How to connect the grounding of underground mobile substation?

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Details for the installation, inspection and measurement of underground protective grounding devices in coal mines

1. General principles

1. When the insulation of electrical equipment is damaged, the metal shell of the equipment Dangerous voltage will be generated on the steel strip (or steel wire) of the cable. If a person comes into contact, an electric shock accident will occur. Protective grounding is to avoid personal electric shock accidents.

2. Metal casings, frames, steel strips (or steel wires) of armored cables, lead and rubber-sheathed (plastic) cables’ grounding core wires or shielding sheaths for electrical equipment above 36V are all Must be grounded.

It is prohibited to use rubber-sheathed or plastic cables without grounding core wires (or without other sheaths for grounding, such as lead, copper, etc.) in mines.

3. All equipment and local grounding devices that must be grounded must be connected to the general grounding grid.

4. The main grounding electrode should be immersed in the water tank, and the main and auxiliary water tanks must each have one. When the mine has several levels, the general grounding grid at each level must be connected to the main grounding electrodes in the main and auxiliary water tanks.

5. Local grounding electrodes should be installed at the following locations:

① Each mining area substation (including mobile substations and mobile transformers).

②Each chamber containing electrical equipment and separately installed high-voltage electrical equipment.

③Each low-voltage distribution point or location where more than 3 electrical equipment are installed.

④ At least one local grounding electrode must be installed in the machine tunnels, return air tunnels, centralized transportation tunnels and excavation working faces that are powered by separate power substations in coal mining working faces without low-voltage power distribution points. .

⑤ Connect each junction box of the power armored cable and the high-voltage cable connection device.

6. It is best to place the local grounding electrode in the ditch in the tunnel. If there is no ditch, it should be buried in a humid place. The local grounding electrodes and grounding leads located in the tunnel ditch shall not affect the normal passage of water and the cleaning of the ditch.

7. All equipment that needs to be grounded inside the mine is directly connected to the grounding bus (or auxiliary grounding bus) or the steel strip (or steel wire) or lead sheath of the armored cable through the grounding wire. Or the grounding core wire (or grounding sheath) of the rubber sheathed cable is connected. The grounding bus (or auxiliary grounding bus) and the grounding parts of all cables connected together are connected to each local grounding pole through each grounding conductor, and finally are directly connected to the main grounding pole, thus forming a whole mine. A complete and uninterrupted general grounding network.

8. If the partitions in the mine have independent power supply from the well, they can set up the main grounding electrode of the partition separately underground or above the well, but the grounding resistance of the total grounding network should not exceed 2Ω.

9. It is strictly forbidden to directly ground the neutral point of underground distribution transformers. It is strictly forbidden to supply power underground from transformers or generators whose neutral points are directly grounded on the ground, but are exclusively used for underground electric locomotive converter equipment. Special transformers are not limited to this.

10. Each device must be directly connected to the grounding grid (grounding bus, auxiliary grounding bus) with an independent connecting wire. It is prohibited to connect several devices to ground in series, or to connect several grounded parts in series.

11. The grounding bus and the auxiliary grounding bus of the substation should use bare copper wire with a cross-section of not less than 50mm2, galvanized iron wire with a cross-section of not less than 100mm2, or galvanized iron wire with a thickness of not less than 4mm and a cross-section of not less than 100mm2. Zinc flat steel. The auxiliary grounding bus of power distribution points and other electromechanical chambers in the mining area should use bare copper wire with a cross-section of not less than 25mm2, galvanized iron wire with a cross-section of not less than 50mm2, or galvanized flat steel with a thickness of not less than 4mm and a cross-section of not less than 50mm2.

12. The connecting wires and grounding wires should be bare copper wires with a cross-section of not less than 25mm2, galvanized iron wires with a cross-section of not less than 50mm2, or galvanized flat steel with a thickness of not less than 4mm and a cross-section of not less than 50mm2. For electrical equipment grounding conductors and connecting conductors with a rated voltage lower than or equal to 127V, bare copper wires with a cross-section of not less than 6mm2 can be used.

13. It is strictly prohibited to use aluminum conductors as ground electrodes, ground bus bars, auxiliary ground bus bars, connecting wires and ground wires.

14. The steel strip (or steel wire) of ungalvanized armored cables must be anti-corrosion treated regularly and should be painted once every 1 to 2 years.

15. The resistance value of the total grounding grid measured from any local grounding device should not exceed 2Ω.

The resistance value of the protective grounding cable core wire (or other equivalent grounding conductor) between each mobile and handheld electrical equipment and the grounding grid shall not exceed 1Ω.

16. These rules only apply to the protective grounding system in coal mines. 2. Installation of underground grounding device

1. Protective grounding electrode

1. Main grounding electrode

①Main grounding electrode of main and auxiliary water tanks The main grounding electrodes of the building and partitions should be made of steel plates with an area of ??not less than 0.75m2 and a thickness of not less than 5mm. If the mine water is acidic, its thickness should be appropriately increased or plated with acid-resistant metal or other corrosion-resistant steel plates depending on its corrosiveness.

② When installing the main ground, it should be ensured that the connection between the ground bus and the main ground electrode does not bear large pulling force, and a traction device should be provided to facilitate the removal of the main ground electrode for inspection.

2. Local grounding electrodes

① For local grounding electrodes buried in tunnel ditches or wet places, steel plates with an area of ??not less than 0.6m2 and a thickness of not less than 3mm can be used.

② Galvanized iron pipes can be used for local ground electrodes buried in other locations. The diameter of the iron pipe shall not be less than 35mm and the length shall not be less than 1.5m. At least 20 holes with a diameter of no less than 5mm must be drilled on the pipe. The iron pipe must be perpendicular to the ground and must be buried in a moist place.

If it is difficult to bury the pipe, two galvanized iron pipes with a length of not less than 0.75m and a diameter of not less than 22mm can be used. At least 10 holes with a diameter of no less than 5mm must be drilled on each pipe. Both iron pipes are perpendicular to the ground and must be buried in a moist place. The distance between the two pipes is more than 5m, and before connecting to the grounding grid, the grounding resistance of the local grounding electrode composed of two iron pipes connected by a connecting wire and a grounding wire must be measured. The grounding resistance value shall not be greater than 80Ω.

2. Grounding method of fixed electrical equipment

1. For the grounding of the transformer, the steel strips and lead sheets of the armored cables on the high and low voltage sides should be connected to the grounding wires respectively. On the dedicated grounding screw on the transformer housing. If a rubber-sheathed cable is used, connect the grounding core of the cable to the internal grounding terminal of the incoming and outgoing line device, and then connect the grounding screw of the transformer shell to the grounding bus (or auxiliary grounding bus) with a connecting wire.

2. To ground the motor, you can directly connect the grounding screw of its shell to the grounding bus (or auxiliary grounding bus). The rubber-sheathed cable should connect the special grounding core wire to the grounding screw in the junction box (box). If armored cable is used, the armored steel strip (steel wire) and lead sheet at the end should be connected to the grounding screw of the shell. It is prohibited to use the motor's foot bolts as the grounding screws of the housing.

3. For the grounding of high-voltage power distribution devices, the grounding parts of the cable heads (armored, lead sheathed or grounded core wire heads) of each inlet and outlet should be connected to the power distribution device with independent connecting wires. on the grounding screw, and then use a connecting wire to connect the imported cable head grounding screw to the chassis grounding screw, and finally connect it to the grounding bus (or auxiliary grounding bus). You can also connect the grounding part of the cable head directly to the grounding bus (or auxiliary grounding bus). ground bus).

4. The grounding of electrical equipment in underground electromechanical chambers, substations in each mining area (including mobile substations and mobile transformers) and distribution points, in addition to the armored layer and shielding layer of the cables In addition to connecting the grounding core wire to the main grounding grid, an auxiliary grounding bus must also be provided. The enclosures of all its equipment must be connected to the auxiliary ground bus with independent connecting wires. The auxiliary ground bus must also be connected to the local ground electrode with a ground conductor.

5. For the grounding of all equipment in the underground central substation, except for the grounding part of the cable, its shells are directly connected to the main grounding electrodes in the main and auxiliary water tanks with independent connecting wires. connected to the ground bus.

6. For grounding of the cable junction box, the ground screw on the junction box should be directly connected to the local ground electrode with a wire.

For the grounding of the armored cables at both ends of the junction box, use the binding method to connect the lead skin and steel strip (steel wire) layers of the cables at both ends through the connecting wires connected to the grounding wire.

When the steel strip layer and lead layer of the cable heads at both ends of the junction box are tied with connecting wires. The lead sheet should be divided into two or three equal parts along the axial direction of the cable and turned upside down 180 degrees. The lead sheet should be attached to the steel strip. The contact point between the lead sheet and the steel strip should be polished and smooth. The length of the binding along the axial direction of the cable should not be less than 50mm. .

3. Grounding method of mobile electrical equipment

1. The grounding of mobile electrical equipment is achieved by using the grounding core of the rubber sheathed cable. One end of the ground core wire is connected to the ground terminal in the inlet device of the mobile electrical equipment, and the other end is connected to the ground terminal in the starter outlet device. When connecting the ground core wire to the ground terminal, make sure the ground core wire is longer than the main core wire. The starter shell is connected to the main ground grid or local ground electrode.

2. For grounding of the mobile substation, first connect the grounding core wires of the high-voltage and low-voltage side rubber-sheathed cables to the internal grounding terminals of the incoming device, and use the connecting wire to introduce the high-voltage side wires into the device. The external wiring terminal is firmly connected to the external ground terminal on the high-voltage switch box. Then connect the external grounding screws on the high- and low-voltage side switch boxes and dry-type transformers to the grounding bus (or auxiliary grounding bus) with independent connecting wires.

4. Connection and reinforcement of grounding wires

1. The connection between the grounding busbar and the main grounding electrode must be welded. The connection between the grounding conductor and the grounding busbar is best done by welding. If unconditional, galvanized bolts with a diameter of not less than 10mm and a locking device can be used to tighten the connection. The connection should be tinned or galvanized. When binding with bare wires, the binding length along the axial direction of the grounding bus shall not be less than 100mm.

2. In electromechanical caves made of concrete and stone, the ground bus or auxiliary ground bus should be fixed on the wall close to the ground with hooks or clips. 3. Inspection and measurement of grounding devices 1. Inspection of protective grounding

1. The protective grounding of electromechanical chambers with personnel on duty and electrical equipment operated by dedicated personnel must be comprehensively inspected every shift. The protective grounding of other equipment shall be comprehensively inspected by maintenance personnel at least once a week. When problems are discovered, they should be dealt with immediately and recorded in a timely manner. If problems cannot be solved, they should be reported to the relevant leaders.

2. After each installation or move of electrical equipment, the completeness of the grounding device of the electrical equipment should be checked in detail. Special attention should be paid to electrical equipment that is highly vibrating and frequently moved -

and inspections should be strengthened at any time.

3. If the grounding device is found to be damaged during inspection, it should be repaired immediately. It is forbidden to receive power until the protective grounding device of electrical equipment is repaired.

4. Check the main grounding electrode and local grounding electrode in detail at least once a year. If defects such as poor contact or severe corrosion are found, they should be processed or replaced immediately, and their grounding resistance should be measured. The main grounding poles of the main and auxiliary water tanks must not be inspected at the same time, and they must work together. When the mine water is highly acidic, the number of inspections should be appropriately increased.

2. Measurement of grounding resistance

1. A dedicated person must be responsible for the measurement of the grounding resistance of the underground general grounding network, at least once a quarter; the newly installed grounding device must be put into operation Before testing, measure the ground resistance value and record the measured data in the ground resistance test record.

2. When measuring ground resistance in mines with the risk of gas and coal dust explosions, an intrinsically safe grounding megger should be used. If an ordinary instrument is used, it is only allowed to measure the gas concentration below 1 location and take certain safety measures.

This article comes from: China Coal Mine Safety Production Network is limited by word limit, you can find the rest by yourself.

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