Sabbin Farkon Kudurwa a Off-Circuit (De-energized) Tap Changers

I. Dukkukan da ke Tap Changers na Off-Circuit (De-energized)

1. Sababin Dukkukan

• Kwamfuta na tap changer contacts, kisan kyauwar kurfofin roller wanda ya kawo tsari masu yawa, ko kisan kyauwar zafi mai girma ta silver-plated layer wanda ya haifar da dukkukan—zai iya haifar da tap changer a lokacin da ake yi.

• Makunshi na tap positions, ko makunshi/welding da ba daidai ba, ba zan iya taka da current surges na short-circuit.

• Zabu na tap position na daɗi, wanda ya haifar da kasa da dukkukan.

• Kwamfuta na phase-to-phase clearance a kan three-phase leads ko kisan kyauwar zafi mai girma ta insulation materials, wanda za iya haifar da insulation breakdown a cikin overvoltage da kuma za iya haifar da inter-phase short circuits a kan tap changer.

2. Ƙiyasin Dukkukan

Operators yana buƙatar ƙarin shirya oil sample don gas chromatography analysis, baya daga ƙarin hawan current, voltage, temperature, oil level, oil color, da kuma sounds da ba daidai ba, don tabbataccen dukkukan da kuma ƙara ƙiyasar lissafin.

II. Dukkukan da ke On-Load Tap Changers (OLTC)

1. Oil Leakage daga OLTC Oil Compartment

Sababin:

• Drain valve a ƙarshen OLTC oil tank ba daidai ba, wanda ya iya haifar da oil mixing bayan OLTC compartment da main transformer tank.

• Kwamfuta na assembly ko sealing materials da ba daidai ba bayan biyu oil compartments.

• Kwamfuta na central drive shaft oil seal.

Handling:
Shirya tap changer daga oil compartment, drain da kuma sautoci compartment da kuma nuna source da ya haifar da leakage—yanayi a kan tap lead bolts ko rotating shaft seals—da kuma yi ƙiyasar lissafin.

2. Broken ko Loose Transition Resistors

Sababin:
Idan transition resistor an haifar da shi da kuma ake yi load tap change, za iya haifar da load current interruption. Full phase voltage zai bazo a kan open contacts da resistor gap, wanda za iya haifar da:

• Breakdown of the resistor gap,

• Intense arcing bayan moving and fixed contacts,

• Short-circuit bayan adjacent tap positions, zai iya haifar da high-voltage winding tap segments.

Handling:
A lokacin da maintenance ta transformer, ƙarin nemi da kuma shirya all transition resistors don mechanical damage, looseness, ko connections da ba daidai ba, don ƙara ƙiyasar lissafin da kuma dukkukan a lokacin da switching.

3. Overheating of Tap Changer Contacts

Sababin:
Frequent voltage regulation zai haifar da severe electrical erosion, mechanical wear, da kuma contamination of contacts. A transformers da high load currents:

• Joule heating zai haifar da contact spring elasticity, wanda zai kawo tsari masu yawa,

• Contact resistance zai ƙare, wanda zai haifar da heat masu yawa,

• Wannan zai haifar da oxidation, corrosion, ko mechanical deformation of contact surfaces, wanda zai haifar da vicious thermal cycle.

Handling:
A lokacin da commissioning, yi DC resistance tests a kan all tap positions. A lokacin da hood-lift inspections, nemi da kuma shirya contact plating integrity da kuma measure contact resistance. Don ƙara oil films ko oxides, manually cycle the tap changer through multiple positions don ƙara clean, firm contact.

4. Tap Changer "Run-On" (Continuous Operation)

Sababin:

• Malfunction of AC contactors (e.g., oil contamination, residual magnetism causing delayed de-energization) ko faulty sequence switches.

• Unreliable AC contactors ko micro-switches; loose screws ko insufficiently long stop tabs on the tap changer mechanism.

Handling:
Nemi contactors don sticking ko delay; verify sequence switch logic. Realign components, use contactors with lower residual magnetism, ko add a capacitor in series to suppress residual flux. Clean oil/contaminants from contactors and tighten all loose fasteners.

5. Tap Changer Exceeding Limit Positions

Sababin:

• Rust on mechanical limit screws, wanda zai haifar da suka iya stopping shaft rotation.

• Insufficient height of positioning blocks, wanda ba zan iya trigger the electrical limit switch ba a cikin extreme positions.

Handling:
Manually adjust upper/lower limit blocks and verify that position indicators match actual tap settings. If mismatched, disconnect the motor drive, manually crank the tap changer to a mid-position, then re-engage electric control.

6. Tap Changer Failure to Operate (Refusal to Switch)

Sababin:

• Excessive or insufficient spring tension in the fast-acting mechanism (leading to breakage or sluggish action).

• Loose flexible connectors; overly tight sealing between the central shaft and oil compartment base, preventing full insertion of contacts.

Handling:
Check for incomplete engagement between motor drive and tap changer:

• Verify interlock switch continuity and spring reset.

• Inspect for poor contact between fixed and moving contacts.
  If failure occurs in both directions, focus on:

• Reset status of manual crank interlock switch,

• Contact integrity of control switches,

• Normalcy of three-phase power supply.
  For delayed or incomplete switching, investigate:

• Weakened, fatigued, or broken energy-storage springs,

• Mechanical binding.
  Repair or replace faulty mechanical components or springs as needed.