JP3293327B2 - Overcurrent protection circuit and its device - Google Patents

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 for protecting a circuit by combining a current limiting fuse and a load switch.

[0002]

2. Description of the Related Art Since a load switch alone does not have the ability to interrupt a short-circuit current, an economical facility is obtained by combining and protecting a short-circuit current with a current limiting fuse. In a current limiting fuse, there is a range in which a fuse element is deteriorated and deteriorated without being blown due to an overcurrent, its conduction time, and repetition. Furthermore, the fusing characteristics of the current-limiting fuse are such that the smaller the fusing current range, the greater the variation in fusing time with respect to the change in the applied current, and the greater the variation. For example, it can be said that protection is basically performed by a three-phase collective load switch.

[0003] These facts 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, particularly the switching current indicating the switching capability, are indicated by the limit of the current that can be turned on and off under the specified circuit conditions specified in the standard. Have been. For example, the load switch standard JIS C4605-1987 states on page 17 that the load power factor of the load current switch test is 0.65-0.75, and the performance at this power factor is guaranteed.

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

[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, PF.S is shown in FIG.
Wiring of the form and the connection of the equipment are shown, and the standard page 30 shows the automatic mechanical operation of the load switchgear by the part of the fuse link which performs a predetermined mechanical operation at the time of the blowing operation of the fuse called a current limiting fuse striker. It is stated that the cut-off current range is expanded by the purposeful trip, and the open phase protection by the current limiting fuse blowing is also achieved at the same time.

Under the conditions of this standard, if an interphase short-circuit occurs between the transformer secondary and, for example, MCCB, a short-circuit current flows to the transformer secondary and an overcurrent also flows to the primary.
After the current limiting fuse is blown from 0.05 to 0.2, the three-phase collective load switch is opened.

[0009]

However, the primary overcurrent when the transformer secondary is short-circuited corresponds to the small fusing current region of the current limiting fuse, and the fusing time varies widely.
Since the time is 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 striker of the blown current-limiting fuse. At this time, the overcurrent is tried to be cut off in the phase where the load switch is not blown.

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

For this reason, the present inventor has found through experiments that a load switch intended to cut off an overcurrent cannot be cut off and rarely causes a serious accident such as an interphase short circuit.

An object of the present invention is to provide a safe overcurrent protection circuit which prevents an arc short circuit of a three-phase load switch.

[0013]

According to the overcurrent protection circuit of the present invention, the time from the blow of the current limiting fuse to the start of the operation of the load switch is electrically and mechanically set to the maximum due to the variation of the current limiting fuse. The delay is longer than the fusing time.

[0014]

As a result, the three-phase current-limiting fuses open the three-phase load switch after all the fuses are blown, so that it is not possible to shut off and prevent short-circuiting between phases, thus providing a safe facility.

[0015]

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

[0016] A circuit that deteriorates the power factor on the load side of the load switch and the current-limiting fuse, for example, a phase-to-phase short circuit may occur when an accident such as a transformer or a motor is connected.

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

For example, when a current-limiting fuse that blows first with a three-phase current-limiting fuse in a short-circuit accident blows, the three-phase collective load switch is opened accordingly. However, the remaining two-phase current-limiting fuses are still blowing and
Since a transformer having a low power factor is connected to the secondary side, the power factor of the overcurrent protection circuit is also low, and the power factor is lower than usual.

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

An embodiment for preventing a short circuit between phases will be described with reference to FIGS. FIGS. 1 and 2 show an overcurrent protection circuit according to the present invention. FIG. 3 shows 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 current limiting fuse used in this protection circuit is shown in FIGS.

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

3 is connected between the secondary side 1 B of the transformer 1 and the power 4.
Phase batch type load switch 5 and current limiting fuses 6A, 6B, 6
C is connected. As shown in FIG. 3, the current limiting fuse 6, for example, 6A, has a fusing current of i1 and 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
To excite the trip coil 9 to open the load switch 5. Reference numeral 10 denotes a DC power supply.

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

The delay circuit 8 includes current limiting fuses 6A, 6B,
When a 6C fusing signal is input, a current flows through the trip coil 9 and the load switch 5 is opened.
Circuit.

Next, when a short circuit accident 0 occurs in the load cable 2, a short circuit current flows. The current limiting fuse 6A blows and the striker 6D jumps out in the direction of the arrow. However, when the current limiting fuses 6B and 6C elapse the blowing times t2 and t3, the striker 6D jumps out 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, a short circuit between the phases of the load switch 5 can be prevented, and the equipment becomes safe.

When the fusing currents of the current limiting fuses 6A, 6B and 6C are blown at the same fusing time, i.e., t5, for all of i1, i2 and i3, the second relay 7X of all phases operates immediately, and the trip coil 9 is turned off. , And the load switch 5 is opened, so that the speed is high and it is possible to prevent the accident from spreading under load, and the equipment is safer.

The three-phase collective load switch 5 used in FIG.
FIG. 4 shows a specific structure of the overcurrent protection device including the current limiting fuse 6A and a load switch (or a load switch with a delay operation) connected thereto since the three phases have the same structure. I do.

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

That is, when the striker 6D protrudes in the direction of the arrow, the lever 25 operates in the direction of the dashed line, and the link 26 rotates counterclockwise to move the insulating operation rod 27 to the left. Presses the first delay relay 7 while rotating via the relay pin 28X. At time t4, a current flows through the delay circuit 8 to excite the trip coil 9 and press the stopper 21 clockwise. Further, the illustrated relay pin 28X is supported by the chassis 40.

The stopper 21 rotates clockwise about the stopper pin 21X as a fulcrum, and the stopper hook 21
When the control lever B is disengaged from the control lever 29A via the control pin 29X, the control link 29B and the insulating operation rod 29C rotate counterclockwise.
The movable contact 2 in contact with the fixed contact in the arc-extinguishing chamber 30
2 rotates counterclockwise to shut off. Movable contact 22
Is connected to the power supply terminal 6E via the electrical connection portion 22A.

When the movable contact 22 is brought into contact with the fixed contact, the operation may be performed in the direction opposite to the direction of the arrow, and a description thereof will be omitted.

The description of the load switch 5A in FIG. 5 will be omitted when the same components as those in FIG. 4 are used, and only different points will be described.

That is, the relay lever 28 is connected to the relay pin 28
While rotating via X, the rotating lever 31 is
Presses the dash-pot 32 when pivoting through. When the dash-pot 32 reaches the time t4 similarly to the delay circuit 8, the rotation of the rotation lever 31 is stopped by the stopper 2.
1, the movable contact 22 which is in contact with the fixed contact by performing the same operation as described above is turned counterclockwise and cut off.
When the movable contact 22 comes into contact with the fixed contact, the operation may be performed in a direction opposite to the direction of the arrow, and the description is omitted.

Since the operation mechanism section 20 may be provided with a dash-pot 32 at a part of the operation mechanism section 20, the structure is simple and easy to assemble, and work efficiency is improved.

[0035]

As a result, according to the overcurrent protection circuit of the present invention, since the three-phase current-limiting fuses are all blown and the three-phase collective load switch is opened, it is possible to prevent interruption and short-circuit between phases. It became safe equipment.

[Brief description of the drawings]

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

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

FIG. 3 is a view showing a fusing characteristic of the current limiting fuse of FIG. 1;

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshimi Hakamada 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture Inside the Kokubu Plant of Hitachi, Ltd. (72) Fumio Wakasa 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd. Kokubu Plant (56) References JP-A-51-85444 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01H 33/59 H01H 85 / 46

Claims (10)

(57) [Claims] In a circuit comprising a current limiting fuse and a load switch, a trip coil is excited by applying a blow signal to at least one phase of a current limiting fuse of each phase. An overcurrent protection circuit comprising a delay means for opening a switch. Wherein Kakukiriryu claim 1, wherein when fusing time of the fuse is approximately the same fusing time and providing a opening means for opening the load break switch and energize the trip coil
Overcurrent protection circuit. At least one of the current limiting fuses of each phase is blown, the striker is blown out, an operation signal of the relay is input, and the current limiting fuse of another phase is blown out, the striker is blown out, and each of the relays is blown. 2. The overcurrent protection circuit according to claim 1, further comprising delay means for exciting a trip coil and opening a load switch when an operation signal is input. Wherein with claim 1, characterized by using a three-phase one-type load break switch in the load switch 4 1
The overcurrent protection circuit according to the item. 5. A delay time is set in the delay means, taking into account the fusing time during which the first phase of each current-limiting fuse blows and the operating time of the last blow-through time of the other current-limiting fuse. The overcurrent protection circuit according to any one of claims 1 to 3, wherein: 6. The overcurrent protection circuit according to claim 1, wherein a circuit having a capacitor and a self-inductance is connected to a secondary side of the load switch and the current limiting fuse. 7. A fixed contact and a movable contact of a load switch are separated from and separated by a rear portion of an operating device, and a power supply terminal and a load terminal electrically connected to one side of the contact. The fuse is blown when the current limiting fuse is blown, and when at least one phase of each current limiting fuse blows, the striker is operated to operate the relay, input to the delay means, excite the trip coil, and operate the operating mechanism. An overcurrent protection circuit characterized in that a movable contact is electrically connected to and separated from a fixed contact by operating a unit. 8. A to the input signal from the striker is input, characterized in that it prevents the operation of the operating mechanism
The overcurrent protection circuit according to claim 7 . 9. The overcurrent protection circuit according to claim 7, wherein a three-phase collective load switch is used as said load switch. 10. The overcurrent protection circuit according to claim 7, wherein a circuit having a capacitor and a self-inductance is connected to the secondary side of the switch and the current limiting fuse.