How it is correct to choose protection, cables and the switching equipment?
In network of 0,4 kV the choice of the switching equipment, zayoshchit and cables is interconnected. For any the prisoyedineyoniya have to be provided:
- Standard duty of work. Rated napryayozheniye and currents of devices and permissible currents of cables have to correspond to the rated voltage and the long design current of loading. Execution of apyoparat and types of cables have to correspond to usloyoviya of their operation.
- Firmness at KZ. Devices and cables have to be resistant at KZ, and protection devices - it is reliable to disconnect design currents of KZ.
- Protection against all types of KZ. Parameters of devices of protection and cables have to provide sufficient sensitivity of protection to all types of KZ at the end of the zashchiyoshchayemy zone. It is recommended to apply automatic cuts with the combined releaser which element with the dependent characteristic is reserve protection.
Have to be provided selectivity (the otyoklyucheniye only of the damaged site), reliability (operation at emergence of conditions on operation and failure at their absence), high-speed performance of protection. Fast shutdown of KZ provides the stoyyokost of devices and cables to thermal action of toyok of KZ, reduces duration of breaks of the power supply of elekyotropriyemnik, facilitates the subsequent self-starting of electric motors, ensures safety of obsluzhiyovayushchy personnel, prevents the possibility of the naruyosheniye of synchronous parallel operation of low-power emergency generators and also synchronous elektrodviyogatel.
Protection against the abnormal modes - the long overload of the electric motors subject to peregruzyoka for the technology reasons and also wires and cables in the cases provided by Rules.
At start-up and self-starting of electric motors devices of protection should not disconnect the chain, and the section of cables has to provide the voltage level, sufficient for the turn of elekyotrodvigatel, on their clips.
Besides, the set of the equipment and its design in the chain of any accession have to obesyopechivat the possibility of the conclusion in repair of accession or the device of protection without stopping of the main tekhnoloyogichesky process.
The choice of the equipment, protection and cables of this prisoyoedineniye carry out in the following order.
Define accession loadings, the place of the podklyuyocheniye, make the preliminary scheme of accession and the closest site of the power line.
Previously choose prisoyediyoneniye cable section under the terms of heating in the standard duty, proyoveryat its sufficiency under the terms of loss the napryazheyoniya in the standard duty and at start-up of elektrodvigateyoly, calculate KZ currents.
Previously choose type and rated parayometra of the protective device of accession under the terms of the standard duty, firmness and selectivity at KZ,
Calculate protection settings, by results of calculation specify type and rated parameters of the device of protection. Check sensitivity of protection. At insufficient sensitivity carry out special events after which the section or the cable lay-up, the scheme of accession, rated current of the automatic cut can change. At the same time all calculations are carried out again.
If accession is intended for protection of assembly, then check firmness at KZ of the devices installed on this assembly.
Check protection of the electric motor and the cable against the overload (if necessary) with possible specification of installations of protection or section of the cable.
Check selectivity of protection with above - and subordinate protective devices by means of map development of selectivity.Top