JPS6148670B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulation testing device capable of measuring leakage current as well as insulation resistance of equipment.

The insulation testing device of the present invention uses a pair of clip-type transformers to clip a power line to measure insulation resistance, and uses one clip-type transformer to measure leakage current. It is something. The present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing the state in which the device of the present invention is used, and the portion IM indicated by the dashed line is a block diagram of the measuring device of the present invention. In Figure 1, LO is the load (equipment) and SO is the pole transformer that transforms high voltage to AC100V.
In a commercial power supply circuit that includes a PT, the secondary side voltage of the PT
AC100V is supplied to the load LO via lines _l1 and _l2 . Line _l2 is at ground potential. Rx
is the insulation resistance of the measured object between the load LO and the ground, and Cl is the capacitance, and leakage power sources _ir and _ic flow through Rx and Cl.

In the measuring device IM according to the present invention, CT is a clip type transformer, and this transformer is an injection transformer CT ₁
and a detection transformer CT ₂ . transformer
Both CT ₁ and CT ₂ are a pair of semicircular cores 11, 1
2, 21, 22, and a coil 13,
23 are wound around each other.
The space between CT ₁ and CT ₂ is magnetically shielded by a shield S. The OSC is a constant voltage oscillator that excites the coil 13 of the transformer CT ₁ , and its oscillation frequency is selected to be sufficiently distinguishable from the commercial frequency. BPA is a bandpass amplifier, which uses an amplifier that does not cause phase angle shift in frequency. SR is a synchronous rectifier circuit that synchronously rectifies the output of the bandpass amplifier BPA using the output of the oscillator OSC as a carrier wave, and LOG is an approximate logarithmic conversion circuit that compresses a large part of the output of the synchronous rectifier circuit SR and adds it to the indicator M. Through this LOG circuit, the scale of the indicator M becomes a logarithmic scale as shown by MΩ in FIG. 2, for example. Although the value of insulation resistance varies considerably, by setting the scale of the indicator M to a logarithmic scale as described above, insulation resistance can be measured over a wide range without a changeover switch. OUT is an analog signal output terminal and is connected to the output terminal of the synchronous rectifier circuit SR. AR is an amplification rectifier circuit,
SW ₁ to _{SW 3} are interlocking changeover switches, each having an insulation resistance measuring terminal MΩ and a leakage current measuring terminal Io.

First, a case in which insulation resistance is measured using a measuring device having such a configuration will be described. When measuring insulation resistance, each movable piece of the switches SW ₁ to _{SW 3} is connected to the terminal MΩ. and transformer CT ₁ ,
The live power lines _l1 and _l2 are inserted into the core from the split ends 14 and 24 of the core of _CT2 , and are clipped. Thereafter, the output of the oscillator OSC is supplied to the coil 13 of the transformer CT ₁ to excite the cores 11 and 12 of the transformer CT ₁ . Since the power lines l ₁ and l ₂ correspond to the secondary conductors of the transformer CT ₁ , by exciting the cores 11 and 12 of CT ₁ , a frequency voltage e is applied to l ₁ and l ₂ , and this application The current due to voltage is the injection current is as shown in the diagram A→B→C→D→E
flows. Assuming that there is a capacitance Cl and a resistance Rx between the load LO and the ground as shown in the figure, the injection current is flowing in the above path is It is expressed as Here, e is the voltage generated in the power supply lines l ₁ and l ₂ which are the secondary conductors of the transformer CT ₁ , and this voltage is a constant value. The injected current is is sensed by electromagnetic action in the sensing transformer CT ₂ and sent to the bandpass amplifier BPA. If there is a leakage current IO between the load LO and the ground due to the power lines l ₁ and l ₂ , the detection transformer CT ₂ also detects this leakage current IO, but the bandpass amplifier BPA cuts this current IO, Amplify only the injection current is of the frequency. The frequency component that has passed through the bandpass amplifier BPA is applied to a synchronous rectifier circuit SR where it is synchronously rectified. Since the output of the oscillator OSC is given as the carrier wave in the synchronous rectifier circuit SR, the output of the synchronous rectifier circuit SR is independent of the capacitive current i _c between the load LO and the ground, and is the leakage current flowing through the pure resistance. Corresponds to the current i _r . The relationship between the leakage current i _r and the insulation resistance Rx to be measured, which is a pure resistance component, is expressed by the following equation.

1/Rx=i _r /e (2) Since e is a constant value, as is clear from equation (2), the value of the insulation resistance to be measured Rx is determined as the reciprocal of the output of the synchronous rectifier circuit SR. Current i obtained from equation (2)
The output of the synchronous rectifier circuit SR corresponding to _r is the output terminal
It is taken out as an analog output from OUT and is applied to the indicator M via the approximate logarithmic conversion circuit LOG. Since the LOG circuit compresses a large portion of the synchronous rectifier circuit SR and approximately converts it logarithmically, the scale of the indicator M becomes a logarithmic scale as shown by the MΩ scale in FIG.

By inputting the analog output obtained from the output terminal OUT to a recorder or the like as the reciprocal of the resistance to be measured Rx, insulation resistance can be measured continuously over a long period of time. In addition, approximate logarithmic conversion circuit
Insulation resistance can be displayed as a digital value by reciprocally converting the LOG output and converting the converted output into a digital signal using an analog-to-digital converter. In addition, the output terminal
OUT is provided as necessary.

Next, the case of measuring leakage current will be explained. In this case, the movable pieces of the switches SW ₁ to _{SW 3} are each connected to the terminal Io. This allows the transformer
CT ₁ is disconnected from the oscillator OSC, and the transformer CT ₂
is connected to the indicator M via the amplification and rectification circuit AR.

In such a state, the difference current Io (Io=| _I1 - _I2 |) between the currents _I1 and _I2 flowing in the lines _l1 and _l2 is detected by the transformer _CT2 . The value of this detection signal indicates the value of leakage current. The detection output of transformer CT ₂ is amplified and rectified by the amplification and rectification circuit AR,
will be instructed. The scale of indicator M is Io in the lower row of Fig. 2.
It is indicated by.

As described above, with the apparatus of the present invention, the insulation resistance and leakage current of equipment can be easily measured while the equipment is in a live state. The measurement results from a live-wire insulation resistance meter do not have legal basis as they are, so by measuring leakage current at the same time, it is possible to accurately assess the safety of the equipment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing how the device of the present invention is used, and FIG. 2 is a scale diagram of an example of an indicator used in the device of the present invention. CT ₁ ... Clip type injection transformer, CT ₂ ... Clip type detection transformer, OSC ... Oscillator, BPA...
...Bandpass amplifier, SR...Synchronous rectification circuit,
LOG...approximate logarithmic conversion circuit, M...indicator,
SW ₁ , SW ₂ ...Selector switch, AR...Amplification rectifier.

Claims (1)

[Claims] 1. An oscillator that generates a voltage with a frequency different from the frequency of the power supply to which the load is connected via the line, which is excited by the output of this oscillator and applies a voltage with a frequency to this power supply line by clipping the line of the power supply. an injection transformer that detects the current flowing between the load and the ground according to the applied voltage, a detection transformer that detects the current flowing between the load and the ground according to the applied voltage, a bandpass amplifier that amplifies only the frequency component of the output of the detection transformer, and this bandpass amplifier. - Approximate logarithmic conversion circuit that compresses a large part of the output of this synchronous rectification circuit through a synchronous rectification circuit that synchronously rectifies the output of the amplifier at the frequency and extracts the leakage current flowing through the pure resistance that exists between the load and the ground. a rectifier circuit that rectifies the output of the detection transformer in a state where the oscillator is disconnected from the injection transformer by the first changeover switch; Insulation test equipment equipped with an indicator connected via a changeover switch.