Type and function of grounding - Solutions - Huaqiang Electronic Network

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There are different grounding methods for the types of grounding and different circuits. The common grounding methods in electronic power equipment are as follows:
1. Safety grounding Safety grounding is to connect the outer casing of the high-voltage equipment to the earth. One is to prevent the accumulation of electric charge on the casing, causing electrostatic discharge and endangering equipment and personal safety. For example, the grounding of the computer case, the tail of the tanker dragged on the ground, is to release the accumulated electric charge and prevent accidents. Second, when the insulation of the equipment is damaged and the casing is charged, the power supply is protected and the power is cut off to protect the safety of the workers, such as the outer casing of the refrigerator and rice cooker. The third is to shield the huge electric field of the equipment and protect it, such as the protective rail of the civilian transformer.
2. Lightning protection grounding When power electronic equipment encounters lightning strikes, whether it is direct lightning strike or induced lightning strike, if there is no corresponding protection, power electronic equipment will be greatly damaged or even scrapped. In order to prevent lightning strikes, we generally set lightning rods on the ground (such as the roof and the top of the chimney) to connect with the earth to prevent the safety of equipment and personnel when lightning strikes. Safety grounding and lightning protection grounding are designed to provide safe protection for electronic power equipment or personnel to protect equipment and personnel.
3. Working Grounding Working grounding is a reference potential provided for the normal operation of the circuit. This reference potential is typically set to zero. The reference potential can be set to a certain point, a certain section or a block in the circuit system. When the reference potential is not connected to the ground, it is regarded as a relative zero potential. However, this relative zero potential is unstable, and it will change with the change of the external electromagnetic field, causing the parameters of the system to change, resulting in unstable operation of the circuit system. When the reference potential is connected to the ground, the reference potential is regarded as the zero potential of the earth, and does not change with the change of the external electromagnetic field. However, unreasonable work grounding will increase circuit interference. For example, the interference caused by the incorrect grounding point, the interference generated by the common end of the electronic device is not properly connected. In order to effectively control the circuit to produce various interferences in the work, so that it can comply with the principle of electromagnetic compatibility. When designing a circuit, depending on the nature of the circuit, the working ground can be divided into different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power ground, and the like. Different groundings should be set separately. Don't mix them together in one circuit. For example, digital ground and analog ground can't share a ground line. Otherwise, the two circuits will generate very powerful interference and make the circuit fall into paralysis!
4. The signal signal ground is a common reference ground of zero potential of various physical quantity signal sources. Since the signal is generally weak and susceptible to interference, unreasonable grounding will cause interference to the circuit, so the signal ground is highly demanded.
5. The analog ground analog ground is the common reference ground of the analog circuit zero potential. There are small signal amplifying circuits, multi-stage amplification, rectifier circuits, voltage regulator circuits, etc. in the analog circuit. Unsuitable grounding can cause interference and affect the normal operation of the circuit. The grounding in the analog circuit has great significance for the whole circuit, and it is one of the foundations for the normal operation of the whole circuit. Therefore, the reasonable grounding in the analog circuit can not be ignored for the whole circuit.
6. Digital ground digital ground is the common reference ground of the digital circuit zero potential. Since the digital circuit operates in a pulse state, especially when the front and rear edges of the pulse are steep or the frequency is high, a large number of electromagnetic wave interference circuits are generated. If the grounding is unreasonable, the interference will be intensified, so the grounding point selection of the digital ground and the laying of the grounding wire should also be fully considered.
7. The power ground is the common reference ground for the zero potential of the power supply. Since the power supply is often supplied to each unit in the system at the same time, and the power supply characteristics and parameters required by each unit may be greatly different, it is necessary to ensure stable and reliable operation of the power supply, and to ensure stable and reliable operation of other units. The power ground is generally the negative pole of the power supply.
8. The power ground power is the common reference ground of the zero potential of the load circuit or the power drive circuit. Since the current of the load circuit or the power drive circuit is strong and the voltage is high, if the grounding resistance of the grounding is large, a significant voltage drop will occur and a large interference will occur, so the interference on the power ground is large. Therefore, the power ground must be separately set with other weak current grounds to ensure that the stable and reliable working shield and grounding of the entire system should be used together to achieve a good shielding effect. Mainly to consider electromagnetic compatibility, the typical two types of shielding are electrostatic shielding and alternating electric field shielding, which are described below:
Electrostatic Shielding: When a complete metal shield is used to enclose the live conductor, an electric charge of the same kind as the charged conductor is induced on the inside of the shield, and the same kind of charge as the charged conductor appears on the outside, so there is an electric field on the outside. exist. If the metal shield is grounded, the outside charge will flow into the earth, and there will be no electric field on the outside of the metal shell, which is equivalent to the electric field of the charged body in the shell being shielded.
There are two types of grounding facilities.
One is the working ground, which is the grounding that connects the live part of the electrical appliance to the earth, such as the grounding of the neutral line of the low voltage point of the three-phase electrical transformer;
One is the protective grounding, which is to prevent the insulation of the electrical appliance from being damaged and the grounding of the metal parts of the outer casing that are charged or otherwise uncharged. The grounding wire must be driven into the depth of the earth by 1.2~1.5m to be qualified.
The three heads of three-phase power are called phase lines, and the three tails of three-phase power are connected together. The neutral line is also called "zero line". The reason for calling the zero line is that no current flows through the neutral line of the three-phase equilibrium moment, and then it is directly or indirectly connected to the earth, and the earth voltage is also close to zero.
The ground wire is a line that reliably connects the earth of the equipment or the electrical appliance to the earth, and is a good solution to prevent electric shock accidents.
Under normal circumstances, the three-phase circuit uses red, yellow, and blue colors to indicate three live lines, and the zero line uses black. In a single-phase lighting circuit, generally yellow indicates a live line, blue is a neutral line, and yellow-green is a ground line. In some places, red is used to indicate the fire line, black is the neutral line, and yellow and green is the ground line.
The electric appliance has a neutral line and a live line, thereby forming a passage, so that the electric current has an electric current to pass through, and the zero line is uncharged.
The ground wire is not powered regardless of whether the switch is off or not. Its main function is the grounding you mentioned. In order to avoid the occurrence of electric leakage accidents or high-potential potential hazards to humans, high-power electrical appliances have a grounding wire that can be used to introduce excess current or strong electric potential into the earth through the ground wire.
If the ground wire is not connected and cannot operate normally, it is a setting that exists for user safety.
The neutral line is the path through which the alternating current is returned to the generator through the electric appliance, and the ground line is the wire directly or indirectly connected to the real earth by the electric appliance (generally the grounding end should be more than 1 m deep into the ground).
Since the earth is the lowest potential (0V) in the general sense, the ground wire connected to the earth can ensure that the lowest potential at both ends of the electrical voltage is the same as the earth, thus making the instrument and equipment work safer.
Poor grounding can cause the neutral voltage to be unstable (not 0V), and even cause ground leakage, making the instrument inoperable.
The difference between the zero line and the ground line:
The neutral line is part of the loop, and when the appliance is working, current flows through the zero line.
The ground wire does not constitute an electrical circuit. It is part of the electrical leakage protection device of the electrical device. Under normal conditions, no current flows.
The main role of the ground wire:
When an appliance fails, the power supply may break down (or: destroy) certain components, charging the enclosure of the appliance. Grounding the outer casing of the appliance to make the leakage protection device
Signal "ground";
The signal "ground", also known as the reference "ground", is the reference point of zero potential, and is also the common segment of the circuit signal loop, the graphic symbol "⊥".
1) DC ground: DC circuit "ground", zero potential reference point.
2) Exchange place: the neutral line of AC power. Should be distinguished from the ground.
3) Power ground: zero current reference point for high current network devices and power amplifier devices.
4) Analog ground: Zero potential reference point for amplifier, sample-and-hold, A/D converter and comparator.
5) Digital ground: also called logic ground, is the zero potential reference point of the digital circuit.
6) “Hot ground”: The switching power supply does not need to use a transformer. The “ground” of the switching circuit is related to the mains power grid. It is called “hot ground”. It is charged and the graphic symbol is “ ”.
7) “Cold ground”: Because the high-frequency transformer of the switching power supply isolates the input and output terminals; and because the feedback circuit is commonly used for photoelectric coupling, it can transmit the feedback signal and isolate the “ground” of both sides; For "cold land", it is not charged. The graphic symbol is “⊥”.
2. Protect "land";
Protection "ground" is a type of wiring that is set to protect personnel. One end of the protection "ground" line is connected to the electrical appliance, and the other end is reliably connected to the earth.
3. The "ground" in the sound.
1) Shielded wire grounding: In order to prevent interference, the sound system of the metal case is connected with the signal “ground”. This is called shield grounding.
2) Audio dedicated "ground": In order to prevent interference, professional audio must be connected to the audio dedicated "ground" in addition to shielding the "ground". This grounding device should be buried specifically and should be connected to the corresponding grounding of the isolation transformer and the shielded regulated power supply as a dedicated audio grounding point in the sound control room.
l Different ground wire processing methods.
1. The digital ground and the simulated ground should be separated;
In high demand circuits, the digital ground must be separated from the analog ground. Even for the A/D, D/A converter, the two "grounds" on the same chip should be separated, and only the two "grounds" are connected at one point in the system.
2. Floating and grounding;
The floating system of the system floats the ground of each part of the system circuit and is not connected to the earth. This connection has a certain anti-interference ability. However, the insulation resistance between the system and the ground should not be less than 50 MΩ. Once the insulation performance is degraded, it will cause interference. The system is usually floating and the chassis is grounded to enhance the anti-interference ability, which is safe and reliable.
3. One point of grounding;
In low frequency circuits, there is not much influence between the wiring and the components. Generally, circuits with a frequency less than 1MHz are grounded at one point.
4. Multi-point grounding.
In high-frequency circuits, the effects of parasitic capacitance and inductance are large. Generally, circuits with a frequency greater than 10 MHz use multi-point grounding in addition to proper grounding design and installation, and proper grounding of various signals. In the control system, there are roughly the following ground lines:
(1) Digital ground: Also called logical ground, it is the zero potential of various switching (digital) signals.
(2) Analog ground: It is the zero potential of various analog signals.
(3) Signal ground: Usually the ground of the sensor.
(4) AC ground: The ground wire of the AC power supply, which is usually the ground where noise is generated.
(5) DC ground: the ground of the DC power supply.
(6) Shielding ground: also called the chassis ground, designed to prevent static induction and magnetic field induction.
These ground wire treatments are an important issue in system design, installation, and commissioning. Here are some thoughts on the grounding problem:
(1) The control system should be grounded at one point. Under normal circumstances, the high-frequency circuit should be grounded at multiple points, and the low-frequency circuit should be grounded at one point. In the low-frequency circuit, the inductance between the wiring and the component is not a big problem. However, the interference of the loop formed by the ground has a great influence. Therefore, the grounding point is often used as a grounding point; but one-point grounding is not suitable for the high frequency because the high frequency At the time, the ground line has an inductance, which increases the impedance of the ground line, and inductive coupling between the lines. Generally speaking, the frequency is below 1MHz, and one point can be grounded; when it is higher than 10MHz, multi-point grounding is used; one point can be grounded between 1~10MHz, and multiple points can be grounded.
(2) The exchange ground and the signal ground cannot be shared. Since there are several mV or even a few V voltages between two points of a power ground, this is a very important interference for low level signal circuits and must be isolated and prevented.
(3) Comparison of floating ground and grounding. The whole system is floating, that is, all parts of the system are floating with the earth. This method is simple, but the insulation resistance of the whole system and the earth cannot be less than 50MΩ. This method has a certain anti-interference ability, but it will cause interference once the insulation is lowered. Another method is to ground the case and leave the rest floating. This method is strong in anti-interference ability, safe and reliable, but it is complicated to implement.
(4) Analog ground. The connection of the analog ground is very important. In order to improve the anti-common mode interference capability, shielded floating technology can be used for analog signals. Grounding of specific analog signals should be designed in strict accordance with the requirements in the operation manual.
(5) Shielding ground. In the control system, in order to reduce the capacitive coupling noise in the signal, accurate detection and control, it is necessary to use shielding measures for the signal. Depending on the purpose of the shielding, the connection of the shielding ground is different. Electric field shielding solves the problem of distributed capacitance, generally connected to the earth; electromagnetic field shielding mainly avoids high-frequency electromagnetic field radiation interference such as radar and radio. Made of high-conductivity of low-resistance metal materials, it can be grounded. The magnetic field shielding is used to prevent magnetic induction of magnets, motors, transformers, coils, etc. The shielding method is to use a high magnetic conductive material to close the magnetic circuit, generally it is better to connect the earth. When the signal circuit is grounded at one point, the shield of the low frequency cable should also be grounded at one point. If there is more than one shield location of the cable, a noise current will be generated, creating a source of noise interference. When a circuit has an ungrounded signal source connected to a grounded amplifier in the system, the shield at the input should be connected to the common terminal of the amplifier; conversely, when the grounded signal source is connected to an ungrounded amplifier in the system, the input to the amplifier The terminal should also be connected to the common end of the signal source.
For the grounding of electrical systems, it should be classified according to the requirements and purpose of grounding. It is not possible to simply and arbitrarily connect different types of grounding. Instead, it should be divided into several independent grounding subsystems, each with its common grounding point. Or ground the trunk, and finally connect together to implement the total grounding.