The importance of lightning protection and grounding for these types of buildings is self-evident and is a very common application direction. There are too many examples to enumerate them one by one.
Types of grounding in building
Work grounding according to the functional classification
In order to ensure that the electrical equipment in the normal case of reliable work, a variety of work grounding have their own functions, such as: transformers, generators, the neutral point of direct grounding can be in operation to maintain the three-phase system in the phase line to ground voltage remains unchanged; another example is the voltage transformer primary coil neutral grounding is to measure the voltage source of the primary system to ground, the neutral point by the arc extinguishing coil grounding can prevent the system from overvoltage, etc..
Protection grounding: the metal shell of the electrical equipment, the frame of the distribution device, the tower of the line and other normal conditions are not charged, but may be charged due to insulation damage and all parts of the ground. Because the purpose of this grounding with copper clad ground wire is to protect personal safety, it is called protection grounding or safety grounding.
Lightning protection grounding: to lightning protection device (lightning rod, lightning wire, lightning protection network) to the earth to provide a channel for the discharge of lightning current.
Anti-static grounding: In order to prevent static electricity caused by flammable and explosive gases or liquids fire or explosion, and the storage of gas or liquid pipes, containers, etc. set the ground. Repeat grounding: three-phase four-wire system of the zero line (or neutral point) a place or more by and grounding device and the earth again reliable connection, called repeat grounding.
1.A variety of different nature of grounding device joint grounding, grounding resistance requirements less than 1 Ω.
Grounding requirements in building
2. The grounding device should give priority to the use of natural grounding body of the building, when the natural grounding body grounding resistance can not meet the requirements should increase the artificial grounding body.
3. The building grounding device is appropriate to use a copperweld ground rod, but direct lightning and induction lightning into the location can not be common point.
The basic steps of lightning protection grounding design in building
1.Receive the building structure conditions and figure out the form of building structure.
2.Determine the lightning protection level, and the form of lightning protection grounding.
3.Collecting process, HVAC, waterway, and self-control conditions.
4.Drawing lightning protection and grounding drawings and preparing lightning protection and grounding instructions.
5.Provide secondary conditions to the building structure.
Grounding process in building
Grounding device using the building foundation ring beam (periphery) diagonal two main reinforcement welded into a ring network (main reinforcement less than 12 shall use 4 main reinforcement), lead wire and ring network welded into one. The connection of the grounding body (line) should be welded, the welding seam should be full and have sufficient mechanical strength, there should be no slag, bite, cracks, false welding, porosity and other defects, the weld is knocked clean after the powder skin, do anti-corrosion treatment. After the completion of the foundation grounding project, the grounding resistance test at each copper clad ground wire, the grounding resistance R < 1 ohm, failure to meet the requirements, shall increase the artificial grounding pole, until it meets the requirements.
The functions of grounding in building
We often only know that grounding can prevent personal electric shock, in fact, in addition to this role, grounding can also prevent equipment and lines from damage, prevent fire, prevent lightning, prevent static electricity damage and ensure the normal operation of the power system.
(1) to prevent electric shock human body impedance and the condition of the environment has a great relationship, the more humid the environment, the lower the impedance of the human body, but also the more likely to suffer electric shock. For example, since the installation of AC radio almost all people have received electric shocks, but almost all can get rid of the power supply, because at this time the person is in a dry environment, the skin is also dry. Grounding is an effective way to prevent electric shock. Electrical equipment through the grounding device grounding, such as copper or galvanized ground rod, so that the potential of electrical equipment close to ground potential. Due to the existence of grounding resistance, electrical equipment to ground potential is always present, the greater the grounding resistance of electrical equipment, the greater the potential of electrical equipment to ground when a fault occurs, the greater the risk of human contact. However, if no grounding device is set, the voltage of the faulty equipment shell is the same as the phase line voltage to ground, compared to the grounding voltage is still much higher, so the danger also increases accordingly.
(2) to ensure the normal operation of the power system power system grounding, also known as work grounding, generally in the substation or substation to the neutral point grounding. Work grounding grounding resistance requirements are very small, for large substations require a grounding network, to ensure that the grounding resistance is small and reliable. The purpose of work grounding is to make the potential between the neutral point of the grid and the ground close to zero. Low-voltage distribution system can not avoid the phase line touching the shell or phase line break after touching the ground, if the neutral point to ground insulation, it will make the other two phases of the ground voltage rise to 3 times the phase voltage, the result may be the working voltage of 220 electrical equipment burned out. For the neutral grounding system, even if one phase is short-circuited to ground, the other two phases can still be close to the phase voltage, so the electrical equipment connected to the other two phases will not be damaged. In addition to prevent system oscillation, electrical equipment and lines as long as the insulation level is considered by phase voltage.
(3) to prevent lightning strikes and electrostatic hazards when lightning occurs, in addition to direct lightning, will also produce induction lightning, induction lightning is divided into electrostatic induction lightning and electromagnetic induction lightning. The most important method of all lightning protection measures is grounding.