CA2008172C - Compound lightning arrester for low voltage circuits - Google Patents

Abstract

A compound low voltage lightning arrester assembled in one unit by connecting in parallel a semiconductor lightning arrester element and a spark gap is proposed in order to secure the co-operation of said semiconductor lightning arrester element and spark gap by inserting a non-inductive resister in series connection into part of the connecting line of said semiconductor lightning arrester element.

Description

- ~nnsl72 The present invention relates to a compound lightning arrester for low voltage circuits.
Automation is now extensively used in plants, laboratories, offices, hospitals, sporting facilities and agricultural facilities. Much electronic equipment related to it is widely used. These devices are vulnerable to the surge voltages from lightning.
Surge voltages will invade the devices from the side of the circuits, such as signal circuit, and from the power source. Lightning arrester counter measures are thus needed at both of these sides. Some of the above facilities may be located in regions of heavy lightning and, furthermore, when they are sited in mountainous regions, dry river beds or sand dunes, the earth resistivity of their site is much higher. Consequently the lightning currents will not immediately dissipate into the ground and further be transmitted through adjacent electric lines to propagate extensively, which results in greater damage.
On the other hand, unmanned facilities will increase with the spread of automation. Automation will thus require the dispatch of maintenance personnel from distant places when troubles occur in the lightning arresters. Accordingly the future demand for lightning arresters is a steadily increasing trend and an improved lightning arrester is strongly desired from the stand point of easier maintenance and reduced control costs which withstands considerably greater energy than the prior art and not only protects the zn~sl72 device from repeated heavy lightning surges but also prevents burning in the lightning arrester itself.
A lightning arrester for high sensitivity low voltage circuits in accordance with the present invention has been proposed for the above-mentioned purpose, and has extensive applications in various fields.
The prior art arresters may be classified into seven major types as follows:
l. Spark gap 2. Gas discharge tube lightning arrester element 3. Semiconductor lightning arrester element 4. Serial circuit of ~2) and (3) 5. Parallel circuit of (2) and (3) 6. Serial circuit of (1) and (3) 7. Parallel circuit of (l) and (3) Type (1) can easily withstand the lightning surges arising from multiple lightning strokes and continuous discharges, and the greater energy of adjacent thunderbolts.
However, (1) has the disadvantage of response time delays in starting its operations.
Type (2), can provide small electrostatic capacities and relatively large current carrying capacities but the weak point is that when used in a power source circuit the dynamic current arising from the power source voltage cannot be cut off immediately after the electric discharge.
A lightning arrester of type (3) has a high sensitivity in response to lightning surges. However, when voltages greatly exceeding the discharge voltage are applied 2f~ 81 7 2 `

frequently or for a relatively long time, the deterioration of the element may take place and reduction in the operation starting voltages. A short circuit may result from the impressed voltage of the circuit which can lead to fire if the circuit power source is not cut off. The type ~2) with a larger surge withstand current rating has a large electrostatic capacity and large volume, and is unsuited for indoor use.
Type (4) has no sensitivity for dynamic current even when used in a power source circuit, and has a small electrostatic capacity. This does not prevent function of protected equipment but there remains a problem that on a lightning surge by continuous discharges, when current flows for a long time, or in cases of a lightning charge of multiple lightning strokes burning may occur because of insufficient energy resistance current rating.
Type (5) has a high sensitivity and relatively large energy to withstand current rating if an appropriate combination is found. However a disadvantage is that its dynamic current cannot be cut off in a power source circuit, and it has no guarantee of withstanding surges of multiple lightning strokes when used in an electronic circuit.
Type (6), though it is unaffected by dynamic currents when used in a power source circuit, results in prevention of sensitivity of semiconductors because of the presence of a spark gap, and at present rarely finds application.
Type (7) has elements of different properties connected in parallel which corrects the disadvantage of each of them.

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A considerable effect can be expected when a proper combination has been obtained. A simple connection of two elements in parallel, however, disperses the operation starting voltages of spark gaps even if the discharge voltage of its lightning arrester element and the operation starting voltage coincided. Further the properties of the semiconductor lightning arrester are complicated, for example, some degree of dispersions is found in the element properties. For these reasons r it is not always easy to obtain co-operation between the operations of the two components which leads to manufacturing difficulties in mass production.
In addition, a discharge maintaining voltage (Vd) appears across the spark gap after the current has been commutated to the spark gap. The voltage value is remarkably smaller than the discharge starting voltage (Vs) of the spark gap and is much lower than the discharge voltage (Vo) of the surge absorber. Therefore the load on the surge absorber is sharply decreased, and there exists no mechanism to control this or the resulting deterioration of the surge absorber.
In a case where a lightning surge is commutated from a semiconductor lightning arrester element (hereinafter called a surge absorber) to a spark gap, it is not only important to achieve the co-operation between the operation startin~
voltage and maximum discharge voltage in both of the surge absorber and spark gap, but also it is necessary to consider that the joule withstand current capacity is not exceeded until the spark gap starts to function. A surge absorber is Z~ 817Z
-essentially a resistor with a resistance varying with its current magnitude and furthermore has dispersions in the properties of the spark gap and the element used.
Consequently it is extremely difficult to achieve operational co-operation in mass production. The resulting products have often had thermal breakdowns in the surge absorbers before the spark gaps starts to function.
In combinations of a gas discharge tube lightning arrester element (hereinafter called a gas discharge tube) the internal resistance becomes extremely small when the gas discharge tube is functioning, which provides difficulties.
The present invention is directed to a high performance low voltage lightning arrester which connects in parallel to form a unit a surge absorber and spark electrodes whose discharge starting voltage coincides fully or approximately with the upper limit value of the discharge voltages of the surge absorber, and has a non-inductive resistor inserted in series with the surge absorber which resistor has a resistance value more than or equivalent to the value given by dividing the difference between the discharge starting voltage of the spark gap and the discharge voltage of the surge absorber with a current ~I) equivalent to the surge withstand current rating of the surge absorber. The invention further has a joule withstand current rating more than the value calculated considering a current (I) equivalent to the surge withstand current rating of the surge absorber.

2~08 172 ~
-Accordingly, in a first aspect, the present invention is a lightning arrester for protecting low voltage electrical apparatus from high energy electrical surges caused by lightning comprising:
a single housing;
a zinc oxide arrester and a spark gap connected in parallel;
a non-inductive resistor connected in series with said zinc oxide arrester to secure cooperation between said zinc oxide arrester and said spark gap;
said zinc oxide arrester, said spark gap and said non-inductive resistor being installed in said single housing;
said resistor having a value RA in ohms where:
RA > (VS - V), Io and V~ is the spark voltage of the spark gap, V is the working voltage of the zinc oxide arrester, Io is the maximum allowable peak current of the zinc oxide arrester, and said resistor is a bifilarly or Ayrton-Perry wound Nichrome wire having a current capacity larger than the maximum allowable peak current Io of said zinc oxide arrester.
In a second aspect the invention is an electrical surge protector comprising:
a housing of electrically insulating material, said housing having a first electrically conducting terminal and a second electrically conducting terminal;

200~ ~72 - 6a -a spark gap disposed in said housing and connected between said first terminal and said second terminal for receiving full voltage of an electrical surge;
arrester means and a non-inductive resistor disposed in said housing and connected in series between said first terminal and said second terminal;
wherein said resistor has a value RA in ohms with RA
Io > V~ - Vw wherein V~ is the spark voltage of the spark gap, Vw is the working voltage of the arrester means, and Io is the maximum allowable peak current of the arrester means; and said resistor is a bifilarly or Ayrton-Perry wound Nichrome wire having a current capacity larger than the maximum allowable peak current Io of said zinc oxide arrester, said non-inductive resistor inhibiting an increase of the working voltage for an assured discharge of the spark gap.

The drawings show an embodiment of the compound lightning arrester for low voltage circuit in accordance with the present invention. In the drawings:
Fig. 1 is a drawing of connection diagram, Fig. 2 is a front view of the lightning arrester above-mentioned whose cover is opened, Fig. 3 is a partial central sectional side view with the cover closed, Fig. 4 is a perspective view of a metal pivot piece and a metal connector piece, æ

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6b Fig. 5 is a partial sectional perspective view of a spark gap, Fig. 6 is an example of the circuit diagram of a lightning arrester of the present invention, , , 2(~8172 ....

Fig. 7 (a) and (b) are perspective views of major components of a non-inductive resister and others, and Fig. 8 (A), (B) and (C) are operational drawings.
Fig. 2 shows the lightning arrester with its cover opened, and an approximately cylindrical receptacle 1 has an upright rim 2 on its circumference. It is provided with partition plates 3 and 4 in its inside and also with reinforcements 5 and 6 to form recessed chambers 7 at 4 places. The receptacle is made of thermal insulation porcelain. The recessed chambers 7 has 2 pairs of oppositely facing contact pieces 8 and 9 standing upright. The oppositely facing contact pieces 8 and 8 are connected to a bar 81 disposed on the backside of the receptacle 1. These oppositely facing contact pieces 8 and 8 are for grounding.
Cut slots 10 for wiring are provided at the top and bottom in the drawing of the upright rim 2, and furthermore mounting holes 11 to a wall are provided in the receptacle 1.
A concave groove 12 is provided at the inside bottom of the receptacle 1, and a metal pivot piece 13 is disposed in the concave groove. The metal pivot piece 13 has bearing arms 14 bent to stand erect at the left and right sides on which bearing arms are provided bearing holes 15.
The numeral 20 denotes a porcelain cover to close the receptacle 1 and provided with a flat rim 21 to for~ a convex surface 22, which is also provided with two pairs of claws, acting as electrodes, standing erect and facing oppositely with and being fitted into said oppositely facing contact pieces 8 and 9. Between the above-mentioned claws 23 and 24 - 2~8~72-are provided grooves 25 to form clearance spaces, and extensions 26 and 27 of the claws 23 and 24 are disposed to face each other and form spark gaps 28. The extensions 26 and 27 are bent at a right angle at their tip and provide pending pieces 29 and 30 inserted along the grooves 25. To these spark gaps 28 are connected in parallel elements 31 and 32 such as surge absorbers and others. The elements 31 and 32 are connected respectively to the claw 23 and 24 with lead wires 35, and are disposed at the center on the back of the cover 20. To save spaces, two pieces of the elements 31 and 32 are stacked one on the other with an insulator 36, such as mica, between the two elements. The stacked pieces of elements 31 and 32 are secured to the cover with a band 38 fixed at its both end by nuts 37. On the cover in the intermediate parts of the lead wires for the elements 31 and 32, non-inductive resister 51 and 52 are inserted in serles .
A concave groove 40 is provided at the top of the cover 20 to secure the metal connector piece 41 on it.
The metal connector piece 41 is provided at its ends with protruding tips 42 to be inserted for connection into the bearing holes 15 of the above-mentioned metal pivot piece 13, and further with a relief 43 under the one protruding tip 42 so as to be easily detached from and attached to the bearing holes 15. A spring 44 is provided onto the protruding tip 42.

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-- 8a -When the protruding tips 42 have been inserted into the bearing holes 15, the cover 20 is connected to the receptacle 2nû8 172 ~;

g 1 so that the cover 20 and receptacle 1 may be free to open and close.
By moving to the left the metal connector piece 41 5 so shown in the drawing and by drawing out the protruding tip 42, the piece 41 is easily detached.
A peep hole 45 so formed as to have a diverging mouth is provided by boring through the centre of the cover 20.
An irreversible thermo-label 46 can be seen through the peep hole 45 of the cover 20. The thermo-label 46 is applied on the surface of the elements 31 and 32, and at least the one of them is applied to the inner element 31 so as to be seen through the peep hole 45. The other one 15 is applied on the element 32 so as to be seen on opening the cover.
The thermo-label 46, sensing heating within the lightning arrester, changes its color, for example from white to red, and from this change the condition within 20 can be observed by viewing from the outside. A compound low voltage lightning arrest of such a structure has a power source side L and earth side E constituting a circuit, as shown in Fig. 6, which disconnects or connects a switch S respectively by the cover opened or 25 closed.
The major resistor is a non-inductive resistor with a large current capacity, and can be made by using Nichrome (trade mark) wire and others as resistance wire, and by applying Bi-filer winding as shown in Fig. 7(a) or 20a8 1 72 ~
-- 9a -the Ayrton Perry winding method where one of the two lines of resistance wires is wound clockwise and the other counterclockwise as shown in Fig. 7(b).

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Z~)~8~72 A surge absorber, though it behaves as if it were a good insulator below its response voltage, can be considered for the current above that voltage as a non-linear resistor whose resistance increases proportionally to 15 - 30 powers of the voltage. Therefore, it has a fast response speed for impulse voltages; delay hardly occurs. An over-voltage arising from ignition delay which is unavoidable in spark electrodes can be excluded by connecting an appropriate surge absorber to spark electrodes, in parallel, and further by approximately coinciding the maximum value of discharge voltages of the surge absorber to the discharge starting voltage of the spark gap. However, just before its breakdown in the vicinity of the maximum discharge voltage of the surge absorber and the value of its internal resistance the element is unstable.
Further dispersions exist in the characteristics of such elements and spark gaps. Therefore, it is practically difficult in mass-production to cause each element to co-operate without any breakdown.
However, these disadvantages can be corrected by connecting in parallel a surge absorber and non-inductive resistor with the above-mentioned characteristics.
Fig. 1 shows a compound low voltage lightning arrester connecting in parallel a spark gap ~G~ and a serial circuit of surge absorber ~A) and an non-inductive resistor ~R).
When a surge absorber and a spark gap are compared, the surge absorber, though sensitive, is small in its energy withstand rating while the spark gap, though insensitive, is large in its energy withstand rating. That is both have properties ~n~sl7z contrary to each other. Therefore, the surge absorber comes to a thermal breakdown generally just before the spark electrodes start the discharge. In the absence of the non-inductive resistor or the presence only of the surge absorber, the voltage-current curve becomes non-linear as shown in Fig. 8(A); and, therefore, when, for example, the operation starting voltage (Vs) is located at the position shown by the broken line (b), the action of the spark gap occurs at the point (Px) just before the joule withstand rating of the surge absorbers has been exceeded. As a consequence, it is difficult to keep the co-operative actions as mentioned above, or a phenomenon may occur that the surge absorber comes to a thermal breakdown before the start of discharge across the spark gap. When the non-inductive resistor (R) has been connected in series to the surge absorber, the voltage-current curve of the resistor section becomes a line as shown in the fine dotted line (c) with a certain slope irrespective of the waveform of the surge current. When the surge absorber and the resistor are connected in series, the voltage-current curve that results becomes the sum of the potentials of both or is shown as a thicker dotted line (d). Further the energy of the surge is also distributed to the resistor and surge absorber element;
and therefore the current can be commutated from the surge absorber to the spark gap without applying any unreasonable burden on the surge absorber. In this case. the relationship between the spark starting voltage Vs. the resistance of Z~lQ8172 the resister R, the discharge voltage of the surge absorber Vo, and surge withstand current rating I can be expressed as Vs < (R . Ia + Vo) (In this invention, the inductance component of the resistor need not be considered as a non-inductive resistor is used.
Therefore the calculation is simple.~
When a compound low voltage lightning arrester having a wiring as shown in Fig. 1 and further conforming to the above-mentioned calculation formula, with a non-inductive resistor of a prescribed value (bi-filer winding) is connected to the lightning arrester, the commutation from the surge absorber to the spark gap is transferred from Px to Py or into the safety zone as shown in Fig. 8~A). Therefore, even when high energy lightning surge may invade the arrester repeatedly, the first step or the surge absorber will not come to a breakdown, and, as a result, the arrester can protect the object of protection moreover without any concern for the breakdown of itself.
The reason why a non-inductive resistor is used in this case is as follows: First while the serial connection of the resistor makes the flat section of the curves smaller, as can be seen from the comparison of both curves (a) and ~b) in Fig. 8tA) (which is an undesirable tendency when viewed simply as a lightning arrester as it causes an increase in its discharge voltage) the purpose of the present invention is to emphasize the advantage of making secure the discharge at the spark gap. Therefore, excessive inductance components included in the resistor are avoided, and thus the operation znos~7z as a lightning arrester is unaffected to the maximum possible extent. Secondly the inductance increases especially in a wire wound resistor because of sharp rise in surge currents.
On the other hand, a smaller size is desired for a component of a lightning arrester, though a large diameter and length of resistance wire will provide a resistor of a large current capacity. Therefore, a wire wound resistor must be selected in a lightning arrester, and thus, a wire wound resistor, though non-inductive one (that is with bi-filer winding) is required for the invention.
By the above structure, a secure commutation is realized from the surge absorber to the spark gap. Since a spark electrode with a large current withstand rating can be easily designed, the surge absorber can be prevented from burning by overloading in cases of a considerable large surge current or multiple lightning strokes only if the surge absorber has a joule withstand rating sufficient for a short active time just before the spark electrodes ignition.
In a similar manner, a combination of a gas discharge tube and a spark gap can commutate a lightning surge to the spark gap without any burning of the gas discharge tube only if a resister of the above-mentioned properties is connected to the gas discharge tube. For reference, an embodiment will be described below to clarify an aspect of the effectiveness accomplished by connecting a resistance (R) to the absorber.
In Fig. 8(B), assuming (a) to be the characteristics of a surge absorber, the commutation at the point P, to a spark gap is desired. If the point P, of the commutation was z~08~7Z

transferred to the point P2, the surge absorber would be overloaded and result in deterioration.
On the other hand, since the discharge starting voltages (Vs~ of spark gaps have essentially some dispersion, (V's) may results, and then the commutation will occur at the point P2, which will lead to the above-mentioned trouble. Absorber elements have similar dispersions, and this may be considered to be a relative problem. The dispersion of the spark gap only may be assumed for explanation purpose.
A case where a resistance (R) is used is shown as Fig. 8 C. When the starting voltage (Vs) of the gap is increased to V's due to its dispersion, the discharge starting point of the spark gap will move to the point P2, which corresponds to the point P2, on the characteristic curve (a). Thus the quantity of overloading (P2 - Pl) will be outstandingly reduced compared to the one in Fig. 8(B).
A compound low voltage lightning arrester of the invention where its spark gap has been deliberately adjusted, and its surge absorber and (A) ( or gas discharge tube (B) ) and non-inductive resistor are connected in series, from the reasons heretofore detailed, can be operated more sensitively than a case where the respective lightning elements are used separately or in a known apparatus. The arrester can therefore prevent even with multiple lightning strokes, since the lightning arrester of the invention will not be damaged by burning even for invasions of considerable high surge voltages.

Z~ 8172 _ In most cases of general multiple lightning strokes r the first stroke gives breakdowns to lightning arresters and the second stroke brings forth the damage to subjects of protection.
While lightning arresters are steadily increasing in numbers and their damages by lightning strokes have been considered inevitable according to prior design philosophies, provided that the subject of their protection has been protected, this incurs much labor for maintenance, is not economical. The lightning arrester of the invention therefore can offer an outstanding contribution to labor saving.

Claims (5)

1. A lightning arrester for protecting low voltage electrical apparatus from high energy electrical surges caused by lightning comprising:
a single housing;
a zinc oxide arrester;
a non-inductive resistor connected in series with said zinc oxide arrester;
a single spark gap for receiving full voltage of the electrical surges, said spark gap being connected in parallel with said series circuit of arrester and resistor to secure cooperation between said zinc oxide arrester and said spark gap;
said zinc oxide arrester, said spark gap and said non-inductive resistor being installed in said single housing;
said resistor having a value RA in ohms where:

RA , and Vs is the spark voltage of the spark gap, V is the working voltage of the zinc oxide arrester, Io is the maximum allowable peak current of the zinc oxide arrester, and said resistor is a bifilarly or Ayrton-Perry wound Nichrome wire having a current capacity larger than the maximum allowable peak current Io of said zinc oxide arrester, said non-inductive resistor inhibiting an increase of the working voltage for an assured discharge of the spark gap.

2. The lightning arrester as claimed in claim 1 wherein said single housing is made of porcelain.

3. An electrical surge protector comprising:

a housing of electrically insulating material, said housing having a first electrically conducting terminal and a second electrically conducting terminal;
a spark gap disposed in said housing and connected between said first terminal and said second terminal for receiving full voltage of an electrical surge;
arrester means and a non-inductive resistor disposed in said housing and connected in series between said first terminal and said second terminal;
wherein said resistor has a value RA in ohms with RA IO VS - VW wherein VS is the spark voltage of the spark gap, VW is the working voltage of the arrester means, and IO is the maximum allowable peak current of the arrester means; and said resistor is a bifilarly or Ayrton-Perry wound Nichrome wire having a current capacity larger than the maximum allowable peak current IO of said zinc oxide arrester, said non-inductive resistor inhibiting an increase of the working voltage for an assured discharge of the spark gap.

4. A surge protector according to claim 3 wherein said arrester means is a zinc oxide arrester.

5. A surge protector according to claim 3 wherein said arrester means is a gas discharge tube.