7 Mijara Key bi ji bo Destpêkirina wekheviyê û Tevaniyê ya Transformerên Gewrê Bêya

1. Pêşkêşkirina û Vegeraşina Şertî Insulasyonê ya Fabrikaya

Dema ku transformator derbarê testên pêşkêşkirina fabrika bigihin, şertî insulasyonê ya we ya herî saz bibe. Li ba serê, şertî insulasyonê deng be dike ve hatine şerqetandina çêdike, û peryodî çavkanîyê dikare peryodî xırûb nebe ji bo şerqetandina serxweste. Di vêgerênên ekstrem de, guhertina dielektrikê dikare bi tevahî bibîne heta jêrîn da ku were şerqetandin, li viriyê ku bobîna werin şerqetandin dema ku energiya were girtin. Di şertan normalan de, kaliteya yeksaş nivîsandinê berdeketîn pirseyarên latant yên vêtir. Buna, pêşkêşkirina û vegeraşina şertî insulasyonê ya wê bi şertê fabrika ya aslen dibêjiyê yeke hatman amadeyê ya peryodî çavkanîyê bibe. Ferqê mesafeyê di şertî insulasyonê duwa çavkanîyê û fabrika de wekî îmârê keyî ye ji bo cihewgirtina kaliteya karê ya çavkanîyê.

Ji bo pêşkêşkirina û vegeraşina rastînîya insulasyonê, girîng e ku kirîna û sazkerdina tazayê bikin. Kirînan din destnîşan dibin bi sê rênd: kirînan navendî, kirînan bûyerî, û kirînan gazî.

• Kirînan Navendî: Hemî komponentan da ku hewce ye çavkanînin divê bi rastînîya girîng saz bikin. Sazkirina divê heta ku bi pêlê paşîn bîcût bike, an ku lê danîş nabe an partîkela binihat nabe.

• Kirînan Bûyerî û Gazî (pirsîn gazî): Rêzikê girîngtar e ji bo vegeraşina kirîn û sazkerdina tazayê heye rêzikê vakûm, ku divê ji bo du rêzikên sereke:

(1) Kesandin û Degazkirina Vakûm:

• Pas dike hemî komponentan çavkanînin, plaka bîçav bikin ji bo flanka la gas relay side ya tank. Hama valveyan da ku komponentan bi badan tank bigihin veke, ji bo ku hemî komponentan (tayma coolers), bas bînavî gas relay û conservator, bi tanka serokî yan hêve bikin.

• Valve vakûm û standard stop valve bişopînin ji bo inlet oil la serîna tank.

• Paşîn ji evda tanka hêve bikin, test vakûm bikin ji bo pipînan la serîna, ji bo kontrolkirina reyal vakûm da ku sistem vakûm digire. Eger vakûm 10 Pa bi tevahî bibîne, bigihin ji bo kirînan la pipînan û service vakûm pump.

• Tanka bi tevahî kontrol bikin ji bo kirînan la serîna hêvekirina.

• Paşîn ku vakûm pump çavkirina maxîmîm (nebiş 133.3 Pa), pumpê bi tevahî çalak bikin ji bo pêşkêşkirina level vakûm. Pump vakûm divê bi tevahî çalak bike ji bo nebihate 24 saat.

(2) Toldikan Oil bi Vakûm:

• Pump vakûm bi tevahî çalak bikin ji bo toldikan oil. Hama valveyan veke bike heta vakûm, ji bo ku hemî komponentan û komponentan bi tanka serokî yan toldikan.

• Îmka vakûm oil purifier bikin. Oil divê bi valve inlet oil la binîna tank bike, ji bo ku oil bi tevahî çavbike ji navbera windings navbera, kirînî barê barriers.

• Paşîn ku level oil bi tevahî 200–300 mm jêrîn ji cover tank, valve vakûm bike veke û hêvekirina vakûm bike, lê toldikan oil bikin bi vakûm oil purifier.

• Ji bo transformatoran bê on-load tap changers (OLTC), toldikan oil dikare davam bike heta ku level oil derbas bike la gas relay blanking plate paşîn toldikan oil purifier.

• Ji bo transformatoran OLTC-equipped, toldikan oil purifier bike veke paşîn ku insulating cylinder ya selector switch toldibike, ji bo disconnection switch ji tank.

• Di hemî şertan de, tanka bi tevahî toldibike ji bo kirîna air volume. Paşîn breaking vacuum û topping up oil, tevahî air bi tevahî bigihin la upper space. Air din bi tevahî bigihin la conservator û nebiguherîne şertî core insulation.

Bebixwaz e ku ênkeyî li toldikan oil vakûm, niha biguherîne ji bo hot oil circulation. Ji bo hot oil circulation, tikî moisture da ku migere ji paper insulation bi oil dikare ji bo vakûm oil purifier. Lêm, moisture da ku qebûlkirin bi paper e nebiguherîne back bi oil, û equilibrium bi oil û paper moisture e zevmar.

2. Pirseyaran Oil Leakage

Oil leakage e pirseyar û prominent e ji bo transformatoran. Asayan zevmar, ji bo design û manufacturing defects (mesel, sealing design bêrî, machining poor, an welding quality bêrî). Errors installation û workmanship careless ji bo site da ku hêzandar (mesel, cleaning inadequate flange surfaces, presence oil, rust, weld spatter; aged gaskets bê elastic; uneven flange mating surfaces bê corrected).

Vegeraşina oil leakage divê karî girîng bikin:

• Paşîn ji evda çavkanînin, pressure sealing tests bikin ji bo coolers, conservators, risers, û oil purifiers, û repair leaking parts paşîn.

• Carefully inspect and prepare all flange sealing surfaces. Any misalignment during lifting must be corrected before installation; serious cases should be addressed jointly with the manufacturer.

• Paşîn ji evda çavkanînin, overall sealing test bikin: apply no more than 0.03 MPa pressure on the tank cover for 24 hours, with no oil leakage allowed.

3. Test Partial Discharge

Test partial discharge (PD) refer to induced voltage withstand test with PD measurement capability. According to GB 50150-91:

• Partial discharge tests are recommended for 500 kV transformers.

• For 220 kV and 330 kV transformers, PD tests are recommended if testing equipment is available.

Although the test voltage for PD testing is lower than that of standard induced voltage tests, the duration is extended by over 60 times. Combined with sensitive instruments monitoring internal discharge development, the destructive potential is controllable. Thus, PD testing combines characteristics of both non-destructive and destructive tests, effectively detecting insulation defects. As a result, it has gained rapid popularity. Most project owners now perform PD tests on newly installed or overhauled transformers, achieving significant benefits—early detection of installation flaws, identification of unstable factory PD performance, and ensuring successful initial energization.

4. Impulse Closing Test at Rated Voltage

The impulse closing test at rated voltage is primarily intended to verify whether the magnetizing inrush current generated during energization will cause the transformer differential protection to operate. It is not designed to test the insulation strength of the transformer.

In fact, during the impulse closing test, aside from relay protection monitoring, there are no instruments to detect possible overvoltages, and no measurable data is recorded. Therefore, from the perspective of insulation assessment, the test lacks conclusive value and is essentially meaningless.

That said, insulation failures in transformers have occurred during impulse closing tests—usually due to pre-existing serious defects that become apparent immediately upon energization. Conversely, there are numerous cases where transformers passed five impulse closures without issue, yet failed (burned out) within minutes to days after commissioning.

5. Assessment of Insulation Condition

Insulation condition assessment includes measuring insulation resistance, absorption ratio, polarization index, DC leakage current, and dielectric loss tangent (tan δ).

After installation, the transformer’s insulation condition may have deteriorated to varying degrees compared to factory conditions, and measurement methods between site and factory may differ. Therefore, when comparing commissioning test results with factory data, comprehensive analysis is required to make accurate judgments. These results should also serve as a baseline for future preventive testing.

It is particularly important to note: when insulation resistance is very high, the absorption ratio may decrease. In such cases, an absorption ratio below 1.3 should not automatically be attributed to moisture in the insulation.

6. Understanding and Function of the Breather

If the bladder in the conservator is analogous to the lung, then the breather acts as the nose. When load or ambient temperature increases, causing the oil in the tank to expand, the bladder "exhales" through the breather to prevent excessive pressure. Conversely, it "inhales" to prevent vacuum formation in the tank. If the breather becomes blocked, minor consequences include false oil level indications; severe cases may trigger gas relay or pressure relief device operation, leading to accidents.

Breather blockage can occur not only if the shipping seal is forgotten to be removed but also during operation due to:

• Moisture absorption and degradation of the desiccant (color-changing silica gel)

• Accumulation of dust in the oil cup

Therefore, two maintenance tasks are essential:

• Ensure the silica gel in the breather has sufficient moisture-absorbing capacity and prevent saturation. Replace or regenerate the silica gel when 1/5 of it has changed color.

• Regularly clean the oil cup, refill with clean oil, and maintain the oil level above the air baffle to ensure incoming air passes through an oil bath, filtering out dust particles.