1-what is earthing systems
Electric vehicles are needed in some parts of the device that has the potential to be one with the earth, the ground is used for this purpose. It is a large land mass on earth as zero-electricity, especially in engineering and all parts of the ground is considered a ground potential are connected, in other words their potential ground zero.
2-types of earthing system
Electrical installations there are two types of land: 1-ground protection2-ground electric
2-1-protection earthing system
Land protection is to ground the metal parts of electrical installations that are not in direct contact with the electrical circuit. The land of the people, especially to protect against high contact voltage is applied.
2-2-electrical earthing system
Earth's electric field to the point of electrical appliances and electrical devices that are part of the electrical circuit. Like the star center of the transformer or generator windings or the middle of the wire or wire between the two constant flow generator series. Grounding of electrical devices for correct operation and prevent the proliferation of devices Fsharalktryky healthy phase toward the ground at the time of contact with the ground is one of the phases.
3-low voltage earthing system
Low-voltage distribution networks, electrical power distribution between the categories is a wide range of end users, the most important concern in the design of grounding system security is a good use of electric appliances used to keep him safe from electric shocks. The system should be designed to ensure that the consumer never a metal object that the electrical potential of the person over potential security threshold (usually about 50 V) is not back.
International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT. The first letter indicates the connection between earth and the power-supply equipment (generator or transformer): "T" — Direct connection of a point with earth (Latin: terra) "I" — No point is connected with earth (isolation), except perhaps via a high impedance. The second letter indicates the connection between earth and the electrical device being supplied: "T" — Direct connection of a point with earth "N" — Direct connection to neutral at the origin of installation, which is connected to the earth
In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer. The conductor that connects the exposed metallic parts of the consumer's electrical installation is called protective earth (PE; see also: Ground). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:
5-1- TN−S network
PE and N are separate conductors that are connected together only near the power source. This arrangement is a current standard for most residential and industrial electric systems particularly in Europe
5-2- TN−C network
A combined PEN conductor fulfils the functions of both a PE and an N conductor.
5-3- TN−C−S network
Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, and separated in the service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of electric shock in the event of a broken PEN conductor - with a similar system in Australia and New Zealand being designated as multiple earthed neutral (MEN).
In a TT (Terra-Terra) earthing system, the protective earth connection for the consumer is provided by a local earth electrode, and there is another independently installed at the generator. There is no 'earth wire' between the two. The fault impedance is higher, and unless the electrode impedance is very low indeed, a TT installation should always have an RCD as its first isolator. The big advantage of the TT earthing system is that it is clear of high and low frequency noises that come through the neutral wire from connected equipment. TT has always been preferable for special applications like telecommunication sites that benefit from the interference-free earthing. Also, TT does not have the risk of a broken neutral.In pre-RCD era, the TT earthing system was unattractive for general use because of its worse capability of accepting high currents in case of a live-to-PE short circuit (in comparison with TN systems). But as residual current devices mitigate this disadvantage, the TT earthing system becomes attractive for premises where all AC power circuits are RCD-protected.
7- IT Networks
In an IT network, the electrical distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems, an insulation monitoring device is used to monitor the impedance.
9-Compare earthing systems
System TN-CS: is the most widely used system. In the UK the system (protective multiple earthing (PME and in Australia and New Zealand (multiple earthed neutral (MEN refers. System TN-S: is used mostly in Eastern Europe.System TN-C: rarely used. System TT: Because this is an off-grid system is used to provide protection for networks containing several electronic devices that generate a lot of static on the conductor Khtsa been considered. Japan is a post-industrial country, but the island is so not like other countries in the peak hours of electrical energy exchange with its neighbors, and electricity is expensive, so the energy storage devices for peak hours is high and dangerous noise emission devices that, so the system has been Japan's favorite TT. It is recommended that the use of residual-current device. System IT: The main use of operating rooms in hospitals and in particular the first and second probability is very low Electrocution phase connected to ground conductor, not a personnel Electrocution and not jump fuse. But it is necessary in case of a connection, turn on the lights on the insulation monitoring device to troubleshoot electrical repairman later action.
11-Some additional tips
A few points that should be considered: 1. TN-C system should switch, neutral conductor also cut because the cut card and thus protect disappears. The keys are single-phase and three-phase two bridges should not result in any of the four bridges.2. In the TN-S system it is possible. Particularly if the consumer because of the possibility of third harmonic currents in neutral, the selection keys cut with recommended neutral. 3. The standard against distributing the neutral in IT systems. If the null distribution should be for each circuit, neutral, direct and protection in case of fault on the part of all conductors (phase and neutral) disconnected. 4-in systems TN-C neutral conductor voltage can cause Khtart life. For the neutral conductor and earth is one and the voltage on the neutral conductor cause the body moves. Therefore, a cross section of a minimum standard for TN-C system neutral recommendation that it reduce the likelihood of unplanned outages. 5. In general, conservation or cutting Knoll is directly related to the distribution of neutral and earth. If the neutral point is greater than or equal to phase current is no need to detect and install the key is not in neutral. This can be done only when the possibility of harmonic currents and power give neutral.