Advantages of the third wire system in the building
Because of the many benefits it has, its electrical power is increased every day. Electric power is also in jeopardy. Electricity risks are generally divided into two categories :
1-Danger of fire
2- The risk of electric shock
The risk of electric shock :
In general, electric current passes through the body as electrical shock or electrical shock. If the current passes through the body, the body shows a severe reaction to it. To generate shock, the amount of current and the individual's condition must be sufficient to accept it. The effects of this electric shock start with a shock, so that syncope or complete anesthetic can be achieved .
The intensity of electrocution depends on :
1- Skin body resistance
2- Body skin moisture
3- The passage of electrical current from the body if the flow passes between the two arms, through one of the hands and the left leg, and the patient becomes more harmful due to the placement of the heart in the flow path. .
The electrical voltage (greater than 50 volts) is usually standardized to maximize the alternating current that does not cause any damage to the body at 30 mAh for 20 seconds. .
How and the mode of electric shock :
Electric shock is created in this way :
1- Body contact with both phase and null wires
2- Call a phase and a point of the device with the body
3- Body contact with device where phase current is connected
Electric shock :
Burn: In this case, the edges of the burn area are white, bloodless, dry and without swelling .
Impact on the heart: First, untimely pulses occur, then doubling rhythms up to 8 times the natural beat may result in heart failure, breathing and death. .
Impact on the nervous system: Direct current is equal to the current of the alternating current, causing seizure. And if the direct current exceeds 2.5 amps, it affects the nervous system and increases the chance of shock and paralysis. .
Complications :
1- Cardiac disorders
2- Hearing and visual impairment
3- Nervous system disorders
The Earth Massage System is a simple and inexpensive security and security system that protects our consumer and electrical equipment from scratches. This method of power transfers the body to a ground through a wire (ground wire), so the person does not get electric shock. .
As you know, the current is always passed through the closed path, which has the lowest resistance, and the ground connection means the connection of a conductive object to the ground by a conductor. The connection and connection of the earth are very effective in objects with good conductors, and it should be noted that the conductive connectors and the ground wire of effective and effective ground should have the same strength and corrosion resistance and elasticity. You can also use bare wire or cable to connect the ground .
In different types of electrical networks, parts of the system and the conductor body of electrical devices are grounded and are considered from two perspectives. :
1- Maintaining the insulation and ensuring the work of electrical appliances and devices, and limiting the supply voltage and helping to properly operate the devices and circuits by interrupting the circuits. This kind of earth connection is called electrical connection or earth connection system. (Nortral connection to the ground)
2- Another type of ground connection is the safety or protection ground. This kind of safety system is used to create safety for people who are in contact with electrical equipment as well as for the community who are the ultimate consumer of electrical power. Another purpose of this kind of earth system is to limit the risk of fire through the rapid cut-off of the circuit board by attaching metal bodies to the neutral conductor or the ground. .
In some cases, the separation of two types of ground connections is not possible for the above two purposes, and therefore the creation of a ground connection is sufficient for both purposes. But in some cases, the separation of the two systems of land is necessary and sometimes issues of another kind of earth connection - the land needed to discharge the load of lightning - makes the subject more complicated. .
In general, the purpose of landing is to achieve the following goals :
A) Reduced electrical tension due to keystroke and lightning effects
B) Supply and control of the supply current to an acceptable level
C) Reduce voltage imbalance
D) Limiting null point voltage
The creation of a desirable land system, even up to recent times, is simply meant to have a lower ground-level ground, but with the creation of large-scale power networks, we naturally come in with super-short circuit currents, which despite the low resistance of ground potential systems It may exceed the permissible safety level .
In general, the Earth system should have three major features :
1- The earth system has a small resistance. This causes the impedance of the component to be seen at zero and has a small amount at the junction point, so that the safe and fast performance of the phase fault detection relay is guaranteed to be guaranteed, and the overvoltages generated in normal phases are less than predicted and allowed .
2- The earth system at the junction with a ground-to-earth ground leads to a low wavelength resistance, resulting in a good level of protection for the power supply. The arrester is intended to deplete the wave voltages to the ground, and therefore, wave currents enter the earth through a significant slope and slope. If the earth's wavelength of earth system at the junction of the arrester is large, there will be no full and rapid discharge of wave currents, and a significant wave voltage will appear around the land of the lightning dome, and therefore the burst protection level will increase and damage may be possible. Equipment comes .
3-The earth system should be able to provide the safety of individuals and equipment. The earth system must be designed in such a way as to ensure that the path to the ground is secured to ensure that persons, even if they are in contact with ground equipment, are not exposed to hazardous electrical shock. A person near or in direct contact with various electrical equipment parts will be exposed to electric shock. .
Earth connectivity feature
Earth resistance testing varies depending on its application. Simple earth connection systems, such as single rod electrodes used for distant equipment (transformer motors or conductors of arrester), which are measured for a grounded ground resistance conductor, should be about 10 ohms, and for other cases, a resistance of 10 ohms It is also less than 0.5 Ohm depending on its application .
Ground connections for telecommunication equipment, which, depending on the type of application, have their own specifications. Earth's ground connection systems are larger and more complex for power plant equipment. In such cases, the measured resistance value should be 1 ohm or less .
The easiest earth connection system is a metal rod or metal pipe that is sunk in the ground and is connected by a conductor to the electrical network or the equipment in question. This metal rod is referred to as an earth jet bonding electrode or a ground connection rod, and in some cases a nailing earth connection .
In order to achieve less resistance, two or more Earth earth electrodes can be planted and connected in parallel. In some earth connection systems, in order to achieve a lower resistance value, metal networks with metal plates dipped in the ground .
The state of the soil at a depth of 6 to 7 meters from the rest of the area is more noticeable .
Ground connection is created by a suitable conductor and available to build a potential reference point in electrical circuits. Therefore, the production and transmission and distribution networks and other electrical devices are connected to this reference point through a ground connection system in order to maintain the potential of each part of the electrical installation to the constant potential of the earth, and when there is a problem in one of the The devices operate on protective equipment and isolate the circuit of the shapes .
Each electrical device has the potential of the ground in normal mode, and when it occurs, its potential is significantly higher than the potential of the earth, which can be prevented by the presence of a reliable system. .
In order for a ground-linking system to perform its task satisfactorily, it must always have a low total resistance to the ground and allow it to flow a lot of flow. Typically, testing a passable flow capacity for a land-based earth connection system is relatively difficult, but measuring ground resistance is not very difficult, and the values obtained are a relatively accurate guide to determining the status of the Earth's system. An earth connection system is usually The shape of an electrode (metal rod, tube, sheet, or grid) is filled with electrodes sunken in the ground, which performs the task by connecting electrical equipment or the network. The ground electrode resistance is not fixed and varies with the moisture content of the earth.