Investigation of dependences of selectivity of devices of protection against the value of short circuit currents in electrical networks up to 1000 V

According to PUE-2017, each group line must be protected against short circuits. Instant disconnection (cut-off) of the line in the event of short circuits provides an electromagnetic release of the circuit breaker. Reliable tripping is possible if the current of a single-phase short circuit is greater than the instantaneous tripping current. Today on the market are widely available circuit breakers with characteristics "B", "C" and "D", which are characterized by different multiplicities of the cut-off current of the electromagnetic release. Some European companies produce circuit breakers with other characteristics, which greatly expands the possibilities protection of electrical equipment. The difficulty in organizing the selectivity of protection is that the circuit breakers of modular design when switching off short circuits are characterized by the same switching time (not more than 0.05 s). The purpose of the research is to find ways to organize the selectivity of protection in electrical networks with voltage up to 1000 V using reliable values of short-circuit currents. In networks with a voltage of up to 1000 V, the current of a single-phase short circuit can be calculated fairly accurately if the exact values of all sections of the electrical network are known. In practice, it is not always possible to obtain reliable data on the numerical characteristics of the 0.4 kV network to which a new energy facility is connected. Therefore, it is proposed to consider part of the network as an active quadrupole, the characteristics of which are obtained by measurements at the point of connection. For further calculations it is necessary to know the voltage at the clamps of the four-pole scheme and the internal impedance. Based on the theory of four-pole scheme, you can get the original data for calculations without calculating the internal parameters of four-poles scheme. Thus, it is proposed to use a hybrid method for estimating the magnitude of probable short-circuit currents in electrical networks up to 1000 V when designing new energy facilities. Credible values of short-circuit currents will allow to organize selective protection of electric networks.

Multiple Fixed Pole-Based Rational Approximation for Fractional Order Systems

Our topic is the rational approximation of fractional order systems under Riemann–Liouville definition. This is a venerable, vast, fundamental area which attracts ongoing attention in coming years. In this work, the multiple fixed-pole scheme is developed. First, new schemes with different relative degree are developed to approximate fractional operators. Then, the fractional order is extended to the case of α>1. A discussion is made on the uniformity between the differentiator-based method and the integrator-based method. Afterward, the multiplicity of pole/zero is further generalized. In this framework, the nonzero initial instant and nonzero initial state are considered. Four examples are finally provided to show the feasibility and effectiveness of the developed algorithms.