The basic function of power system protective relays is the detection of anomalous and/or potentially harmful or undesirable operating conditions. The conditions may occur in the steady state or as transients. Most relays detect steady state conditions, they issue trip signals, and they cause protective steps to be taken -- usually the operation of a circuit breaker. Power system protective relays are complex engineering designs because they must expect the unexpected. They must detect failures and harmful modes of operation; and if they themselves fail, they must detect this as well. Their design is often made more robust by the addition of backup systems that detect failures or other undesired operation of the main system. Many power engineers agree that power system protective relaying is as much an art as it is an engineering science. The basic technology of power system relaying includes such factors as: voltage and current measurement; digital and analog signal processing; impedance and phasor techniques; threshold detection; frequency domain techniques; time domain techniques; microprocessor applications; solid state designs; induction disk technology; time signal methods and timing; and overvoltage and overcurrent detection.There are several classic difficulties that have faced protective relay engineers for many years -- and have never really been resolved satisfactorily. Most of these difficulties center around the fundamental problem of distinguishing between normal load current (which should be served without interruption), and anomalous current that arises from an undesired and intolerable condition. A main element of anomalous currents are due to power system faults. Faults by their nature often cause high current amplitudes, but many load currents are also (indistinguishably) high. To compound the difficulty, many fault currents are of low amplitude. Therefore one finds the classic quandary of distinction of load current and fault current.Researchers at Arizona State University have devised a relay that uses the detection of chaos in electric power systems to develop either a trip or a blocking (inhibit) signal to protect the power system. For example, the identification of electrical discharges may be used in the protection of power circuits that energize electric arc furnaces and other loads that use the phenomenon of electric arcs in their operation. In the case of arc furnace loads, the circuit must be protected against faults and other unwanted conditions, yet the electric arc process that is normally encountered may be identified and the power system protective relay may then be inhibited under normal load conditions.
|Original language||English (US)|
|State||Published - Jan 1 1900|