75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper
The 75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper is engineered for regional 66–75 kV transmission and industrial step-down applications. It adopts 99.99 % electrolytic copper windings, high-grade grain-oriented silicon steel S13 core, corrugated tank + ONAN cooling, and ±5 % off-circuit tap changer (on-load optional). Fully compliant with IEC 60076, lightning impulse withstand 350 kV peak, PD <10 pC, noise ≤58 dB. Fully sealed or conservator design with vacuum oil filling and nitrogen sealing ensures >30-year maintenance-free operation even in high-altitude or polluted areas. Ideal for mining, metallurgy, wind farms, and urban 75 kV substations requiring high reliability and low loss.
- Primary Voltage Ratings 69kV 66kV 75kV or others
- Secondary Voltage Ratings 33/13.8/11 kV or customized
- H.V. Tap Range ±8×1.25% or others
- Type Oil-immersed power transformer
- BIL Up to 350kV
- Standards IEEE, ANSI, IEC, CSA
- Application wind/solar grid connection, petrochemical facilities, railway traction, urban high-voltage distribution
- Power Rating 1250kVA
- Certificate UL ,CESI ,ISO
- Cooling Method ONAN/ ONAF
- Opeartion Step Down & Step Up
Technical Specifications
Customization Optional
Packing and Shipping
Manufacturer Test
Routine Testing
Application
Technical Specifications
75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper
Technical Specifications
Accessories
| Rated Power | 1250kVA |
| Rating Primary Voltage | 69kV 66kV 75kV or others |
| Secondary Voltage |
33kV 13.8kV 11kV Customized |
| Frequency | 50/60Hz |
| Vector Group | Dyn11, YNd1, Dyn1, YNd11 or others |
| Winding Material | Aluminum/Copper |
| Efficiency | As IEEE, CAS Std or Customized |
| Impedance Voltage | As IEC |
| Altitude | ≤1,000m or Customized |
| Enclosure material | Mid Steel |
| HV Bushing |
| LV Bushing |
| OLTC/NLTC |
| Lifting hook for complete transformer |
| Name plate |
| Oil temperature |
| Winding temperature |
| Radiators |
| Oil level |
| Pressure relief valve |
| CT |
Customization Optional
75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper
The 75kV 1250kVA transformer offers virtually unlimited customization to meet exact project requirements. Capacity can be scaled from 800 kVA to 3150 kVA while maintaining the same footprint. Clients may select 100 % high-conductivity electrolytic pure copper windings for maximum efficiency and thermal endurance, or cost-optimized copper-aluminum hybrid construction. Core options include conventional grain-oriented silicon steel (S11/S13/S20 series) or advanced amorphous metal cores for up to 70 % lower no-load losses. Primary voltage covers full 66 kV, 69 kV, 72.5 kV, and 75 kV classes with tap ranges of ±5 %, ±2×2.5 %, or extended ±10 %. Secondary voltages include 11 kV, 13.8 kV, 10.5 kV, 6.3 kV, 0.69 kV, 0.4 kV, or any dual-voltage/tertiary winding configuration. Vector group is fully selectable: Dyn11, YNd11, Yyn0, Dyn5, or special auto-transformer connections for harmonic filtering. Tap changer choices range from standard off-circuit to high-speed resistor or vacuum on-load types (±8×1.25 % or ±12×1.5 %) with parallel operation capability and remote RTU control. Cooling systems include pure ONAN, multi-stage ONAF with redundant automatic fan groups, or ODAF for continuous 160 % overload. Tank designs comprise fully sealed corrugated fins for zero maintenance, a conservator with an oil-conservator bladder to eliminate air contact, or detachable radiator banks with butterfly valves for easy transport and future expansion.
Advanced optional features transform the transformer into a complete intelligent asset. Integrated CT/PT compartments with high-accuracy metering class (0.2 s) and protection class (5P20/10P20) are available. Real-time monitoring includes 8–16 channel fiber-optic direct hot-spot temperature sensors, online multi-gas DGA (9 gases + moisture), bushing monitoring (tanδ & capacitance), and partial discharge UHF sensors. Protection suite offers a sudden pressure relay with fast trip (<15 ms), a pressure relief device with directional shield, and internal arc-fault detection. Enclosure options range from IP54 weatherproof housing with acoustic canopy (noise <55 dB) to full walk-in IP65 substations. Special environmental adaptations cover high-altitude operation above 5000 m (enhanced BIL & cooling), seismic qualification up to 0.6 g, extreme temperature versions (-60 °C arctic or +55 °C desert with forced ventilation), and marine/offshore C5-M + CX anti-corrosion epoxy systems. Smart grid readiness includes IEC 61850, DNP3, Modbus TCP/IP, and a built-in edge gateway for predictive maintenance and remote OLTC control. Every customization is executed under full IEC 60076, GB/T 1094, and IEEE C57 compliance, backed by type test reports from KEMA, CESI, or STL laboratories, ensuring seamless integration and decades of reliable service in the most demanding 75 kV applications worldwide.
Packing and Shipping
75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper
Immediately after FAT sign-off, the transformer undergoes final vacuum dehydration below 0.5 mbar for 72 hours and hot-oil circulation until moisture ≤6 ppm and dielectric strength ≥75 kV/2.5 mm. The tank is then filled with 99.999 % ultra-dry nitrogen to 0.03–0.04 MPa positive pressure and hermetically sealed. A high-precision digital pressure & temperature data logger (180-day memory, 1-minute interval) is permanently installed on the conservator pipe to provide continuous evidence of internal integrity. All flanges receive double-sealed blind covers and tamper-evident seals. Nitrogen purity certificate, vacuum retention certificate, and real-time pressure trend report are supplied with shipping documents, guaranteeing zero insulation degradation even during 90-day ocean transits.
All 75 kV porcelain bushings, neutral bushing, conservator (if fitted), detachable radiators, OLTC drive mechanism, cooling fans, Buchholz relay, oil level indicator, temperature gauges, sudden pressure relay, and marshalling box are carefully dismantled by senior technicians. Each component is wrapped in VCI film, placed in custom IPPC-fumigated marine-plywood crates lined with ≥60 mm high-density anti-shock foam, and packed with 300 kg color-indicating silica-gel desiccant. Four 3-axis shock recorders (±250 g) and two electronic tilt indicators are fixed to every crate. Crates are clearly labeled in English/Chinese with part number, transformer serial number, gross/net weight, and “Extremely Fragile – This Side Up” warnings.
The main tank (gross weight approx. 17–21 tons) is welded onto a DNV 2.7-1 certified heavy-lift steel skid with 16 certified lashing points and four 100-ton lifting lugs. The entire body is enclosed in a fully sealed composite crate constructed from 28 mm marine plywood reinforced with 100×100 mm galvanized steel beams, then triple-wrapped with aluminum-foil vapor barrier and heavy-duty heat-sealed tarpaulin. Ten high-resolution digital impact recorders (trigger >3 g) and real-time GPS/4G tilt & vibration monitors are permanently attached. External surfaces are painted bright yellow with permanent stenciling: “75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper – Gross Weight 21 Tons – Do Not Roll – Keep Dry – Use Spreader Beam Only”.
Inland transport uses low-bed or hydraulic axle trailers (total height ≤4.5 m). Sea freight is performed as break-bulk under-deck or on 40 ft heavy-duty flat-rack containers with CCS/DNV-GL approved lashing using Φ28 mm steel wire ropes and 80-ton turnbuckles. Complete documentation includes a detailed packing list, IPPC fumigation certificate, certificate of origin (Form A/E), nitrogen pressure & trend report, shock recorder baseline data, 110 % all-risk marine insurance, third-party loading survey report, and full installation manual. These rigorous measures ensure every unit arrives worldwide in perfect, ready-to-energize condition with zero damage and full traceability.
All 75 kV porcelain bushings, neutral bushing, conservator (if fitted), detachable radiators, OLTC drive mechanism, cooling fans, Buchholz relay, oil level indicator, temperature gauges, sudden pressure relay, and marshalling box are carefully dismantled by senior technicians. Each component is wrapped in VCI film, placed in custom IPPC-fumigated marine-plywood crates lined with ≥60 mm high-density anti-shock foam, and packed with 300 kg color-indicating silica-gel desiccant. Four 3-axis shock recorders (±250 g) and two electronic tilt indicators are fixed to every crate. Crates are clearly labeled in English/Chinese with part number, transformer serial number, gross/net weight, and “Extremely Fragile – This Side Up” warnings.
The main tank (gross weight approx. 17–21 tons) is welded onto a DNV 2.7-1 certified heavy-lift steel skid with 16 certified lashing points and four 100-ton lifting lugs. The entire body is enclosed in a fully sealed composite crate constructed from 28 mm marine plywood reinforced with 100×100 mm galvanized steel beams, then triple-wrapped with aluminum-foil vapor barrier and heavy-duty heat-sealed tarpaulin. Ten high-resolution digital impact recorders (trigger >3 g) and real-time GPS/4G tilt & vibration monitors are permanently attached. External surfaces are painted bright yellow with permanent stenciling: “75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper – Gross Weight 21 Tons – Do Not Roll – Keep Dry – Use Spreader Beam Only”.
Inland transport uses low-bed or hydraulic axle trailers (total height ≤4.5 m). Sea freight is performed as break-bulk under-deck or on 40 ft heavy-duty flat-rack containers with CCS/DNV-GL approved lashing using Φ28 mm steel wire ropes and 80-ton turnbuckles. Complete documentation includes a detailed packing list, IPPC fumigation certificate, certificate of origin (Form A/E), nitrogen pressure & trend report, shock recorder baseline data, 110 % all-risk marine insurance, third-party loading survey report, and full installation manual. These rigorous measures ensure every unit arrives worldwide in perfect, ready-to-energize condition with zero damage and full traceability.
32
32 years of industry experience
Manufacturer Test
75kV 1250kVA Three Phase Oil Immersed Power Transformer Copper
Progress test
During manufacturing, the transformer undergoes strict staged Progress Tests with client-witness option:
- Core-coil stage: winding DC resistance at all taps, insulation resistance & PI ≥ 2.5, core grounding current <80 mA, preliminary no-load loss check.
- Pre-tanking: voltage ratio at principal and extreme taps (deviation ≤ ±0.5 %), vector group verification (Dyn11/YNd11), polarity, and magnetic balance test.
- After vapor-phase drying & vacuum oil filling: final insulation resistance (>15,000 MΩ), tanδ ≤ 0.004 (20 °C), partial discharge <10 pC at 1.5Um/√3, oil BDV ≥ 72 kV/2.5 mm, moisture <10 ppm.
- Final sealing: 48-hour static leakage test, 0.4 bar positive/negative pressure test for 24 h each, OLTC contact resistance, and mechanical operation (if applicable).
All results are fully recorded and submitted for client/third-party approval before proceeding to FAT, ensuring flawless quality.
Design Tests
All transformers will be tested after finishing the production test items as below:
♦ Leak testing with pressure for liquid-immersed transformers
♦ Test of transformer oil
♦ Measurement of voltage ratio and check of phase displacement
♦ Measurement of winding DC resistance
♦ Measurement of d. c. Insulation resistance between each winding to earth, and check of the core and frame insulation
♦ Capacitive bushing test
♦ Measurement of dissipation factor (tan δ) of the insulation system capacitances, and determination of capacitances windings-to-earth
♦ Measurement of no-load loss and current at 90%,100%,110% of rated voltage
♦ Operation test on on-load tap-changer
♦ Measurement of short-circuit impedance and load loss
♦ Lightning impulse test
♦ Induced-voltage test with partial discharge measurement
♦ Auxiliary wiring check
♦ Current transformer test
♦ Frequency response analysis test
Transformer Factory Acceptance Test
FAT is performed strictly per IEC 60076 with full client/third-party witness and signed protocol:
- Winding resistance at all taps (corrected to 75 °C)
- Voltage ratio & polarity at principal/extreme taps (≤ ±0.5 %)
- Vector group (Dyn11/YNd11) and magnetic balance
- No-load loss & current at 90 %, 100 %, 110 % rated voltage
- Load loss and impedance at 75 °C/rated current
- Separate-source & induced withstand voltage with PD <10 pC at 1.5Um/√3
- Full-wave lightning impulse test 350 kV peak (75 kV side)
- Insulation resistance, PI ≥ 2.5, tanδ ≤ 0.004, oil BDV ≥ 72 kV
- Tap-changer 8–10 full cycles + 50 auxiliary cycles
- Cooling system, Buchholz relay, sudden pressure relay, temperature indicators function test
- Sound level measurement (≤ 58 dB)
- Final visual, painting, nameplate and nitrogen pressure inspection
The official FAT report with raw data and calibration certificates is signed, confirming 100 % readiness for immediate energization.
Routine Test - No Load Loss Test
Purpose of Testing
The purpose of No Load Loss Test is to measure the power loss of the equipment when it is not loaded to evaluate the iron loss and other core losses. This test can help understand the energy efficiency of the equipment and help determine the performance of the transformer or motor when it is running at no load.
Testing Equipment
No Load Loss tester (e.g. OMICRON, Megger, Schneider Electric, etc.)
Voltage source (usually 230V, 400V or customized according to customer requirements to adapt to different equipment)
Power analyzer (used to measure power loss and efficiency)
Ammeter and voltmeter
Temperature and humidity meter
Voltage source (usually 230V, 400V or customized according to customer requirements to adapt to different equipment)
Power analyzer (used to measure power loss and efficiency)
Ammeter and voltmeter
Temperature and humidity meter
Pre-Test Preparation
Disconnect the power supply of the device and ensure that the device is properly grounded and discharged to ensure safe operation.
Please ensure that the test is carried out in a suitable environment with a relative humidity of less than 75% and avoid rainy days or extreme weather (recommended temperature range: 20-30°C).
Please ensure that the test is carried out in a suitable environment with a relative humidity of less than 75% and avoid rainy days or extreme weather (recommended temperature range: 20-30°C).
Test Progress
Connect the Test Instrument:
Connect the test equipment to the high voltage side of the transformer, making sure the wiring is correct and the equipment is grounded.
Apply Test Voltage:
Usually it is 110% of the rated voltage, for example, if the rated voltage of the transformer is 33 KV, apply 36.3 KV (110%).
Connect the test equipment to the high voltage side of the transformer, making sure the wiring is correct and the equipment is grounded.
Apply Test Voltage:
Usually it is 110% of the rated voltage, for example, if the rated voltage of the transformer is 33 KV, apply 36.3 KV (110%).
Measure and Record
Start the test and record the following parameters:
No Load Current
No Load Loss
Power Factor
Current
Voltage
Temperature and Humidity
No Load Current
No Load Loss
Power Factor
Current
Voltage
Temperature and Humidity
Temperature Correction
The power loss of the test results is corrected to a reference temperature (usually 20°C) to ensure an accurate evaluation.
Repeat Testing (if necessary)
Test at different rated voltages, especially when the transformer has multiple capacity levels, and perform no-load loss tests for each capacity level separately.
Evaluation Criteria (Reference)
No-load loss ≤ 0.2% rated power (excellent)
No-load loss < 0.2% ≤ 0.5% rated power (good)
No-load loss > 0.5% rated power (further inspection or corrective action required)
No-load loss < 0.2% ≤ 0.5% rated power (good)
No-load loss > 0.5% rated power (further inspection or corrective action required)
*These comprehensive tests ensure that each transformer meets performance standards and operates
reliably under various conditions.
Application
75 kV regional substations, mining & metallurgy plants, wind/solar grid connection, petrochemical facilities, railway traction, urban high-voltage distribution.
Technical Advantages
● 30+ years of manufacturing experience
● ISO and UL certified production
● Customized cable and transformer solutions
Product Packaging
Transformers Packaging (1)
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