During creation of current network for the choice of sections on its certain sites it is required to know current capacities. When calculating network on losses of tension it is necessary to take into account not only loading, but also length of all sites of network. Therefore calculation of the consumed current begins with drawing up the rated scheme with the indication of loading and length of sites of all chains entering into network.
Instruction
1. For simplicity of calculation of three-phase network you recognize that loadings of all three phase wires are identical. In real practice such condition is feasible only for the power networks incorporating three-phase engines. Single-phase receivers in network can have certain unevenness of load dispatch on phases. However for preliminary general calculations this circumstance can be neglected.
2. Execute the single line diagram of wires of network for evenly loaded line phases. Specify the loadings attached to network and length of each its site. Note on the rated scheme of installation site of safety locks and other protective devices.
3. If the scheme provides display of electric wiring in the building, use its floor plan, including cuts on which there has to be wiring with the obligatory indication of points of connection of receivers of energy.
4. Make the external rated scheme of the network equipped at large enterprise or in the small settlement with use of the plan of all area of construction or point. Separately specify on the scheme of the house or the separate buildings representing points of joining of groups of electroreceivers.
5. According to the drawing measure length of each site of current network taking into account scale. If scale is not established, make direct measurement of sites on the area. When drawing sites of network on the scheme observe the correct sequence of connection of elements of the scheme among themselves.
6. After drawing up the rated scheme define design current on the line both for each electroreceiver, and for group of the elements connected among themselves on formula: I = 1000 x P / (1.73 x U x cosφ), gder – the electroreceiver power determined by calculation; U – rated voltage on receiver clips; cosφ – receiver power factor; x - the sign of multiplication; / - division sign.
7. Determine by the formula given above also design current for group of the electroreceivers attached to the line of single-phase current. For glow lamps and heating devices accept power factor equal to unit that simplifies calculations.