The lightning protection technology of electronic weighing instrument is a complex comprehensive protection system, which requires that the metering performance of electronic weighing instrument cannot be changed while lightning protection is carried out. This is not only the key and characteristic of lightning protection of electronic weighing instrument, but also the difficulty of design. According to the requirements of modern lightning protection technology, we have established the comprehensive protection concept of "comprehensive protection, system protection and step-by-step voltage limiting" to achieve: optimized scheme, reasonable technology, economic efficiency, safety and reliability.
1. Provide special equipotential lightning protection for all components of the whole electronic weighing instrument, such as sensors and secondary instruments. Equipotential protection is the core and foundation of lightning protection system of electronic weighing instrument. When lightning strikes, at the moment when powerful lightning flows into the earth, the whole weighing instrument system can generate tens of thousands or even hundreds of thousands of volts of high potential to the earth due to the resistance and inductance of the grounding wire, which is devastating to all parts of the electronic weighing instrument and even the whole system. The system provides corresponding equipotential protection for various interfaces of the whole weighing instrument system (sensor, instrument, computer), so that the basic potential of the whole weighing instrument system changes with the change of ground potential, and the damage of high potential generated by lightning current to electronic weighing instruments is avoided. 2. Cut off the connection channel between the sensor and the weighing platform, and provide the current discharge channel. ?
It is not enough to do equipotential protection, but also to cut off the electrical connection between the sensor and the scale. A shunt device is added to the output end of the sensor, which is connected with the scale body and grounded. When there is lightning current, the lightning current flows into the earth through the shunt device of the sensor without passing through the sensor, thus avoiding the damage of the electromagnetic field generated by the lightning current to the sensor. ?
3. The power supply system should provide multilevel lightning protection. ?
The power supply system of secondary instrument and computer system adopts multilevel lightning protection and equipotential connection, and then it is connected to the grounding electrode. The power supply system of electronic weighing instrument adopts three-level lightning protection. The first lightning protection module is installed behind the system power switch, the second lightning protection module is installed in front of the regulated power supply, and the third lightning protection module is installed in front of the equipment. In addition, the third-level lightning protection is * * * ground, which is equipotential with the scale.
4. Build lightning protection grounding grid (grounding well) around the platform (including platform foundation).
A lightning protection grounding grid (grounding well) including the foundation is built around the platform, and the whole system is connected to a single grounding electrode near the platform. In this way, the whole weighing instrument system has only one basic potential, which is connected with the equipotential connector of indoor equipment and the grounding of the house to realize * * * grounding. When lightning strikes, this potential will change with the potential fluctuation of the grounding point, ensuring that the whole electronic weighing instrument system is safe and sound.
Lightning disaster is one of the top ten serious natural disasters in the world. Frequent lightning disasters in China pose a serious threat to national economic development, social harmony and stability, especially the safety of people's lives and property. There are 3,000 or 4,000 casualties caused by lightning strikes in China every year, and the property loss is about 50-65.438+000 billion yuan.
With the rapid development of modern science and technology, electronic and microelectronic devices, especially large-scale and very large-scale integrated circuits, are widely used in various fields, and their withstand voltage level is quite low. For example, the withstand voltage levels of integrated circuits are all below 100 volts, and the induced overvoltage caused by lightning electromagnetic pulse (LEMP) on the possible lightning entry channels of these microelectronic devices is usually above kilovolts, which is enough to cause equipment abnormality or damage.
Weighbridge (truck scale) is generally exposed, and the data collection and control of weighbridge need to be very detailed and complete. Its stress element (sensor), amplifier and display equipment are easily damaged by lightning. If the lightning protection measures are not perfect, when the sensor equipment is damaged by direct lightning or induction lightning, the indirect loss is quite large. In most cases, the damage of the ground scale is caused by transient overvoltage coupled by resistance or capacitance. All the power and signal wires introduced into the exhibition room and the signal wires and power wires connected to the stressed parts (sensors) of the weighbridge outdoors shall be equipped with overvoltage protection devices.
Second, on-site investigation (taking XX unit weighbridge survey as an example)
1, lightning damage
According to the relevant personnel of the station, the weighbridge was hit by strong lightning a few days ago, causing serious damage to some equipment of the weighbridge, and the approximate losses are as follows.
(1) Weight shows complete damage;
(2) Three sensors are damaged;
2. Field investigation
The weighbridge is located in an open space in the factory. The house is an isolated building with no high-rise buildings and structures around it.
(1) Weighbridges and pound houses are not equipped with ground nets;
(2) The weighbridge equipment is not grounded;
(3) The weighbridge equipment is not equipped with signal arrester;
(4) The power input terminal is not equipped with a power arrester;
Generally speaking, there are no lightning protection facilities in weighbridges and pound houses, so it is impossible to ensure the lightning protection safety of equipment. Lightning damage of equipment is caused by lightning induced by direct lightning. Therefore, the existing lightning protection facilities should be rectified and comprehensive lightning protection projects should be implemented.
Third, the lightning protection engineering design scheme
1. Design basis and related standards:
GB 50057-94 Code for Lightning Protection Design of Buildings (version 20 10)
GB50343-2004？ Technical specification for lightning protection of building electronic information system
GB 50054-95 Code for Design of Low Voltage Distribution
Code for design of computer room GB 50 174-93
GB 50 169-92 Code for Construction and Acceptance of Grounding Devices in Electrical Equipment Installation Engineering
IEC 6 1024 Building Lightning Protection
T c 61312 lightning electromagnetic pulse protection
d？ 562? Installation of lightning protection facilities for buildings and structures
99D562？ Atlas of lightning protection facilities installation in buildings
XQ3-2000？ Code for lightning electromagnetic pulse protection of meteorological information system
YD 5078 Technical Specification for Lightning Protection of Power System in Communication Engineering
Second, the lightning protection design content
With the arrival of summer, lightning strikes of electronic weighbridges occur frequently. How to prevent electronic weighing instruments from being struck by lightning has become an urgent problem.
1, external direct lightning protection
A lightning rod should be installed above the scale body to neutralize the charge in the cloud through the tip discharge effect, so that the electronic truck scale will not be damaged by lightning. The height of lightning rod can be determined according to the length of electronic truck scale or calculated by rolling ball radius method, and the protection radius of lightning rod is equal to a circular area of its height.
Ignition and discharge lightning rod THZ-05C
principle of operation
LDY series lightning rods are made of foreign advanced technology and technology, and obtained national patents. Energy is mainly absorbed and stored by the exciter from the natural electric field. The tips of the reflector and arrester have good electrical connection with the earth and are in equipotential state. So in general, there is an electric field intensity between the exciter and the emitter, which will increase rapidly before lightning occurs. The potential difference between the exciter and the reactor is roughly equivalent to the potential between Lei Yun and the earth, and the voltage between the exciter and the reactor will rise rapidly, which will cause the needle tip to catch fire, ionize the air around the needle tip and form the phenomenon of needle tip discharge.
The electric field between the central collecting rod of lightning rod and the exciter increases rapidly, which makes the air generated at the tip ionize and discharge in a very short and accurate time. Due to the existence of a large number of electric ions, the natural corona effect is reduced, and the expected upward discharge channel is generated, which can quickly and safely intercept lightning and discharge to the earth.
Product features:
Maintenance-free, non-electronic, long life.
◆ Without electronic system, it will not be damaged by surge impact, and the protection quality will not change after lightning strike.
◆ Different protection radii are available for customers to choose.
◆ When there is lightning, it will automatically activate and actively intercept the lightning system.
◆ Safe and reliable, imported advanced foreign technology and passed the inspection of relevant state departments.
product mix
◆? Central collecting rod
◆? plate
◆? Trigger device
◆? Mercury gas rectifier tube
◆? Exciter fixing plate
◆? The exciter is insulated from the reflector and the central light collecting rod.
◆? The reflector and the central light collecting rod have good electrical connection with the earth.
◆? The base of the exciter is made of synthetic resin and is suitable for any corrosive conditions.
Protected domain
According to the national standard NFC 17- 102, when the tip of ESE(PDA) is 2m, 3m, 4m, 5m, 6m, 7m, 10m, 20m higher than the protected object, its protection range is related to pre-discharge time △t, needle height and lightning protection category of the building: =
Where: protection radius of horizontal plane (ground) (m)
H is the height difference (m) of the needle relative to the display surface of the protected object.
D is the ball radius:
Take 30m for the first lightning protection building, 45m for the second lightning protection building and 60m for the third lightning protection building.
△L is the lightning height of the uplink, and△ l =△ t× v.
△t Early discharge time, 25μs,? 35 microseconds, 45 microseconds, 60 microseconds
V= 1m/μs (pilot speed), that is, △L is 25, 35, 45 and 60m respectively. Therefore, different types of lightning rods have different protection radii for the protected objects at different heights.
2. Power supply protection
The power supply system of secondary instrument and computer system adopts multilevel lightning protection and equipotential connection, and then it is connected to the grounding electrode. The power supply system of electronic scale adopts three-level lightning protection. The first lightning protection module is installed behind the system power switch, the second lightning protection module is installed in front of the regulated power supply, and the third lightning protection module is installed in front of the equipment. In addition, the third-level lightning protection is * * * ground, which is equipotential with the scale.
Specific measures
(1) Level 1 lightning protection: As there are fewer chances of indoor power lines being struck by lightning, level 1 indoor power supply can be omitted (if the power supply lines are laid overhead, lightning arresters with large current capacity, such as TSPD-B 100 RM/4, should be installed at the front end of the main distribution box as level 1 protection);
(2) Secondary lightning protection: A box-type single-phase power lightning protector (TSPD-B+C80RM/4) is installed at the power inlet end of the distribution box in the duty room as the secondary protection for indoor electrical equipment.
(3) Three-level lightning protection: lightning protection sockets (TKA-GZ/PDU06) are installed at the front end of the main engine and the weighing display in the duty room to provide good lightning protection for the power lines of these devices.
3. Lightning protection of network monitoring system
Because electronic weighbridge metering has realized remote unattended, its "eyes" are network monitoring systems, so the lightning protection of network monitoring systems is also very important. According to the needs of the site and the characteristics of the monitoring system, equipotential connection is carried out for hard disk video recorders, switches and other equipment, and lightning protection modules are installed for video signals and control signals for equipotential connection.
4. Grounding system
1) Do special equipotential lightning protection for all parts of electronic scales, such as sensors and secondary instruments. Equipotential protection is the core and foundation of lightning protection system for electronic scales. When lightning strikes, at the moment when powerful lightning flows into the earth, the whole electronic scale system can generate tens of thousands or even hundreds of thousands of volts of high potential to the earth due to the resistance and inductance of the grounding wire, which is devastating to all parts of the electronic scale and even the whole system. The system provides corresponding equipotential protection for various interfaces of all parts of the whole weighing system (sensors, meters and computers), so that the basic potential of the whole weighing system changes with the change of ground potential, and the damage of high potential generated by lightning current to electronic weighing instruments is avoided. ?
2) Cut off the connection channel between the sensor and the weighing platform, and provide a discharge channel for current. ?
It is not enough to do equipotential protection, but also to cut off the electrical connection between the sensor and the scale. A shunt device is added to the output end of the sensor, which is connected with the scale body and grounded. When there is lightning current, the lightning current flows into the earth through the shunt device of the sensor without passing through the sensor, thus avoiding the damage of the electromagnetic field generated by the lightning current to the sensor. ?
3) Establish lightning protection grounding grid (grounding well) around the platform (including platform foundation).
A lightning protection grounding grid (grounding well) including the foundation is built around the platform, and the whole system is connected to a single grounding electrode near the platform. In this way, the whole weighbridge system has only one basic potential, which is connected with the equipotential connector of indoor equipment and the grounding of the house, so that it can be grounded. When lightning strikes, this potential will change with the potential fluctuation of the grounding point, ensuring that the whole electronic weighbridge system is safe and sound. Grounding is an important part of lightning protection and the foundation of lightning protection device, which makes lightning current leak into the earth better. According to the actual situation, it is necessary to make a comprehensive grounding body again. In order to ensure the grounding resistance of the computer room system, the resistance of the upper lead should be reduced as much as possible.
Vertical grounding body can adopt nonmetallic grounding body, copper clad steel, copper material, hot-dip galvanized steel (steel pipe, round steel, angle steel and flat steel) or other new grounding materials, and horizontal grounding body generally adopts hot-dip galvanized flat steel.
A, hot-dip galvanized steel pipe is adopted, and the wall thickness of the steel pipe is not less than 3.5m
B, using hot dip galvanized angle steel, angle steel is not less than 50 mm× 50 mm× 5 mm;
C, using hot dip galvanized flat steel, flat steel is not less than 40 mm * 4 mm.
D, when hot-dip galvanized round steel is used, the diameter of the round steel is not less than 8m;
When the grounding resistance is difficult to meet the requirements, measures can be taken, such as burying grounding body, setting extended grounding body, installing resistance reducer recognized by environmental protection department or other new technologies and materials around grounding body.
When the grounding body is difficult to avoid sewage discharge and places with corrosive soil, the vertical grounding body should be graphite grounding body, and the horizontal grounding body should be made of corrosion-resistant materials. When hot-dip galvanized flat steel is used, the coating should not be less than 80um.
If the grounding resistance can't meet the requirements, a separate grounding system should be made to be safe and firm. Considering the long-term use and corrosion resistance of grounding grid, it is suggested to adopt galvanized angle steel and component diameter reduction. The grounding grid is designed according to the terrain. What is the layout of the grounding grid? L type. The horizontal grounding body adopts 40×4mm hot-dip galvanized flat steel, and the vertical grounding body adopts long-term physical nonmetallic grounding module or galvanized angle steel.
When the grounding resistance is difficult to meet the requirements, measures such as burying grounding body, setting extended grounding body, installing resistance reducer around grounding body or other new materials recognized by environmental protection department can be taken.
This content was originally recommended by the weighbridge manufacturer and may not be reproduced without permission.