High impedance fault arcing on sandy soil in 15 kV distributionfeeders: contributions to the evaluation of the low frequency spectrum

The measured values of current harmonics at a staged high-impedance ground fault on sandy soil are presented. The measured low-frequency spectrum is compared with current harmonics recorded continuously for one week at the substation. This comparison was carried out to determine to what extent 120 Hz and 180 Hz components can be used to help detect a high-impedance fault. The field measurements are supported by a simple theoretical model and laboratory measurements. It is concluded that, for the studied feeder, detection of high-impedance arcing faults may be possible by monitoring of the second-harmonic current     

Cloud effects on distributed photovoltaic generation: slowtransients at the Gardner, Massachusetts photovoltaic experiment

The Photovoltaic Generation Effects project was undertaken to verify that no serious consequences arise from the interconnection of distributed photovoltaic generation on electric power distribution systems. Here, slow transient responses at frequencies corresponding to fluctuations of photovoltaic generation resulting from the passage of clouds over the experiment site in Gardner, Massachusetts, are described. A statistical basis is developed extending the measured results to the entire area served by the distribution circuit in Gardner, as it might be both loaded and equipped with photovoltaic generation in the twenty-first century. Observations and analyses of the solar irradiance and photovoltaic system performance at a single point indicate that there are insufficient step changes in load levels to cause voltage flicker problems. Numerical techniques developed for interpolation of irradiance conditions over the experiment site are adequate for estimating the irradiance at intermediate points and times. The technique appears to be adaptable to extrapolation over larger areas     

New England Electric's 39 years of experience with resonant neutralgrounding of unit-connected generators

Since 1951 all unit connected generators of the New England Electric System Companies have been grounded using ground fault neutralizers (GFNs). This grounding method permits protection against phase-to-ground faults on the generator bus that is more sensitive than with resistor grounded units. In addition, the fault current is limited to such a low value that the possibility of stator iron burning is practically eliminated. Also, because of the limited fault current, overvoltage due to arcing is not possible. These advantages of ground-fault neutralizer generator protection are illustrated through discussion of actual operating experience and by calculations for a typical generator     

Voltage distortion in distribution feeders with nonlinear loads

The voltage of three real-life 13.8 kV feeders supplying customers with nonlinear loads was analyzed by means of computer simulations. Three classes of nonlinear loads were considered. Each class is characteristic for different types of AC to DC converters such as the input DC supply used for adjustable-speed-drives, battery chargers, PCs, TVs and electronically ballasted lights. The analysis is based on the determination of the most harmonic susceptible busses and their response to each harmonic frequency. A new expeditive method that takes into account the background harmonic voltage phasor, and an equivalent bus impedance was developed and used to compute the maximum nonlinear loads that yields VTHD=5%, (voltage total harmonic distortion). The main conclusion of this work is that when mitigation methods are not used, for a 15 kV class feeder with a maximum 10 MVA installed load, the total nonlinear residential load should not exceed 300 kW if the ITHD<90% (current total harmonic distortion), and 100 kW if ITHD>100%