INVESTIGATION OF ERRORS OF CURRENT TRANSFORMERS IN THE PROTECTION SYSTEMS IN STEADY AND TRANSIENT CONDITIONS OF ENERGY SYSTEM

Abstract

Purpose. The main idea of the paper is investigation of the maximum values of current and angle errors of the current transformers and the nature of their changes in steady-state and transient power system conditions in which the possible output of errors beyond the normalized range of values, as well as a comparison of the degree of change of current and angle errors of the current transformers for power supply auxiliary wiring devices of relaying protection in these conditions. Research methods. The authors used the method of simulation and visualization of the current transformer operation of computers, intended for supply of secondary circuits of relay protection devices in steady and transient conditions of supply power system and different operating modes. The obtained results. The authors defined the percentage of the maximum current and angular error of the primary current transformation to the secondary circuit of the current transformer which are caused by the presence of the magnetizing current and resistive losses in the magnetic system of the test current transformer; their comparison is performed and conclusions are drawn regarding their changes in steady-state and transient conditions, in particular, the fact is established that the current errors in emergency conditions vary to a much greater extent than the angular and under certain conditions may extend beyond the value of the normalized state standards. Scientific novelty. The authors developed the modern method of investigation of current and angle errors of the current transformers for auxiliary supply of relay protection devices based on the use of a computer model of an ideal current transformer with a linear no hysteresis B-H curve, which has similar characteristics and primary and secondary circuit parameters to study the real transformer current. Practical significance. The results can be used in researching the optimum operating current transformers conditions and the development of new principles of perform measurement and logical circuits of relaying protection, in particular, it was concluded that in order to provide the more sensitive and selective protection we can use the devices based on the principle of their action to respond only to the phase relation between the currents of the current transformers and connections that have to be rebuilt only from the angle measurement errors.