Jeong-Yong Heo

An enhanced zone 3 algorithm of a distance relay using transient components and state diagram

Zone 3 of a distance relay is used to provide the remote backup protection in case of the failure of the primary protection. However, the risk of maloperation under stressed conditions such as heavy loading, voltage, and transient instability is quite high. Zone 3 is used in combination with the derivatives of the voltage and current, etc. to prevent maloperation. At times, the impedance characteristics that restrict the tripping area of relay are used to avoid maloperation due to load encroachment. This work presents a novel zone 3 scheme based on combining the steady-state components (i.e., 60 Hz) and the transient components (TCs) using a state diagram that visualizes the sequence of studies that emanate from the sequence of events. The simulation results show that the novel zone 3 distance relay elements using the proposed method operate correctly for the various events.

An Adaptive Autoreclosure Scheme with Reference to Transient Stability for Transmission Lines

Autoreclosure provides a means of improving power transmitting ability and system stability. Conventional reclosure adopts the fixed dead time interval strategy, where the reclosure is activated after a time delay to restore the system to normal as quickly as possible without regard to the system conditions. However, these simple techniques cannot provide optimal operating performance. This paper presents an adaptive autoreclosure algorithm including variable dead time, optimal reclosure, phase-by-phase reclosure and emergency extended equal-area criterion (EEEAC) algorithm in order to improve system stability. The reclosure algorithm performs the operations that are attuned to the power system conditions. The proposed adaptive reclosure algorithm is verified and tested using ATP/EMTP MODELS, and the simulation results show that the system oscillations are reduced and the transient stability is enhanced by employing the proposed adaptive reclosure algorithm.

A Simulator for Calculating Normal Induced Voltage on Communication Line

The current flowing through the overhead transmission lines causes induced voltage on the communication lines, which can be prevented by calculating the induced voltage at the planning stage for overhead transmission line installment through an agreement between the communication and electric power companies. The procedures to calculate the induced voltages, however, are complicated due to the variety of parameters and tower types of the overhead transmission lines. The difficulty necessitates the development of a simulator to measure the induced voltage on the communication lines. This paper presents two simulators developed for this purpose; one using the Data Base (DB) index method and the other using the Graphic User Interface (GUI) method. The simulators described in this paper have been implemented by the EMTP (Electromagnetic Transient Program).

Dynamic Simulation of Voltage Instability with Particular Reference to Protection Strategies Using EMTP

Abstract The simulation of voltage instability and voltage collapse can be basically classified into static simulation and dynamic simulation; initially, the static simulation was the one used. The static method requires less CPU resource, provides the voltage stability indices and gives much insight into the voltage and the power problem. However, this is a less accurate method than the dynamic simulation performed in the time domain. When it becomes difficult to secure the voltage stability margin via the static stability simulation approach, it becomes necessary to perform the dynamic simulation; in this case, it is required to model the dynamic components of the power system such as a generator and a load. The dynamic simulation provides the accurate results of the voltage instability. However, this method also has some drawbacks in that, it cannot provide the sensitivity information and the margin of the stability, is time consuming and needs much CPU resource. Nonetheless, system transient stability studies based on dynamic simulation are important in order to ascertain the protection / critical fault clearance time strategies that need to be adopted. This paper uses EMTP MODELS to perform a dynamic simulation of voltage instability and voltage collapse. The load model is implemented with EMTP MODELS and this model is then interfaced with a test power system. The test results clearly show that we can simulate the voltage instability and the voltage collapse dynamically using EMTP MODELS.