INFLUENCE OF THE REMNANT MAGNETIZATION OF THE CURRENT TRANSFORMER CORES UPON THE COMPLIANCE OF THEIR TECHNICAL CHARACTERISTICS WITH THE REQUIREMENTS FOR MICROPROCESSOR TYPE PROTECTIVE RELAYS

Work objective is finding rational technical and economic solutions for examining current transformers for techspecs compliance satisfying the requirements of reinstalled microprocessor type protective relays and automation devices manufactured by NP EKRA LLC, taking into account DC component. Research methods: analytical methods for calculating the time of remnant magnetization in the core of a current transformer. Research results and novelty: it is understood that the saturation time of current transformers of the basic and backup protections, according to the results of the analytical method, was more than 25 ms, and for current transformers of differential bus bar protection was more than 5 ms. The obtained saturation time values for all types of current transformers built into oil circuit-breaker bushings (HV line) of 110 kV and bus bar coupling connector (BCC) of 110 kV (main protection, backup protection, differential bus protection), both in the absence and in the presence of remanent induction magnetic in CT cores with three-phase and single-phase short circuits, satisfy completely technical requirements either of microprocessor type protective relays or CT differential bus bar protection. Conclusion: built into CT BCC circuit-breaker bushings of 110 kV and oil circuit-breaker bushings (HV line) of 110 kV Foundry substations do not necessitate a mandatory replacement in case of non-complex redesign of microprocessor type protective relays and automation devices. When replacing oil circuit breakers with gas-insulated ones, it is recommended to use CT with similar characteristics.

Current Protection Applicability Analysis of Flexible DC Power Supply Network

In the flexible AC/DC distribution system supplying passive network, when the modular multi-level converter (MMC) inverter AC line fault occurs, the MMC short-circuit current amplitude is greatly affected by the control strategy, which may affect the operation performance of three-stage current protection. In view of this, a flexible AC/DC distribution network system supplying power to the passive network is built on the RTDS platform, and then the AC fault traverse strategy is designed in the MMC controller. Based on the thinking of coordinated control and protection of the fault through the strategy into two cases with no input to higher current protections performance simulation contrast, the simulation results show that asymmetric fault occurred when MMC inverter AC line, under the effect of communication failure through the strategy, the current main protection I, II period of refusing action, only by this line nearly backup protection current section III delay removal of fault. The three-stage current protection based on the fault current characteristics of pure AC system has poor action performance and is no longer suitable for the AC line of MMC inverter station.

Substation-area Backup Protection Scheme for the Failure of 10kV Line Protection Device

The research on wide-area backup protection for high-voltage transmission lines has made certain progress in recent years, but there are few reports published on substation-area backup protection for low-voltage 10kV transmission lines. Based on the characteristics of shared information in intelligent substation, a substation-area backup protection scheme to deal with the failure of 10kV line protection device is proposed in this paper. This scheme uses the device self-test information and heartbeat mechanism to monitor the operation status of 10kV line protection devices; to realize the substation-area backup protection for the 10kV transmission lines when any line protection device fails, the protection criterion is constructed by the action results of power directional elements of transformer protections and other 10kV line protections. The proposed scheme can greatly improve the speed of the fault isolation and has low requirements for data demand and synchronization. PSCAD simulation results show that the proposed method is with high correctness and feasibility.

Preventive Control Strategy of Cascading Fault considering Safety and Economy

The operation and structure of the power system are becoming increasingly complex, and the probability of cascading fault increases. To this end, this paper proposes a cascading fault preventive control strategy that considers safety and the economy. First is to give a mathematical form to discriminate the cascading fault according to the action characteristics of the current-type backup protection. Second, the safety and economy of the system are evaluated in terms of power grid safety margin and generation operation cost, respectively, the initial faults are selected based on the power grid vulnerability and safety margin, and a cascading fault preventive control model is constructed for different initial faults’ scenarios. The model is a two-layer optimization mathematical model, with the inner model being solved by particle swarm optimization to minimize the power grid safety margin. The outer model is solved by the multiobjective algorithm to minimize generation cost and maximizing power grid safety margin. Finally, the calculated Pareto set is evaluated using fuzzy set theory to determine the optimal generator output strategy. The feasibility of the proposed method is verified by conducting a simulation study with the IEEE39 node system as an example.