Commutation failure (CF) may be caused by AC fault in AC/DC interconnected system, and it will affect the performance of distance protection. The transient characteristic of equivalent current of power-frequency of the dc-ac inverter is first analysed by introducing the concept of quadrant. Then, the effect of CF on distance protection is studied in detail with consideration of the connection mode of distance relay. The analysis results show that both the fault position and fault resistance contribute to the effect of CF on the performance of distance protection significantly. Furthermore, a novel countermeasure based on the amplitude of second harmonic is put forward, and a concept of 'successive trip' by using the change of measured reactance is also presented. Simulation results based on PSCAD/ EMTDC prove the correctness of these conclusions.
Short-term frequency stability (STFS) is becoming a great concern for a regional receiving-end power system such as the East China Power Grid (ECPG) mainly for two reasons: (i) the increasing percentage of power injected from multi-infeed (ultra-) high-voltage DCs (HVDCs) with the skyrocketed capacities; (ii) the replacement of traditional generation by the continuously growing inertia-less renewables. However, the existing emergency control is not adaptive enough to maintain STFS under varying operation conditions. In this study, a real-time optimised control is proposed to solve the issue more efficiently. It combines emergency power boosting (EPB) of HVDC and emergency demand response (EDR) in a coordinated way. The optimal control problem is formulated based on the online-updated models that reflect the current state of the system and the dynamic responses of multiple types of generators. By converting the non-linear constraint into a linear matrix inequality, the allocation of EPB and EDR can be optimised in a real-time and coordinated way. The performance of the proposed control and its advantages over the existing one are verified by simulation studies on the model of ECPG with low, normal and high penetrations of renewables.
SUMMARYIf the wye-delta connected three-phase transformer energizes non-synchronously, the first energized phase will induce an electromotive force into the other two phases via delta winding. Then, the flux in transformer core maybe increasing greatly and causes severe saturation. The second harmonic ratio (SHR) of the three-phase differential currents in such a case is small, which can cause the conventional second harmonic restraint principle failure and the mal-operation of differential protection. In this paper, the mechanism of non-synchronous energization (NSE) is firstly introduced. Then, a novel method for detecting the NSE of unloaded transformer is proposed. If the change of neutral current does not coincide with the line currents of transformer, the NSE can be identified. To avoid the mal-operation of the transformer differential protection due to the inrush currents occurred during the NSE, a new method, taking advantage of the changing trend of the SHR in the differential currents, is also put forward to discriminate inrush current from fault current during NSE. The effectiveness of the proposed scheme has been verified by simulation results.
In order to realize the scientific management of the light environment and achieve the purpose of saving energy and increasing efficiency for the hotel, this paper designs and implements an intelligent lighting control system for the room, manual control and automatic control of dual management for the room lighting [6]. The system uses the multi-layer distributed structure, combining organically with the embedded technology, Internet of things technology, sensor technology, CAN bus technology and so on, and the embedded ARM microprocessor is the core of the system, combining with the intelligent gateway module, I/O weak current digital input and output module, dimming module, illuminance sensor module and power module, and communicating with each other by the CAN bus, to realize the intelligent management of the room lighting. The Lighting Control System for Smart Hotel Rooms is facing up to the high star hotel, to improve the management level and service quality of the hotel, and save energy, scientific and intelligent management, and enhance the competitiveness for the hotel, it will be an important part of the Smart Hotel System which has a certain application value [14]. As a new and most promising light source, all kinds of lighting have attracted more and more attention for their energy saving, environmental protection and other advantages.
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