Grounding and protection of electrical equipment / Chen Jing is one of the important measures to ensure the normal operation and safety protection of electrical equipment. Grounding of electrical equipment is achieved by grounding.
The grounding device consists of a grounding body and a grounding wire. The metal body in direct contact with the soil is called a grounding body; the wire (or conductor) connecting the electrical equipment to the grounding body is called a grounding wire.
Resistance Protection To ground a point in the power system in order to meet the operational requirements of the power system or electrical equipment. Such as the neutral point of the power system, the working place of various circuits, and so on.
In order to prevent the insulation damage of the electrical equipment, the voltage of the metal casing to the ground must be limited to the safe voltage, to avoid causing personal electric shock, and the exposed part of the electrical equipment can be grounded. Such as: motor, transformer, lighting fixture shell; metal casing of civil electrical appliances such as washing machine, refrigerator, etc.; base or bracket of various electrical equipment of power distribution station; steel bar of overhead line or steel bar of reinforced concrete tower and pole tower The overhead ground wire and the outer casing and bracket of the equipment installed on the tower.
In order to prevent the lightning overvoltage from causing harm to the person or equipment, the overvoltage protection device is grounded. Such as lightning rods, lightning arresters, etc.
In order to eliminate the grounding caused by static electricity to the human body and equipment, such as the metal transmission pipeline of certain liquid or gas or the grounding of the vehicle and the computer room grounding. In order to prevent electrical equipment from being affected by electromagnetic interference, equipment that affects its work or causes electromagnetic interference to other equipment is grounded. Such as the metal casing of various high-frequency electronic equipment grounding.
All electrical equipment must be used for other purposes in accordance with GB14050 or protective earthing requirements. Grounding with special requirements, such as weak current systems, computer systems and medium voltage systems, shall be carried out in accordance with the relevant special regulations when the neutral point is directly grounded or passed through a small resistance ground.
2. Grounding problem from the mountain launching station 2.1 Main reasons for grounding in the broadcasting and television industry Safety grounding: Equipment using alternating current must be grounded through a yellow-green safety ground wire, otherwise the insulation resistance between the power supply and the casing in the equipment will change. Hours can cause electric shock damage.
Lightning grounding: The lightning protection system of the facility is a separate system consisting of a lightning rod, a lower conductor and a joint connected to the grounding system. This grounding system is typically shared with the ground used as the power ground and the yellow-green safe ground.
Electromagnetic compatibility grounding: Grounding required for EMC design, including: Shield grounding: In order to prevent mutual interference between circuits due to parasitic capacitance, circuit radiated electric field or sensitive to external electric field, necessary isolation and shielding must be performed. The isolated and shielded metal must be grounded.
Filter grounding: The filter generally includes a signal line or a power supply line to ground bypass capacitor. When the filter is not grounded, these capacitors are in suspension and do not function as a bypass.
Noise and interference suppression: Control of internal and external disturbances requires many points on the device or system to be connected to ground to provide a "lowest impedance" channel for interfering signals.
Circuit: The signal between the circuits must be transmitted correctly. There must be a common potential point. This common potential point is ground. Therefore all interconnected circuits must be grounded.
Can be divided into work ground, protective grounding, overvoltage protection grounding, anti-static grounding, shielding grounding, signal ground and many other. The following is an explanation of the actual combination of radio and television technology.
Protective grounding: Protective earthing is a protection device designed to prevent the insulation from being damaged and causing personal safety. It has two ways: grounding and receiving the piano. According to the power regulations, for systems with three-phase four-wire power supply, since the neutral line is grounded, the zero connection method should be adopted, and the metal casing of the equipment should be connected to the neutral line through the conductor, and the equipment casing should not be directly grounded. This is especially common in switchgear, central air conditioners, transmitters and other power switchgear and power consuming equipment in power distribution rooms of radio and television systems. When planning and designing, the grounding busbar should be taken from the grounding grid to each equipment, and then the conductor of the machine casing should be connected to the grounding busbar. It is worth pointing out that the grounding wire should be connected to the grounding special terminal of the equipment, and the other end should be welded.
Shielding ground: To prevent electromagnetic induction, the shielding metal sheath of the visual and audio lines, the metal casing of the electronic equipment, the shielding cover, and the metal shielding net of the building (such as the shielding room for measuring sensitivity and selectivity) are grounded. Kind of protective measures. Among all the grounding, the shielding ground is the most complicated, and there is a kind of unclear and unclear feeling. Because the shielding itself can prevent external interference, and it may interfere with the outside world through it, and electromagnetic interference must also be prevented between the components in the equipment. For example, the well-known mid-circle outer casing and the electron tube shielding cover are examples. Poor shielding and improper grounding can cause interference. These interferences mainly include: AC interference: This is mainly caused by AC power. High-frequency interference: This kind of interference comes from the frequency conversion or over-conversion signals of various wireless transmitting stations. After they enter the electronic equipment, they are abnormally demodulated in the machine to form audio interference. Shielding and proper grounding are the best protection against electromagnetic interference.
The equipment casing can be connected to the PE wire: the shielding grounding of the wire requires reliable connection between the two ends of the shielding pipe and the PE wire: the indoor shielding should also be reliably connected to the PE wire.
Signal ground: Various electronic circuits have a reference potential point, which is the signal ground. Its role is to ensure that the circuit has a uniform reference potential, not sub-floating and causing signal errors. The connection of the signal ground is: the signal input end of the same device and the signal output end cannot be connected together, but should be separated; the output ground of the front stage (device) is only connected to the input ground of the latter stage (device). Otherwise, the signal may form feedback through the ground, causing the signal to float. In the test of the device, the connection of the signal ground is particularly noticeable. Otherwise it will result in inaccurate test results.
Grounding is literally simple, but it may be the hardest to master for people experiencing electromagnetic interference and lightning frustration. In fact, in electromagnetic compatibility design, grounding is the most difficult technology. In the face of a system, no one can propose an absolutely correct grounding solution, and some will leave some problems. Lightning protection and grounding are unified, and both are indispensable. Only lightning protection measures without grounding, can not discharge discharge quickly, on the contrary, the equipment will be directly impacted by s strong current, in any case the system will be damaged or even paralyzed. As long as it is properly integrated and integrated into one, it can effectively ensure the stable operation of the system, thus exerting the best effect of the system protection work.
During the oil circulation flushing process, there must be sufficient oil flow (normal operation oil flow) to ensure that the system is fully flushed and the impurities are taken away. During the oil circulation, the samples should be sampled and analyzed frequently. Only after the oil quality meets the standard requirements can the oil be used. Pour into normal system operation. Pipe elbows, â–¡ and the corners of the equipment are the concentrated places of impurities. Therefore, the elbows and dead corners in the system should be carefully checked to thoroughly clean the residual impurities in the system; also to prevent the influence of external factors, such as: Environmental ash, water, and impurities such as rain and snow enter the oil system to contaminate oil.
The damage caused by the failure of the oil system is very big. The lesson is also profound. How to reduce and avoid the occurrence of accidents? The key is to do a good job in quality control. It is extraordinary in the manufacture and installation of equipment. In addition, the operation and management cannot be relaxed. It is necessary to grasp intensively and carefully from every link, and neglecting any link may cause the occurrence of the accident and bring unnecessary losses.
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