Since electricity was applied to lighting, there have been categories of incandescent lamp, fluorescent lamp, iodine tungsten lamp, high-pressure mercury lamp and low-pressure mercury lamp. So far, new types of high-pressure sodium lamps and metal halide lamps have appeared in the market, which greatly improve the types and quantity, luminous efficiency and service life of lighting lamps. At the same time, with the development of technology, the color rendering performance of lighting lamps has also been greatly improved, but at the same time, the fault types of indoor circuits have also increased.
1 related technologies of indoor lighting circuits
The lighting circuit consists of power supply, wires, switches and loads (lighting lamps). The power supply also includes a low-voltage lighting distribution box, and all the energy required for lighting comes from the low-voltage lighting distribution box. Power supply also includes two different types: DC and AC. Generally, AC power is supplied by Y/yn three-phase transformer, and the neutral wire of each phase box is single-phase power supply. In the process of load distribution, it is best to make the three-phase load symmetrical, and the power supply is connected with the lighting lamp by wires. The processes that should be noted here include:
1. 1 conductor selection
The allowable value of its current carrying capacity is very important, which is based on the allowable current density. For open wires, the selection values of wires made of different materials are: aluminum wire 4.5A/mm2, copper wire 6A/mm2 and flexible wire 5A/mm2.
Type and form of 1.2 switch
The switch has absolute control over the current. Its load is an illuminating lamp, and it is the carrier that converts electricity into light. According to the different types of switches, line installation generally adopts the following three forms:
1.2. 1 A switch controls a lamp.
In order to ensure the safety of use and maintenance, when wiring, the switch must be connected to the phase line (that is, the live wire), that is, after the switch is turned off, the current of the lamp holder will disappear.
1.2.2 Set two double switches in different positions to control one lamp.
Often used in stairs or corridors. This form obviously expands the control range of line connection or disconnection, and this operation can be completed upstairs and downstairs or at both ends of the corridor.
1.2.3 three places are provided with two double switches and one triple switch to control one lamp.
This form is also common in stair corridors. For local lighting technical requirements below 36V, step-down transformers are often used for power supply. When installing, it is necessary to ensure that the primary and secondary windings of the transformer are connected in series with appropriate fuses, which can not only serve the needs of transformer failure and overload of the secondary winding, but also ensure that the transformer is not damaged when power is cut off in time. In addition to the above process requirements, the iron core and secondary winding of the transformer must be foolproof when installed in grounding or zero connection.
2 indoor lighting circuit failure and maintenance
2. 1 short circuit fault and maintenance
2. 1. 1 Cause of short circuit fault
Short circuits in indoor circuits are mostly caused by excessive current. Once the fuse cannot be blown in time, it may burn out electrical equipment such as wires, and even cause fire in serious cases. Short circuit can generally be divided into two different types: interphase short circuit and relative short circuit. The latter includes short circuit between phase line and neutral line and short circuit between phase line and ground. The main causes of short circuit are: ① wiring error, resulting from contact between phase line and zero line. ② Poor wiring or loose connection at the joint. ③ The plug was not installed according to the design requirements, but the thread was inserted into the hole, resulting in mixed wires. ④ The insulation layer or insulation resistance inside the electrical appliance is damaged, resulting in contact with the metal shell. ⑤ Water leakage in the house causes the lamp holder or switch to get damp or get water. ⑥ The conductor is insulated and damaged by external force, and the damaged part is in contact with the power line or the ground.
2. 1.2 short circuit fault maintenance
When checking and eliminating short circuit, the electrical equipment in the fault area must be powered off first, and then the troubleshooting situation should be observed. If it cannot be eliminated, the switch and the corresponding protection device should be re-checked. In addition, the maintenance of wire insulation aging should be done well. The reasons for insulation aging include: ① insulation aging is easy to occur due to leakage or overload of pipeline lines and sheathed lines and long-term overload of conductors. (2) External mechanical damage destroys the insulation layer of the conductor. In order to prevent the failure caused by this problem, the insulation resistance of the conductor and the structure of the insulation layer should be checked regularly and irregularly. Once the insulation resistance is reduced or the insulation layer is cracked, it must be replaced in time to ensure the safety of electricity use. (3) check the fuse fuse, remember that the fuse should not be too thick, and copper wire, aluminum wire and iron wire should not be used, otherwise there is a risk of short circuit.
2.2 Open circuit fault and maintenance
2.2. 1 Cause of open circuit fault
Open circuit will also limit the normal operation of the line. The causes of open circuit failure include: ① Loose or falling off the joint of thread head. ② The mouse bit off the conductor with small cross section. (3) The wires break under the action of external force, which may be caused by mechanical hooks. (4) Small-cross-section wires are burned under long-term overload or short circuit. ⑤ The poor quality of a single small cross-section conductor or its damage during installation will affect the normal function of the core wire in the insulation layer. ⑥ The connecting wires of moving parts are damaged due to overwork.
Maintenance of open circuit fault
When the wire is disconnected, the fault points should be gradually reduced to ensure the safety of inspection and handling. The general inspection steps are as follows: ensure that the fuse in the fuse is in a blown state, and if it is blown, check the short circuit or load in the circuit; If the fuse is not blown and the phase line at the power supply side is not connected with the power supply, the fuse at the next higher level should be checked immediately. If you still find that the fuse is not blown, check the switches and lines on the switchboard (board). Through the above troubleshooting methods, the cause of the fault is determined, and corresponding measures are taken to restore the smooth flow of the line.
2.3 Leakage Fault and Maintenance
2.3. 1 Cause of leakage fault
Leaks are mostly caused by damage to insulators. Including phase-to-phase leakage and phase-to-ground leakage, the most obvious leakage fault is the increase of electricity consumption, and then there are phenomena related to overload or short circuit fault, such as easy fusing, easy loosening of protection devices, overheating of wires and equipment. The main causes of line leakage are: ① insulation aging of lines and equipment. (2) The installation of line devices is not completed according to the construction technical requirements. (3) In the humid, high-temperature and chemically corrosive environment, the insulation performance of lines and equipment decreases. ④ The repaired insulation layer is unqualified or the insulation tape is loose, which affects its normal function.
2.3.2 Electric leakage fault maintenance
In troubleshooting, troubleshooting methods include: ① use megger telemetry to determine whether there is leakage. (2) Determine the nature of the leak. For example, when checking the ammeter, cut off the zero line and observe the current change. ③ The leakage range can be determined by removing shunt fuse or opening shunt breaker. (4) turn off the light switch of the line in turn, analyze the indication mode of the ammeter, and find out the specific leakage point. In short, corresponding solutions should be made according to specific reasons, including replacing new wires or equipment, ensuring that the installation form and technology meet relevant construction standards, and ensuring that the working environment of the line is suitable, such as no humidity, no hot air, etc.
2.4 fever fault and maintenance
2.4. 1 Reasons for heating failure
When the conductor in the indoor circuit is hot or the conductor joint is hot, the common failure factors are as follows: ① The specifications of the conductor used do not meet the design technical requirements, and when its cross section is small, the conductor will be hot due to overload. (2) When the capacity of electrical equipment increases beyond the conductor load, but the conductor area of the line does not increase with it, it will also lead to the occurrence of heat. (3) There are leakage problems in lines, equipment and various devices. ④ When a single current-carrying wire passes through a magnetic metal such as a steel pipe, it will generate heat. ⑤ The connection position of the conductor increases the contact resistance due to looseness or looseness, causing fever.
2.4.2 Overhaul of fever fault
There are many problems with fever faults, but they are easy to find. Usually, the factors causing the failure are not complicated, and it is easy to eliminate as long as the heat source is found.
3 Conclusion
In a word, the installation of indoor lighting circuit is an important unit in the production practice teaching of maintenance electrician in technical school, and the fault analysis and maintenance of indoor lighting circuit is the focus of this unit. Only when students understand the relevant installation technology and master the causes of indoor lighting circuit failures and corresponding maintenance methods can they take corresponding measures to eliminate failures and provide guarantee for safe electricity use.
refer to
[1] ginger. Fault analysis and maintenance methods of indoor lines [J]. Technology and Enterprise, 20 12(09).
[2] Yang Jianhua. Discussion on practical teaching of indoor lighting circuit troubleshooting [J]. Occupation, 20 15(24).
[3] Guo Jian. 10k V Overhead Lines Common Faults Analysis and Finding Methods [J]. Urban Construction Theory Research, 20 1 1(29).
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