This paper introduces wavelets and shows that they may be efficient and useful for power distribution relaying. The wavelet transform of a signal consists in measuring the "similarity"between the signal and a set of translated and scaled versions of a "mother wavelet". The "mother wavelet" is a chosen fast decaying oscillation function. Wavelets are used to analyse transient earth faults in a 20 kV resonant grounded network as generated by EMTP. It is shown that wavelets may be employed for analysing records to study efficiently the faulted network. Moreover, this new technique can actually be implemented in real time for protection devices. Thus, it is suitable for application to protective relays.

Wavelets: a new tool for the resonant grounded power distribution systems relaying

Prony's method is a technique for estimating the modal components present in a signal. Every modal component is defined by four parameters frequency, magnitude, phase, and damping. This method is used to analyse earth fault currents in Petersen-coil-protected 20 kV networks. The variations of Prony's parameters in terms of some of the power systems characteristics (distance between the busbar and the fault, fault resistance and capacitive current of the whole network) are presented. It is shown that some of the Prony's parameters relating to the fault current transient may be useful to determine what kind of fault occurred, and where it occurred. >

Prony's method: an efficient tool for the analysis of earth fault currents in Petersen-coil-protected networks

Features-clustering-based earth fault detection using singular-value decomposition and fuzzy c-means in resonant grounding distribution systems

Earth-phase faults are the most frequent faults likely to occur in a power distribution network. In the case of Petersen-coil-protected power networks, meaningful information is contained in the transient fault signals and should be used in the protections to increase their speed and accuracy. An earth-phase fault is simulated with EMTP (ElectroMagnetic Transient Program). Then, a recursive wavelet transform is applied on two kinds of fault currents that are the zero-sequence currents in the faulty feeder and in the healthy one. The instantaneous time-frequency information obtained may be useful for the design of a fast relay algorithm. >

A recursive wavelet transform analysis of earth fault currents in Petersen-coil-protected power distribution networks

Some Engineering Features of Petersen Coils and Their Application

Accidental arcing grounds on transmission lines constitute the foremost problem to be solved in the transmission of electrical energy over great distances. There has come into use to a limited extent, arcing ground suppressors. This device consists in principle, of a switch in the station which is automatically closed in parallel with the accidental arc at any point out on the system. The parallel path through the switch shunts the current from the arc and thereby extinguishes the arc. This development is not yet completed. This paper gives the results of some experiments on an entirely different device for suppressing accidental grounds?a device that was first advocated by Prof. W. Petersen of Darmstadt, Germany. The essential part of this new apparatus is a suitable reactor connected between the neutral of the circuit and ground. This reactance is chosen of such a value as to neutralize the capacitance of the circuits when an accidental ground of one phase takes place. Under this acc dental condition the reactor is electrically in parallel with the active capacitances and, by the wellknown fundamental law, the only current that flows to the combination of the inductance and capacitance in parallel is the current necessary to supply the energy loss in the combination. The simplified equivalent conditions are shown in Fig. 4. This energy current can be made very small and it is this relatively small current that passes through the accidental arc to ground.

R. N. Conwell

Papers

The Petersen Earth Coil