Pagkabana sa Transformer Neutral Grounding

• Ang seguridad, reliability, ug economics sa power grid;
• Pilihan sa insulation levels para sa system equipment;
• Overvoltage levels;
• Relay protection schemes;
• Electromagnetic interference sa communication lines.

• High-Ground-Fault-Current System: Kapag may single-phase-to-ground fault, ang resulting ground fault current labi ka dako. Halimbawa includs ang mga systems rated 110 kV ug mas taas, same as 380/220 V three-phase four-wire systems. Mas kilala usab isip effectively grounded systems.
• Low-Ground-Fault-Current System: Durante sa single-phase ground fault, wala'y kompleto nga short-circuit loop giporma, kungtod ang fault current labi ka gamay kay normal load current. Mas kilala usab isip non-effectively grounded systems.

• Solidly grounded neutral
• Neutral grounded through a resistor

• Ungrounded neutral
• Neutral grounded through an arc suppression coil (Petersen coil)

• A single-phase ground fault requires immediate tripping of the faulty equipment, interrupting power supply and reducing reliability.
• The large short-circuit current generates significant electrodynamic and thermal stress, potentially expanding damage.
• Strong magnetic fields from high fault currents cause electromagnetic interference to nearby communication and signaling circuits.
• During a single-phase fault, the faulted phase voltage drops to zero, while unfaulted phase voltages remain near normal phase voltage. Thus, equipment insulation can be designed for phase voltage only—reducing cost, especially beneficial at higher voltage levels.

• High-resistance grounding
• Medium-resistance grounding
• Low-resistance grounding

• Enables automatic fault clearance and simplifies operation/maintenance.
• Quickly isolates ground faults, resulting in low overvoltages, elimination of resonant overvoltages, and allowing use of lower-insulation-grade cables and equipment.
• Reduces insulation aging, extends equipment life, and improves reliability.
• Ground fault currents (hundreds of amperes or more) ensure high sensitivity and selectivity of relay protection—no need for complex fault line selection.
• Reduces risk of fire.
• Allows use of gapless ZnO surge arresters with high energy absorption and low residual voltage for overvoltage protection.
• Suppresses 5th harmonic components in arc grounding overvoltages, preventing escalation to phase-to-phase faults.

• High-resistance grounding: Suitable for distribution networks with capacitive ground current <10 A, large generators where single-phase ground current exceeds allowable limits but remains <10 A. Resistance values typically range from hundreds to thousands of ohms.
• Medium- and low-resistance grounding: No strict boundary, but generally:
• Medium resistance: Neutral fault current between 10 A and 100 A
• Low resistance: Neutral fault current >100 A

Anaa adunay kasinatikan sa mga urban nga network sa distribusyon na dominado sa mga cable, auxiliary system sa power plant, ug dako nga mga industrial plants—diin ang capacitive currents mao ang taas ug ang transient ground faults mao ang dili pila.

• Ang kuryente sa ground fault nga single-phase <10 A; ang arko mawala sa wala, ug ang insulasyon mahimo molihok sa automatic.
• Gipabilin ang simetriya sa sistema; ang sistema mahimo mogamit temporary sa usa ka fault aron makapangita og lugar sa fault.
• Minimal ang komunikasyon nga pag-interfere.
• Simple ug ekonomikal.
• Pero kon capacitive current >10 A, high-magnitude intermittent arc grounding overvoltages mahimo mag-occur. Kini nga mga overvoltage nagpaulan, nakakaapekto sa tanang network, ug naghatag og serius nga banta sa mga equipment nga may weak insulation—espesyalmente sa mga rotating machines. Ang mga overvoltage niini nagsabot sa multi-point ground faults, equipment burnout, ug major outages.
  Ang resonant overvoltages kasagaran mag-lead sa blown fuses sa voltage transformers (VTs), VT burnout, o pati na main equipment damage.

• Ang inductive current gikan sa arc suppression coil compensates ang capacitive ground current sa sistema, nagbawas sa fault current ngadto sa <10 A—allowing arc self-extinction.
• Ang insulasyon sa fault point mahimo molihok sa automatic.
• Nagbawas sa probability sa intermittent arc grounding overvoltages.
• Gipabilin ang system symmetry sa panahon sa single-phase faults, nag-enable sa temporary continued operation para sa fault location.
• Pero, kini nagbawas lamang sa probability—dili gi-eliminate—ang arc grounding overvoltage, ug dili nagbawas sa magnitude. Ang overvoltage multiplier gisigurohong taas, naghatag og significant insulation stress—espesyalmente dangerous para sa compact switchgear and cable systems, diin mahimo magpadayon sa insulation breakdown o phase-to-phase short circuits, leading to catastrophic equipment failure.

• Ang 110 kV o 220 kV high-voltage side sa wind farms typical nga gigamit ang neutral grounding via a disconnector (isolator).
• Ang 35 kV collector system side usual nga gigamit ang arc suppression coil or resistor grounding.
  • Kon ang collector system gigamit ang all-cable lines, ang capacitive current adunay relatiwamente large; tungod niini, recommended ang resistor grounding.