M.M. Eissa

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.

Ground distance relay Compensation based on fault resistance calculation

The fault resistance introduces an error in the fault distance estimate, and hence may create an unreliable operation of a distance relay. A new compensation method based on fault resistance calculation is presented. The fault resistance calculation is based on monitoring the active power at the relay point. The compensated fault impedance measures accurately the impedance between the relay location and the fault point. The relay has shown satisfactory performances under various fault conditions especially for the ground faults with high fault resistance. This new compensation method avoids the under-reach problem in ground distance relays

A Novel Digital Distance Relaying Technique for Transmission Line Protection

Parallel transmission lines often pose more difficult protection problems than single lines. In the case of parallel lines, a number of problems arise when using the distance protection. This paper discusses problems associated with parallel line distance relaying schemes and presents a novel technique to overcome these problems. Two relays instead of four are proposed for the double lines. One relay is located at the beginning and another one at the end. Each relay is fed by three voltage and six current signals from the two lines. The suggested technique is based on the comparison of the measured impedance of corresponding phases. So, the complexity of the possible types of faults, high path fault resistance, mutual effects, current in-feed, inter-system faults are solved. Moreover, 100% of line is protected and the problem of balance-point locations is avoided. Alternative transient program models the power system and simulates different fault conditions.

A novel digital directional transformer protection technique based on wavelet packet

This paper presents a novel digital technique for transformer protection. The technique is based on deriving a directional quantity proportional to the fault current signal and the prefault voltage signal. Standard fast wavelet transform (FWT) schemes may not be as effective for data that has chiefly oscillatory features. An effective solution to discrimination involves examining the signal in both the time and frequency domains simultaneously. The wavelet packet transform is an extension of the FWT that allows for finer characterization of signal content for both time and frequency together. A 11/132-kV transformer connected to a 132-kV power system was simulated using Alternative Transient Program/Electromagnetic Transient Program (ATP/EMTP). Results indicate that the proposed technique is stable, reliable, and fast during the discrimination between internal and external faults, magnetizing inrush currents, and internal faults, ratio-mismatch, and saturation of current transformers (CTs).

Evaluation of a new current Directional Protection technique using field data

A novel current polarized directional element technique to determine the fault direction on a transmission line is evaluated using fault data recorded in the field. The post-fault current signal and a directional reference current signal are used. A directional current element is derived from these quantities. The directional normal power flow before fault occurrence is also used. The voltage signal is excluded from the study after fault occurrence. Test results show that the new technique is not affected by the system operating parameters. The technique has a high degree reliability, selectivity and stability for a majority of practically encountered problems.

Laboratory Investigation of Using Wi-Fi Protocol for Transmission Line Differential Protection

Pilot wire differential protection is one of the most common methods for protecting short transmission lines. The conventional protection scheme has drawbacks, such as malfunction due to line disconnection and limited line length. A laboratory investigation of transmission line protection using Wireless Fidelity (Wi-Fi) communication protocol for data sharing between the relays located at the two ends of the transmission line is presented in this paper. The protection algorithm is based on current signals measured at both ends of the transmission line. The data is exchanged through the wireless communication network. The relay decision is based on data sharing obtained through wireless communication network. The suggested technique satisfies high degree of reliability and stability.

A novel digital directional technique for bus-bars protection

This paper presents a novel digital technique for bus-bars protection. The technique is based on deriving a directional quantity proportional to the postfault current signal and the prefault voltage signal. The prefault current signal is also used to compensate the current signal during the current transformer (CT) saturation. The performance of the technique was investigated for a variety of operating conditions, for CT saturation, high fault resistance, source impedance, and for several bus-bar configurations. Results show that the technique is stable during early and severe CT saturations and it is able to offer very high accuracy and speed in fault detection.

Experimental results of a supplementary technique for auto-reclosing EHV/UHV transmission lines

A technique to discriminate between the line charging inrush current and the current resulting on closing or auto-reclosing a faulted EHV/UHV transmission line has been implemented on a 32-bit digital signal processor (DSP) board. The technique is based on the voltage signals before switching and the current signals. This technique is proposed to be a supplement to the main protection schemes for both single-circuit and double-circuit lines. The scheme is tested on a physical model of a transmission system with a source at each end. Laboratory tests show that the proposed technique is effective for three-pole and single-pole reclosing on a faulted or healthy line.

A novel approach for auto-reclosing EHV/UHV transmission lines

A technique to discriminate between the line charging inrush current and the current resulting on closing or auto-reclosing a faulted EHV/UHV transmission line is proposed in this paper. The technique is based on the voltage and current signals before and after the switching process. This technique is proposed to be a supplement to the main protection scheme.

Laboratory investigation of a distance-protection technique for double circuit lines

A novel digital distance scheme has been implemented on a 32-bit digital signal processor board. The scheme is tested on a physical model of double circuit lines of equal impedance with a source at each end. Two relays instead of four are proposed for the two lines. Each relay is fed by three voltage and six current signals. The technique is based on the comparison of the measured impedance of the corresponding phases. Tests conducted on the physical model for various faults show that high fault resistance, current in-feed, balance-point location, out-of-step operation, and far-end faults are solved. Moreover, 100% of the line is protected.