. 1 to 8 described above, but it should be noted that the outputs of the first and second subtracting means 25 and 29 are changed to the level discriminating means 8.
The levels are discriminated at 4 and 85, stored in the memories 86 and 87, and the alarm means 11a and 11b are operated.

FIG. 10 is a block diagram showing the overall construction of another embodiment of the present invention. This embodiment is similar to the previous embodiment, and corresponding parts bear the same reference numerals. It should be noted that in this embodiment the output of the low pass filter 24 is applied to the analog / digital conversion means 89 and the output of the high pass filter 26 is applied to the other analog / digital conversion means 90 to represent their respective digital values. The signal is given to the processing circuit 91 to perform arithmetic processing, to perform addition and level discrimination operations, and to operate the alarm means 11.

FIG. 11 shows the analog / digital conversion means 8
It is a figure which shows the resolution of 9. The higher the output level from the low-pass filter 24, that is, the input level of the analog / digital converting means 89, the higher the resolution by converting the digital value for each smaller level difference ΔV. As a result, the ground impedances Z1 and Z2 are small, and the series circuit 12
The ground impedances Z1 and Z2 can be reliably measured and monitored even if they are relatively smaller than the resistances R1 and R2. This is analog / digital conversion means 9
The same applies to 0.

The processing circuit 91 is realized by, for example, a microcomputer, stores the respective outputs of the analog / digital converting means 89 and 90 in a memory, adds the digital values thereof, and the ground fault current value to be monitored is 2 mA. When the value exceeds, the alarm means 11 is activated. Instead of the high-pass filter 28, the frequency f3 of the AC power supply 17
It may be a band-pass filter or the like that extracts and filters the component.

[0050]

As described above, according to the present invention, a DC voltage is applied between a neutral point obtained by a series circuit composed of a pair of resistors connected between the secondary outputs of an insulating transformer and the ground, which is ground. The voltage and the alternating voltage having a frequency f3 different from the frequencies f1 and f2 of the system power supply, which is the secondary output of the isolation transformer, are alternately and repeatedly monitored, for example by using a changeover switch. Since the direct current and the alternating current are given by the current detecting means and the level is discriminated, the insulation impedance between the non-grounded circuit connected to the secondary side of the insulation transformer and the ground is stabilized. In addition, the resistance value of the pair of resistors is increased so that even if a human body comes into contact with the electric path, a ground fault current value to be monitored, for example, an electric current exceeding 2 mA. It is possible to prevent the risk of flows.

Further, according to the present invention, the frequency of the power supply for monitoring is set to a value in the vicinity of the second harmonic frequency of the power supply and different from the second harmonic frequency, which causes beat. The detected current does not become unstable.

Further, according to the present invention, even if the ground impedance is smaller than the high resistance value of each of the pair of resistors for obtaining the neutral point, the first and second subtraction circuits enable
The detection can be easily performed. Further, according to the present invention, the configuration can be simplified by providing each output of the first and second subtraction means to one addition means.

Further, according to the present invention, the respective outputs of the first and second subtracting means are held by the sample and hold means and given to the subsequent adding means, whereby the sum of the real part and the imaginary part of the ground impedance is obtained. It is possible to perform level discrimination, and it is possible to accurately monitor insulation.

Further in accordance with the present invention, the output of the low pass filter and the output of the AC voltage frequency filtering filter are
And a second analog / digital converting means, and these first and second analog / digital converting means are configured so that the higher the output level is, the higher the resolution is, and the digital value is converted. Even if the ground impedance is relatively small as compared with the high resistance value of each pair of resistances for obtaining points, it is possible to accurately and accurately discriminate the level of the ground impedance.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a part of the embodiment shown in FIG. 1 showing a state where a ground fault current flows.

FIG. 3 is an electric circuit diagram showing a specific configuration of a monitoring power supply 13.

FIG. 4 is an electric circuit diagram showing a specific configuration of a timer 38 for generating a timer signal for controlling the DC power supply 16 of the monitoring power supply 13 and a timing signal generation circuit 42 for giving a timing signal to the sample hold means 26, 30. is there.

5 is a waveform diagram for explaining the operation of the monitoring power supply 13 shown in FIG.

FIG. 6 is a current detection resistor R included in a current detection unit 19.
3 is an electric circuit diagram showing a specific configuration of 30, a low-pass filter 24, and a first subtracting means 25. FIG.

FIG. 7 is an electric circuit diagram showing a specific configuration of a high-pass filter 28 and a second subtraction means 29.

FIG. 8: Sample and hold means 26, 30 and addition means 2
7 is an electric circuit diagram showing a specific configuration of 7 and level discriminating means 31 and the like. FIG.

FIG. 9 is an electric circuit diagram showing the configuration of another embodiment of the present invention.

FIG. 10 is a block diagram showing the configuration of still another embodiment of the present invention.

FIG. 11 is a diagram showing characteristics of the analog / digital conversion means 89.

[Explanation of symbols]

 1 Commercial AC power supply 2 Insulation transformer 3 Primary coil 4 Secondary coil 5,6 Non-grounded electric circuit 7 Electric equipment 8,15 Earth 9 Insulation monitoring device 10 Human body 11 Alarm means 13 Monitoring power supply 14 Connection point 16 DC power supply 17 AC power supply 19 Current Detection Means 21 Grounding 24 Low Pass Filter 25 First Subtraction Means 26 Sample Hold Means 27 Addition Means 28 High Pass Filter 29 Second Subtraction Means 30 Sample Hold Means 31 Level Discrimination Means R30 Current Detection Resistors Z1, Z2 Ground Impedance

Claims (5)

[Claims] 1. A large resistance value is connected between an isolation transformer whose primary input is supplied with power source power and a secondary output of the isolation transformer so that a current sufficiently smaller than a ground fault current value to be monitored flows. A series circuit composed of a pair of resistors each having, a mutual connection point of the pair of resistors of the series circuit, and a DC voltage interposed between the ground and an AC voltage having a frequency different from the power source, A monitoring power supply which is alternately switched and provided; a current detecting means for detecting a direct current and an alternating current flowing through the monitoring power supply; and a means for discriminating a detection output of the current detecting means at a predetermined level. Insulation monitoring device for non-grounded wiring circuit. 2. The frequency of the power supply for monitoring is set in the vicinity of a harmonic frequency which is twice the frequency of the power supply, and is set to a value different from the harmonic frequency. Non-grounded wiring circuit insulation monitoring device. 3. The current detecting means is a low-pass resistor having a cutoff frequency lower than the frequency of the power source, to which a current detecting resistor connected in series to a monitoring power source and a voltage across the current detecting resistor are applied. A filter, a first subtraction unit for subtracting a predetermined first voltage from the output of the low-pass filter, a filter for applying a voltage between both ends of the current detection resistor, and filtering and extracting the frequency of the AC voltage; 2. The non-grounded device according to claim 1, further comprising: second subtracting means for subtracting a predetermined second voltage from the output of the voltage frequency filtering filter, and means for adding respective outputs of the first and second subtracting means. Wiring type electric circuit insulation monitoring device. 4. The insulation monitoring apparatus for a non-grounded wiring type electric circuit according to claim 3, further comprising sample holding means for holding respective outputs of the first and second subtracting means. 5. The current detecting means is a low-pass resistor having a cutoff frequency lower than the frequency of the power source, to which a current detecting resistor connected in series to a monitoring power source and a voltage across the current detecting resistor are applied. The first and second analog / digital conversion means for converting the output of the filter and the low-pass filter into a digital value by increasing the resolution as the output level increases, and the voltage between both ends of the current detection resistor is applied to the alternating voltage. A filter for filtering and extracting the frequency of the second voltage, and a second output for converting the output of the AC voltage frequency filtering filter into a digital value with higher resolution as the output level increases.
2. The insulation monitoring apparatus for a non-ground wiring type electric circuit according to claim 1, further comprising: an analog / digital converting means of 1) and a means for adding respective outputs of the first and second analog / digital converting means.