Mohamed F. Abdel-Fattah

A transient fault detection technique with varying fault detection window of earth modes in unearthed MV systems

This paper presents a transient fault detection technique in unearthed medium voltage systems. The system is simulated by ATP/EMTP program. A suitable fault detection window is introduced. The window width is the most sensitive part in the transient period. It is varying according to fault characteristics. The average impedance of the earth mode is calculated from voltage and current earth modes in the window. Based on the amplitude of the impedance, the feeder is confirmed to be faulted or not. The setting of detection is proposed from the simulation results that cover different fault inception angles and fault resistances.

Simple fault path indication techniques for earth faults

Fault indication is the key element in any fault management system. In case of short circuits, fault indication is straightforward, but especially in ungrounded and compensated neutral networks, the single phase fault currents are typically so small that simple fault current threshold detection hardly gives any satisfactory results. The problem can be solved by combining neutral voltage measurement to the sum current measurement using directional relay characteristics. However, the requirement of both current and voltage measurements makes the solution cost prohibitive especially when retrofitting in the existing secondary substations. Hence, there is the need for a simple but reliable earth fault indicator which is based on current measurements solely. This paper takes the above mentioned challenge and compares a number of possible fault indication solutions which are using local current measurements at the secondary substations only. The methods presented use either the sum current measurement directly, or are based on the comparison of the measured phase currents using symmetrical components.

Evaluation of probabilistic-based selectivity technique for earth fault protection in MV networks

In [1], a Bayesian selectivity technique has been introduced to identify the faulty feeder in compensated medium voltage (MV) networks. The proposed technique has been based on a conditional probabilistic method applied on transient features extracted from the residual currents only using the Discrete Wavelet Transform (DWT). In this paper, the performance of this selectivity technique is evaluated when the current transformers (CTs) impacts are considered. The CTs are modeled considering their frequency characteristics. Furthermore, network noises are added to the simulated signals. Therefore, the algorithm can be tested at different practical conditions, such as nonlinear characteristics of the measuring devices and the impact of noise as well. The fault cases occurring at different locations in a compensated 20 kV network are simulated by ATP/EMTP. Results show a reduction in the algorithm sensitivity with considering CT and noise effectiveness.

Transient-based protection as a solution for earth-fault detection in unearthed and compensated neutral medium voltage distribution networks

This paper highlights the earth fault problem in unearthed (isolated) and compensated neutral medium voltage distribution networks and the transient-based protection as a solution. The technique of transient-based analysis will be discussed considering the sampling window, frequency and data updating. The required transient simulation analysis and its validation will be presented. Many important practical investigations will also be discussed such as the required measured quantities, polarity criterion, magnitude criterion and suitable earth-fault indication tools. Finally, some of the developed techniques and algorithms from the previous work in this area will be summarized.

The effect of fault resistance on the earth fault characteristics in unearthed and compensated neutral medium voltage networks

In unearthed neutral medium voltage network the maximum earth fault current, at zero fault resistance, is limited by the total earth capacitance however for compensated neutral network the maximum earth fault current is limited by the total leakage conductance and the compensation branch. The effect of the fault resistance on the earth fault characteristics, in both unearthed and compensated neutral networks, is investigated in this paper. The investigations include the effect of the fault resistance on the fault current, fault voltage, the transient recovery voltage (TRV) and the rate of rise of the transient recovery voltage (RRTRV). A realistic 20 kV medium voltage network model is used for the required investigations. The network model has been implemented using EMTP-ATP program. Based on the simulation results, it is found that the fault resistance has a significant effect on the earth fault characteristics which is found different in compensated from unearthed neutral networks.