JPH087720A - Overcurrent protection circuit and its device - Google Patents

Abstract

PURPOSE:To prevent disability of breaking and phase short-circuiting by opening a three-phase load opening/closing lid after all current limiting fuses for the three phases are blown off. CONSTITUTION:The secondary side 1A of a transformer 1 is connected with a plurality of motors 3 through a load cable 2 while the load side is connected with a motor 3 having an inductance, the transformer 1, or a circuit having a poor power factor such as a capacitor. A three-phase load switch 5 and current limiting fuses 6A, 6B, 6C are connected between the secondary side 1B of the transformer 1 and the power 4. When a striker 6D of the fuse 6A is operated, the first delay relay 7 is actuated, and a trip coil 9 is energized so that the load switch 5 is opened. When blow-off signal of the fuses 6A, 6B, 6C is fed to the delay circuit, a current is fed to the trip coil 9, and the load switch 5 is opened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit which protects a circuit by combining a current limiting fuse and a load switch.

[0002]

2. Description of the Related Art Since a load switch does not have the ability to cut off a short-circuit current by itself, it is economical to obtain a short-circuit current by combining a current limiting fuse. In the current limiting fuse, there is a range in which deterioration and deterioration of the fuse element occur due to overcurrent, its energizing time, and repetition, even if the fuse does not blow, and there is a risk of unexpected blowout and loss of phase. In addition, the fusing characteristics of current limiting fuses are such that the smaller the fusing current region, the greater the variation of the fusing time with respect to changes in the energizing current, and the variation is large. It can be said that the basic usage is, for example, protection with a three-phase batch type load switch.

These matters are described in the standards of current limiting fuses, for example, pages 34 and 35 of JIS C4604-1988, and the allowable range of variation is ± 20%.

On the other hand, the switching characteristics of a load switch used together with a current limiting fuse, especially the switching current showing the ability to open and close, is indicated by the limit of the current that can be turned on and off under the prescribed circuit conditions specified in the standard. Has been done. For example, the standard JIS C4605-1987 for load switchgear states on page 17 that the power factor of the load in the load current switching test is 0.65 to 0.75, and the performance at this power factor is guaranteed.

However, with other power factors, for example, a power factor of the exciting current of about 0.1, the table of the standard page 5 is shown below.

[0006]

[Table 1]

According to this table, the rated excitation current switching capacity is significantly reduced to 1/20 of the load current switching capacity. As a circuit using these current limiting fuses and load switches, see JIS C 4620-1992 Page 16 Appendix Figure 4 PF.S.
Type wiring and equipment connections are shown, and page 30 of the same standard shows that automatic load switch mechanical operation is performed by a part of a fuse link called a current limiting fuse striker that performs a predetermined mechanical operation when the fuse is blown. It is said that the tripping current is expanded and the protection of the open phase by the blowout of the current limiting fuse is achieved at the same time.

When an interphase short circuit occurs between the transformer secondary side and, for example, MCCB under the conditions of this standard, a short-circuit current flows to the transformer secondary side and an overcurrent also flows to the primary side.
After the current limiting fuse has blown out from 0.05 to 0.2, the 3-phase batch type load switch is opened.

[0009]

However, the primary side overcurrent when the secondary side of the transformer is short-circuited corresponds to the small fusing current region of the current limiting fuse, and the fusing time has a large variation, which is usually less than 0.5.
Since it takes 3 to 1.5 seconds, even if only one phase of the three-phase current limiting fuse is blown, the three-phase batch type load switch is opened by the blower of the blown current limiting fuse. At this time, the overcurrent is attempted to be shut off in the phase where the load switch has not melted.

On the other hand, the power factor of the primary side overcurrent when the secondary side of the transformer is short-circuited varies depending on the condition of the transformer, but is generally 0.1.
Before and after. This power factor overcurrent is a condition that exceeds the switching capability of the load switch.

For this reason, the present inventor has found through experiments that the load switch attempting to interrupt the overcurrent becomes incapable of interrupting, and a serious accident such as a phase-to-phase short circuit rarely occurs.

An object of the present invention is to provide a safe overcurrent protection circuit that prevents arc short circuits in a three-phase batch type load switch.

[0013]

In the overcurrent protection circuit of the present invention, the time from the blowout of the current limiting fuse to the start of operation of the load switch is maximized electrically or mechanically due to variations in the current limiting fuse. It is to delay more than the fusing time.

[0014]

As a result, since the three-phase batch type load switch is opened after all the three-phase current limiting fuses are blown, it becomes possible to prevent the interruption and the interphase short circuit, thus providing a safe facility.

[0015]

The present inventor has found from the experimental results of the overcurrent protection circuit that
As a result of examining the case where an arc short circuit occurs between the load switches of the phases, the following has been found.

.. In some cases, a circuit that deteriorates the power factor on the load side of the load switch and the current limiting fuse, such as a transformer or a motor, is connected to cause an interphase short circuit.

[0017] As shown in FIG. 3, the current limiting fuse of each phase causes an interphase short circuit when the fusing time varies.

For example, if the current limiting fuse, which is the earliest of the three-phase current limiting fuses in a short circuit accident, blows, the three-phase batch type load switch is opened accordingly. However, the remaining two-phase current limiting fuses are still blown, and
Since the transformer with a poor power factor is connected to the secondary side, the power factor of the overcurrent protection circuit also deteriorates, and the power factor is lower than usual.

Generally, a load switch has a power factor of 0.65 to 0.7.
The one that can perform the breaking operation in 5 is defined as the breaking performance. When the power factor is lower than this, the phase of the voltage and the current are different, so the cut-off current value becomes extremely small. In such a case, the power factor decreases and when the current limiting fuse is not blown out, , It was found that the load switch could not completely interrupt the arc and could not be interrupted, and that the load switch connected to the current limiting fuse being blown caused an interphase short circuit.

An embodiment for preventing a short circuit between phases will be described with reference to FIGS. 1 and 2 show an overcurrent protection circuit of the present invention, and FIG. 3 is a fusing characteristic diagram of a current limiting fuse 6 showing a relationship between a fusing time t and a fusing current i on a vertical axis and a horizontal axis. Is an allowable fusing characteristic diagram. The structure of the load switch with a current limiting fuse used in this protection circuit is shown in Figs.

The secondary side 1A of the transformer 1 is connected to a plurality of loads, for example, a motor 3 via a load cable 2. The load side is connected to the above-mentioned circuit having a poor power factor, such as a motor 3 having a self-inductance, a transformer 1 or a capacitor.

Between the secondary side 1B of the transformer 1 and the electric power 4, 3
Single-phase load switch 5 and current limiting fuses 6A, 6B, 6
C is connected. The current limiting fuse 6, for example, 6A, has a fusing current i1 as shown in FIG. 3 and has variations in fusing times t1, t2, and t3. When the striker 6D of the current limiting fuse 6A operates, the first delay relay 7 operates and the delay circuit 8
A current is passed through to excite the trip coil 9 and open the load switch 5. Reference numeral 10 is a DC power supply.

The delay circuit 8 is a timer that causes a current to flow at a time t4 slightly delayed from the fusing time t3, which is the latest fusing time in each current limiting fuse. In addition, each current limiting fuse 6A, 6
When the strikers 6D of B and 6C operate at the same fusing time t5, the second relay 7X shown in FIG. 2 immediately supplies a current to the trip coil 9 to open the load switch 5.

The delay circuit 8 is composed of current limiting fuses 6A, 6B,
When the 6C fusing signal is input, a current is passed through the trip coil 9 and the load switch 5 is opened, so a kind of AND
Circuit.

Next, when a short circuit accident 0 occurs in the load cable 2, a short circuit current flows. The current limiting fuse 6A is blown and the striker 6D flies in the direction of the arrow, but when the current limiting fuses 6B and 6C have passed the fusing times t2 and t3, the striker 6D flies in the direction of the arrow and at time t4. Since a current flows through the delay circuit 8 to excite the trip coil 9 and open the load switch 5, the load switch 5 can be prevented from short-circuiting between phases, and the equipment is safe.

If the fusing currents of the current limiting fuses 6A, 6B and 6C are all the same fusing time at i1, i2 and i3, for example, at t5, the second relays 7X of all phases are immediately operated and the trip coil 9 is operated. Since the load switch 5 is opened by exciting, the speed is fast and it is possible to prevent the accident from spreading due to the load, and the equipment is safer.

The load switch 5 of the three-phase collective type used in FIG.
4 will be described with reference to FIG. 4. Since all three phases have the same structure, an overcurrent protection device including a current limiting fuse 6A and a load switch (or a load switch with delay operation) connected to the current limiting fuse 6A will be described. To do.

The current limiting fuse 6A is detachably mounted between the power source side terminal 6E and the load side terminal 6F supported by the insulator 6G. When the current limiting fuse 6A is blown and the striker 6D jumps in the direction of the arrow, the operation mechanism portion 20 of the load switch 5 operates to release the engagement with the stopper 21.
Moving contact 2 in contact with a fixed contact (not shown)
2 rotates counterclockwise and shuts off.

That is, when the striker 6D jumps out in the direction of the arrow, the lever 25 operates in the chain line direction, the link 26 rotates counterclockwise, and the insulating operation rod 27 is moved leftward, and the relay lever 28 is moved. Presses the first delay relay 7 while rotating via the relay pin 28X, and at time t4, current flows through the delay circuit 8 to excite the trip coil 9 and press the stopper 21 clockwise. The relay pin 28X shown in the figure is supported by the chassis 40.

The stopper 21 rotates clockwise about the stopper pin 21X as a fulcrum, and the stopper hooking portion 21
When the engagement between B and the restriction lever pin 29A is released and the restriction lever 29 rotates via the restriction pin 29X, the restriction link 29B and the insulating operation rod 29C rotate counterclockwise,
Moving contactor 2 in contact with fixed contactor in arc-extinguishing chamber 30
2 rotates counterclockwise and shuts off. Movable contact 22
Is partially connected to the power supply side terminal 6E via the electrical connection portion 22A.

Further, when the movable contact 22 is brought into contact with the fixed contact, the operation may be carried out in the direction opposite to the above-mentioned arrow direction, and the description thereof will be omitted.

When the load switch 5A of FIG. 5 has the same components as those of FIG. 4, the description thereof will be omitted, and only different points will be described.

That is, the relay lever 28 is the relay pin 28.
While rotating via X, the rotation lever 31 moves to the pin 31X.
When rotating through, the dashpot 32 is pressed. As with the delay circuit 8, the dashpot 32 is rotated at the time t4 and the rotation of the rotation lever 31 is stopped by the stopper 2.
1 and performs the same operation as described above to rotate the movable contactor 22 in contact with the fixed contactor in the counterclockwise direction to cut off the movable contactor 22.
Further, when the movable contact 22 is brought into contact with the fixed contact, an operation opposite to the above-mentioned arrow direction may be performed, and therefore the description thereof will be omitted.

Since the operating mechanism section 20 may be provided with the dashpot 32 in a part of the operating mechanism section 20, the construction is simple and easy to assemble, and the working efficiency is improved.

[0035]

As a result, according to the overcurrent protection circuit of the present invention, the three-phase current limiting fuses open the three-phase batch type load switch after all the three-phase current limiting fuses are blown, so that uninterruptible and inter-phase short circuit can be prevented. It became a safe facility.

[Brief description of drawings]

FIG. 1 is an overcurrent protection circuit of a power distribution system as an embodiment of the present invention.

FIG. 2 is an overcurrent protection circuit of a power distribution system shown as another embodiment of the present invention.

3 is a fusing characteristic diagram of the current limiting fuse of FIG. 1. FIG.

FIG. 4 is a vertical sectional view of the overcurrent protection device used in FIG.

FIG. 5 is a vertical sectional view of an overcurrent protection device shown as another embodiment of the present invention.

[Explanation of symbols]

1 ... Transformer, 5 ... Load switch, 6A-6C ... Current limiting fuse, 6D ... Strikeer, 7 ... Delay relay, 8 ... Delay circuit, 9 ... Trip coil.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshimi Hakada 1-1-1, Kokubun-cho, Hitachi-shi, Ibaraki Hitachi Co., Ltd. Kokubun factory (72) Inventor Fumio Wakasa 1-1-1, Kokubun-cho, Hitachi-shi, Ibaraki No. 1 Stock company Hitachi Kokubu factory

Claims (10)

[Claims] 1. In a circuit formed by connecting a current limiting fuse and a load switch, a fusing signal is input to at least one phase of the current limiting fuses of each phase, and a fusing signal of a current limiting fuse of another phase is input. The overcurrent protection circuit is characterized in that a delay means for exciting the trip coil to open the load switch is provided under the condition. 2. An overcurrent protection circuit according to claim 1, further comprising opening means for exciting the trip coil to open the load switch when the melting times of the current limiting fuses are substantially the same. 3. At least one phase of the current limiting fuse of each phase is blown out, the striker is blown out, and the operation signal of the relay is input, and the current limiting fuse of the other phase is blown out and the striker is blown out. The overcurrent protection circuit according to claim 1, further comprising delay means for exciting the trip coil to open the load switch when the operation signal is input. 4. A load switch of a three-phase type is used as the load switch, as claimed in any one of claims 1 to 4.
The overcurrent protection circuit described in the paragraph. 5. The delay means is set with a time in which the first one phase of each current limiting fuse is melted, the last melting time of the current limiting fuse of the other phase and the operating time of a striker, etc. The overcurrent protection circuit according to claim 1, wherein the overcurrent protection circuit is provided. 6. The overcurrent protection circuit according to claim 1, wherein a capacitor and a circuit having self-inductance are connected to the secondary side of the load switch and the current limiting fuse. 7. A current limiting fuse is provided between a load side terminal and a power source side terminal electrically connected to one side of the contactor by contacting and separating the movable contactor of the load switch with an operating mechanism section. Is inserted, the current limiting fuse is blown, and the striker that pops out when at least one phase of each current limiting fuse is blown activates the relay to input to the delay means, and the delay means is from the striker of the current limiting fuse of the other phase. When the input signal is input, the trip coil is excited to operate the operation mechanism section to electrically connect the movable contact to the fixed contact and separate the movable contact from the fixed contact. 8. A fixed contactor and a movable contactor of a load switch are brought into contact with and separated from each other by an operation mechanism section, and a current is limited between a power supply side terminal and a load side terminal electrically connected to the contactor. The operation mechanism until the input signal from the striker of the current limiting fuse of the other phase is input at the dashpot by the striker that inserts the fuse and blows out when at least one phase of each current limiting fuse blows. An overcurrent protection device characterized by blocking the operation of a part. 9. The overcurrent protection device according to claim 7, wherein a three-phase batch type load switch is used as the load switch. 10. The overcurrent protection device according to claim 7, wherein a capacitor and a circuit having self-inductance are connected to the secondary side of the load switch and the current limiting fuse.