Calculation of power supply and selection of electrical equipment of the main mechanical workshop 10/0.4 kV
- Added: 07.04.2021
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The thesis includes an explanatory note, drawings and a presentation for protection.
At present, it is impossible to imagine the life and activities of modern man without the use of electricity. Electrical energy is used in all spheres of human life. The main consumers of electric energy are industry, transport, agriculture, communal services of cities and towns. The main advantage of electric energy is the relative simplicity of production, transmission and conversion.
Power supply is a set of devices for the production, transmission and distribution of electric energy. Each electric receiver is designed to operate at certain parameters of electric energy: nominal frequency, voltage, form of electric signal, therefore, for its normal operation, the required quality of electric energy must be ensured. In Russia, GOST 1310997 "Standards for the quality of electric energy in general-purpose power supply systems" operates, which establishes indicators and standards for the quality of electric energy. Unfortunately, it must be stated that GOST 1310997 standards are not sufficiently controlled and often not respected.
Power supply systems are created to provide industrial electric power receivers, which include electric motors (drives) of various mechanisms, electric furnaces, welding plants and other industrial electric power receivers. Energy savings should be realized by reducing all types of electrical losses, by switching to energy-saving production technologies.
The basis of energy in Russia is the construction of large-capacity power plants. In the near future, energy is faced with the task of worldwide development and use of renewable energy sources: solar, geothermal, wind, tidal, etc. Currently, more than 600 thousand km of overhead and cable transmission lines with a voltage of 35 kV and more than 2 million km with a voltage of 0.4... 20 kV, over 17 thousand substation with a voltage of 35 kV and above with a total transformer capacity of almost 575 million kV∙A and more than half a million transformer points 6... 35/0.4 kV with a total capacity of 102 million kV∙A.
The Russian electricity industry is the most important life-supporting industry in the country. It consists of more than 700 power plants with a total capacity of 215.6 million kW; the industry employs more than 1 million people.
1.1Recapitulation of electrification objects
According to the operating mode, all equipment is divided into 3 groups:
A continuous mode is a mode of operation in which the receiver operates for a long time, but its current-carrying parts do not exceed the permissible temperature. Resistance furnaces operate in this mode.
A short-term mode is such a mode of operation in which the working period is not so long that the temperature of individual parts of the machine can reach a steady value, the period of stopping the machine for so long that the machine manages to cool to ambient temperature. In this mode, the sharpener and dampers operate.
A re-short-term mode is a mode of operation in which working periods alternate with periods of pauses, and the duration of the entire cycle does not exceed 10 minutes. At the same time, the heating does not exceed the permissible one, and cooling does not reach the ambient temperature. In this mode, a bridge crane, a beam crane and a stacker crane operate.
According to the power of electric receivers, there are: low power - up to 10 kW; average power - up to 100 kW; high power - more than 100 kW. In terms of power, the electric receivers of the mechanical workshop relate to consumers of medium and low power, except for the electric resistance furnace No. 19, which refers to consumers of greater power .
By voltage, electric receivers are distinguished by low-voltage and high-voltage. Low-voltage - their voltage is up to 1000 V, and high-voltage - with a voltage of more than 1000 V. All electrical equipment refers to low-voltage consumers, since all installations operate from the 220/380 V network.
All electric receivers at this enterprise operate at an alternating current of industrial frequency of 50 Hz.
All sources shall ensure reliability in power supply. This workshop belongs to 2 categories of power supply. It is recommended to provide this category with power from two independent sources, for electric receivers, interruptions in the power supply for the time required to turn on the backup power by the actions of the duty personnel or the field operational team are permissible. Power supply from one transformer is allowed, power supply interruption is allowed for no more than 24 hours.
When designing the power supply system of the mechanical workshop, the main task is to determine the value of supply voltages.
Voltages of 110, 150, 220, 330 and 500 kV should be used to power large and especially large enterprises.
The voltage of 35 kV is used to power medium-capacity enterprises and to distribute electric energy at the first stage of power supply, at such enterprises using deep bushings in the form of mains, to which shop substations 35/10 kV are connected.
Deep input - power supply system with high voltage approach to electrical installations with minimum number of stages of intermediate transformation.
At the second stage voltage is equal to 10 kV, it feeds shop transformer substations. This 10 kV voltage is used in the in-plant energy distribution. And also at an enterprise with powerful engines that allow direct connection to a 10 kV network, at enterprises of small and medium capacity. A voltage of 10 kV should be used as the main voltage as the most economical in contrast to a voltage of 6 kV. A voltage of 6 kV is usually used when there are a significant number of electric receivers for 6kV at the enterprise.
In the third stage, voltage equal to 380/220 V is used mainly in electrical installations up to 1000 V, to supply electric receivers from common transformers, but, as a rule, from individual networks.
Voltage 220V is designed to power single-phase electric receivers - these are such electric receivers as lighting lamps, and also for power supply to household appliances.
At this enterprise, the main power supply is made with a voltage of 6 kV. Since low power substations are powered by 6kV. Mainly at the mechanical workshop, all consumers are powered by an AC industrial frequency of 50 Hz with voltages of 380 and 220 V.
Selection of power supply scheme
The power supply system is a set of electrical installations designed to provide consumers with electric energy. Power supply schemes of industrial enterprises are divided into external and internal power supply schemes.
In this workshop, the power supply scheme of the transformer-main unit was chosen, since it is more suitable for technical and economic reasons. The transformer-main unit is a mixed power supply circuit, it contains elements of the radial and main circuits. Large and responsible consumers are fed according to the radial scheme, and medium and small consumers - according to the main.
At the enterprise, the main lowering substation is installed, at a voltage of 35kV, which reduces the voltage to a value of 6kV. The mechanical workshop has a complete transformer substation KTP6/0.42 × 1000 with transformers TM1000/6.
In the workshop, a main bus line (SHMA) for a nominal current of 4000 A. is laid from the complete transformer substation. Cable lines for supplying distribution bus lines (SHRA) in the amount of two pieces and distribution points (RP) in the amount of three pieces depart from it. Then, specific electric receivers are powered from the SR or SR. The selected section of wires and cables is from 2.5 to 185mm2. ShRA1pitaet the first group of electroreceivers which enter: presses and hammers. And SHRA2 feeds the second group of electric receivers, consisting of: furnaces, hardening unit and nitrate bath.
Short-circuit current protection is provided by circuit breakers with electromagnetic and combined disconnectors. For welding equipment, current protection k.z. is made by fuses. Overload current protection is provided by magnetic starters with built-in thermal relay.
To increase the power factor and compensate for reactive power, a compensating device UK20.3850 is used.
As a result of the course design, the power supply of the mechanical workshop was designed.
In the workshop, power supply is made according to the "transformer line" block scheme. The transformer-main unit is a mixed power supply circuit, it contains elements of the radial and main circuits. Large and responsible consumers are fed according to the radial scheme, and medium and small consumers - according to the main. As the main busline ShMA59N with a permissible load 4000A was chosen. To power the presses and hammers, the SHRA1 distribution bus duct with a permissible load of 600A was chosen. For power supply of furnaces, the hardening unit and a selitrovy bathtub the distributive ShRA2 busline which is broken into three buslines with a permissible load 600A everyone was chosen. The most powerful electric receiver is powered by cable from the main bus line. Distribution points in the amount of three pieces were selected to supply the remaining electric receivers.
Asynchronous motors with a short-circuited rotor were chosen for presses, hammers, machines, and saws, and asynchronous motors with a phase rotor for cranes and trolleys. To reduce power outages, starting and protective equipment was chosen. For motor drives, circuit breakers from short-circuit currents and magnetic starters with an integrated thermal relay from overload currents were selected. To protect welding equipment from short-circuit currents, fuses were selected together with choppers. Electrical loads were calculated for normal operation of electric receivers. Compensating device UK20,3850 is selected to reduce reactive power and increase power factor. The number of transformers in the substation is selected. Since the workshop belongs to consumers of the second category of power supply, two transformers with a rated capacity of 1000 kVA are installed at the substation.
Short-circuit currents were calculated. Protection of distribution points and distribution busbars against short-circuit currents and overloads is provided by automatic circuit breakers with combined disconnectors. Earthing devices were calculated to protect the workers.
During the course project, a single-line power supply scheme and a mechanical workshop plan with distribution networks were built. The entire list of electrical equipment located in the proposed workshop was indicated in the diagram. Power supply of the mechanical workshop was designed taking into account all the conditions necessary for reliable and safe work of personnel.
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