JPH0453583Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a leakage current detector for a low-voltage circuit.

Conventional detectors of this type detect leakage current using a current transformer 4 attached to the second type grounding wire 3 of a transformer 2 connected to a low-voltage line 1, as shown in FIGS. 3 and 4. After the signal is amplified to a processable level by the amplifier 5, it is converted into a DC signal by a rectifier circuit 6 and a smoothing circuit 7. This DC signal is input to the comparator 8 and compared with the leakage current alarm setting value, that is, the reference voltage 9. If the detected leakage current value exceeds the reference voltage 9, the comparator 8 outputs the alarm signal to the alarm signal output circuit 10. At the same time, the alarm signal output circuit 10 lights up the light emitting diode 11, and at the same time, the contact 1 is output to the outside.
2 is configured to send out a signal.

This detector may detect a surge current 14 that may flow through the second type grounding wire 3 due to turning on or off of the power load 13, and may output an alarm signal.

Possible causes of this surge current include the load capacitance 15 and the stray capacitance 16 of the electric line 1, which are not directly related to insulation deterioration of the electric line.

The above-mentioned leakage current detector automatically detects insulation deterioration in low-voltage electrical circuits and outputs an alarm to automatically manage the electrical circuit's insulation condition, and only when an abnormality occurs, maintenance personnel can request inspection. Even though the equipment is used for on-the-go use, if alarms are output frequently due to capacitive surge currents unrelated to insulation deterioration of low-voltage circuits, the meaning of automating leakage current detection will be diminished. .

The present invention can solve the above conventional problems by adding a switch to both ends of the capacitor of the smoothing circuit in the conventional detector and controlling this switch with a new circuit called a 1-pulse clear circuit. The present invention attempts to provide a leakage current detector for a low-voltage circuit.

An embodiment of the present invention will be described below based on FIGS. 1 and 2 of the drawings. Reference numeral 17 indicates the second type grounding wire of the transformer connected to the low-voltage power line, and numeral 18 indicates the second type grounding wire 1.
7 is a current transformer attached, 19 is an amplifier circuit that amplifies the output signal A of the current transformer 18, 20 is a rectifier circuit that rectifies the output signal B of the amplifier circuit 19, and 21 is a smoother output signal C of the rectifier circuit 20. The capacitor in this circuit 21 is a smoothing circuit that converts into a direct current signal D.
Switch S ₁ such as a relay or semiconductor on both ends of C ₁
is connected. 22 is a comparator that inputs the output signal D of the smoothing circuit 21, compares it with the alarm setting value based on the reference voltage 23, and outputs an alarm signal E when the output signal D exceeds the alarm setting value; 24 is a 1-pulse clear circuit Then, the output signal of the comparator 22 is input to the input gate G ₁
When you enter the switch S ₁ at a certain time T ₁
A timing element A 1 such as a monostable multivibrator that operates to close the capacitor C ₁ of the smoothing circuit 21 to discharge the charge accumulated in the capacitor C ₁ of the smoothing circuit 21 and to make the output signal from the comparator 22 0 for the above-mentioned certain time T _{1 .} and a pulse signal F that blocks the output signal from the comparator 22 from entering the timing element A ₁ for a certain time T ₂ simultaneously with the operation of the timing element A ₁ .
It consists of a timing element A ₂ such as a monostable multivibrator that operates to give input gate G ₁ . 25 is an alarm signal output circuit that receives the output signal from the comparator 22 and transmits an alarm signal to the light emitting diode 26 and the contact 27.

Next, to explain the operation of the leakage current detector for a low-voltage circuit having the above configuration, when a surge current 28 flows through the second type grounding wire 17, the operation of the one-pulse clear circuit 24 causes the switch S ₁ is closed for a certain time T ₁ to discharge the charge accumulated in the capacitor C ₁ of the smoothing circuit 21, and the smoothing circuit 2
Since the output signal D of 1 is set below the reference voltage, no signal is sent from the comparator 22 to the alarm signal output circuit 25. On the other hand, if the leakage current 29 due to insulation deterioration of the low-voltage circuit continues to flow in the second type grounding wire 17, the output signal of the smoothing circuit ₂₁ is signaled for the time _T1 during which the switch S1 is closed by the timing element _A1 . The time during which the output signal from the comparator 22 is prevented from inputting to _the timing element A1 by the timing element _A2 , although D becomes below the reference voltage.
Since the output signal D of the smoothing circuit 21 exceeds the reference voltage within T ₂ , the signal E is sent from the comparator 22 to the alarm signal output circuit 25, and at the same time, the circuit 25 turns on the light emitting diode 26, and at the same time, the signal E is sent to the outside. The contact 27 operates to send out a signal.

Since the present invention is configured as described above, when the current flowing through the second type grounding wire is a surge current,
An alarm is issued when no alarm is issued and leakage current is flowing due to the insulation of the low-voltage circuit.
It is possible to provide a leakage current detector for a low-voltage circuit that fully satisfies the intended purpose of use.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a leakage current detector for low voltage electrical appliances according to the present invention, and FIG. 2 is a waveform diagram of output signals at various parts of the block diagram.
FIG. 3 is a block diagram of a conventional leakage current detector, and FIG. 4 is a waveform diagram of output signals at various parts of the block diagram. 18...Current transformer, 19...Amplification circuit, 20...
Rectifier circuit, 21... Smoothing circuit, 22... Comparator,
24...1 pulse clear circuit, 25...alarm signal output circuit, _S1 ...switch, _A1 ...timing element, _A2 ...timing element.

Claims (1)

[Scope of utility model registration request] An amplifier circuit that amplifies the output signal of the current transformer, a rectifier circuit that rectifies the output signal of the amplifier circuit, a smoothing circuit that smoothes the output signal of the rectifier circuit, and a DC signal output from the smoothing circuit that leaks. A leakage current detector for a low-voltage line, comprising a comparator that sends out a signal that operates an alarm signal output circuit when the DC signal exceeds the alarm set value by comparing it with a current alarm set value, in the smoothing circuit. A first switch is connected to both ends of the capacitor, and when the output signal of the smoothing circuit exceeds the alarm set value and the comparator is activated, the first switch receives the signal from the comparator and operates to close the switch for a certain period of time. and a pulse signal that prevents the output signal from the comparator from entering the timing element.
a second timing element that operates to provide the input gate of the first timing element for a longer time than the operating time of the timing element;
Leakage current detector for low voltage circuits equipped with a pulse clear circuit.