Pre-press plate company power supply and grounding
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For a long time, the problem of power supply in factories has always been a concern. How to ensure the convenience of equipment connection and ensure the stability of the power supply voltage, the selection of the load of the intermediate switchgear is extremely important. In particular, prepress plate-making companies, due to the use of a large number of sophisticated electronic equipment, need to be in the standard specifications in the continuity of the input voltage and the stability of the grounding voltage to ensure their work, the printing department of the general printing company should supply power Has the following characteristics:
1. Devices with different voltages should not be directly connected on the wires. They should be tapped by the air switch of the total points to prevent the three-phase four-wire tapping error from being caused to burn out.
2. In addition to installing the total sub-switch in the power distribution room, it is also necessary to set up lighting switches, socket switches, air-conditioning switches and independent equipment switches in the department to facilitate management;
3. Most imported electrical extensions and equipment such as imagesetters and CTPs use 110V voltages in Europe and the United States. Therefore, be sure to use 220/110V transformers and mark the output voltage at the output to prevent mixing with 220V equipment. , causing the problem of equipment burnout;
4. Monitor the internal supply voltage and current value of the entire company at any time, pay attention to the voltage and current value under abnormal conditions;
5. All energized equipment must be effectively connected to the ground wire, and ensure that the resistance of the ground wire and the neutral wire is below 6 ohms, and the voltage value is below 2V;
6. For computers with computers and important data storage, UPS uninterruptible power supplies of appropriate power must be provided.
7. All the switches installed in the department must be the rated air safety air switch and have the switch test function;
First, the power supply layout of the workshop
The power supply arrangement of the plate making workshop is mainly based on the wire, supplemented by independent wire troughs. The indoor wiring usually adopts insulated wires, which requires the insulation sheath of the wire to have good insulation performance, the texture is flexible and has considerable mechanical strength, and can withstand acid oil and ozone. For erosion, the wire trough is made of insulated PVC fireproof material.
(1) The selection of the carrier surface of the wire is based on the following principles:
1. Select by allowable current capacity
The allowable current carrying capacity of the wire is also called the safe current carrying capacity or safe current value of the wire. The maximum allowable working temperature of the wire is 65 degrees. If the temperature exceeds this temperature, the insulating layer of the wire will age rapidly, deteriorate and damage, and even cause fire. The so-called allowable current carrying capacity of the wire is the maximum current value that can be passed for a long time when the working temperature of the wire does not exceed 65 degrees.
Since the operating temperature of the wire is related to the current through which the wire passes, it is also related to the heat dissipation condition and environment of the wire. Therefore, the allowable current carrying capacity of the wire is not a fixed value. The same wire is laid in different ways, or at different ambient temperatures. The allowable current carrying capacity is also different. The general principle is that the air current of 1 square millimeter of the cross section at ambient temperature +25 degrees is 20A, but the current passing through is different due to the different laying methods.
2. Select by mechanical strength
When the load is too small, if the selected conductor cross-section size is calculated according to the allowable current carrying capacity, the thin wire often fails to meet the requirements of mechanical strength and is prone to wire breakage accidents. Therefore, there is a special provision for the minimum allowable cross-section of the indoor wiring core. The regulations are based on the current used.
3. Select the voltage loss allowed by the line
If the wiring line is long and the cross-section of the wire is too small, the voltage loss may be too large, which may cause the motor to have insufficient power or heat to burn, and the illuminance of the electric lamp is also greatly reduced. Therefore, the voltage of the electric device or the illuminating device is generally prescribed. And the receiving voltage of the lighting equipment should not be lower than 95% of the rated voltage.
(2) The connection of the wires shall have the following requirements:
1. The wiring is tight, the joint resistance is small, the stability is good, and the ratio of the resistance of the same length of the same surface conductor should not be greater than 1;
2. The mechanical strength of the joint is not to be less than 80% of the mechanical strength of the wire;
3. Corrosion resistance;
4. The insulation strength of the joint should be the same as the insulation strength of the wire.
Second, the connection of the ground wire, the prevention of static electricity
Static electricity refers to a relatively static charge that can generate static electricity when the object is rubbed or when the two materials are in close contact. Electrostatic phenomenon is a common charging phenomenon. It is very easy to generate static electricity in some industrial production departments. It is easy to cause pre-press precision equipment failure after static electricity. The prevention of static electricity should include the following aspects.
The static electricity carried by any object will always disappear if there is no external expansion. Changing the external conditions can affect the speed at which static electricity disappears.
There are two main ways in which static electricity disappears, namely neutralization and leakage. The former mainly occurs through air, and the latter mainly occurs through the charged body itself.
1. Grounding
Grounding is the simplest and most common way to eliminate static hazards. Grounding is primarily used to eliminate static buildup on conductors and is not intended to eliminate static buildup on high-resistance insulators.
The electrostatically charged insulator is directly grounded through the conductor, which is equivalent to directing the earth potential to the insulator, which in turn increases the risk of spark discharge. A solid material having a resistivity of 109 Ω/cm or less and a liquid material having a resistivity of 109 Ω/cm or less are less likely to accumulate static electricity. Therefore, in order to allow static electricity on the insulator to leak faster, the insulator should be grounded through a resistor of 106-108 ohms.
2. Humidification
As the humidity increases, a thin water film is formed on the surface of the insulator, which greatly reduces the surface resistance and accelerates the leakage of static electricity. Therefore, in the production site where static electricity is generated, a humidifier can be installed to increase the humidity of the air and eliminate the danger of static electricity. High-temperature air with a temperature slightly higher than the surface temperature of the insulator can also be blown to the surface to form a water film, which leaks static electricity and eliminates danger. The effect of eliminating static electricity by humidification is also significant.
3. Antistatic agent
Impurities have a great influence on static electricity, some impurities increase static electricity, and some impurities can reduce static electricity. Antistatic agents are essentially impurities that reduce static electricity. Therefore, antistatic agents are also called antistatic additives. The antistatic agent is a chemical agent and has good electrical conductivity or strong hygroscopicity. Therefore, antistatic leakage is added to a high insulating material which is likely to generate static electricity, thereby eliminating the danger of static electricity.
4. Process control
Process control refers to taking appropriate methods from the process to limit the generation and accumulation of static electricity. It can reduce static electricity by appropriately selecting materials, reducing friction speed, and eliminating impurities.
Third, technical measures to ensure safety
To work on all electrical equipment that has been blacked out or partially powered down, the following measures must be completed:
1. Power outage;
2. Power inspection;
3. Install the grounding wire;
4. Hang the signboard and install the fence.
Fourth, the factory grounding electrical circuit
1. In the low-voltage neutral point ungrounded circuit, it is necessary to install a grounding automatic shut-off device or a grounding automatic alarm device that can act quickly when the grounding or leakage occurs.
2. In the low-voltage neutral point grounding circuit, the grounding automatic cutting device that can operate quickly when the single machine is grounded must be installed.
3. The grounding wire connecting the components to be grounded to the grounding trunk should use multiple stranded wires. The cross section should not be less than one third of the phase line cross section, and the minimum cross section copper wire should not be less than 4 mm2. The steel wire is not less than 6 square millimeters.
4. In the neutral grounding low voltage circuit, the protective grounding trunk should be connected to the neutral point.
5. The working zero line in the electrical circuit is insufficient, and it is used as a protective grounding wire.
6. The dedicated grounding or zero-protection line for electrical equipment and luminaires shall be connected to the grounding mains separately.
7. Lightning protection grounding.
8. Anti-static grounding.
Five, grounding resistance regulations
The factory neutral point ungrounded system, the grounding resistance value is not more than 10 ohms, the factory neutral point grounding system, the grounding resistance value is not more than 4 ohms, the lightning protection grounding resistance value is not more than 10 ohms, the electrostatic protection grounding resistance value Not more than 100 ohms.
The power supply of the prepress department must be implemented according to the specified requirements. At the same time, according to the requirements of the specific equipment, the safety and stability of the power supply can be ensured, so that the equipment can keep the work and the equipment normal under the condition of long-term operation.