Quae sunt communia vitia quae in operatione protectionis differentialis longitudinalis transformatoris electrici occurunt?

Protectio Differentialis Longitudinalis Transformatoris: Questiones Communes et Solutiones

Inter omnes protectiones differentialis componentium, protectio differentialis longitudinalis transformatoris est maxime complicata. Saepe operationes erratae in operatione occurrunt. Iuxta statistica anno 1997 ab Energetica Sinensis Septentrionalis pro transformatoribus supra 220 kV, erant operatio incorrecta tota numero 18, quorum 5 ex protectione differentiali longitudinali—circa unam tertiam. Causae maloperationum vel non-operationum includunt res pertinentes ad operationem, maintenance, et management, sicut et problemata in fabricatione, installatione, et designo. Hoc articulus analysat questiones communes in campo et praebet methodos mitigationis practicas.

1. Currentis Inaequabilis Causatus per Inrush Currentem Transformatoris

In operatione normali, currentis magnetizans fluit tantum in latere energizato et creat currentem inaequabilem in protectione differentiali. Saepissime, currentis magnetizans est 3%–8% de currente nominale; pro magnis transformatoribus, solito est minus quam 1%. In casu defectus externi, decrementa voltage reducunt currentem magnetizantem, minimizando eius impactum. Tamen, in energizatione transformatoris sine onere vel restoratione voltage post clearance defectus externi, potest occurrere magnus inrush current—ascendens ad 6–8 vices currentis nominale.

Hic inrush continet significativam partem non-periodicam et harmonicos alti ordinis, praecipue secundum harmonicum, et exhibet discontinuitates waveform (anguli mortui).

Methodi mitigationis in protectione differentiali longitudinali:

(1) Relays BCH-type cum current transformer rapidi saturandi:
In defectibus externis, alta pars non-periodica celeriter saturat nucleum current transformer rapidi, praeveniens transferentiam currentis inaequabilis ad spiram relay—sic evitans falsam operationem. In defectibus internis, licet initio existant partes non-periodicae, decrescunt intra ~2 cycli. Postea, tantum fluxit periodicus defectus, permitting sensitivam operationem relay.

(2) Relays microprocessor-based utentes restraint secundi harmonic:
Plurimi relays digital moderni utuntur restraint secundi harmonic ad distinguendum inrush a defectibus internis. Si maloperatio occurrit in clearance defectus externi:

• Commute de modo restraint phase-by-phase ("AND") ad modo restraint maximum-phase ("OR").

• Reduce ratio restraint secundi harmonic ad 10%–12%.

• In systematis magni capaciti ubi contentus quinti harmonic etiam altus post clearance defectus, add fifth-harmonic restraint.

• Pro transformatoribus instructis dualibus protectionibus differentialibus, considera uti principiis symmetriae waveform ad identificandum inrush—hic methodus est sensibilior et fidelior quam sola restraint harmonic.

2. Incorrect Wiring in CT Secondary Circuits

Causa recurrens maloperationis est reversio polaritatis terminalium secondary current transformer (CT)—resultatum insufficiens training, deviation ab design drawing, vel insufficientes commissioning checks.

Praxis preventiva:
Priorquam protectionem differentialis longitudinalis in servicium ponas—post novam installationem, testationem periodicam, vel modificationem circuiti secondary—transformator debet oneri, et sequentes inspectiones faciendas esse:

• Mensura voltage inaequalis in loop differentiali utendo voltmeter high-impedance; debeat conformari limitibus codice.

• Mensura magnitudinem et angulum phase currentium secondary in omnibus lateribus.

• Construe diagramma vector hexagonale ad verificandum summa vectorem currentium eadem phase esse zero vel quasi-zero, confirmante correctam wiring.

Solum post has verificationes debet protection formaliter commissionari.

3. Contactus Malus vel Circuitus Apertus in Circuitis Secondary

Maloperationes ex connexionibus laxis vel circuitibus apertis in circuitis secondary CT annualiter occurrunt.

Recommendationes:

• Strengthen monitoring real-time currentis differentialis in operatione.

• Post installationem/commissioning relay vel majoribus overhauls transformatoris, inspecta omnia connexiones secondary CT.

• Tighten vinctores terminalium et uti spring washers vel clips anti-vibration.

• Pro applicationibus criticis, uti duobus parallelis cabulis pro wiring secondary differentiali ad mitigandum periculum circuitus aperti.

4. Questiones Grounding in Circuitis Secondary Protectionis Differentialis

Quaedam loca violant measuras anti-accidentia habendo duos punctos grounding—unum in cabinet protectionis et alterum in switchyard terminal box. Differentia potentialis ground, praecipue in fulgure vel welding vicina, potest inducere currentem differential spurium et causare falsam operationem.

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

5. Deterioratio Insulationis Cabulorum Secondary CT

Defectus insulationis cabulorum secondary CT—saepe ex mala praxis constructionis—quoque ducit ad maloperationes. Causae communes includunt:

• Damnum sheath cabuli in laying,

• Splicing duorum cabulorum quando longitudo insufficiens,

• Welding conduits cabuli cum cabulis intus, causando damnum thermicum.

Haec creant pericula abscondita fidei protectionis.

Measures preventivae:

• In maintenance majoribus equipment, periodically test resistance insulationis inter core-to-ground et core-to-core utendo 1000 V megohmmeter; valores debeant conformari requisitis codice.

• Maneant terminales wire ends breves ut possibile ut praeventa sit accidental grounding vel short circuit phase-to-phase ex vibratione.

6. Selectio Current Transformers pro Protectione Differentiali Longitudinali

Protectio differentialis involvit CTs inter varios niveles voltage, cum variis rationibus et modellis, ducens ad transient characteristics mismatch—a potential source of misoperation or failure to operate.

• Latus 500 kV: Utere TP-class CTs (transient-performance class), cuius cores gapped limit remanence ad <10% saturation flux, magno meliorantes transient response.

• 220 kV et infra: Saepe utere P-class CTs, qui nullum habent air gap, maiorem remanence, et pejorem transient performance.

Guidance selectionis: Quamvis TP-class CTs offer superior technical performance, sunt costosi et voluminosi—praecipue in latere low-voltage, ubi installation in enclosed bus ducts difficilis. Ergo, nisi specialia requirementa systematis existant, P-class CTs debent preferri si satisfaciant actualibus necessitatibus operationalibus—evitando costum et installation challenges superfluas.

Additionally, secondary cable cross-section must be adequate:

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