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Olga Ivanova
Olga Ivanova
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For a 75/95 MVA transformer rated 220/110-70/15 kV, the typical vacuum level during insulation drying is usually in the sub-millibar range, around 0.2-0.5 mbar, and in many procedures it is kept below 1 mbar depending on temperature and moisture condition. During oil processing and degassing, vacuum oil purification units normally operate at a slightly higher level, commonly around 1-3 mbar, which is sufficient to efficiently remove dissolved gases and moisture from transformer oil.
Small distribution transformers hours-days; large power transformers days-months depending on failure mode, spares, logistics, and utility procedures.
一月 27, 2026 7:25 上午 回复至： What is the difference between power transformer and voltage transformer? #332197A power transformer transfers bulk apparent power between grid voltage levels and is designed for high MVA capacity, thermal performance, and short-circuit withstand. A voltage transformer (instrument transformer, VT/PT) is a metering/protection device that reproduces primary voltage at a reduced, accurate level for relays and meters. Power transformers focus on efficiency, impedance, cooling, and insulation coordination; VTs focus on accuracy, phase error, burden rating, and dielectric strength.
The cost of a power pole (distribution) transformer depends on rating, voltage class, insulation type and region. Small single phase overhead units for low voltage distribution are far cheaper than large three phase pad mounted designs. Prices are driven by copper and steel costs, insulation system, accessories and certification requirements. Utilities often buy through framework contracts and do not pay “retail” prices. Instead of one fixed number, engineers estimate cost ranges during planning and then obtain project specific quotations that include transport, accessories, testing and warranty conditions.
一月 26, 2026 4:46 下午 回复至： Why is power transform required before electricity reaches low-voltage consumers? #332085HV is required for efficient transmission; LV is required for end-use safety. Transformers bridge voltage levels from generation to consumption.
一月 26, 2026 12:19 上午 回复至： What can a power transformer picture reveal about cooling and bushings? #331939Visible features include radiator banks, fans, oil pumps, bushings, OLTC compartments, and nitrogen/oil conservators, indicating cooling class and voltage level.
Typical buyers include transmission and distribution utilities, IPPs, generation companies, industrial plants (steel, mining, petrochemicals, cement), railways, metro systems, data centers, large commercial campuses, EPC contractors, and sometimes large commercial buildings. They purchase transformers for new substations, plant expansions, grid upgrades, renewable interconnections, and replacement of aging fleet assets, usually via tendering or negotiated framework agreements.
Servicing uses de-energized and energized diagnostics. De-energized tests include insulation resistance, winding resistance, TTR, OLTC contact resistance, and oil sampling for DGA and dielectric strength. Energized tests include infrared thermography, partial discharge monitoring, and load-loss measurements. Results are trended to detect insulation aging, moisture ingress, overheating, and mechanical displacement.
一月 23, 2026 9:41 下午 回复至： What is the difference between a distribution and a power transformer? #331541Power transformers handle high voltage and operate near full load between generation and transmission; distribution transformers operate at lower voltage, lower utilization and deliver energy to end users.
一月 23, 2026 5:06 上午 回复至： Why does a power line transformer require dielectric oil replacement over time? #331395Mineral oil degrades from heat, moisture, and oxidation. Replacement restores dielectric strength, cooling performance, and prevents insulation breakdown.
一月 22, 2026 10:37 上午 回复至： What does a power voltage transformer do in electrical distribution? #331238It provides voltage transformation, isolation, and coordination between medium-voltage feeders and low-voltage service circuits.
一月 22, 2026 6:10 上午 回复至： What is the typical nominal capacity of the CMM-12R oil regeneration systems in liters per hour? #331174Typical nominal capacity of the CMM-12R oil regeneration systems ranges from around 1,000 to 2,000 liters per hour, enabling efficient processing of insulating oil for large transformers and industrial applications.
It covers handling, lifting, oil filling, grounding, tap setting, testing, commissioning, and safety instructions for field installation.
一月 21, 2026 8:38 下午 回复至： What customization options exist for the US-6S chamber and accessories? #331036Customization includes chamber size (to fit various transformer dimensions), door types (manual or automatic), heating types (direct electric or oil-based), convection agitation, lighting, control points, and additional instrumentation. Clients can specify loading systems (manual or automated sliding carriage), insulation monitoring, and integration with plant control systems.
IEC 60076-3 specifies dielectric testing requirements, including applied voltage, induced voltage, lightning impulse, and switching impulse tests. These tests verify insulation strength, withstand capability, and partial discharge limits for transformers intended for transmission and distribution systems.
一月 21, 2026 7:12 上午 回复至： Does the permissible moisture level depend on the type of fluid used in the transformer? #330821Yes, the permissible moisture level depends very strongly on the type of insulating fluid, and this is a critical point in modern diagnostics. Mineral oil has relatively low water solubility, so even 20-40 ppm can represent a high relative saturation at low temperature and a real risk for paper wetting. In contrast, natural and synthetic esters dissolve much more water, so values of 200-400 ppm or more can still correspond to a safe relative saturation. That is why absolute ppm limits are misleading across fluids. For all fluids, the correct criterion is relative saturation or water activity, not ppm, and alarm thresholds must be adapted to the specific oil type.
40 ppm at 65 °C is not critical for moisture, because at this temperature the oil saturation level is high and relative saturation is likely low. The more serious concern is tan delta > 1, which usually indicates oxidized or contaminated oil, high acidity, or conductive aging products. DP = 520 means the paper is aged but still serviceable, so slowing further aging is important. An online dryer can help stabilize moisture and protect the paper, but it will not correct a high tan delta. First, check TAN, IFT, resistivity, and DGA. If oil quality is poor, oil reclamation or replacement is needed before relying on online drying.
一月 20, 2026 2:39 上午 回复至： What role does a control power transformer play in low voltage control circuits? #330448Control transformers supply stable low-voltage AC for relays, contactors, and control logic isolated from MV/HV feeders.
Areva transformers (heritage now in GE Grid) were widely deployed in transmission and sub-transmission infrastructure, HV substations, nuclear plants, and industrial complexes that require long-life transformer fleets.
Apparent power is conserved minus losses; stepping up increases voltage while decreasing current, not creating power. Losses arise from copper, core, and stray effects.
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