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Ingantaccen Maimaitar Differensial na Turanci Masana: Matattuka da Dalilai da Koyarwa

Ingantaccen maimaitar differensial na turanci masana shi ne mafi yawan karkashin cikakken duk ingantaccen maimaitar differensial. Ana iya faruwa a tushen rayuwa. A ranar 1997, bayanin Northern China Power Grid ta nuna cewa a kan transformashi da sauran 220 kV ko da ya fi, akwai 18 fadada faruwar gaba, daga cikinsu 5 suna so ku maimaitar differensial na turanci—wanda ya zama kusan shekaru. Dalilan faruwar gaba ko ba a yi abin da ake bukata sun haɗa da matattuka da inganta, yanayi, da kuma al'amari, wato kuma nasara, da kuma matsalolin gyara, da kuma sakamakon da kuma tsarin gyara. Littafin ya nuna matattuka masu yawan faruwar gaba da kuma hanyoyi da za su iya amfani da su don koyarwa.

1. Karamin Karamin Yadda Da Ta Samu Na Tsakiyar Inrush Na Turanci

A tushen rayuwa, karamin tsakiya yana samu kawai a tafkin da aka baka da zuwa, wanda ya zama karamin karamin a maimaitar differensial. Tushen da aka sani, karamin tsakiya yana da 3%–8% daga asali; a cikin turanci masu yawa, yana da yawa daidai mai girma. A cikin fadada gwargwadon gaba, mutanen karamin tsakiya suna da yawa, wanda ya zama babbar da ita. Amma a lokacin da aka baka da turanci da ba da abin da kuma a lokacin da aka ci gaba tsakiyar gaba, zai iya samun karamin inrush mai yawa—da take zama 6–8 daga asali.

Karamin inrush yana da muhimmiyar karamin da ba da tarihi ba da kuma harmonikin maye, musamman harmonikin biyu, da kuma yana nuna karamin da ba da kontinuwata (dead angles).

Hanyoyi a maimaitar differensial na turanci:

(1) Relays na karamin BCH da current transformers da take samu kace:
A cikin fadada gwargwadon gaba, karamin da ba da tarihi ba yana zama ziyartar tsakiya na transformer da take samu kace, wanda ya zama babban karamin karamin karkashin baka zuwa coil na relay—don haka ya zama ba a yi faruwar gaba. A cikin fadada na tsakiya, idan karamin da ba da tarihi ba ana cika, zai zama da yawa a kwanaki ~2 cycles. Ba nan, zai da yake karamin tsakiya da tarihi, wanda zai iya amfani da relay mai kyau.

(2) Relays na microprocessor da take amfani da harmonic restraint na biyu:
Yankin digital relays masu yanzu suna amfani da harmonic blocking na biyu don koyar inrush da fadada na tsakiya. Idan faruwar gaba ya faru a lokacin da aka ci gaba fadada gwargwado:

• Saka daga phase-by-phase ("AND") restraint zuwa maximum-phase ("OR") restraint mode.

• Gudda ratio na harmonic restraint na biyu zuwa 10%–12%.

• A cikin systems da suka da yawan capacity da kuma fifth-harmonic content da take samu da yawa a cikin ci gaban fadada, add fifth-harmonic restraint.

• Idan an samu turanci da dual differential protections, consider using waveform symmetry principles don koyar inrush—wani yana da kyau da kuma zama da yawa da harmonic restraint kawai.

2. Karamin Wiring Da Ba Daidai A Cikin Circuits Na Secondary Na CT

Wannan shi ne mafi yawan dalilai da ke faruwar gaba, wanda polarity na terminals na secondary na current transformer (CT) yana da rarrabe—wanda ya faru saboda ilimi mai daidai, kudaden drawa da design, ko kuma kudaden commissioning checks.

Amfani da wannan hanyoyi:
Kablar da aka baka maimaitar differensial na turanci zuwa aiki—ba da new installation, periodic testing, ko kuma kudaden modification na circuits na secondary, turancin ya kamata a yi abin da kuma koyar da:

• Measure the unbalanced voltage in the differential loop using a high-impedance voltmeter; it must comply with code limits.

• Measure magnitude and phase angle of secondary currents on all sides.

• Construct a hexagonal vector diagram to verify that the vector sum of same-phase currents is zero or near-zero, confirming correct wiring.

Ba a nan, protection ya kamata a yi formal commissioning.

3. Karamin Contact Mai Yawa Ko Open Circuit A Cikin Circuits Na Secondary

Faruwar gaba da suka faru saboda connections da ba da yawa ko open circuits a cikin loops na secondary na CT suna faruwa shekaru baki baki.

Tambayar:

• Strengthen real-time monitoring of differential current during operation.

• After relay installation/commissioning or major transformer overhauls, inspect all CT secondary connections.

• Tighten terminal screws and use spring washers or anti-vibration clips.

• For critical applications, use two parallel cables for the differential secondary wiring to mitigate open-circuit risk.

4. Karamin Grounding A Cikin Circuits Na Secondary Na Maimaitar Differensial

Wasu wurare sun faru anti-accident measures da suka samu ground points biyu—wanda babu a cabinet na protection da kuma a box na terminal na switchyard. Wannan suna zama ground potential difference, musamman a lokacin da there is lightning or nearby welding, wanda ya zama babban karamin differensial current da kuma faruwar gaba mai daidai.

Solution:
Strictly enforce single-point grounding. The only reliable ground point should be located inside the protection cabinet.

5. Karamin Insulation Degradation Na Cables Na Secondary Na CT

Karamin failure na insulation na cables na secondary na CT—wanda ya faru saboda construction practices da ba daidai—yana zama babban karamin faruwar gaba. Dalilai masu yawan faruwar gaba sun haɗa da:

• Cable sheath damage during laying,

• Splicing two cables when length is insufficient,

• Welding cable conduits with cables inside, causing thermal damage.

Waɗannan sun zama risks mai mahimmanci ga reliability na protection.

Preventive measures:

• During major equipment maintenance, periodically test insulation resistance between each core-to-ground and core-to-core using a 1000 V megohmmeter; values must meet code requirements.

• Keep exposed wire ends at terminals as short as possible to prevent accidental grounding or phase-to-phase short circuits due to vibration.

6. Selection of Current Transformers for Longitudinal Differential Protection

Differential protection involves CTs across different voltage levels, with varying ratios and models, leading to mismatched transient characteristics—a potential source of misoperation or failure to operate.

• 500 kV side: Use TP-class CTs (transient-performance class), whose gapped cores limit remanence to <10% of saturation flux, greatly improving transient response.

• 220 kV and below: Typically use P-class CTs, which have no air gap, higher remanence, and poorer transient performance.

Selection guidance: While TP-class CTs offer superior technical performance, they are expensive and bulky—especially on the low-voltage side, where installation in enclosed bus ducts is difficult. Therefore, unless special system requirements exist, P-class CTs should be preferred if they satisfy actual operational needs—avoiding unnecessary cost and installation challenges.

Additionally, secondary cable cross-section must be adequate:

• For long cable runs, use ≥4 mm² conductor size to minimize burden and ensure accuracy.