Power Quality Indices

The Electric distribution Companies (EDCs) are responsible for keep power quality indices (PQIs) under the standard limits. Magnitude of the supply voltage, harmonic distortion and unbalance are taken into consideration among the PQIs. These indices are considered not to be exceeded on low voltage and medium voltage distribution networks. Voltage variations are small deviations from the nominal or desired value. Voltage variations are mainly due to load pattern, changes of load or nonlinear load. The voltage unbalance causes increased unbalance harmonic currents, mainly non-zero sequence triple harmonic distortion. Harmonic distortion is caused by nonlinear devices in the power system; sources of distortion are different at different voltage levels. At low voltage level all kinds of non-linear loads are connected, which globally is the main source of distortion at all voltage levels. The harmonic indices are total harmonic
distortion, spectrum harmonic and harmonic loss factor. The voltage distortion levels depend on both the circuit impedances and the overall harmonic current distortion. Modern industrial facilities are characterized by the widespread application of nonlinear loads. These loads can make up a significant portion of the total loads and inject harmonic currents into the power system, causing harmonic distortion in the voltage waveforms . Commercial loads are
characterized by a large number of small harmonic-producing loads. The unbalanced and nonsinusoidal working conditions have a negative impact on both individual components of the electrical system and the whole system. End users expecting an improved level of service may actually experience more problems. Equipment failure, mal-functioning, pre-aging, and
telephone interference can locally be a server problem, at all voltage levels. Middle Egypt Electricity Distribution Company (MEEDC) is using the PQIs to improve their systems. One productive use of the indices is to compute the POIs power delivery system at distributors as well as the PQIs for several of the industrial networks. This paper reflects and focuses on the PQIs survey in MEEDC networks. The results of the PQIs survey are presented.