JPH0454818A - AC/DC contact detection device - Google Patents

Abstract

PURPOSE:To surely detect contact by providing the positive and negative electrodes of a DC power supply, respectively, with AC voltage detectors grounded through capacitors. CONSTITUTION:Positive pole of a DC power supply 20 is grounded through an AC voltage detector 101 and a capacitor 111 whereas the negative pole of the DC power supply 200 is grounded through an AC voltage detector 102 and a capacitor 112. Upon occurrence of contact, an AC current flows along a route shown by a dot and dash line and an AC voltage, divided according to the impedance ratio with respect to the capacitor 111, is applied on the voltage detector 101. Subsequently, the AC voltage detector 101 functions to close an output contact 101a and the contact output is introduced to a supervi sory control board in order to produce an alarm. In case of contact of an AC power supply l and the negative electrode of the DC power supply 20, the AC voltage detector 102 functions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for detecting cross-contact caused by a contact accident between a low-voltage AC system and a low-voltage DC system that constitute a control power source of an electric station.

[Conventional technology]

Figure 2 shows the phenomenon when this type of contact occurs. In the figure, 1 is a low-voltage AC power supply, 20 is a low-voltage DC power supply, 21 is a center point grounding device for detecting a DC ground fault, and 3
Reference numeral 1 indicates a device serving as a load of the DC power supply, 310 indicates a noise absorber inserted in the DC power supply circuit, and 50 indicates AC/DC interference. Note that the AC power system is grounded at one end to prevent a healthy phase voltage increase in the event of an AC system ground fault.

When cross-contact 50 occurs, an alternating current from the alternating current power supply l flows through the route shown by the dashed line in FIG. Since this route is a conductor except for the noise absorber 310, an AC voltage is applied to both ends of the noise absorber 3100. Since the DC power supply is usually 110V, the limit voltage of the noise absorber 310 is set to about 200V. On the other hand, since the voltage of the AC power supply l is 220V, 440V, its peak value is doubled, and a voltage exceeding the rated voltage is applied to the noise absorber 310. leads to destruction. The destruction modes of the noise absorber 310 are "short circuit J mode" and "open" mode, and if it is a "short circuit", the DC circuit will be grounded, so the midpoint grounding device 21 will operate and a ground fault will occur in the DC circuit. Detect that. Also,
The short-circuit current generated due to the short-circuit of the noise absorber is removed by a protector of the AC circuit (not shown).

[Problem to be solved by the invention]

If the destruction mode of the noise absorber 310 is "open", no DC ground fault or short circuit on the AC side will occur, so the device 31 can be expected to operate as expected, but if the noise absorber 310 is damaged. Therefore, if noise enters the device 31, it will cause the device 31 to malfunction.

In this way, when AC/DC cross contact occurs, a serious problem arises in that it damages the device 31 connected to the DC power supply 20 and, in some cases, cannot be detected.

This invention was made to solve the above problem.
It is an object of the present invention to provide an AC/DC cross-contact detection device that can reliably detect the occurrence of the above-described cross-contact.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention has a low-voltage DC power supply system and a low-voltage AC power supply system that is grounded at one end. It is equipped with a voltage detector.

[Effect]

In this invention, when contact occurs, an AC voltage divided according to the impedance ratio with the capacitor is applied to the AC voltage detector, and when the AC voltage exceeds the operating voltage of the AC voltage detector, the AC voltage detector works.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, 100 is an AC/DC contact detection device. 101.102 is AC voltage detector (relay), 11
1.112 is a capacitor, the positive pole of the DC power supply 20 is grounded via the AC voltage detector 101 and the capacitor 111, and the negative pole of the DC power supply 20 is grounded via the AC voltage detector 102 and the capacitor 112. 101a is an output contact of the AC voltage detector 101, and 102a is an output contact of the AC voltage detector 102.

In this configuration, when contact 50 occurs, an alternating current flows along the route shown by the dotted chain line, and an alternating current voltage divided according to the impedance ratio with the capacitor 111 is applied to the alternating current voltage detector 101. Since the impedance of the capacitor 111 is known, the voltage applied to the AC voltage detector 101 can be calculated in advance, and by setting the operating voltage of the AC voltage detector 101 based on this, the above-mentioned crosstalk can be avoided. 50, the AC voltage detector 101 operates and the output contact 101a closes, so that the output contact 10
If the contact output of 1a is guided to a monitoring control panel (not shown) to generate an alarm, the above-mentioned cross contact 50 can be detected.

This contact 50 is a contact between the AC power source l and the positive electrode of the DC power source 20, but when the contact occurs with the negative electrode, the AC voltage detector 10
2 works.

In addition, although the said Example described the case where cross-contact is detected by alternating current voltage, you may make it detect cross-contact by alternating current.

〔Effect of the invention〕

As explained above, this invention can reliably detect cross-contact between AC and DC, thereby preventing malfunction of the DC-side device due to cross-contact, and is inexpensive because it only requires an AC voltage detector and a capacitor. You can easily obtain the above effects at a reasonable cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a system diagram for explaining the problem of AC/DC mixing. In the figure, 1- AC power supply, 20- DC power supply, 21-.
- Center point grounding device, 100 - AC/DC cross contact detection device, 1
01, 101 - AC voltage detector, 111. 112 - Capacitor, 101a, 102 a - Output contact Note that in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In the case where there is a low-voltage DC power supply system and a low-voltage AC power supply system that is grounded at one end, each of the positive and negative poles of the DC power supply is equipped with an AC voltage detector that is grounded via a capacitor. AC/DC contact detection device.