WO2005112056A1

WO2005112056A1 - A method and an equipment for reducing stray currents in the earthing systems of houses and buildings

Info

Publication number: WO2005112056A1
Application number: PCT/IS2005/000012
Authority: WO
Inventors: Saevar Baldursson
Original assignee: Rafal Ehf.,
Priority date: 2004-05-17
Filing date: 2005-05-17
Publication date: 2005-11-24
Also published as: IS7269A

Abstract

The invention relates to a method and an equipment for keeping electrical currents in a neutral point connected electrical distribution systems, where the earth connected neutral points are in the main switch boards and/or in the distribution boards in as much equilibrium as possible between the phase conductor and the neutral conductor. The invention mostly prevents other currents than short-circuit currents to flow through earthing conductors of houses and buildings. The method consists of placing equipment (1), which is electrical coil (3) wound on iron core, between neutral busbar N (11) and earth busbar PE (12) in main switchboard and/or distribution switchboards of buildings and houses instead of the N-PE-connection. Equipment (1) consists of El-iron core (2), plastic socket (4) and insulated wire (3). The wire is wound around the plastic socket (4), which is again placed around the middle part of the iron core and thus creating a coil (13). The coil makes sufficient impedance to prevent undesired current to flow from the neutral point connection to the earth system.

Description

A METHOD AND AN EQUIPMENT FOR REDUCING STRAY CURRENTS IN THE EARTHING SYSTEMS OF HOUSES AND BUILDINGS.

The invention relates to a method and an equipment for keeping electrical currents in neutral point connected electrical distribution systems, where the earth connected neutral points are in the main switch boards and/or in the distribution boards, in as much equilibrium as possible between the phase conductors and the neutral conductor in the supply service cable from the electrical distribution net in question. In this way it is possible to minimize the so called "stray current" i.e. to prevent that other currents than short-circuit currents flow through the earthing conductors and the earthing systems of houses and buildings.

BACKGROUND ART In the neutral point of an electrical distribution net, where the neutral points are in the main switch board and/or in the distribution boards, it has been a permanent problem that only a part of the current in the phase conductor goes through the neutral conductor in the supply service cable (30%). The rest of the current, up to 70%, goes through the earth conductor and equlpotential system. Such currents (stray currents) create undesired magnetic effects causing corrosion in pipes and difficulties when using gauges and computers. In recent years these stray currents have called for increased attention. They flow through heating- and tapwater-systems of houses and buildings, creating problems that have proven to be hard to solve. The reason is the voluminous equipment to minin ize stray currents and the considerable amount of costs for the solutions that have been tried so far.

The following solutions are known in this respect: Interphase transformers. Electrical main cable is placed through an iron core, called interphase transformer. The interphase transformer is mounted around the main cables in distribution stations and does therefore not work for small service cables that most often are connected from so called "street cubicle" from where branches to individual users occurs. The interphase transformer is voluminous and its installation is very expensive.

Insulation transformer: 1:1 Dyn. The supply service line is connected to a primary winding of a special insulation transformer at the customer's house and the customer's distribution net to the secondary winding. Such a transformer takes up space, is very expensive and its efficiency coefficient is unpractical. Besides, it does not completely solve the problem in question. Electrical system neutral point connection installed in the distribution station and supply service (5 wires) cable to the customer. This refers to new electrical net installations, but power companies have not yet taken decision about this solution. Changing from the current system to this solution causes disturbance and is costly, both in apartments and at the distributing stations.

Special electrodes. Special earthing electrodes have been installed for each house and the neutral point system disconnected. This is obviously a difficult solution in densely populated areas with short distances between houses. For this to be possible it is necessary to rewire the main board and/or the distribution board. A connection to special earthing electrodes causes earth dislocation and most of the time considerable cost.

Considering the above, it is clear that a convenient and publicly available solution is far from being available. DISCLOSURE OF THE INVENTION The object of the invention is therefore to set forth a simple and inexpensive method and equipment to reduce stray currents in electrical circuits in houses and constructions. The invention is a unique solution and is unique with the respect to how little installation work is needed and for its low cost.

This object is achieved since the method and the equipment, in accordance with patent claims 1 and 4, are unique in the way that an electrical coil is made, such that an insulated conductor of a fixed length and diameter is wound around an iron core of a fixed size. The coil is placed between the neutral point busbar (N) and the earth busbar (PE) in the respective switchboard instead of the N-PE-connection. There the coil creates sufficient impedance to prevent undesired current through the earthing electrodes of houses and constructions.

This object is also accomplished by that the method is distinct and new according to dependent patent claims 2 and 3. It can therefore truly be said, that the equipment that makes it possible to carry out the method of the invention is distinct in the way that it reduces the current flow through the earth conductor and guides it the correct way through the neutral conductors. The equipment is therefore a kind of a "current guide" which generates reactive resistance, which stray currents cannot overcome. It is also small enough to be, in most cases, installed in the switchboard in question. The equipment is very easily installed and does not affect short-circuit current in the system. The invention is based on knowledge in physics that is now for the first time used for solving a problem that electrical distribution companies have not paid much attention to, but is greater than the representatives of the electrical distribution companies have until now considered it to be. Nowadays there is under development, to use phase conductors in the electrical system of houses for dataflow. Whereas the invention is a current filter between the neutral and the earth it can be expected that systems using the invention have an advantage in using the neutral and even the earth for dataflow in future.

By means of the invention, the following is especially gained:

• The method gives expected result. • Experiments and measurements show that stray currents are considerably reduced or they vanish totally. • Magnetic effects have proven to be reduced or to vanish completely by using the method. • The equipment fits to most of the ordinary switchboards of buildings and houses without any major changes. • The method and equipment are a simple and inexpensive solution to an undesired situation.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained according to drawings were appropriate. Where:

Figure 1 - shows in schematic way (line diagram) arrangement of the equipment/ current guide in a switchboard of a house distribution net; Figure 2-4 - show the main parts of the equipment/ currentguide, unassembled. Figure 5 - shows isometric view of the equipment/ currentguide fully assembled. MODES FOR CARRYING OUT THE INVENTION The Method: The method is, as shown in a schematic way in figure 1, to install equipment between neutral point busbar (N) (11) and earth busbar (PE) (12) in main switch board and/or distribution switch board (-s) of houses and buildings instead of current connection (10) which is simultaneously removed. The method consists also of choosing together a fixed length and diameter of insulated wire (3) and wind it around plastic tube (4) covering the middle part of an El-iron core (2) of fixed size and building in this way an electrical coil (13), which is the main part of the equipment (1). The number of windings in the coil (13) and the size of the iron core (2) determine the impedance and accordingly the current prevented in earth connection. With the saturation of the iron core, the current is not prevented from the earth connection, but that is necessary to maintain the safety of the electrical system.

With this method it can be said that the current is "guided" in the correct conductor through the neutral conductor to the power company's transformer. The equipment (1) plays therefore a role of a kind of a "current guide". The method is supposed to be used in main or distribution boards where protection method according to "RUR 207 Null method" is used.

The table A below shows measurements which have been made and show the magnitude of currents through neutral conductor (14) and earth conductor (15) in a typical domestic electrical installation. First measurements were made without the equipment/current guide (1) and then after the current guide had been installed in the switchboard, according to the method of the invention. Wire according to picture 1, i.e. N-PE- connection (10) was removed and the current guide installed instead by connecting the wires (7, 8) of the coil (13) on the one hand to the neutral point busbar (11) and on the other hand to earth busbar (12). Table A - Currents in supply service cable

Table A shows that about 98,6 % of the current flows now through the neutral conductor but 33 % before.

The equipment: In figures 2-4 the basic parts of a typical equipment or current guide (1) are shown. The current guide consists of El-iron core (2), plastic cylinder (4) and insulated wire (3), which is wound around the plastic tube (4), which surrounds the middle part of an iron core (2). The iron core is made of many iron fins (5, 6) stacked together as many as suitable each time. The wire (3) is enamel coated 15 mm² wire and there are about 8-12 windings in the prototype which form a coil (13), but the number of windings will be determined as suitable for each application. The plastic socket, which has a square cross- section with fastening screw eyes, surrounds the middle arm of the core for keeping the insulated wire (3) from the iron core to prevent the wire to be harmed and also to enable the coil to be wound. Fastenings are screwed to the iron core and the whole equipment dipped into enamel and baked at the temperature of 80°C. The size of the prototype is 95x79x36 mm. Figure 5 is an isometric view of the equipment/current guide (1) fully assembled. The wires (7, 8) are the conductors of the coil, which are to be connected to the neutral busbar (N) (11) and earth busbar (PE) (12) respectively.

Wire (9) is on the other hand for earthing the equipment and is to be connected to the earting busbar in the switchboard.

This design of the equipment (1) creates suitable impedance and allows limited current to flow through until the magnetic flux has gained specific strength (1,7 T). Then the core reaches pervasion and releases unlimited current through.

Experiments show the saturation limit of the iron core, see table B below. When the voltage 1,07 Volts are put over the coil, the current 0,297 Amp. flows through it. Then the resistance is calculated 3,6027 Ohm. When the voltage 3,6 Volts are put over the coil, the current 3,6 Amp. flows through it. Then the resistance is calculated 1,000 Ohm. When the voltage 8 Volts are put over the coil, the current 80 Amp. flows through it. Then the resistance is calculated 0, 1000 Ohm. The results are according to Ohms law: [E = I x Rj, were: E = voltage in Volts, I = current in Amp. and R = resistance in Ohm. In this country the size of the supply service cables from electrical companies to houses and apartments is rated for 63 A main in switchboard. The power made by 63 A current and 230 Volts and one phase is 14,5 kW. The average electrical consumption is between 1 to 7 kW. At maximum load in one phase system with 7 kW consumption, the current through phase conductor is about 30 A. ((P = E x I) (6.900 = 230 x 30)).

In table A above it is shown that when the current in the phase conductor is 30 Amp. the current in the neutral conductor is 9 Amp. and earth conductor 21 Amp. if current guide is not used, i.e. only 30% of the current flows through the neutral conductor. When the current guide has been installed the current through the neutral conductor is nearly the same as through the phase conductor or 29,4 Amp. and only 0,6 Amp. in the earth conductor. Almost all the current flows now the correct way through the neutral conductor in the supply service cable. According to table B below only 2 Volts are over the current guide when the current in the circuit is 0,6 Amp. and the resistance is 3,2 Ohm. When the voltage is E = 3,6 Volts, the current I = 3.6 Amp. and the resistance R = 1,000 Ohm the functionality of the coil comes to a certain turning point. Then the iron core has reached magnetical saturation point and the electric current flows free through the coil and through the earth conductor and through the earth electrode of the house.

Table B - Measured values in coil on the iron core of the currentguide

The invention described is not limited to the above description because it can be implemented in many ways according to individual circumstances. For acceptable results the iron core could be required to be of different dimension and the diameter of wire and number of windings therefore different. Preparation of the invention can change according to circumstances.

Claims

PATENT CLAIMS: 1. Method for keeping an electrical current in a neutral point connected electrical distribution systems, where the earth connected neutral points are in the main switch boards and/or in the distribution boards, in as much equilibrium as possible between the phase conductor (16) and the neutral conductor (14) in the supply service cable from the electrical distribution net in question, where the method is c h a r a c t e r i s e d by choosing simultaneously a certain diameter and certain length of insulated wire (3), and wind it around a plastic socket (4) placed around the middle part of an iron core (2) of a fixed size, making in this way the electrical-coil (3) of an equipment (1), and place the equipment between the neutral point busbar (N) (11) and the earth busbar (PE) (12) in the respective main switchboard and/or distribution switchboards of buildings and houses instead of the N-PE-connection.

2. Method according to claim 1, c h a r a c t e r i s e d by that the connecting wire (7) of the electrical-coil (13) of equipment (1) is connected to the neutral busbar and the connecting wire (8) of the same coil (13) is connected to the earth busbar (12) in the respective main switchboard and/or distribution switchboards of buildings and houses.

3. Method according to claim 1 and 2, c h a r a c t e r i s e d by that the N-PE-connection (10) is removed from the switchboard at the same time the equipment (1) is installed.

4. Equipment for keeping electrical currents in a neutral point connected electrical distribution systems where the earth connected neutral points are in the main switch boards and/ or in the distribution boards of buildings and houses, in as much equilibrium as possible between the phase conductor (16) and the neutral conductor (14) in the supply service cable from the electrical distribution net in question which is c h a r a c t e r i s e d by that the equipment (1) consists mainly of an insulated wire (3) of specific diameter and specific length plastic socket (4) and iron core (2) of specific size where the insulated wire (3) is wound around plastic socket (4), which is placed round the middle part of an iron core (2), where these units make in this way an electrical-coil (13) with connecting wires (7, 8) and earthing connection (9).