Search

This paper presents a simplified method for determination the separation of hysteresis and eddy current losses characteristic of power transformer. The model tuning is performed by energized the transformer core in no-load condition with sinusoidal voltage waveform, different frequencies and the magnetic flux density in transformer core always constant maintained. The core loss splitting is obtained by using two-frequency method. The results show that at low frequency, the appearance of hysteresis loss is visible, but at higher frequency, the eddy current loss is more significant.

This paper describes an adaptive distance relaying scheme which can eliminate the effect of fault resistance on distance relay zone reach. Distance relay is commonly used as main protection to protect transmission line from any type of fault. For a stand-alone distance relay, fault resistance can make Mho type distance relay to be under reached and thus the fault will be isolated at a longer time. In this scheme, the relay detects the fault location using a two-terminal algorithm. By knowing fault location, fault voltage at the fault point can be calculated by using equivalent sequence network connection as seen from local terminal. Then, fault resistance is calculated by using simple equation considering contribution from remote terminal current. Finally, the compensation of fault resistance is done onto calculated apparent resistance as seen at relaying point. The modeling and simulation was carried out using Matlab/Simulink software. Several cases were carried out and the results show the validity of the scheme.

Main source voltage sags are short circuit faults in power systems. These fault currents propagate entire the circuits connected with them. After the fault is removed by circuit breaker opened, the system voltage may recover to its normal value, the motor will re-accelerate during recovering process accompanied by high transient currents. This paper presents an experimental test to investigate effect of various characteristics of voltage sags such as magnitude, duration, repetitive and multistage of voltage sags on performance of induction motors. Several small induction motors were used to this purpose. Sag magnitude significantly influenced on the current peaks and speed variation whereas sag duration significantly influenced only on the speed. The motor responses to magnitude and sag duration in repetitive and multistage events are different.