Analyses and Comparisons of Generic and User Writing Models of HVDC System Considering Transient DC Current and Voltages

Analyses and comparisons of generic models and a novel modeling method of line-commutated converter (LCC)-based high voltage direct current (HVDC) systems are presented for the power system simulator for engineering (PSS/E) simulation tool. The main purposes are to describe the dynamics of the DC voltage and current of HVDC system and to improve estimation of the maximum values using the generic and proposed HVDC models when AC line-to-ground faults are occurred. For the generic HVDC models, the characteristics and limitations as well as parameter investigations are conducted. Three modules are also are developed for the proposed HVDC model, which are composed of (a) AC/DC conversion; (b) controller selection; and (c) DC line model. Case studies were conducted considering the real-operated HVDC system in Korea under the PSS/E and power systems computer aided design (PSCAD) simulation environments. The simulation results were compared with measured data from the real-operated HVDC system and the results from the PSCAD HVDC models considering single- and three-phase line-to-ground faults. The case study results show that a specific generic HVDC model in PSS/E can simulate the dynamics of the DC voltage and current after the AC line-to-ground faults. The case studies also showed that the proposed modeling method is effectively improves the estimation of the maximum DC voltage and current values for the AC line-to-ground faults.

Modelling of Stator Coil–To–Ground Faults in Induction Motor

Three–phase squirrel cage induction motors are the most widespread types of electrical motors which can be found in both industrial and tertiary applications. There are some reasons why they are so often used, such as simple construction, nearly maintenance-free, advantageous price and the possibility to feed them directly from the AC network. Even if their reliability is very high, some unexpected breakdowns can occur during their operation. In this paper, coil–to–ground faults of motor stator winding have been taken into consideration. These failures have been modelled in several points of one stator phase using COMSOL software. As seen from simulation results these failures have a significant impact on current distribution in stator phases causing changes in rotor currents, motor inner torque, speed, etc., depending strongly on the actual point of the failure.

Digital technologies for monitoring and implementation of smart diagnostics of the isolation of power supply systems with isolated neutral in the operating mode

Nowadays, 75% of emergencies at power supply facilities are caused by single-phase ground faults. The currently used methods of thermal imaging and ultrasonic testing do not allow accurately identify the cause of accidents in electric power distribution systems. The current search generators, due to their low power, cannot cover the entire section of the diagnosed network. The article suggests the use of digital technologies for the intelligent diagnostics of the insulation of power supply system with insulated neutral in the operating mode, allowing on-line diagnostics of the network and analyzing the data obtained for the early prevention of emergency situations. In order to avoid disconnecting sections and diagnose the system in operating mode, it is proposed to check the system using a currentlimiting capacitor, which will be connected to the live parts of each phase under voltage and accurately determine the location of a single-phase short circuit for any number of feeders. The relevance of these studies is due to the fact that, for example, during two years at one of the manufactures 19 emergencies related to single-phase ground faults were recorded. Four of these cases led to a complete stop of the production. Therefore, the development of digital technologies for the implementation of smart diagnostics of the insulation of an energized power supply system with insulated neutral will be of interest to practitioners, scientists, researchers, graduate students and other specialists seeking to study the latest achievements in smart agribusiness for their subsequent application in the real world.