| Abstract: Industrial loads consisting to some extent of induction motors or synchronous machines are liable to severe over-voltages when isolated on a long transmission line due to breaker operation at the sending end. The over-voltage is produced by self-excitation of the rotating machines when left connected to the mainly capacitive reactance of the unloaded transmission line. The paper investigates the phenomena of self-excitation, the equivalencing of motor loads, the representation of the transmission line, and presents a simple criteria which can be used to determine if a remote load is subject to self-excitation. The results of the study are validated using digital simulation of a representative remote load on the Manitoba Hydro system. |
| Abstract: Induction motors operating in HVDC converter stations can be subjected to damaging torques if the ac filters become isolated on the motor supply. This problem has occurred at the Nelson River Bipole I converter stations with the flywheel motor-generator sets supplying first grade power to the valves. The dynamic torques resulted in damaged keys and keyways on the motor and flywheel shafts. The system was modelled using an electromagnetic transients program with a special subroutine to model the nonlinear mechanical dynamics of the couplings between the motor, flywheel and generator. The paper will briefly discuss the modelling of the system and examine possible causes of damaging torques. The results clearly indicate that when the motor bus is left isolated onto the 138 KV filter bus, machine torques consistent with the observed damage can occur. |
| Abstract: This paper deals with modelling details of static var systems (SVS) for electromagnetic transient studies in time domain. Interfacing the SVS model with rest of the power system and stabilizing techniques during simulation are presented. The SVS connected to the commutating bus of a HVDC is used to illustrate the application of the model. |
| Abstract: A double three phase generator model has been developed and interfaced with EMTDC (Electromagnetic Transient Direct Current) program to simulate unit connection of double three phase generator directly connected to HVDC converters. From the simulation results, harmonics in the generator windings have been computer and the additional losses in the generator have been calculated. The derating factors have been evaluated based on the losses in the generator due to harmonic currents. |
| Abstract: not available |
| Abstract: With HVDC transmission feeding into weak ac systems, the system recovery performance is strongly influenced by such factors as control parameters, transformer saturation and instant of fault application, etc. Further, control parameters optimized for a particular fault may provide inferior or unacceptable performance for other fault conditions. To study these effects, a test system consisting of a point-to-point 810 MW, 450 kV, monopolar transmission system, operating in constant current mode, is considered. the ac networks are represented as voltage sources behind their respective system impudences and the dc system is modelled in considerable detail. the impedances are represented as R-RL networks having the same damping at the fundamental and the second harmonic frequencies. the impedance angles of the receiving and sending end are selected to be 78 and 85 degrees respectively. The short circuit ratios of the sending end and receiving end ac networks are maintained at 4.0 and 1.5 respectively. The simulations are performed digitally on Electromagnetic Transient Program for DC (EMTDC) that allows three phase representation of the ac network, effect of harmonics, unbalances and nonlinearities, etc. The system performance was evaluated based upon the Dynamic Overvoltage (DOV), energy lost by the receiving end ac network and the time to recover to 80% of pre-disturbance power. the system performance was studied varying the following factors under different faults: (i) transformer saturation and instant of fault application, (ii) pole controller gain constants, (iii) current order ramp rates. |
