Transformer Cooling Systems Flashcards

Transformer Heating and Cooling

• In liquid type transformers, hot oil rises, cools in radiators, and then returns to the bottom.
• Heat in transformers is generated from losses in cores and windings.

Cooling Classes and Methods

• Two cooling classes for dry type transformers: forced air (FA) and ambient air (AA).
• AA refers to a natural air cooling system without added cooling.
• FA enhances cooling by incorporating fans to circulate air through cooling ducts.

Cooling Liquids and Systems

• Cooling options for liquid transformers include oil, water, and air.
• Air cooling can be achieved using fans or naturally circulating air.
• Water cooling involves heat exchangers that circulate cold water alongside hot oil.

Radiators, Coolers, and Pumps

• Types of radiators include panel, tube, and coolers.
• Coolers operate continuously with pumps and fans for efficiency.
• Oil pumps are deployed to enhance oil circulation and expedite cooling.

Cooling Terminology

• Directed flow indicates a targeted pathway for oil movement.
• Definitions of key components:
  • O: oil
  • A: air
  • N: natural
  • F: forced
  • D: directed
  • W: water

Operational Classifications

• ONAN: Oil Natural Air Natural, no mechanical assistance.
• OFAF: Oil Forced Air Forced, combines circulating oil and fan cooling.
• OFWF: Oil Forced Water Forced, integrates oil movement with water cooling.
• Multi-stage cooling improves a transformer’s cooling capacity.

Transformer Tanks and Sealing

• Sealed tank transformers contain no breather unit, conservator, or gas bottle.
• Nitrogen blanketed transformers have a nitrogen system for pressure maintenance.
• Low pressure in sealed transformers requires the addition of nitrogen to sustain pressure.

Conservators

• A conservator serves as an expansion chamber for oil in transformers.
• Without a conservator, transformers cannot be filled to maximum oil capacity.
• Two types of conservators: open (no bladder) and sealed (with bladder).

Open vs Sealed Conservators

• Sealed conservators utilize an air-tight bladder to manage oil expansion and contraction.
• Open conservators feature a breather unit to regulate gas exchange without contamination.
• The breather unit prevents contaminants by using silica gel/desiccant and an oil trap.

Maintenance and Functionality

• Silica gel in breather units changes color as it absorbs moisture, indicating replacement is needed at 75% saturation.
• Dry type transformers are encased in materials like plastic, epoxy, or fiberglass.
• Cooling for dry transformers is achieved via fans that force air through winding gaps.

Convection and Tank Types

• Convection describes fluid movement driven by temperature-induced density variations.
• Various tank types include sealed, nitrogen blanketed, sealed conservator, open conservator, and free breathing configurations.
• If a bladder in a sealed conservator cannot be replaced, it can operate as an open conservator with a breather unit.