This paper firstly reveals the problem of centralized multi-infeed HVDC being connected into Guangdong and Guangxi power grid at present, then aiming at Wudongde multi-terminal UHVDC transmission project which will be put into operation in 2020,compares and analyzes the stability of Guangdong and Guangxi Power Grid when LCC or VSC is used at inverter side of Wudongde DC transmission project from three aspects including multi-infeed effective short circuit ratio(MIESCR), the risk of commutation failure of DC projects caused by AC system faults, and the influence of AC faults on the stability of receiving-end grid. Research results show that using VSC converter at receiving-end of Wudongde UHVDC will not decrease the MIESCE of each DC project in Guangdong and Guangxi Power Grid, and will enhance the ability of withstanding severe AC system faults significantly.

A major problem in the operation of HVDC infeeded to a weak AC system is that the faults occurred in the receiving AC system may cause commutation failures of the inverters, and in the event of faults removal, the receiving system will be further weakened, so that the AC/DC system will be difficult to restore to a stable operation state, and even may lead to DC system blocking. Based on electromagnetic transient simulations, this paper studies the characteristics of commutation failures of a DC transmission system infeeded to a weak AC system induced by AC faults near the inverter station, as well as the fault recovery characteristics of the AC/DC system with further weakened receiving systems. The HVDC transmission capability of the steady-state operation is evaluated by the dynamic process of fault recovery. The analysis method can be used as an evaluation method to check the steady-state transmission capability of HVDC transmission systems in actual operations.

Grounding electrode is an important part of HVDC systems, and the determination of design conditions is the key of grounding electrode optimal design. The operational states of grounding electrodes in CSG are researched, and the rules of performance period, number of times and ampere-hour are counted. According to actual running data, the design conditions of conventional grounding electrode are optimized,to effectively reduce the area and cost requirements of conventional grounding electrodes. The concept of short-time grounding electrode conception is proposed, and it’s design conditions are put forward according to engineering operation experience for reducing the difficulty of station site selection and improving the economy of grounding electrodes.

This paper investigates the dynamic characteristics of active power and reactive power during HVDC commutation failure period. The quantitative index for assessing voltage supporting capability of AC system for HVDC system is introduced. The influence of simultaneous commutation failures of Guangdong multiple HVDC on the secure operation of the power grid is analyzed from three aspects: AC area where AC fault may cause multiple HVDC simultaneous commutation failure; multi-infeed effective short circuit ratios and the number of power grid instability under severe AC system failure conditions. Technical countermeasures including HVDC control strategy optimizing, dynamic reactive power compensation installation, AC power grid topology reconfiguration and VSC HVDC utilization are proposed for dealing with voltage instability risk of Guangdong power grid.

Superconducting fault current limiter(SFCL) can offer rapid and effective current limitation, which is used to improve the reliability and security of electric power network. Experimental modal analysis is performed on a prototype of saturated core superconducting fault current limiter to study the natural characteristics of iron core/winding, and tank of the SFCL. A special vibration measurement system is constructed to investigate the characteristics of SFCL, in which fiber optic sensors are used to directly measure the core and winding vibration. The results show that the vibration spectrum of SFCL during normal operation consists of many high order harmonics with typical vibration characteristics of transformers under DC bias. It indicates that it’s of great necessity to conduct experimental modal analysis on SFCL’s key components during the stage of structure dynamic design to keep them away from resonance caused by high order harmonics, and the vibration of SFCL’s core/winding and oil tank should be monitored on-line during development, test, and operation as both of them have to withstand high intensity vibration with different properties.

In view of frequent failures of compensation metal oxide voltage limiter (MOV) in China Southern Power Grid (CSG), verification test plan is set up based on the internal fault condition of series compensation system, a power-frequency withstand voltage endurance capability test circuit is built, and eight MOVs are tested. Test results show that a single MOV has strong power-frequency energy absorption capability, MOV can absorb discharge energy again after a few minutes. On the other side, the temperature of MOV valve plate may increase rapidly because of voltage stress and thermal stress, and will lower the lateral insulation of varistor, then trigger surface flashover across the MOV varistors.

The technical scheme of 252 kV、85 kA short-circuit current breaking device is proposed. The device has two parallel connected branches, each branch consists of a 252 kV、63 kA SF₆ breaker in series with a high coupled split reactor(HCSR). In order to study the current sharing and limiting characteristics of SF₆ high pressure arc under the action of HCSR, the magnetofluid dynamics arc model of the device is established through the coupled split reactor and external circuit. The current sharing condition, current limiting condition, arc characteristic and interrupting process of the device are simulated and analyzed. According to the actual interrupting condition and calculation results, the factors influencing the device’s current sharing and limiting characteristics are studied and the theory direction for its development and field application are provided.

Flexible integration and consumption of renewable energy in DC distribution network has good application prospects. The ability of renewable energy consumption of DC distribution system and the quantitative evaluation method of the constraints are studied, and it is proposed that the impedance of DC network, the short circuit capacity of AC grid and the capacity of converter are three key factors affecting the ability of renewable energy consumption. Based on a typical DC distribution system structure, the impact of factors at DC and AC sides limiting the ability of renewable energy in DC distribution network are calculated. A practical algorithm for quantifying the ability of renewable energy consumption in DC distribution network is given. Results of calculation on a typical DC distribution system verify the correctness of the factors. Conclusion of this paper can provide a design and operation reference for renewable energy capacity configuration in DC distribution system.

With the wide application of modular multilevel converter (MMC) power electronic devices and the rapid development of AC&DC hybrid power grid, the higher demand is required for the power system simulation technology. A multi-time scale hybrid real-time simulation system for AC & DC large-scale power grid is presented, which is based on the “FPGA+RTDS+PC(parallel computer)” heterogeneous platform and is able to carry out hybrid simulation of fast electromagnetic transient, electromagnetic transient and electromechanical transient. The simulation system is composed of several simulation sub-systems such as VSC device, HVDC system and AC power system. Connected together by closed-loop interfaces, the system can implement multi-mode united calculation in multi-time scale and multi-grain parallelism. The system can also be interfaced with the EMS (energy manage system) as well as the dispatch control and characteristics display platform. Thus an accurate and efficient simulation tool for the test and study on complex AC&DC large-scale power grid is provided.

Modern power grid has set up a hybrid operation framework with AC & DC multi-components and multi-systems. The characteristics of operation and control are complex and appear as the coupling of electromagnetic transient and electromechanical transient process of each type of electric components. Either the tranditional ‘N-1’ power flow calculation method or the electromechanical transient simulation has great weakness in the simulation and control analysis of hybrid power systems. Key points when real-time simulation technology are applied to AC & DC hybrid power system analysis are investigated in this paper. A practical method of electromagnetic and electromechanical transient hybrid real-time simulation with hardware in loop is exploited to build a panoramic simulation environment that can take account of not only fast HVDC transient responses but also the system oscillation characteristics. The introduced simulation technology has been applied to system operation boundary assessment, anti-accident measures study and system stability control strategy testing of CSG. It is a very impactful simulation platform for the precise simulation and control technologies research of hybrid power systems.

After energy-saving optimization of turbine governing valve of a 1 000 MW unit, more than 40 low-frequency oscillation cases have occurred within a year with unknown reasons, where the amplitudes were from 10 to 30 MW, the oscillation period were from 4 to 27 seconds, and the duration time were from a few seconds to tens of minutes. By analyzing the logic circuits of coordinated control system (CCS) of the unit and by carrying out corresponding modeling and simulation, it is confirmed that the causes of power oscillation include improper parameter settings of the macro-filtering module for power signal in CCS, too large parameter setting of control ratio in the CCS power controller, and improper computing sequence of logic configuration in distributed control system (DCS), while the inducement factor is that the gradient of valve flow characteristics is too large after turbine governing valve being optimized. By tuning the parameters of the macro-filtering module of CCS power signal and that of the power controller, and by reconfiguring the computing sequence of logic group in DCS, the phenomenon of low-frequency power oscillation is eliminated.