Introduction
Construction
Example Drawings
100 MVA power transformer diagram drawing and size.
Manufacturing
4.1 Core
The iron core of our power transformer uses high-permeability silicon steel sheets, subject to strict quality control, and is wrapped in high-quality insulating materials to ensure safety, stability and low energy consumption. Advanced stamping and laser cutting technologies are adopted in manufacturing for high-precision processing, and the specially designed laminated structure reduces eddy current losses to improve energy efficiency. In design, the core shape is optimized to match magnetic circuit requirements, controlling magnetic vibration noise and extending equipment service life. Meanwhile, advanced damping and soundproofing technologies are used to minimize operational noise to the greatest extent. With high-quality materials, advanced processes, meticulous design and comprehensive noise reduction, the core boasts excellent performance, durability and reliability.
4.2 Winding
SCOTECH’s power transformer windings are engineered to meet stringent electrical and mechanical requirements across different voltage levels. For high-voltage (HV) windings, they adopt either entangled or inner-screened continuous designs, integrated with phase insulation to ensure strong insulating capacity for stable operation.
Medium-voltage (MV) and low-voltage (LV) windings utilize high-strength or transposed conductors, which not only enhance electrical performance but also facilitate forced cooling to keep temperature rise in check. This design effectively boosts short-circuit withstand capability, ensuring safety and long-term durability.
A range of construction techniques-including interleaved, shielded disk, helical, and layered designs-are employed, each tailored to the specific voltage and impulse rating needs of the transformer. With precise coil winding processes, SCOTECH’s transformer windings deliver exceptional efficiency, reliability, and consistent performance, making them well-suited for demanding operational scenarios
4.3 Tank
SCOTECH’s power transformer tanks are constructed using high-quality stainless steel or mild steel, ensuring robust pressure resistance and corrosion resistance. The manufacturing process adheres strictly to design specifications, employing cutting and laser cutting technologies for precise sheet metal processing, which enhances welding quality and the adhesion of subsequent coatings. Welding operations utilize argon arc welding or CO₂ shielded welding, with thorough post-welding inspections-including visual checks and ultrasonic testing-conducted to guarantee weld integrity.
High-performance sealing materials, such as rubber washers and graphite sealing rings, are used at tank connection points to secure reliable sealing. The external surface undergoes anti-corrosion treatment, featuring a primer coat followed by an environmentally friendly topcoat for superior corrosion resistance. All seals incorporate a stepped limit sealing design; internal and external metal components are uniformly deburred, and welds and seals undergo three leakage tests (visual inspection, pressure testing, and vacuum testing) to ensure the tank meets standard requirements for sealing and leak resistance.
4.4 Final assembly
First, the HV and LV windings are precisely assembled onto the core limbs, followed by core lamination stacking to ensure magnetic circuit integrity and structural stability. The completed active part (core and windings) then undergoes thorough vacuum drying to eliminate moisture completely. The dried active part is carefully lowered into the meticulously cleaned tank using specialized lifting equipment. Next, vacuum oil filling is performed to ensure the highest purity of insulating oil. This is followed by the installation of key accessories including bushings, radiators, conservators, pressure relief devices, Marshalling Box and so on.
Components
Filters air entering the conservator to prevent moisture and dust from entering the transformer. Typically contains silica gel (color-indicating desiccant), which changes color when saturated and requires periodic replacement.
Used to release trapped air or small amounts of oil inside the Buchholz Relay, ensuring accurate operation.
A connection box for bushing current transformers (BCTs), transmitting current signals to protection or measurement devices.
Located at the bottom of the transformer tank, used for draining old oil, filling new oil, or removing sediment during maintenance.
Installed in the pipe between the conservator and the tank, it detects internal faults (e.g., overheating or arcing). Triggers an alarm or trip when gas accumulation or abnormal oil flow occurs.
Isolates the transformer tank from cooling systems (e.g., radiators), allowing component removal during maintenance without fully draining the oil.
An expansion tank that accommodates oil volume changes due to temperature fluctuations, balancing pressure via the breather.
An electrical cabinet housing protection, monitoring, and control circuits, including temperature controllers and fan operation modules.
Used in forced-air cooled (ONAF) transformers to enhance radiator cooling, typically activated by temperature signals.
Dissipate heat from the transformer oil via natural convection or forced airflow, consisting of multiple finned tubes.
The magnetic circuit of the transformer, made of laminated silicon steel to reduce eddy current losses. Must be single-point grounded to prevent induced voltages.
Ensures reliable grounding of the core to avoid floating potentials and discharges.
The bushing for the HV winding neutral point, which may be directly grounded or grounded through impedance.
Insulated bushings for HV winding leads, designed to withstand system voltage and secure conductors.
Reinforced points on the transformer base for lifting during installation or transportation.
Provides safe access for maintenance personnel, usually equipped with anti-fall railings.
Sealing valve for oil or gas systems, ensuring leak-free operation.
Lifting points on the transformer tank or components, designed for standard load capacity.
Insulated bushings for LV winding leads, similar in structure to HV bushings but rated for lower voltage.
An access point for personnel to enter the transformer tank for inspection or maintenance.
A junction box for secondary wiring, facilitating connections for protection, measurement, and control signals.
The motorized mechanism for on-load tap changers (OLTC), enabling remote or automatic voltage regulation.
A metal plate displaying key transformer parameters (e.g., rated capacity, voltage, current, impedance).
Monitors oil level and triggers alarms if the level is too high or too low.
Measures top oil temperature and activates cooling systems or alarms if overheating occurs.
Adjusts the transformer ratio under load to stabilize output voltage, incorporating mechanical switching and arc control mechanisms.
Rapidly releases excess pressure during internal faults to prevent tank rupture.
Used to collect oil samples for dissolved gas analysis (DGA) or dielectric strength testing.
The main enclosure housing the core, windings, and insulating oil, designed to withstand internal pressure and resist corrosion.
An enclosed box for external electrical connections, with an ingress protection (IP) rating suitable for the environment.
A separate conservator dedicated to the OLTC’s oil expansion and sealing, independent of the main conservator.
Measures hotspot temperature (via thermal simulation or fiber optics) and triggers alarms or trips if overheating occurs.
The conductive coils (HV and LV) made of copper or aluminum, responsible for energy transfer.
Applications
• Stepping Up Voltage for Transmission: At power plants (e.g., thermal, hydro, wind, or solar), generators produce electricity at relatively low voltages (typically 11 kV to 33 kV). Power transformers step up this voltage to ultra-high levels (e.g., 132 kV, 220 kV, 400 kV, or even 800 kV) for long-distance transmission. Higher voltages reduce current, minimizing energy loss due to resistance in transmission lines (by Joule’s law: P_loss=I^2 R).
• Connecting Generation Sources: Transformers integrate renewable energy sources (e.g., wind farms, solar parks) into the grid. For example, solar inverters output low-voltage AC, which is stepped up by transformers to match transmission line voltages.
• Stepping Down Voltage for End Users: After long-distance transmission, high-voltage electricity reaches substations, where power transformers step down the voltage to medium levels (e.g., 33 kV, 11 kV) for distribution to local areas (cities, towns, or industrial zones).
• Further Voltage Reduction for Consumers: Smaller distribution transformers (installed on poles or in substations) step down medium voltages to low voltages (e.g., 230 V or 400 V) suitable for residential, commercial, and small industrial use.
• Heavy Industries: Industries like steel, mining, and manufacturing use high-power machinery (e.g., motors, furnaces) that often require specific voltages (higher or lower than the grid supply). Power transformers (including dry-type transformers for indoor use) adjust voltages to match equipment requirements, ensuring efficient operation.
• Electrolysis and Metallurgy: Processes like aluminum smelting or electroplating require large currents at low voltages. Transformers step down high voltages to provide the necessary low-voltage, high-current supply.
• Residential Communities: Pole-mounted or pad-mounted distribution transformers (a type of power transformer) supply low-voltage electricity to homes, apartments, and small buildings, powering appliances, lighting, and electronics.
• Commercial Buildings: Malls, offices, and hospitals use transformers to distribute power across large facilities, ensuring stable voltage for HVAC systems, elevators, and medical equipment.
• Wind farms: Variable AC from wind turbines is converted via step-up transformers (per turbine or at central substations) to match grid transmission voltages for efficient grid feed-in.
• Solar power plants: Low-voltage DC from solar panels is converted to AC by inverters, then stepped up via transformers for grid or local distribution network connection.
• Hydropower and geothermal plants: Like conventional power plants, they use transformers to step up generated voltage for transmission.
In data centers, power transformers are critical for stable, safe power supply, with key roles including:
1. Step down high-voltage mains (e.g., 10kV) to medium/low voltages (e.g., 400V) for UPS, servers, and cooling systems.
2. Enable redundant setups to avoid outages if a unit fails, ensuring high availability.
3. Provide isolation to shield sensitive equipment from grid interference like harmonics or surges.
4. Distribute loads across multiple units to prevent overloads and boost efficiency.
5. Integrate with backup power (generators, batteries) for seamless switching during mains failures.
Available ratings
Table1.product scope
| standard | IEC, ANSI, IEEE, CSA or AS |
| Size(kVA) | Up to 240 MVA |
| Voltages | Available in Δ or Y configuration |
| High voltage | Up to 230kV |
| HV BIL | Up to 900kV BIL |
| Frequency | 50/60 HZ |
| Cooling Class | ONAN, KNAN,ONAF, KNAF, OFWF, OFAF, ODWF |
| Applicable scene | Suitable for indoor and outdoor application |
| Ambient temperature | -50℃~40℃ |
| Relative humidity | Ambient air relative humidity should be below 93% |
| Altitude | ≤1000m |
| Max wind speed | ≤35 m/s |
| Earthquake acceleration | Horizontal acceleration≤0.3g |
| Vertical acceleration | ≤0.15g |
| Special conditions | Customized products are available |
Table2. Requirements and tests for different categories of transformers based on the Um of the highest voltage windings
| Um ≤ 72,5 kV | 72,5 kV < Um ≤ 170 kV | Um > 170 kV | ||
| Insulation | Uniform | Uniform | Non-uniform | Uniform and non-uniform |
| Full wave lightning impulse test for the line terminals (LI) | Type | Routine | Routine | Not applicable (included in LIC) |
| Chopped wave lightning impulse test for the line terminals (LIC) | Special | Special | Special | Routine |
| Lightning impulse test for the neutral terminals (LIN) | Special | Special | Special | Special |
| Switching impulse test for the line terminal (SI) | Not applicable | Special | Special | Routine |
| Applied voltage test (AV) | Routine | Routine | Routine | Routine |
| Induced voltage withstand test (IVW) | Routine | Routine | Routine | Not applicable |
| Induced voltage test with PD measurement (IVPD) | Speciala | Routinea | Routinea | Routine |
| Line terminal AC withstand voltage test (LTAC) | Not applicable | Special | Routineb | Special |
| Auxiliary wiring insulation test (AuxW) | Routine | Routine | Routine | Routine |
| a The requirements of the IVW test can be incorporated in the IVPD test so that only one test is required. b The LTAC test for this category of transformers can be replaced by a switching impulse test by agreement between manufacturer and purchaser. | ||||
Tests
Routine tests
1. Measurement of winding direct resistance
2. Measurement of voltage ratio and check of phase displacement
3. Check of Voltage Ratio and Vector Group
4. Measurement of Impedance Voltage and Load Losses
5. Measurement of short-circuit impedance
6. Measurement of no-load loss and no-load current
7. Dielectric routine tests
8.Ratio on all connections and tap positions
9.Angular displacement
10. Applied Voltage Test
11. Induced Voltage Withstand Test With pd Measurement (IVPD)
12. Seal test
13.Magnetic balance test
Type tests
1. Dielectric type tests
2. Temperature-rise test
3. Tests on on-load tap-changers
4. Lightning Impulse Test
5. Oil leakage test
6.Dynamic short circuit test
Special tests
1. Dielectric special tests
2. Determination of capacitances windings-to-earth, and between windings
3. Determination of transient voltage transfer characteristics
4. Measurement of zero-sequence impedance(s)
5. Determination of sound levels
6. Measurement of the harmonics of the no-load current
7. Measurement of the power taken by the fan and oil pump motors
8. Insulation Resistance and absorption Ratio measurement
9. Measurement of dissipation factors and capacitance of bushing
10. Measurement of main body dissipation factor and capacitance
11. Current transformer measurement
12. On-load tap changers-operation test
13. Line terminal AC withstand voltage test (LTAC)
14. Measurement of frequency response
15. Insulation of auxiliary wiring (AuxW)7/8/2025
* Any of the special test can be arranged on special requirement of customer.
Test report
• Complete IEC-compliant reports with optional FAT video or witness testing
SCOTECH advantages
High-performance materials (amorphous alloy/silicon steel cores) and optimized electromagnetic design minimize no-load & load losses, exceeding 98% efficiency (compliant with IEC, IEEE ,CSA and other standards).
Rigorously tested (lightning impulse, partial discharge) with 30+ year lifespan; vacuum oil immersion and corrosion-resistant construction ensure stability in extreme conditions.
Fully customizable voltage (11kV–500kV), capacity (10kVA–500MVA), and designs (dry-type, autotransformers, offshore wind models) for industrial, renewable energy, and grid applications.
IoT-enabled real-time monitoring (temperature, vibration, oil levels) and predictive maintenance; optional OLTC and automatic voltage regulation.
Sustainable materials (ester-based oils, resin-cast dry types) reduce environmental impact; noise levels ≤55dB and fire-safe designs.
Certified (CE, UL, CSA, RoHS) for worldwide markets; rapid delivery (15-day urgent orders) and 24/7 technical support.
