There are five kinds of grounding purpose, grounding method, grounding role is different, as follows:
1, protective grounding
Case safety grounding is the system is usually not electrically charged metal parts (cabinet shells, console shells, etc.) and the ground to form a good conductive connection between the protection of equipment and personal safety.
The reason is that the power supply system is a strong power supply (380, 220 or 110V), usually the enclosure is not charged, when a fault occurs (such as a host power failure or other faults) caused by the power supply line of fire with the enclosure and other conductive metal parts of the shell of the conductive short-circuited, these metal parts or the shell of the formation of a charged body, if there is no good grounding, then the charged body and the ground between there are A very high potential difference, if a person accidentally touches these charged bodies, it will form a path through the person, resulting in danger.
Therefore, it is necessary to make a good connection between the metal casing and the ground so that the casing and the ground are equipotential. In addition, protective grounding prevents the buildup of static electricity.
2, working ground
Working ground is in order to make the system as well as the instrumentation connected to it can operate reliably and ensure the accuracy of measurement and control and set up the ground. It is divided into machine logic ground, signal circuit ground, shielding ground, in petrochemical and other explosion-proof systems and intrinsically safe ground.
3, lightning grounding
Lightning grounding is subject to lightning strikes (direct, induction or line introduction), in order to prevent damage to the grounding system. Often signal (weak) lightning ground and power (strong) lightning ground points, the reason for the distinction is not only because of the requirements of the grounding resistance is different, and in engineering practice, the signal lightning ground is often attached to the signal on an independent ground, and the power supply lightning ground separate construction.
Lightning protection ground as part of lightning protection measures, its role is to introduce the lightning current into the earth. Lightning protection of buildings and electrical equipment is mainly lightning arrester (including lightning rods, lightning straps, lightning nets and lightning devices, etc.) one end of the connection with the protected equipment, the other end is connected to the grounding device, when a direct lightning strike occurs, the lightning arrester will be led to itself, the lightning current into the earth through the lead wire and grounding device.
4, shielding grounding
It is an effective measure to eliminate the hazards of electromagnetic fields on the human body, but also an effective measure to prevent electromagnetic interference. High-frequency technology has been widely used in electrothermal, medical, radio broadcasting, communications, television and navigation, radar, etc., the human body under the action of electromagnetic fields, the absorbed radiant energy will occur in the biological role of the human body, causing harm, such as slight trembling of the fingers, skin scratches, vision loss, etc..
The generation of magnetic field equipment shell shielding device, and shielding body grounding, not only can reduce the shielding body outside the electromagnetic field strength, to reduce or eliminate the harm of electromagnetic fields on the human body, but also protect the shielding of the grounding of the body's equipment from the outside world from the interference of electromagnetic fields.
5, anti-static grounding
To prevent the effects of electrostatic hazards and discharge, is the most important part of electrostatic protection.
Expanded informationFactors affecting the grounding resistance measurement:
1, the ground network around the soil composition is inconsistent, geological inconsistency, close, dry and wet degree is not the same, with the dispersion of the ground surface stray currents, especially overhead ground lines, underground water pipes, cable sheaths and so on, the test is particularly influential. Solution: take different points for measurement, take the average value.
2, the test line direction is not right, the distance is not long enough. Solution: Find the right test direction and distance.
3, auxiliary grounding electrode resistance is too large. Solution: Splash water at the ground stake or use resistor to reduce the grounding resistance of the current pole.
4, the test clip and grounding measurement point contact resistance is too large. Solution: Grind the contact point with a file or sandpaper, and use the test line clamp to fully clamp the grounding contact.
5, interference effects. Solution: adjust the direction of release, try to avoid interference in the direction of the meter readings to reduce the jump.
6, meter use problems. Insufficient battery power, the solution: replace the battery.
7, the meter accuracy decline. Solution: Recalibrate to zero.
The accuracy of the test value of the grounding resistance is one of the important factors to determine whether the grounding is good. Once the test value is inaccurate, either a waste of manpower and resources (measured value is large), or it will bring safety hazards to the grounding equipment (measured value is small).
Baidu Encyclopedia - Grounding
Baidu Encyclopedia - Grounding Resistance