Operation of in-store electrical networks
When operating indoor electrical networks, the condition of the electrical insulation materials used in electrical wires and cables is of great importance. When it is dusty and dirty, the electrical insulating properties of the insulation are reduced. Overheating the insulation along with reducing its electrical insulating properties makes it brittle and mechanically less durable. As a result, electrical damage occurs, leading to premature failure of the electrical wiring.
Another element of in-store electrical networks, ensuring their reliable operation, are electrical contacts, which gradually oxidize and weaken during operation. As a result, the transient resistance of the contacts increases, which causes their unacceptable overheating and a decrease in quality.In order to ensure the uninterrupted operation of internal store electrical networks and their normal service life, supervision and necessary checks are carried out during operation and, if necessary, timely repairs are carried out afterwards. The required frequency of internal electrical network checks depends mainly on operating conditions and the environment.
In workshops that are wet, dusty and contain vapors and gases that are harmful to the insulation of electrical networks, the inspection is carried out more often than in workshops with a normal environment. The terms and content of inspections of power transmission networks are approved by the chief energy engineer of the enterprise in accordance with the current rules for technical operation, taking into account the specific features of each enterprise.
In rooms with a normal environment, an inspection of internal electrical networks is usually produced once every six months, and in rooms with an unfavorable environment (moist with caustic vapors, etc.) — once every three months. The repair of in-store electrical networks is carried out if necessary based on the results of inspections and checks.
Inspection of internal electrical networks is allowed to be carried out by suitably qualified personnel subject to mandatory compliance with caution. During inspections, it is prohibited, in particular, to remove warning posters and fences for electricity, as well as to approach parts of electrical installations that are under voltage.If during the inspection of the electrical networks malfunctions are found, then the immediate supervisor is notified of this and at the same time a corresponding entry is made in the operational log.
When inspecting the internal electrical networks, they check the general condition of the external part of the electrical insulation and the absence of visible damage in it: the strength of the fastening of the electrical wires and the structures supporting the cables and other elements of the electrical network, the absence of tension in the wiring at the points of the fork.
When checking machines, control stations and fuses, they check their operability and compliance with the load and the cross-section of wires and cables. In places dangerous in terms of electric shock, check for the presence of warning posters, inscriptions and barriers, as well as the condition of the cable funnels, the absence of leaks in them, the presence of labels, the density of contacts at the connection points of the cable cores.
When checking the electrical networks, it is also necessary to check the condition of the grounding devices and the reliability of the contact connections in them. During the check of the internal electrical networks, the electrician on duty is allowed to turn on the machines, change the tube and plug fuses without removing the tension. Replacement of open type fuses and minor repairs to lighting wires can only be done when the power is off.
In addition to these checks, it is necessary to carry out control over the condition of internal store electrical networks using periodic measurements of the resistance values of their electrical insulation, loads and electrical voltage of the network at different points. The frequency of these measurements, as well as the choice of measurement points, depend on local conditions. They are given in the instructions of the enterprises. Normally, the value of the insulation resistance of electrical networks is checked in damp and dusty rooms twice a year, and in rooms with a normal environment — once.
Taking in-store electrical networks after major repair, their insulation is tested with a voltage of 1000 V industrial frequency for 1 min. If the insulation resistance measured with a 1000 V megohmmeter is at least 0.5 MΩ, then the test with increased power frequency voltage can to be replaced by an insulation test using a megohmmeter 2500 V. Frequency is optional.
Considering the state of electrical insulation, it should be borne in mind that even under the most favorable operating conditions for electrical networks, their insulation under the influence of various reasons gradually deteriorates (aging) and periodically the wiring must be replaced with a new one.
During the operation of internal shop electrical networks control electrical loadsthis may change. Overloading electrical networks for a long time leads to deterioration of their insulation and reduction of the duration of operation.If the checks carried out show that the overloading of the electrical networks is systemic, then it is necessary to take measures to unload the networks or to restore them. When strengthening the electrical network, it is necessary to ensure that the currents in the new wires and cables do not exceed the values \u200b\u200bset for them by the PUE.
The voltage supplied to electrical receivers is important for the proper operation of electrical equipment, as it does not remain constant throughout the day. During the hours of maximum electricity consumption, the voltage in the electrical networks decreases, and during the hours of minimum consumption it increases. Fluctuations in network voltage can be caused by other reasons.
Electrical receivers operate normally as long as voltage fluctuations do not exceed certain limits. Fluctuations are considered acceptable for internal shop electrical networks: for electric motors within +5% of the nominal voltage (in some cases, deviations from the nominal from -5 to +10% are allowed), for the most distant working lighting lamps in industrial enterprises — from -2.5 to + 5%. If, through checks, it is found that the voltage fluctuations exceed the specified values, then it is necessary to take measures, for example, to use transformers that allow voltage regulation.
If during operation any line has been without voltage for more than a month, then before turning it on, carefully check and check the condition of its insulation.
Minor repairs of internal electrical transmission networks include the following work: replacement of defective insulators, switches and sockets, fixing of sagging electrical wires, restoration of the electrical network in the places of its interruptions, replacement of circuit breakers and fuses, etc.
The scope of ongoing repairs includes: repair of defective sections of the internal marketing electrical network, including replacement of electrical wiring with damaged insulation, including in pipelines, pulling out wires with unacceptably large sag.
The content of the overhaul is a complete re-equipment of the internal workshop electrical networks, including the restoration of all worn elements.