JPH0687626B2 - Circuit breaker for ungrounded transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a circuit breaker for a non-grounded transformer for preventing an electric shock accident in a circuit in which a secondary circuit of a transformer is floated from the ground (referred to as a non-grounded state). Regarding

[Conventional technology]

Conventionally, in a secondary circuit that is completely floating from the ground, an electric shock is unlikely to occur, so it has been generally used in a control panel of equipment.

However, even in such a secondary circuit, one side is mistakenly grounded, or a line on one side of the secondary circuit is touched and then a line on the other side is touched. .

Therefore, conventionally, a high frequency oscillation circuit is superposed on a secondary circuit of a floating transformer, and a circuit breaker is operated by using a frequency change or the like due to leakage as a signal input.

[Problems to be Solved by the Invention] In the method for detecting the frequency change of the high frequency, there is a problem that the reliability is poor because the oscillation frequency changes depending on the ambient temperature, and there is also a problem that the structure is complicated.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a circuit breaker for an ungrounded transformer that is relatively simple and operates reliably regardless of ambient temperature.

[Means for solving problems]

In the circuit breaker for an ungrounded transformer according to the present invention which meets the above-mentioned object, a secondary side circuit that receives power in a non-grounded state from a secondary side of a transformer whose primary side is connected to a power supply line grounding one line is connected to the secondary side of the transformer. A circuit breaker for an ungrounded transformer that operates a circuit breaker provided immediately after the secondary side to prevent an electric shock accident on the secondary side, and is connected in series to the circuit after the circuit breaker on the secondary side of the transformer. A pair of capacitors are connected, and the primary side ungrounded line of the transformer and the midpoint of the series-connected capacitors are connected by a high resistance and a low resistance connected in series. The voltage generated across the low resistance is amplified by an amplifier to operate the circuit breaker.

[Action]

In the circuit breaker for a non-grounded transformer according to the present invention, a pair of capacitors connected in series to the rear circuit of the circuit breaker is connected on the secondary side of the transformer, and the primary side ungrounded other end of the transformer and the transformer are connected. The middle point of the capacitors connected in series is connected by a high resistance and a low resistance connected in series. Therefore, if a leakage occurs on the secondary side of the transformer, it goes from the non-grounded side of the primary side of the transformer to the ground side through high resistance, low resistance, and a capacitor connected to the grounded side. Alternatively, current flows in the opposite direction. As a result, a voltage due to a leakage current is generated in the low resistance, and this is amplified by an amplifier to activate the circuit breaker. On the other hand, when there is no leakage, the secondary side is almost completely floating, so
No current flows through the high resistance and low resistance connected to the non-grounded side of the primary side. Therefore, when there is no leakage, no voltage is generated across the low resistance and the circuit breaker does not operate.

If the leakage is due to contact with the human body, an electric current will flow through the human body, but in this case, since it flows through a high resistance, the leakage current is greatly limited, and since it is for a short time, there is no risk of electric shock. Does not occur.

〔Example〕

Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

Here, FIG. 1 is a circuit diagram of a circuit breaker for an ungrounded transformer according to an embodiment of the present invention, and FIG. 2 is an operation explanatory diagram thereof.

As shown in FIG. 1, the circuit breaker for an ungrounded transformer according to the first embodiment of the present invention includes a high resistance 1 whose one end is connected to the primary side P of the transformer 4 and to the ungrounded side. A low resistance 2 having one end connected to the other end of the high resistance 1, a pair of capacitors 3 and 3 having one end connected to the other end of the low resistance 2, and a voltage across the low resistance 2. Signal input amplifier 5 and electromagnetic breaker driving amplifier 6 that input
And circuit breakers 7, 7. These will be described in detail below.

The power supply of the transformer 4 is a general commercial line, and one line thereof is grounded, so the high resistance 1 is connected to the other line side which is not grounded. This high resistance 1 is about 300 kΩ to 3 M ohm. Then, one end of the low resistance 2 is connected to the other end of the high resistance 1. Here, the low resistance 2 is about 10 KΩ to 100 KΩ.

The circuit breakers 7, 7 are connected to the secondary side S of the transformer 4, and the output side thereof has a pair of capacitors 3 connected in series,
3 are connected. The capacitors 3 and 3 have a capacity of 0.
It is about 01 μF to 0.1 μF. This condenser 3, 3
The other end of the low resistance 2 is connected to the neutral point.

A signal input amplifier 5 and an electromagnetic circuit breaker driving amplifier 6 are connected to both ends of the low resistance 2. The signal input amplifier 5 and the electromagnetic circuit breaker driving amplifier 6 constitute an electromagnetic circuit breaker driving amplifier.

Next, the operation of the circuit breaker for an ungrounded transformer will be described. As shown in FIG. 2, when an electric shock accident occurs on any line of the secondary side circuit, the high resistance 1, the low resistance 2 and the capacitor 3 are connected. A leakage current flows through the leakage current, which causes a voltage drop in the low resistance 2. This is amplified by the signal input amplifier 5 and the electromagnetic circuit breaker driving amplifier 6, and the circuit breakers 7, 7 are operated to open the secondary circuit. Therefore, the present invention is different from the conventional example in that the secondary circuit of the transformer 4 simply acts as an electrode for detecting the ground state.

In this case, a current will flow through the human body due to leakage, but the current is determined by the resistance value of the high resistance 1. If the high resistance 1 is excessively large, the input voltage of the amplifier is too small and the circuit breaker 7, 7 will not work. In an experiment in which the amplifier was actually manufactured by using an IC and a transistor, the circuit breakers 7 could be sufficiently operated when the leakage current was 10 μA. The human body will not be electrically shocked even if a current of 10 μA is passed at the time of leakage, and as long as the current flows, there is no dangerous electric shock condition.

〔The invention's effect〕

As is clear from the above description, the circuit breaker for a non-grounded transformer according to the present invention has a simple structure, and since the operating state does not change depending on the ambient temperature, it has effects such as high reliability.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a circuit breaker for an ungrounded transformer according to an embodiment of the present invention, and FIG. 2 is an operation explanatory diagram. [Explanation of symbols] 1 ... High resistance, 2 ... Low resistance, 3 ... Capacitor, 4
...... Transformer, 5 …… Signal input amplifier (amplifier), 6…
... Electromagnetic circuit breaker drive amplifier (amplifier), P ... Transformer primary side, S ... Transformer secondary side

Claims (1)

[Claims] 1. A secondary side circuit that receives power from a secondary side of a transformer whose primary side is connected to a power supply line whose ground is grounded in an ungrounded state operates a breaker provided immediately after the secondary side of the transformer. A circuit breaker for a non-grounded transformer that prevents an electric shock accident on the secondary side by connecting a pair of capacitors connected in series to a rear circuit of the circuit breaker on the secondary side of the transformer, and The primary side ungrounded line of the transformer and the middle point of the series-connected capacitors are connected by a high resistance and a low resistance connected in series, and the voltage generated across the low resistance at the secondary side leakage is amplified by the amplifier. A circuit breaker for an ungrounded transformer, characterized in that the circuit breaker is operated by amplifying the circuit breaker.