Cewirina Yekê ya Vêjê ya Daftarên 35kV

Daxoyên Daştan: Yek Parçeyê Serhêlî yên Sistemanên Elektrik

Daxoyên daştan parçeyê serhêlî yên sistemanên elektrik in. Li ser barê daştayek bi hejmarê daştê yên din, daxoyên zorî yên daştan (ji bo derbas an derketina) hatine girtin, çi wê li ser her demê yên vegirîn û radîyelî yên dişînin da ve ji hêla transformatoranên daştan hatine girîng kirin. Pas ku ji nivîsên ber bi rêzandina transformatoran vê, karkerdina elektrik ji bo karûbarên binihêrên pêwist hatine dan. Di şebêkanên daştan de, kesayên wekî short circuit ên phase-to-phase, overcurrent (overload), û kesaya single-phase-to-ground her dem dikarin bas bibe. Lîstik, kesayên single-phase-to-ground her dem dikarin bas bibe, ku 70% ya jima hesabê kesayên sistemê taybetand. Belîda, birayên short-circuit dikarin ji kesayên single-phase-to-ground re vêne, ku divêneke kesayên multi-phase ground bikin.

Kesayên single-phase-to-ground bigere ku yek ji sê phase'yan (A, B, an C) li ser demê daştan hatiye kevir û hatiye piştî werger, çi wê li ser daristan, bin, pole, an tower hatiye girîngkirin, ku rastîna girîngkirina leya hatiye were bike. Li gorîna kesayên overvoltage ji çawa lightning an şeriyên atmosferî yên din, izolyasyonê yên ekipmanan daştan hatiye kevir û hatiye piştî werger, ku resistansa îzolasyona ji hêla leya hatiye were kevir.

Gava kesaya single-phase-to-ground li ser sistemê da ke currenta grounding-a zêdetir ne hatiye basdar, loopa tamamî yên kesayê were ne form kirin. Currenta grounding-a capacitance hatiye bi currenta load-a ber dest, û voltajên line'a li ser sistemê hatiye simetrik bane, ji bo ku pêdiviyekariya elektrik ji bo karûbaran were ne kevir. Ji bo li vir, qaydan hatiye bêtirin ku operasyon bi yek kesaya grounding-a were devam kirin ji bo saetan 2. Belîda, voltaja phase'yan non-faulted hatiye were çalak kirin ji bo leya, ku tehlîka ji bo izolyasyon were bike. Ji bo li vir, demên yên li ser kesaya grounding-a were têkildar bike û çareserkirin.

I. Îdentifikasyonê Kesayên Single-Phase-to-Ground li Barên 35kV

Gava kesayên single-phase-to-ground, ferroresonance, phase loss, an high-voltage fuse blowouts ji voltage transformers (VTs) were bas bibe, şanînên were hate hateşîn, lê li gorîna analîzê were hate farkîn.

• Kesaya Single-Phase-to-Ground:
  Substation û SCADA system signals ji bo "35kV busbar grounding" an "Arc Suppression Coil No. X activated" were hate derbas bike. Relay protection were ne trip bike, lê alarm signals were hate derbas bike. Voltaja phase'yan faulted were hate kevir, ji bo phase'yan din du were hate çalak. Indicator light VT ji bo phase'yan faulted were hate dim, ji bo phase'yan din du were hate brighten. Li ser kesaya solid (metallic) ground, voltaja phase'yan faulted were hate kevir ji bo zero, û phase-to-ground voltages ûther two were hate çalak ji bo √3 times, ji bo line voltages were hate nekevir. Output 3V₀ VT were hate around 100V, û harmonic suppression light were hate illuminate. Arc suppression coil were hate carry current, equal to the compensation current corresponding to its tap setting. Gava small-current fault line selector were hate install, were hate activate û identify the faulted line. Gava kesaya were hatiye li ser substation, şanînên fîzikî yên visible arcing, smoke, û loud electrical noises were hate make the fault point easier to identify.

• Ferroresonance:
  Voltage neutral point displacement were hate generate, changing the three-phase phase voltages. Typically, one phase voltage increases while the other two decrease, or vice versa, and line voltages also change accordingly. Since the neutral voltage is non-zero, current flows through the arc suppression coil, and “busbar grounding” signals may appear depending on the magnitude of the displacement voltage.

• Phase Loss:
  The voltage on the upstream side of the lost phase rises to 1.5 times the normal voltage, while downstream voltage drops to zero. The current in the faulted phase becomes zero, and the other two phase voltages slightly decrease. Line voltages remain unchanged. 3V₀ reads around 50V, the arc suppression coil carries current, and a grounding signal is issued. Users are likely to report power outages.

• VT High-Voltage Fuse Blowout:
  The voltage of the blown phase drops significantly (typically below half the normal phase voltage), while other phase voltages do not rise. Line voltages become unbalanced. All outgoing circuits on the busbar trigger a “voltage circuit open” alarm. 3V₀ reads approximately 33V, and a grounding signal is issued.

Although these four conditions—single-phase-to-ground, ferroresonance, phase loss, and VT fuse blowout—exhibit similar symptoms, a thorough analysis of phase voltage, line voltage, 3V₀, arc suppression coil current, SCADA automation signals, and reports from control room operators can accurately distinguish a single-phase-to-ground fault.

II. Process Handling for 35kV Auxiliary Bus Single-Phase-to-Ground Faults

When a 35kV line grounding fault occurs, the Wan’an substation’s 35kV busbar issues a grounding alarm. Personnel at the central control station should be notified immediately to inspect in-station equipment and protection status (including 3V₀ voltage, small-current fault line selector status, arc suppression coil temperature/current, etc.), and the line operation team should be dispatched for line patrol. After receiving feedback from the central station confirming a ground fault, trial switching (trial tripping) of lines should be performed. Before trial switching, critical users must be notified. 

For systems without trial switching devices, remote tripping via SCADA is possible, but loads at downstream substations must first be transferred. In systems with internal bridge connections, automatic transfer switches (ATS) must be disabled to prevent them from transferring the fault to healthy sections.Once a specific line is identified as faulted, priority should be given to transferring its load before taking the faulty line out of service. The line operation team and central station personnel should then be notified to patrol the 35kV line and inspect the 35kV equipment within the associated 35kV substation. 

To prevent the fault from escalating into a phase-to-phase short circuit—which could cause sudden outages—faulty equipment must be quickly located and isolated. Additionally, to prevent overheating and damage to the arc suppression coil, the faulted equipment should generally be isolated within 2 hours. The coil’s temperature rise should be monitored and kept below 55°C. If exceeded, single-phase-to-ground operation must be stopped immediately, and the faulted equipment disconnected. If the grounding condition persists beyond 2 hours, the situation must be reported to senior management.

III. Conclusion

When a single-phase-to-ground fault occurs on a distribution line, the line voltage magnitude and phase remain unchanged, allowing short-term continued operation without disconnecting the faulty equipment. While this improves supply reliability, the voltage on the two healthy phases rises to line-to-line levels, increasing the risk of insulation breakdown and subsequent two-phase-to-ground short circuits. This poses significant risks to the safe and economical operation of substation equipment and the distribution network. Therefore, such faults should be prevented where possible, and once they occur, the fault point must be quickly located and eliminated to enhance overall power supply reliability.