CN1077734C

CN1077734C - New lightning-protection method for distribution transformer and low-voltage power network

Info

Publication number: CN1077734C
Application number: CN96119128A
Authority: CN
Inventors: 徐毅军
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-16
Filing date: 1996-08-16
Publication date: 2002-01-09
Anticipated expiration: 2016-08-16
Also published as: CN1174437A

Abstract

The present invention relates to a new lightning protection method for a distribution transformer and a low voltage power network. Aiming at the defect that a current distribution transformer, a three-point common grounding transformer and low voltage electric equipment are easy to suffer from lightning strike damage, the present invention proposes that a transformer casing and a neutral point of a low voltage winding are connected and are grounded near the transformer, and a lightning protector on a high voltage side is grounded at another position; the distance between grounding ends of two grounding wires is 2 to 10 meters, and when the two grounding wires need connecting in the ground, electrical distance between grounding points of head ends of the two grounding wires is controlled between 15 to 100 meters. The present invention has the advantages of good lightning protection effect, simple wiring, easy implementation and low cost.

Description

A kind of new distribution transformer and low-voltage power network lightning-protection method

The present invention relates to a kind of distribution transformer and low pressure 380/220V supply network lightning-protection method.

All the time, the lightning protection of distribution transformer adopts the mode of high pressure lightning protection earthing end and low pressure winding neutral point and 3 common grounds of transformer case.But the lightning protection effect of this lightning protection mode of connection is very poor.The distribution transformer year spoilage whole nation of being struck by lightning is average about 1% according to statistics, and area with more lightning activities can be up to more than 10%, and the spoilage of low voltage equipment is also very high, annually causes direct economic loss more than several hundred million units to country.Its indirect economic loss is then more huge.

(patent No.: 92114541.1) earth terminal with the on high-tension side lightning arrester of distribution transformer is connected on the earth electrode 1 at transformer place " a kind of distribution transformer and the low-voltage power network lightning-protection method " that the inventor proposed in 1992; and low pressure winding neutral point, zero line are connected with transformer case; be attempted by from becoming on 10～40 meters earth electrodes 2 of device; because earth electrode 2 is far away from transformer; unfavorable at transformer case because of the serious voltage protection that occurs when asymmetric of low-voltage equipment or line fault and three-phase load, historical facts or anecdotes border poor operability.

The purpose of this invention is to provide a kind of new distribution transformer and low-voltage power network lightning protection mode, its lightning protection effect is good, and wiring is simple, and required expense is lower, easily implements at the scene.

Concrete grammar of the present invention is: establish two earth electrodes near transformer, the earth terminal of the on high-tension side three-phase lightning protector of distribution transformer is connected on the earth electrode 1; The shell of transformer is connected with neutral point, the zero line of low pressure winding, is attempted by on the earth electrode 2.

To the grounding resistance of earth electrode 1 by former rules requirement.Require to reach more than 25 ohm in 1 microsecond of the impulse earthed resistance of new earth electrode after lightning wave arrives.

Two earth electrodes are gone into distance between the place for general geology soil, be advisable with 2～10 meters, for the soil resistivity condition with higher, two earth electrodes suitable position in ground can be connected for reducing power frequency earthing resistance, generally require two earth electrode head ends to go into the electrical distance in place between 15 meters～100 meters.Do the time spent at lightning impulse voltage like this, can make that the lightning wave that is delivered to low-pressure side decays to the value that is allowed.

Below in conjunction with drawings and Examples principle of the present invention is done simple the description.

Fig. 1 is conventional at present lightning protection winding diagram;

Fig. 2 is the inventor proposed No. 92114541.1 patents of invention in 1992 a lightning protection winding diagram.

Fig. 3 is a lightning protection winding diagram of the present invention.

Conventional lightning protection winding diagram shown in Figure 1; adopt the earth terminal of high-voltage arrester; the mode of transformer case and 3 common grounds of low pressure neutral point; at high pressure or low when being pressed with lightning surge intrusion; because the wave head time of the lightning wave on the distribution network, the ground connection impulse resistance can reach higher value mostly less than 2 microseconds.Surge voltage on the earth resistance is also higher, and consequent inverse transformation overvoltage can surpass distribution transformer withstand voltage several times, so distribution transformer very easily damages.Only need go into the ground lightning current greater than 500 amperes to the 10KV distribution transformer, distribution transformer is burnt.So merely reduce power frequency earthing resistance, damage poor effect because of thunderbolt to preventing distribution transformer.

Because a shared earth electrode, on high-tension side lightning wave also can be delivered to secondary network by earth electrode, and this is the main cause that causes the low voltage equipment thunderbolt to damage.

Low voltage surge arrester reduces the direct transform overvoltage, but very little to the effect of inverse transformation overvoltage.Mainly be when t＜1 microsecond, its weber discharge curve can't with transformer weber fine cooperation of discharge curve.When the lightning surge intrusion of high-pressure side, overvoltage is added on the low voltage surge arrester by earth electrode, and this also makes the protective effect of lightning arrester reduce.Theoretical Calculation and test show that earth resistance is high more, and the direct transform overvoltage of generation is just lower.

Described No. 92114541.1 patents of Fig. 2; the earth terminal of the on high-tension side lightning arrester of distribution transformer is connected on the earth electrode 1 at transformer place; and low pressure winding neutral point, zero line are connected with transformer case; be attempted by from becoming on 10～40 meters earth electrodes 2 of device; because earth electrode 2 is far away from transformer; unfavorable at transformer case because of the serious voltage protection that occurs when asymmetric of low-voltage equipment or line fault and three-phase load, historical facts or anecdotes border poor operability.

The present invention has adopted connection plan as shown in Figure 3, and low pressure winding neutral point is connected with transformer case, inserts earth electrode 2 ground at the transformer place.With the earth terminal of high-voltage arrester and transformer case insulation, and contact with soil at the earth electrode that distance earth electrode 2 is gone into 2 meters-10 meters, place.Since the earth to the decay of lightning wave can make the inverse transformation overvoltage be reduced to transformer withstand voltage below because the impulse resistance of earth electrode 2 is higher, so the direct transform overvoltage greatly reduces.So distribution transformer has been played effective protective effect.Simultaneously intrude into low-voltage circuit along zero line, prevented that the thunderbolt of low-voltage equipment from damaging owing to prevented the lightning voltage ripple that the high-pressure side is invaded to the earth electrode 1.

Connection plan of the present invention is in Zhanjiang, 4 counties in two areas, Maoming, city, the enforcement of area with more lightning activities; 2000 have been accumulated; operating experience more than year; to at present for extremely; its thunderbolt spoilage is zero; and the distribution transformer that adopts original lightning-protection method the thunderbolt year of this area spoilage be more than 5%, the highest town can reach more than 16%, operation result shows that lightning protection effect of the present invention is quite desirable.Secondly, two earth electrodes of the present invention all are located at the transformer next door, avoided the low-pressure end three-phase load serious when asymmetric since ground connection far to be directed at the transformer case contact potential too high, and workable during enforcement.

Claims

1, a kind of new distribution transformer and low-voltage power network lightning-protection method; comprise and be provided with two earth electrodes (1 and 2); the earth terminal of high-voltage arrester is connected on to be located on the other earth electrode 1 of transformer; transformer case is connected with neutral point, the zero line of low pressure winding and is connected on the earth electrode 2; it is characterized in that: earth electrode 2 also is located at by the transformer, and earth electrode 2 is 2～10 meters with the distance of earth electrode 1 to general soil.

2, a kind of new distribution transformer according to claim 1 and low-voltage power network lightning-protection method is characterized in that; Two earth electrodes (1 and 2) can be connected in ground, the electrical distance of this connector is 15～100 meters.