HK1122910B - Surge protection device and surge protection apparatus using thereof - Google Patents

Description

Surge protection device and surge protection equipment adopting same

Technical Field

The present invention relates to a surge protection device (hereinafter referred to as "SPD") and to a surge protection apparatus employing the SPD, which is a protector for protecting electrical equipment, communication electrical equipment, and other target equipment from abnormal voltages caused by lightning surges, such as indirect lightning strikes or direct lightning strikes.

Background

Conventional SPDs for alternating current (hereinafter "AC") power supplies include, for example, a combination of a gas discharge tube (hereinafter "gas arrester") and a varistor. It is intended for protection against indirect lightning strikes and is protected according to the (compliant) JIS (japanese industrial standard) class II protection level. If a gas arrester is used separately for a power supply circuit, the life of the gas arrester may be shortened after the arrester is discharged by a lightning surge, or may even be burned out due to a phenomenon of a continuous current in which discharge is maintained by an AC power supply after the surge disappears. To interrupt this continuous current, a gas arrester and a varistor are combined in series. If a varistor is used alone for a power supply circuit, the characteristics of the varistor may deteriorate with an increase in the number of operations due to lightning surge, resulting in an increase in leakage current and eventually burn-out. Therefore, in order to interrupt the continuous current, a gas arrester and a varistor connected in series are used.

SPD technology using a gas arrester and a varistor in series is described, for example, in the following patent documents.

[ patent document 1 ] Japanese patent laid-open publication No.2006-

[ patent document 2 ] Japanese patent laid-open No.2006-60917 (noise filter circuit for switching power supply)

[ patent document 3 ] Japanese patent laid-open No.2004-

[ patent document 4 ] Japanese patent laid-open No.2001-268888 (Surge protection circuit and Power supply Unit)

[ patent document 5 ] Japanese patent laid-open publication No.9-172733 (Surge voltage absorption Circuit)

[ patent document 6 ] Japanese patent laid-open publication No.9-103066 (switching regulator)

[ patent document 7 ] Japanese patent laid-open No.7-39136 (Power supply Unit for electronic apparatus)

[ patent document 8 ] Japanese patent laid-open No.5-199737(AC input power supply)

Fig. 1 is a schematic block diagram illustrating a conventional surge protection device for protecting a target device connected to a power distribution system (e.g., a low-voltage distribution line in a building or the like) from a lightning surge.

For example, if 6.6 kv high voltage AC of three-phase (3 Φ) three-wire system (3W) is input in the high voltage insulation transformer 1, it is supplied to two low voltage distribution lines L1 and L2 and one neutral line N after being converted into low voltage (200v AC) of a single-phase (1 Φ) three-wire (3W) commercial power system by the insulation transformer 1. The 200-volt low-voltage AC supplied to the two low-voltage distribution lines L1 and L2 and one neutral line N is supplied to a target device 3, such as an electrical device, via the earth leakage breaker 2, so as to drive the target device 3. the low-voltage neutral line N is grounded. Since lightning surges may occur not only with respect to ground but also between lines, in order to protect the target device 3 from lightning surges, it is necessary to provide protection between the device and ground and between lines.

Thus, one of the low voltage distribution lines L1 is connected to the neutral line N, for example, via a fuse 4-1 and an SPD10-1, the fuse 4-1 being manufactured according to JIS grade I protection level and intended for protection from direct lightning strikes, and the SPD10-1 being manufactured according to JIS grade II protection level and intended for protection from indirect lightning strikes. Similarly, another low-voltage distribution line L2 is connected to the neutral line N via a fuse 4-2 and an SPD10-2, the fuse 4-2 being manufactured according to JIS class I protection level and intended for protection from direct lightning strikes, the SPD10-2 being manufactured according to JIS class II protection level and intended for protection from indirect lightning strikes. The neutral line N is grounded via the ground side SPD 20. SPD10 (i.e., SPDs 10-1 and 10-2) are each constituted of a gas arrester and a varistor as described in patent document 1, for example. The ground side SPD20 is formed of, for example, a lightning arrester.

FIG. 2 is a schematic circuit diagram showing the structure of conventional SPD10(SPD10-1 or 10-2) in FIG. 1.

SPD10 has an input terminal 11 and an output terminal 12, for example, as described in patent document 1. A plurality of gas arresters 13-1 to 13-6 are connected in series between the input 11 and the output 12. That is, the input terminal 11, the node 15-1, the gas arrester 13-1, the node 15-2, the gas arrester 13-2, the node 15-3, the gas arrester 13-3, the node 15-4, the gas arrester 13-4, the node 15-5, the gas arrester 13-5, the node 15-6, the gas arrester 13-6, the node 15-7, and the output terminal 12 are connected in series, the varistor 14-1 is connected between the node 15-1 and the node 15-6, and the varistor 14-2 is connected between the node 15-2 and the node 15-7. Also, varistor 14-3 is connected between node 15-2 and node 15-5, varistor 14-4 is connected between node 15-3 and node 15-6, and varistor 14-5 is connected between node 15-3 and node 15-4.

The operation of SPD10 shown in FIG. 2 will next be described.

If a lightning surge voltage is applied between the input terminal 11 and the output terminal 12 (i.e., between the node 15-1 and the node 15-7), the lightning surge voltage is generated in the series circuit composed of the gas arrester 13-1 and the varistor 14-2, and similarly, the lightning surge voltage is generated in the series circuit composed of the varistor 14-1 and the gas arrester 13-6. When the lightning surge voltage is applied to the series circuit composed of the gas arrester 13-1 and the varistor 14-2, most of the lightning surge voltage is applied to the gas arrester 13-1 due to the capacitance difference between the two, similarly, in the series circuit composed of the varistor 14-1 and the gas arrester 13-6, most of the lightning surge voltage is applied to the gas arrester 13-6.

At this time, the gas arresters 13-1 and 13-6 to which overvoltage is applied due to lightning surge try to start discharging. However, both rarely start discharging at the same time. One of them starts discharging first due to a slight difference in performance (i.e., a slight difference in discharge voltage) attributable to the manufacturing lot. It is assumed here that the gas arrester 13-1 starts to discharge first.

When the gas arrester 13-1 starts discharging, electrical continuity is established between the nodes 15-1 and 15-2, and thus a lightning surge current flows to the varistor 14-2. Thus, varistor 14-2 limits the voltage between nodes 15-2 and 15-7 to a varistor voltage due to its own characteristics. As a result, the voltage between the nodes 15-2 and 15-7 becomes equal to the sum (x volts) of the arc voltage at which the discharge of the gas arrester 13-1 is stabilized and the varistor voltage. Incidentally, x volts is larger than the discharge voltage value of the gas arrester.

At this time, a voltage of x volts is generated in the series circuit composed of the varistor 14-1 and the gas arrester 13-6 and between the nodes 15-1 and 15-7, but most of the voltage of x volts (x1 volts) is applied to the gas arrester 13-6 due to the capacitance difference between the varistor 14-1 and the gas arrester 13-6. The voltage of X1 volts is greater than the discharge voltage value of the gas arrester 13-6, so that the gas arrester 13-6 starts discharging, electrical continuity is established between the nodes 15-6 and 15-7, and a lightning surge current flows to the varistor 14-1. Thus, varistor 14-1 limits the voltage between nodes 15-1 and 15-6 to a varistor voltage due to its own characteristics.

Subsequently, the gas arresters 13-2 to 13-5 are discharged in a similar manner in succession until finally all the gas arresters 13-1 to 13-6 have been discharged and the lightning surge current is discharged via the gas arresters 13-1 to 13-6. When the gas arresters 13-1 to 13-6 are discharged, the voltage between the nodes 15-1 and 15-7 is equal to the sum (y volts) of the arc voltages of the gas arresters 13-1 to 13-6. Although the arc voltage varies between the individual gas arresters according to the arrester specifications, it is approximately ten-odd volts to several tens of volts, and therefore y volts is not an excessive value. Therefore, the target apparatus is protected from overvoltage, so that it is possible to prevent damage to the target apparatus.

Next, a description will be given of an operation performed between the low-voltage distribution lines (L1 and L2) and the ground when an overvoltage (pulse) such as a lightning surge is generated on the low-voltage distribution lines L1 and L2 in the surge protection device of fig. 1. This description will be provided by referring to the following cases (1) to (4).

(1) Case 1

FIG. 3 is a circuit diagram showing fuse 4-2 and SPD10-2 in FIG. 1. Fig. 4 is a voltage waveform diagram according to case 1, in which pulses are generated in the low-voltage distribution line L2 in fig. 3. In fig. 4, reference numeral 21 denotes a pulse, 22 denotes the start of arrester discharge, and 23 denotes arrester arc discharge. Incidentally, it is assumed in fig. 5 that the arc voltage of each arrester during arc discharge is 15 volts, but the arc voltage varies depending on the specification of the gas arrester, and may be set to various values.

In the low-voltage distribution line L2 in fig. 3, when the 200VAC supply voltage is in a positive half cycle, if a positive pulse 21 such as that shown in fig. 4 is generated, the gas arresters 13-1 to 13-6 in SPD10-2 begin to discharge, which is triggered by pulse 21. Therefore, the voltage between the low-voltage distribution line L2 and the neutral line N reaches the arc discharge voltage. The arc discharge voltage is, for example, 90 volts as shown in fig. 5. On the other hand, the supply voltage is between +0 volts and +300 volts (200 VACrms). As the pulse 21 weakens (falls), the gas arresters 13-1 to 13-6 are no longer able to sustain the arc discharge.

The conditions that make it impossible to sustain the arc discharge include, for example, the following three conditions: (a) condition 1 to (c) condition 3.

(a) Condition 1

Fig. 6 is a diagram showing an example of conditions regarding arc discharge of SPD13 constituted by a series circuit of, for example, four gas arresters 13-1 to 13-4. Fig. 7 is a diagram showing a case where the arc discharge in fig. 6 is not continued (interrupted).

Assume that a supply voltage of, for example, +48VDC (volts direct current) is applied across SPD13 as shown in FIG. 6. As shown in FIG. 7, if the arcing voltage of SPD13 is, for example, +60 volts, which is higher than the supply voltage of +48VDC, then the arcing of SPD13 in FIG. 6 does not continue (in this case never continues).

(b) Condition 2

Fig. 8(i) and 8(ii) are diagrams showing a case where arc discharge does not proceed (is interrupted), for example, with respect to SPD13 in fig. 6.

As shown in FIG. 8(i), if the arc voltage of SPD13 is +60 volts and the supply voltage is +100VAC, i.e., if the arc voltage is lower than the supply voltage but the difference is not large, then arcing of SPD13 does not continue in many cases, also, as shown in FIG. 8(ii), if the arc voltage of SPD13 is +30 volts and the supply voltage is +48VDC, i.e., if the arc voltage is lower than the supply voltage but the difference is not large, then arcing of SPD13 does not continue in many cases. Incidentally, the phenomenon that the gas arresters 13-1 to 13-4 of the SPD13 continue the arc discharge due to the fed supply voltage is referred to as "continuous current".

(c) Condition 3

Fig. 9 is a diagram showing a situation where an arc discharge, for example, with respect to SPD13 in fig. 6 stops.

If the arc voltage of SPD13 is +60 volts and is lower than the supply voltage, which is +100VAC, then the continuous current typically stops when the current of the supply voltage waveform reaches the zero current point 24. It stops at most at the half-wave point of the supply voltage.

Thus, in (1) case 1, although the arc voltage of SPD13 is lower than the supply voltage, the arc discharge stops relatively quickly because there is only a small difference between the arc voltage and the supply voltage (this corresponds to condition 2 above).

(2) Case 2

Fig. 10 is a diagram showing case 2 in which arc discharge stops, for example, with respect to SPD13 in fig. 6.

In case 2, for example, the power supply voltage is 100VAC and the arc voltage is 60 volts, and the power supply voltage is in a negative half cycle and there is a negative pulse. In this case (case 2), the polarity is opposite to that in case 1. As with case 1, during arcing, there is a small difference between the arc voltage of-30 volts and the supply voltage of-100 VAC, so arcing stops relatively quickly (this corresponds to condition 2 above).

(3) Case 3

Fig. 11 is a diagram showing case 3 in which arc discharge stops, for example, with respect to SPD13 in fig. 6.

In case 3, for example, the power supply voltage is 100VAC and the arc voltage is 60 volts, and the power supply voltage is in the positive half cycle and there is a negative pulse, in this case (case 3), during the arc discharge, there is a large difference between the arc voltage and the power supply voltage, so the arc discharge does not stop quickly. It stops when the current of the 100VAC supply voltage reaches the zero current point 24 (this corresponds to condition 3 above).

(4) Case 4

Fig. 12 is a diagram showing case 4 in which arc discharge stops, for example, with respect to SPD13 in fig. 6.

In case 4, for example, the supply voltage is 100VAC and the arc voltage is 60 volts, and the supply voltage is in the negative half cycle and there is a positive pulse. In this case (case 4), the polarity is opposite to that in case 3. As in case 3, during the arc discharge, there is a large difference between the arc voltage and the power supply voltage, and therefore the arc discharge does not stop quickly. It stops at time 24 when the current of the 100VAC supply voltage reaches 0 (this corresponds to condition 3 above).

Now, a description will be given of the relationship between the fuses (4-1 and 4-2) and the SPDs (10-1 and 10-2) in the surge protection device shown in fig. 1.

If SPDs 10-1 and 10-2 short circuit or are otherwise damaged, fuses 4-1 and 4-2 blow, thereby cutting low voltage distribution lines L1 and L2 from ground, fuses 4-1 and 4-2 also blow when an overcurrent equal to or greater than a predetermined value flows through fuses 4-1 and 4-2.

Conventionally, the fuses 4-1 and 4-2 have a common specification, and they do not have a very high trip performance. Their rated current is, for example, about 200 amperes (a). They have a high capacity in this respect and therefore a large profile.

Since the conventionally used fuses 4-1 and 4-2 are of this type, the fuses 4-1 and 4-2 do not blow even if the SPDs 10-1 and 10-2 operate in any of the above cases 1 to 4. Thus, in cases 3 and 4 above, the mains current flows through the fuses 4-1 and 4-2 (for at most a half cycle) until the zero current point 24 is reached, but the fuses 4-1 and 4-2 do not blow because the rated current is not exceeded.

Recently, however, the specifications of the fuses 4-1 and 4-2 have been revised, for example, as described in (A) and (B) below.

(A) Fuse Specification 1

The rated current may be small. For example, 200A of rated current is excessive.

(B) Fuse Specification 2

As the rated current is reduced, the profile of the fuse can be reduced accordingly. For example, conventional fuses have outer dimensions of 100mm (millimeters) × 100mm × 200mm and a weight of several kilograms (Kg), but they are preferably more compact in outer dimensions.

This change in specifications 1 and 2 has made the fuse size smaller, but also reduced the rated current. That is, fuses have been made to trip at lower currents. From another perspective, this may be seen as a performance improvement.

However, the conventional surge protection device such as that shown in fig. 1 has a problem in that the conventional SPDs 10-1 and 10-2 are affected by the changed specifications 1 and 2 of the fuses 4-1 and 4-2.

That is, in cases 3 and 4, since the mains current flows through SPDs 10-1 and 10-2 and fuses 4-1 and 4-2 for at most half a cycle, fuses 4-1 and 4-2 blow by reacting to the current. Once the fuses 4-1 and 4-2 are blown, they must be manually reset, which requires an operator to operate by going to the installation location of the surge protection device. This is neither convenient nor advantageous.

To cope with this situation, the circuit structures of SPDs 10-1 and 10-2 must be improved. However, by simply combining the techniques of patent documents 1 to 8 and the like, it is difficult to provide a small, reliable, inexpensive, and relatively simple-structured SPD and a surge protection device employing the SPD.

Disclosure of Invention

A first object of the invention is to provide a small, reliable, inexpensive SPD that is relatively simple in structure and able to cope with direct lightning strikes.

A second object of the present invention is to provide a surge protection apparatus capable of preventing a circuit breaking device installed in front of or behind an SPD from tripping.

To achieve the first object, according to a first aspect of the present invention, there is provided an SPD for a power supply, the SPD protecting a target device operating at an AC power supply voltage from an abnormal voltage applied to the target device, the SPD comprising: a gas arrester applying an AC power supply voltage; a varistor group connected in series with the gas arrester and including a plurality of varistors having a high withstand capacity, wherein the varistors are connected in parallel with each other, and each varistor has a varistor voltage set higher than a peak value of an AC power supply voltage; and a resistor connected between two electrodes of the resistor group, discharging the electric charges stored in the capacitance of the resistor group.

In order to achieve the second object, according to a second aspect of the present invention, there is provided a surge protection device including: a circuit breaking device that protects a target apparatus operating with an AC power voltage from an abnormal voltage applied to the target apparatus by blocking the abnormal voltage; and an SPD for a power supply, connected in series with the circuit breaking device, protecting the target device from the abnormal voltage, wherein the SPD includes: a gas arrester applying an AC power supply voltage; a varistor group connected in series with the gas arrester and including a plurality of varistors having a high withstand capacity, wherein the varistors are connected in parallel with each other, and each varistor has a varistor voltage set higher than a peak value of an AC power supply voltage; and a resistor connected between two electrodes of the resistor group, discharging the electric charges stored in the capacitance of the resistor group.

As described above, in the SPD according to the first aspect of the present invention, the gas arrester is connected in series with the varistor group composed of a plurality of varistors having high withstand capacity and connected in parallel with each other, and the discharge resistor is connected between both electrodes of the varistor group. Furthermore, since the varistor voltage is set higher than the peak value of the AC power supply voltage, the varistor is usually insulated from the power supply circuit by a gas arrester. Even if an abnormal voltage is applied, since the operating voltage of the varistor is set higher than the peak value of the AC power supply voltage, no AC power supply current flows.

Further, the current-resistant capacity of the varistor depends on, for example, its area, and thus a varistor group having a high-resistant capacity has a high capacitance. During operation of the gas arrester, the capacitor is charged and the voltage is maintained. Therefore, when the polarity of the AC power voltage is reversed, the voltage maintained by the varistor is added to the AC power voltage applied to the gas arrester, which may cause re-ignition. According to the first aspect of the invention, since the resistor is connected between the electrodes of the varistor group, the charge stored in the varistor is quickly discharged through the resistor.

The surge protection device according to the second aspect of the present invention can reliably protect the target device from direct lightning strikes and prevent a circuit breaking device installed in front of or behind the SPD from tripping because the circuit breaking device is connected in series with the SPD according to the first aspect. This makes it possible to dispense with troublesome operations such as replacing or resetting the circuit breaking device.

These and other objects and novel features of the present invention will become more fully apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. The drawings, however, are provided for illustration only and are not intended to limit the scope of the present invention.

Drawings

FIG. 1 is a schematic block diagram illustrating a conventional surge protection device for protecting target devices connected to a power distribution system (e.g., low voltage distribution lines in a building or the like) from lightning surges;

FIG. 2 is a schematic circuit diagram showing the structure of conventional SPD10(SPD10-1 or 10-2) in FIG. 1;

FIG. 3 is a circuit diagram showing fuse 4-2 and SPD10-2 in FIG. 1;

fig. 4 is a voltage waveform diagram according to case 1, in which case 1, a pulse is generated in the low-voltage distribution line L2 in fig. 3;

FIG. 5 is a graph illustrating the split voltage, etc., during an arc discharge of SPD10-2 of FIG. 1;

fig. 6 is a diagram showing an example of conditions regarding arc discharge of SPD13 constituted by a series circuit of four gas arresters 13-1 to 13-4;

fig. 7 is a diagram showing a case where the arc discharge in fig. 6 is not continued (interrupted);

FIG. 8 is a diagram showing a scenario in which arcing does not continue (is interrupted) with respect to SPD13 in FIG. 6;

FIG. 9 is a diagram showing a situation in which arcing ceases with respect to SPD13 in FIG. 6;

FIG. 10 is a diagram showing case 2 where arcing ceases with respect to SPD13 in FIG. 6;

FIG. 11 is a diagram showing case 3 where arcing ceases with respect to SPD13 in FIG. 6;

FIG. 12 is a diagram showing case 4 where arcing ceases with respect to SPD13 in FIG. 6;

FIG. 13 is a schematic block diagram illustrating a surge protection device used to protect target devices connected to a power distribution system (e.g., low voltage distribution lines in a building or the like) from lightning surges in accordance with a preferred embodiment of the present invention;

fig. 14 is an exemplary structural view showing a series circuit composed of one gas arrester 41 and one varistor 42-1 in fig. 13;

fig. 15 is an exemplary structural view illustrating the varistor 42-1 in fig. 14;

fig. 16 is a diagram showing a modified example of the structure in fig. 14;

FIG. 17 is a circuit diagram corresponding to each SPD40(40-1 or 40-2) in FIG. 13 and obtained by solving the circuit problem in FIG. 16 (i);

FIG. 18 is a graph illustrating the required performance of SPD40(40-1 and 40-2) in FIG. 13 tested in accordance with rank I;

FIG. 19 is a graph showing current values for three levels of a direct lightning strike;

fig. 20 is an operation waveform diagram obtained by applying a pulse voltage to a prototype constructed to be used as the special gas arrester 41 in fig. 13;

FIG. 21 is a diagram of operating waveforms obtained when resistor 43 is not mounted on SPD40(40-1 and 40-2) in FIG. 13;

fig. 22 is an operation waveform diagram illustrating the operation load test in fig. 21;

FIG. 23 is a diagram showing operating waveforms across varistors 42(42-1 to 42-5) in each SPD40(40-1 or 40-2) in FIG. 13 when resistor 43 is mounted between the ends of the varistors; and

fig. 24 is an operation waveform diagram illustrating the operation load test in fig. 23.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

(examples)

(general construction of Surge protection device according to the preferred embodiment)

Fig. 13 is a schematic block diagram illustrating a surge protection device used to protect target devices connected to a power distribution system (e.g., low voltage distribution lines in a building, etc.) from lightning surges in accordance with a preferred embodiment of the present invention.

In the circuit of fig. 13, for example, as in the case of the conventional circuit shown in fig. 1, if 6.6 kv high-voltage AC of three-phase (3 Φ) three-wire system (3W) is input in the high-voltage insulation transformer 31, it is supplied to two low-voltage distribution lines L1 and L2 and one neutral line N after being converted into low voltage (200v AC) of a single-phase (1 Φ) three-wire (3W) commercial power system by the insulation transformer 31, the 200v low-voltage AC supplied to the two low-voltage distribution lines L1 and L2 and the one neutral line N is supplied to a target device 33, such as an electric device, via the earth leakage breaker 32 so as to drive the target device 33. The low voltage neutral line N is grounded. Since lightning surges may occur not only with respect to ground but also between lines, in order to protect the target device 33 from lightning surges, it is necessary to provide protection between the device and ground as well as between lines.

Therefore, one of the low-voltage distribution lines L1 is connected to the neutral line N via the overcurrent circuit breaking device (e.g., fuse) 34-1 according to specifications 1 and 2 different from the conventional specifications and the SPD40-1 having a circuit configuration different from the conventional circuit configuration shown in fig. 1. Also, another low-voltage distribution line L2 is connected to the neutral line N via an overcurrent circuit breaking device (e.g., fuse) 34-2 according to specifications 1 and 2 different from the conventional specifications and an SPD40-2 having a circuit configuration different from the conventional circuit configuration shown in fig. 1. Also, the neutral line N is grounded via a ground-side SPD (e.g., gas arrester) 50.

Each SPD40 (i.e., 40-1 or 40-2) is composed of one gas arrester 41, a plurality of (e.g., five) varistors 42-1 to 42-5 connected in parallel with each other and in series with the gas arrester 41, and a discharge resistor 43 connected in parallel with the varistors 42-1 to 42-5.

(Structure of each SPD40 (i.e., 40-1 or 40-2))

Fig. 14(i) and 14(ii) are diagrams showing an exemplary structure of a series circuit composed of one gas arrester 41 and one varistor 42-1 in fig. 13, in which fig. 14(i) is a circuit diagram of the series circuit, and fig. 14(ii) is a characteristic curve showing a relationship between a voltage V and a time t in the series circuit.

To solve this conventional problem, it is conceivable to change the circuit configuration of SPD4(4-1 and 4-2) to the circuit configuration shown in FIG. 14(i), for example.

The SPD in fig. 14(i) has a circuit structure in which a series circuit composed of one gas arrester 41 and one varistor 42-1 is connected to two terminals T1 and T2.

In the circuit having this structure, when, for example, the commercial power 200VAC power supply voltage is applied, the arc discharge is rapidly stopped as in cases 1 and 2 above, rather than cases 3 and 4 above, in which the commercial power supply current flows for a certain period of time.

Fig. 15(I) and 15(ii) are diagrams showing an exemplary structure of the varistor 42-1 in fig. 14, in which fig. 15(I) is a circuit diagram of the varistor 42-1, and fig. 15(ii) is a graph of the current (I) versus voltage (V) of the varistor 42-1.

The operation of the circuit in fig. 14(i) will be described below with reference to fig. 14(ii), 15(i) and 15 (ii).

When the high voltage V applied between the two terminals T1 and T2 exceeds the +600 volt discharge voltage of the gas arrester (60), the gas arrester 41 discharges and becomes conductive, causing a pulse current to flow through the varistor 42-1 as shown in fig. 14(ii), the pulse current I flowing through the varistor 42-1 increases with time T, but the voltage V across the varistor 42-1 is limited to an almost constant (e.g., 350 volts) varistor clamping voltage 61.

In this way, in the circuit of fig. 14(i), the voltage between terminals T1 and T2 slightly exceeds +350 volts, which is higher than the mains 200VAC supply voltage. Therefore, the gas arrester 41 does not cause a continuous current, and the arc discharge is rapidly stopped. Accordingly, such an overcurrent, which would cause the fuse 34 (specifically 34-1 or 34-2) connected to the terminal T1 to respond, does not flow through the fuse 34 in FIG. 13. Therefore, the fuse 34 does not blow, and seems to solve the conventional problem.

However, the use of the varistor 42-1 makes it impossible to meet other requirements. That is, the SPDs 40(40-1 and 40-2) used to protect against direct lightning strikes in fig. 13 pass pulsed currents as large currents, so they require high withstand capacity (e.g., 25 KA.) for the SPDs 10(10-1 and 10-2) of the conventional structure in fig. 1, large currents are carried by the gas arrester alone when the discharge is stable, but there is no problem because the gas arrester structurally has high withstand capacity. However, the varistor has a lower withstand capacity than the gas arrester. Therefore, it is conceivable to mount a plurality of varistors 42-1 in parallel.

Fig. 16(i) to 16(iv) are diagrams showing a modified example of the structure in fig. 14.

Fig. 16(i) is a circuit diagram showing an exemplary structure in which a plurality of (e.g., five) varistors 42-1 to 42-5 are connected in parallel with each other in the circuit of fig. 14 (i).

When the plurality of varistors 42-1 to 42-5 are connected in parallel to each other as in the case of the circuit of fig. 16(i), since a large current flowing through the gas arrester 41 is distributed among the plurality of varistors 42-1 to 42-5, the withstand capacity of the entire SPD in fig. 16(i) improves according to the number of varistors 42-1 to 42-5. However, the circuit configuration in fig. 16(i) poses a new problem.

Fig. 16(ii) is a diagram showing a capacitance equivalent circuit of the circuit of fig. 16 (i).

The equivalent circuit in fig. 16(ii) is constituted by the capacitance C41 of the gas arrester 41 and the total capacitance C42 of the plurality of varistors 42-1 to 42-5 connected in parallel with each other, wherein the capacitance C41 and the capacitance C42 are connected in series with each other. The plurality of varistors 42-1 to 42-5 each have a large capacitance, which when connected in parallel results in a very large total capacitance C42. therefore, after a large current flows through the circuits in FIGS. 16(i) and 16(ii), a large amount of charge accumulates in the plurality of varistors 42-1 to 42-5.

Fig. 16(iii) is a plot of current I versus voltage V, which represents the varistor clamping voltage 61 in the varistors 42-1 to 42-5. Fig. 16(iv) is a graph of time T versus voltage V, which represents the mains 200VAC supply voltage applied between terminals T1 and T2 in fig. 16 (i). Also, FIG. 17 is a circuit diagram corresponding to each SPD40(40-1 or 40-2) in FIG. 13 and obtained by solving the circuit problem in FIG. 16 (i).

As shown in fig. 16(iii), after the discharge of the gas arrester 41 is stopped, the charging voltage of 350 volts in the varistors 42-1 to 42-5 is maintained for a long time, but the gas arrester 41 will not start discharging (i.e., reigniting the arc) only at the charging voltage of 350 volts.

However, as shown in fig. 16(iv), when the polarity of the commercial power 200VAC power supply voltage is reversed at time t, the sum of the charging voltage 350 volts and the reversed commercial power 200VAC power supply voltage (-200VAC) (for example, 350 volts- (-200 volts) 550 volts) is applied to the gas arrester 41. Therefore, the total voltage (for example, 550 volts) may exceed the discharge voltage of the gas arrester 41, and in this case, the gas arrester 41 may be discharged again. In the worst case, the gas arrester 41 is repeatedly ignited and extinguished in synchronization with the period of the commercial 200VAC power supply voltage.

In this case, the mains current will also flow during conduction, causing current to flow through the fuses 34-1 and 34-2 in fig. 13 for a long period of time, thus blowing the fuses 34-1 and 34-2. Then, it is impossible to solve the conventional problem. Accordingly, as shown in fig. 17, the discharge resistor 43 is connected in parallel to the varistors 42-1 to 42-5.

In the circuit shown in fig. 17, when the gas arrester 41 stops discharging, the terminals T1 and T2 are disconnected from each other while the varistors 42-1 to 42-5 are charged with 350 volts. However, the charging voltage is rapidly discharged via the resistor 43, and the gas arrester 41 does not reignite.

(concrete design example of SPD40(40-1 and 40-2))

FIG. 18 is a graph illustrating the required performance of SPD40(40-1 and 40-2) in FIG. 13 tested in accordance with rank I.

In order to protect the target device 33 in fig. 18 from lightning surges, the class I SPDs 40(40-1 and 40-2) in fig. 13 for providing shunt current from direct lightning strikes are now required by JIS (japanese industrial standards) C5381-1 and related JIS code, rather than the conventional class II SPDs 10(10-1 and 10-2) in fig. 1 intended for protection from indirect lightning strikes, where JIS C5381-1 is newly formulated to comply with, for example, the international standard IEC (international electrotechnical commission). For example, JIS (japanese industrial standard) C0367 evaluates the current of direct lightning strikes in three-level scale.

Fig. 19 is a graph showing current values of three levels of a direct lightning strike.

As shown in FIG. 19, three levels of protection are provided according to the importance of a target object, such as a building, and one magnitude of lightning current is specified for each protection level, for example, the highest protection level I indicates that lightning protection should be designed such that the target object will be protected from an extreme lightning current with a peak current value of 200 kA.

When it is difficult to calculate the shunt current of a direct lightning stroke, it should be assumed that 50% of the original magnitude of the lightning current is diverted to the distribution system. The number of cables in the distribution line is based on the assumption of a single-phase two-wire system and the lightning current flowing to one line is 50kA at maximum. JIS C0367 assumed that a direct lightning strike had a current waveform of 10/350 μ s (microseconds). SPDs 10(10-1 and 10-2) that were conventionally intended for indirect lightning strikes have been rated based on a 8/20 μ s current waveform.

On the other hand, the performance requirements of SPD40(40-1 and 40-2) tested in accordance with class I include, for example, the following two.

At each Protection level assumed by JIS a 4201 "Lightning Protection of Buildings and the like", an SPD tested according to class I should have sufficient performance to withstand the shunt current of the Lightning current. In the case of the single-phase two-wire system, the maximum value calculated for each phase of 10/350 μ s is 50 kA.

The SPDs tested in accordance with class I should be able to operate in cooperation with the SPDs 10(10-1 and 10-2) tested in accordance with class II most of the lightning current must be handled by the class I test-compliant SPDs 40(40-1 and 40-2). to this end, as shown in FIG. 18, the operating voltages must satisfy the following relationships: SPD40(40-1 and 40-2) tested according to grade I < SPD10(10-1 and 10-2) tested according to grade II.

When considering both functions described above, the probability that a direct lightning stroke with a peak current exceeding 200kA will currently occur is less than 10%. Further, in view of the fact that most power distribution systems in japan employ a three-phase or single-phase three-wire system, it can be said that it is sufficient to allow a shunt current of about 25kA (10/350 μ s).

Thus, according to the first embodiment, SPD40(40-1 and 40-2) tested in accordance with rank I has been developed as follows.

As shown in FIG. 18, SPDs 40(40-1 and 40-2) tested in accordance with class I not only have very high current endurance capacity as described above, but also need to operate in cooperation with SPDs 10(10-1 and 10-2) tested in accordance with class II when SPDs 40(40-1 and 40-2) tested in accordance with class I are mounted on the power supply side and SPDs 10(10-1 and 10-2) tested in accordance with class II are mounted on the same wires but on the side of the target device 33, if electromagnetic induction or the like is taken into consideration, it is desirable to pass main current through SPDs 40(40-1 and 40-2) tested in accordance with class I mounted on the power supply side, while hardly passing current through SPDs 10(10-1 and 10-2) tested in accordance with class II.

With respect to the basic performance requirements of SPD40(40-1 and 40-2) for a power supply, the SPDs need to have sufficient continuous current interrupt ratings. If this performance requirement cannot be met by the SPD alone, it must be met in conjunction with a backup circuit breaker (e.g., fuses 34-1 and 34-2 in FIG. 13), or the like. In particular, SPDs 40(40-1 and 40-2) installed at power supply points in accordance with the class I test are expected to also have large continuous current interrupt ratings because the power supply has high short circuit capacity.

Thus, the following development goals were set for the performance of the most common SPD40(40-1 and 40-2) in accordance with the class I test, and specifications (A) through (D) were designed.

Current capacity (pulse current): iamp 10/350 mus 25kA

Maximum supply voltage: uc 230 v

-voltage protection level: up 1500 v or less (lowest possible value)

(required to cooperate with SPDs tested according to level II)

Continuous current interruption rating: ifi 50kA (Uc 23050/60Hz)

(must be greater than the short circuit current of the power supply)

-leakage current IPE of 3 μ a or less at 320VDC

(A) Specifications of apparatus for SPD40(40-1 and 40-2) in FIG. 13

For example, if a gas arrester is used alone, switching to low voltage will occur during operation, which will result in a continuous current. If during operation there is no voltage between the terminals of the SPD that exceeds the supply voltage, the operating state will be maintained by the supply voltage. In order to supply this voltage during operation, from the viewpoint of preventing a continuous current, an element that generates a voltage higher than the peak value of the power supply voltage is used in combination with the gas arrester. For these reasons, the SPD40(40-1 or 40-2) according to the present embodiment is constituted by a series circuit of the special gas arrester 41 and the varistor 42.

(B) Varistor 42(42-1 to 42-5) specification

The operating voltage V1 of the varistor is typically limited to milliamperes (mA). The operating voltage of varistor 42 for SPD40(40-1 or 40-2) is set to 320 volts or more, for example, which allows for a maximum supply voltage Uc of 230 volts (AC). The current withstand capacity of a varistor 42 may be doubled by connecting varistors of nearly the same operating voltage in parallel in SPD40(40-1 or 40-2), five varistors 42(42-1 to 42-5) with current withstand capacities of 5500A (10/350 μ s) are used in parallel to meet Iimp 25kA and to meet size constraints.

(C) Specification of special gas arrester 41

The special gas arrester 41 should be designed such that the lower limit of the operating voltage does not fall below, for example, 320 volts even if the pulse current is applied multiple times. Typically, the gas arrestors used in SPDs 40(40-1 and 40-2) for power supplies are easily turned off due to self-heating with a portion of the active gas, e.g., hydrogen, during operation, but at the same time, this heating promotes electrode wear, resulting in operating voltage fluctuations. To prevent this, an inert gas is used instead of hydrogen for the special gas arrester 41 in SPD40(40-1 and 40-2).

Fig. 20 is an operation waveform diagram obtained by applying a pulse voltage to a prototype constructed to be used as the special gas arrester 41 in fig. 13.

In fig. 20, by partially setting the operating voltage 62 of the waveform to a sufficiently large value higher than the power supply voltage and employing the varistor 42 having a sufficiently high current withstanding capacity, it is possible to obtain characteristics that do not cause a continuous current and do not pass a current other than a pulse current.

(D) Adding resistor 43

This applies equally to the varistors 42(42-1 to 42-5) used in SPD40(40-1 and 40-2) without exception. The increase is, for example, about 5600 picofarads (pF) per varistor. Needless to say, high capacitance means that a large amount of charge is stored, and the voltage is maintained even after the surge disappears.

Thus, each SPD40(40-1 or 40-2) in FIG. 13 is configured to rapidly discharge the charge stored in the capacitance of varistors 42-1 through 42-5 via resistor 43 mounted between the electrodes of varistors 42-1 through 42-5. The mains available voltage continues to be applied to SPD40(40-1 or 40-2) for the power supply. SPD40 must begin operation when a lightning surge enters and turn off quickly after the surge.

FIG. 21 is a diagram of operating waveforms obtained when no resistor 43 is mounted on SPD40(40-1 and 40-2) in FIG. 13.

Fig. 21 shows the waveform of the commercial 200VAC power supply voltage and the waveform of the voltage (i.e., the voltage across the varistor) 63 held by the capacitance of the varistor 42(42-1 to 42-5).

When the resistor 43 is not installed, the commercial 200VAC power supply voltage and the voltage 63 held by the capacitances of the varistors 42-1 to 42-5 are applied to the gas arrester 41. Thus, when voltage 64 becomes higher than the operating voltage of gas arrester 41, gas arrester 41 reignites the arc and remains on, destroying SPD40(40-1 and 40-2) itself in the worst case.

Fig. 22 is an operation waveform diagram illustrating the operation load test in fig. 21.

FIG. 22 shows voltage waveform 65 across the SPD, surge application point 66, and current waveform 67 of the current flowing through SPD40(40-1 or 40-2). The voltage waveform 65 is a 200VAC waveform. Incidentally, a 1000:1 probe is used, which means that one scale is equal to 200 millivolts. The current waveform 67 is actually obtained by transformation. That is, since a 1000:1 probe is used, the vertical axis is scaled at 5A/1 current intervals. Thus, current waveform 67 is the result of a voltage-to-current conversion. On the other hand, the delay in fig. 22 represents the ability to display past data in units of milliseconds.

Since the resistor 43 is not installed, when a surge is applied, the voltage 63 held by the capacitance of the varistor 42(42-1 to 42-5) causes the gas arrester 41 to continue to reignite after the SPD40(40-1 and 40-2) operates. This is because the operating voltage of the varistor 42(42-1 to 42-5) is low, the electric charge continues to be stored in the capacitance of the varistor 42(42-1 to 42-5), and the operating voltage of the gas arrester 41 drops.

Fig. 23 is a diagram showing operation waveforms across the varistors 42(42-1 to 42-5) in each SPD40(40-1 or 40-2) in fig. 13 when the resistor 43 is mounted between the ends of the varistor.

Fig. 23 shows the waveform of the mains 200VAC supply voltage and the waveform of the voltage 68 across the varistor.

When the resistor 43 is mounted across the varistor 42(42-1 to 42-5), the charge stored in the capacitance of the varistor 42(42-1 to 42-5) is rapidly discharged after the surge disappears. Thus, the gas arrester 41 does not reignite unless its operating voltage drops below the mains 200VAC supply voltage. With this structure, SPD40(40-1 and 40-2) passes only the surge without unnecessarily affecting the mains supply voltage.

Fig. 24 is an operation waveform diagram illustrating the operation load test in fig. 23.

FIG. 24 shows a voltage waveform 69 across the SPD, a surge application point 70, and a current waveform 71 of current flowing through SPD40(40-1 or 40-2). The voltage waveform 69 is a 200VAC waveform, as in the case of fig. 22. Incidentally, a 1000:1 probe is used, which means that one scale is equal to 200 millivolts. The current waveform 71 is actually obtained by transformation, i.e., since a 1000:1 probe is used, the vertical axis is scaled at 5A/1 current intervals. Thus, current waveform 71 is the result of a voltage-to-current conversion. On the other hand, the delay in fig. 24 represents the ability to display past data in units of milliseconds.

By using a special gas arrester 41, setting the operating voltage of the varistor 42(42-1 to 42-5) to be higher than the mains 200VAC supply voltage and lower than 400 volts, connecting five varistors 42-1 to 42-5 of the same operating voltage in parallel, and connecting a suitable resistor 43 across the varistors 42-1 to 42-5, it is possible to provide an SPD40(40-1 and 40-2) according to class I test that can operate in cooperation with the SPDs 10(10-1 and 10-2) according to class II test without affecting the power supply system.

(advantages of the embodiment)

According to this embodiment, SPDs 40(40-1 and 40-2) are connected in series with respective fuses 34-1 and 34-2, hi addition, they are connected in series with respective gas arresters 41, respective groups of varistors 42-1 to 42-5 connected in parallel with each other, and respective resistors 43. This makes it possible to reliably protect the target device 33 from direct lightning strikes and prevent the fuses 34-1 and 34-2 installed in front of or behind the SPDs 40(40-1 and 40-2) from tripping, which also makes it possible to extend the product life compared to the conventional SPDs 10(10-1 and 10-2). Furthermore, the relatively simple circuit structure makes it possible to provide a small, reliable, inexpensive product. Also, since JIS (Japanese Industrial Standard) has adopted measures against direct lightning strikes to comply with IEC standards, SPD40(40-1 and 40-2) can replace conventional SPD10(10-1 and 10-2).

(variants)

The present invention is not limited to the above embodiments, and various applications and modifications are possible. Such applications and modifications include, for example, (a) to (d) below.

(a) The overall structure of the surge protection device in fig. 13 may be changed to another circuit structure.

(b) The configuration of SPD40(40-1 and 40-2) in fig. 13 may be used for surge protection devices other than the device in fig. 13.

(c) The number of varistors per SPD40(40-1 or 40-2) in fig. 13 may be different from five (42-1 to 42-5).

(d) Other circuit interrupting devices (e.g., circuit breakers or various circuit breakers) may be used in place of the fuses 34-1 and 34-2 of fig. 13.

Claims (5)

1. A surge protection device for a power supply, which is arranged in a front section of another surge protection device for protecting a target apparatus from an indirect lightning strike, and is connected to a power supply side of a line, protecting the target apparatus operating with an alternating power supply voltage supplied from the power supply side of the line from a direct lightning strike applied to the target apparatus, comprising:

a gas arrester for applying an alternating-current power supply voltage;

a varistor group connected in series with the gas arrester and including a plurality of varistors having a high withstand capacity, wherein the varistors are connected in parallel with each other, and each varistor has a varistor voltage set higher than a peak value of an alternating-current power supply voltage; and

a resistor connected between two electrodes of the resistor bank, discharging charges stored in a capacitance of the resistor bank,

wherein the surge protection device for the power supply operates at a voltage that is less than the voltage of the other surge protection device.

2. The surge protection device of claim 1 wherein the gas arrester uses an inert gas.

3. A surge protection device comprising:

a breaking device arranged in a front section of another surge protection device for protecting a target apparatus from an indirect lightning strike, and connected to a power supply side of a line, the target apparatus operating at an alternating power supply voltage supplied from the power supply side of the line being protected from an abnormal voltage applied to the target apparatus by blocking the abnormal voltage due to the direct lightning strike or the indirect lightning strike; and

a surge protection device for a power supply, connected in series with the circuit breaking device, protecting the target equipment from the direct lightning strike,

wherein this surge protection device for power includes:

a gas arrester for applying an alternating-current power supply voltage;

a varistor group connected in series with the gas arrester and including a plurality of varistors having a high withstand capacity, wherein the varistors are connected in parallel with each other, and each varistor has a varistor voltage set higher than a peak value of an alternating-current power supply voltage; and

a resistor connected between two electrodes of the resistor bank, discharging charges stored in a capacitance of the resistor bank,

and the surge protection device for the power supply further operates at a voltage less than the voltage of the other surge protection device.

4. The surge protection device of claim 3 wherein the gas arrester uses an inert gas.

5. A surge protection device according to claim 3 or 4, wherein the breaking means is a fuse or a circuit breaker.