JPH02698Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an electrical circuit insulation monitoring device.

As shown in Figure 1, a common method for monitoring the insulation of electrical circuits is to detect the zero-sequence current Ig flowing back into the transformer's second class grounding wire SEL using the zero-sequence transformer ZCT. Although this method is effective when the stray capacitance of the circuit is small, that is, when the capacitive leakage current I _C generated by the stray capacitance of the circuit is small, If is large, I _C becomes large, making it impossible to accurately monitor the insulation of the electrical circuit.

Originally, electrical path insulation monitoring would be more accurate if the resistance component current I _R , that is, the insulation resistance, could be evaluated from the zero-sequence current Ig, but separating the resistance component current I _R from the zero-sequence current Ig is In a single-phase three-wire circuit, if insulation failure occurs in both phases, the current due to the detected insulation resistance will be:
This is the difference between the currents I _R1 and I _T1 flowing in each phase, and in a three-phase three-wire circuit, the difference in capacitive current due to the unbalance of each phase causes an error in the insulation resistance component, and all causes of errors are This is due to phase difference.

Generally, the quality of the insulation condition of low-voltage circuits can be determined by
Conventionally, this is done by shutting off the electrical circuit and periodically measuring the insulation resistance to ground using a megger, but insulation resistance changes greatly depending on changes in the season, facilities, environment, etc., so it is necessary to measure it at appropriate intervals. Due to constraints such as social circumstances and production activities, it is no longer always possible to shut down power lines for measurements easily.

The present invention was proposed in view of the above circumstances, and aims to provide an insulation monitoring device for electrical circuits that can be carried out without power outages in electrical circuits, and that reduces measurement work and improves accuracy. The aim is to amplify the zero-sequence current flowing back into the second class grounding wire of the zero-sequence transformer using a pre-processing circuit, and monitor the insulation quality of the electrical circuit by detecting the magnitude of the zero-sequence current. The invention is characterized in that it includes an integrating circuit that inputs the output of the pre-processing circuit, and monitors the quality of the insulation based on the magnitude of the output of the integrating circuit.

An embodiment of the present invention will be explained with reference to the drawings.
Figure 3 is a block diagram showing the circuit configuration, Figure 4
Figures A and B are equivalent circuit diagrams of the power supply and electric circuit in Figure 1, Figure 5 is a vector diagram of the zero-sequence current in Figure 4B, and Figure 6 is a zero-sequence diagram showing the action of the integrating circuit in Figure 3. It is a waveform diagram of a current component.

First, in Fig. 3, 1 and 2 are the weak zero-sequence currents Ig detected by the zero-sequence transformer ZCT, respectively.
3 is preamplifier 2, which inputs the signal and amplifies it to a level that can be handled by the subsequent processing circuit.
AC/DC converter that converts the output of
and 5 are the outputs of AC/DC converter 3, respectively.
A meter drive amplifier and a recorder buffer amplifier that input the Ig component signal; 6 a notch filter that removes the commercial power supply component from the Ig component signal output from the preamplifier 1 and extracts the component due to AC signal wave superimposition, which will be described later; 7 a three-phase 3φ/1φ switching amplifier that switches single phase and outputs it as zero-phase current Ig signal A;
8 generates a 210Hz AC signal wave from an AC100V power supply and connects it to a zero-phase transformer via an inductance.
AC stabilized power supply superimposed on the second class grounding wire of ZCT,
9 is a phase shifter that outputs the output of the AC stabilized power supply 8 as the voltage reference phase V _STD , and 10 is a waveform shaper that creates a square wave from the output of the phase shifter 9 and outputs it as the resistance component I _R separation signal B. The device 11 inputs the Ig signal A output from the 3φ/1φ switching amplifier 7 and the _IR separation signal B output from the waveform shaper 10, and outputs the _IR separation signal B.
Synchronous rectifier circuit that extracts I _R components from Ig signal A by switching an analog switch at
2 is an integrating circuit, 13 is a meter driving amplifier, 14
15 is a buffer amplifier for the recorder, 15 is an Ig/I _R selector switch, and 16 is an I _R component output from the integrating circuit 12, which is compared with the setting value of the alarm sensitivity setting circuit 18 set by the external rotary switch 17, and the former is determined. When the latter is exceeded, the alarm contact 2 of the buzzer is activated via relay 19.
This is a comparison circuit that operates 0.

In such a device, in addition to the commercial power supply V _COM , the AC signal wave power supply V _SS is superimposed on the class 2 grounding wire of the zero-phase transformer, so the electrical circuit in Figure 1 is changed to the one shown in Figure 4A. As will be described later, if the commercial power supply component is sufficiently removed by a filter or the like, A in the figure becomes equivalent to a single-phase circuit using the AC signal power supply V _SS as the power source, as shown in B in the figure.

The higher the level of the superimposed alternating current signal, the larger the Ig component to be circulated, and the better the _IR separation performance, but the maximum number of volts is the limit in consideration of the influence on the load equipment. The measurement accuracy of the AC superimposition method depends on the separation accuracy of separating the signal wave component from the commercial power supply component. Separation of the commercial power supply and the signal wave component is more advantageous as the frequencies of the two are further apart, but the capacitive leakage current I _C depends on the frequency and increases as the frequency becomes higher. In order to accurately separate the _IR component from the I _VO component generated by an AC signal wave power source, it is advantageous that the capacitive leakage current I _C is smaller.
Therefore, contradictory performances are required for the superimposed signal frequency: the higher the frequency is, the better, in order to extract signal components from the commercial power source, and the lower, the better, in order to accurately extract the resistance component current.

In this example, the zero-sequence current Ig flowing back to the second type grounding wire is the vector sum of I _V from the commercial power supply and Iv from the AC superimposition power supply, and the ratio of I _V and Iv is approximately the voltage ratio of each. So, Iv is 1/10 of I _V
It is said that

In addition, considering current filter technology, it is impossible to sufficiently remove commercial power components unless the frequency of the superimposed power source is at least 150Hz or higher, and the upper frequency limit is approximately 400Hz, which is better than the separation performance of the resistive component separation circuit. becomes.

Therefore, in this embodiment, 210 Hz, which is approximately halfway between the above two limits, is taken as the frequency of the AC stabilized power supply 8, and the total zero-phase signal A detected by the zero-phase transformer ZCT is converted to the commercial power supply component through the notch filter 6. By removing , the _AC signal component output from the 3φ/1φ switching amplifier 7 is converted to the equivalent circuit of FIG. Switching.

As shown in FIG. 5, the zero-sequence current Ig is the vector sum of the resistance component current I _R and the capacitance component current I _C. In this embodiment, in order to extract the I _R component from Ig, the synchronous rectifier circuit 11 Input the output of Ig to the integrating circuit 12
is integrated from 0 to π with reference voltage phase.

Then, as shown in FIG. 6, I _C is delayed by π/2 with respect to the reference phase V _STD , and when integrated from 0 to π, it becomes zero, and only the I _R component can be extracted.

In this way, the I _R component output from the integrating circuit 12 is constantly compared with the set value by the comparator circuit 16, and the I _{R component} is
When the component exceeds the set value, the alarm contact 20 is activated and a buzzer sounds.

According to such a device, the zero-sequence current flowing back into the second class grounding wire of the power transformer is amplified in a pre-processing circuit, and by detecting the magnitude of the zero-sequence current, it is possible to determine whether the insulation of the electrical circuit is good or not. The monitor includes an integrating circuit inputting the output of the pre-processing circuit,
By monitoring the quality of the insulation based on the magnitude of the output of the integrating circuit, an uninterruptible, labor-saving, and highly accurate electric circuit insulation monitoring device is obtained, so the present invention is extremely useful industrially. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a known method for monitoring insulation resistance of electric circuits, Fig. 2 is an equivalent circuit diagram for the single-phase three-wire system shown in Fig. 1, and Fig. 3 is a block diagram showing an embodiment of the present invention. , Figures 4A and 4B are equivalent circuit diagrams of the power supply and electric circuit in Figure 3, Figure 5 is a vector diagram of the zero-sequence current in Figure 4B, and Figure 6 shows the action of the integrating circuit in Figure 3. FIG. 2 is a waveform diagram of a zero-sequence current component shown in FIG. 1, 2... Preamplifier, 3... AC/DC converter, 4... Meter drive amplifier, 5... Recorder buffer amplifier, 6... Notch filter, 7...
3φ/1φ switching amplifier, 8... AC stabilized power supply, 9
... Phase shifter, 10 ... Waveform shaper, 11 ... Synchronous rectifier circuit, 12 ... Integrating circuit, 13 ... Meter drive amplifier, 14 ... Buffer amplifier for recorder,
15...Ig/I _R changeover switch, 16...Comparison circuit, 17...Rotary switch, 18...Alarm sensitivity setting circuit, 19...Relay, 20...Alarm contact.

Claims (1)

[Scope of utility model registration request] In a device that monitors the insulation quality of an electric circuit by amplifying the zero-sequence current flowing back into the second class grounding wire of a zero-sequence transformer in a pre-processing circuit and detecting the magnitude of the zero-sequence current, the above-mentioned 1. An insulation monitoring device for an electrical circuit, comprising an integrating circuit inputting the output of the pre-processing circuit, and monitoring the quality of insulation based on the magnitude of the output of the integrating circuit.