Positive Sequence Voltage Magnitudes Research Articles

A protection scheme based on impedance for LV and MV lines in microgrids with high-impedance fault detection capability

Microgrid properties including bidirectional power flow in feeders, fault level decrease in the islanded mode, and intermittent nature of distributed generators (DGs) result in the malfunctioning of microgrid conventional protection schemes. In the present article, a protection scheme based on impedance is suggested for fault detection in LV and MV overhead and cable distribution lines in both grid-connected and islanded modes. To determine a fault detection index, new suggested equivalent circuits for doubly fed lines are applied. Relay location data and magnitude of positive sequence voltage of the other end of the line are used. It is simulated by PSCAD and MATLAB software in order to evaluate its performance and approve its validity. This scheme can detect even high-impedance faults in both grid connected and islanded modes in LV and MV overhead and cable distribution lines. In addition, it is robust against load and generation uncertainty and network reconfigurations. Low sampling rate and minimum data exchange are among the advantages of the proposed scheme.

An integrated scheme for a directional relay in the presence of a series-compensated line

This paper presents an integrated method to identify the fault direction in the presence of a series compensator via also identifying the power flow direction. The presented method relies on monitoring both measured angle of the positive-sequence (PS) currents and magnitude of PS voltage. The change of PS voltage magnitude is used to detect the current inversion case. The presented criteria depend on the power flow direction before the fault occurrence. Therefore, a power flow direction identification method is presented using only the change of the phase angle of the PS current. Different system configurations are investigated to test the reliability of the proposed protection scheme (PPS). The power and protection systems’ configurations contain different capacitor ratios leading to current and voltage inversion scenarios, reversing the power flow direction and single-pole tripping. Simulation experiments conducted via the software ATP-EMTP has shown the proper operability of the PPS.

A Novel Back Up Wide Area Protection Technique for Power Transmission Grids Using Phasor Measurement Unit

Current differential protection relays are widely applied to the protection of electrical plant due to their simplicity, sensitivity and stability for internal and external faults. The proposed idea has the feature of unit protection relays to protect large power transmission grids based on phasor measurement units. The principle of the protection scheme depends on comparing positive sequence voltage magnitudes at each bus during fault conditions inside a system protection center to detect the nearest bus to the fault. Then the absolute differences of positive sequence current angles are compared for all lines connecting to this bus to detect the faulted line. The new technique depends on synchronized phasor measuring technology with high speed communication system and time transfer GPS system. The simulation of the interconnecting system is applied on 500 kV Egyptian network using Matlab Simulink. The new technique can successfully distinguish between internal and external faults for interconnected lines. The new protection scheme works as unit protection system for long transmission lines. The time of fault detection is estimated by 5 msec for all fault conditions and the relay is evaluated as a back up relay based on the communication speed for data transferring.

Effects of various unbalanced voltages on the operation performance of an induction motor under the same voltage unbalance factor condition

Abstract This paper investigates the effects of different unbalanced voltages with the same voltage unbalance factor (VUF) on the performance of a three-phase induction motor and its feedback influence on the power system. Under eight different voltage unbalance conditions, the performance of a three-phase induction motor was measured through a real load test. The loss, efficiency, power factor and temperature rise of the motor under different unbalanced voltages are investigated. According to the test results and analysis, the importance of the positive-sequence voltage on the motor’s apparent performance and the negative-sequence voltage in the hidden damage were pointed out. Finally, it is strongly suggested that (1) the derating and temperature rise curves and related regulations should consider the VUF percent and the magnitude of positive-sequence voltage, and (2) the effects of unbalanced voltage on induction motors should also be modeled in power system voltage stability studies.