A generator step-up (GSU) transformer may operate close to rated load for long periods. Its cooling system must remove core and winding losses without exceeding the approved oil and winding temperature limits. Poor radiator selection can accelerate insulation ageing, restrict transformer output and increase outage risk.
Selecting a transformer radiator for a generator step-up transformer requires more than comparing panel dimensions. Cooling duty, oil circulation, tank interfaces, site conditions and inspection requirements must be considered together. The transformer designer should control the thermal calculation, while the radiator manufacturer builds to the approved drawings.
1. Define Transformer Losses, Rated Capacity and Cooling Duty
Selection should begin with guaranteed losses rather than MVA alone. Transformers with the same rating may produce different heat because of their core, conductors, impedance and operating profile.
The designer should calculate the cooling duty after considering no-load, load and stray losses, plus heat dissipated by the main tank. An RFQ for a power plant transformer radiator should include transformer rating, voltage class, total losses, permitted temperature rises, oil type, ambient-temperature range and altitude. Copying the radiator count from an earlier transformer is unsafe unless the thermal conditions are genuinely comparable.
2. Select the Appropriate ONAN or ONAF Cooling Arrangement
In an ONAN system, hot oil rises naturally into the upper radiator header and returns through the lower connection after cooling. Radiator height, header diameter and oil-flow resistance influence this thermosiphon circulation.
An ONAF transformer radiator uses fans to increase airflow and support a higher transformer rating. The design should define fan quantity, airflow direction, switching stages, auxiliary power and alarm signals. It should also state the permitted load if one fan group is unavailable. For forced or directed oil systems, pump performance and circuit pressure loss must be reviewed as part of the complete GSU transformer cooling system.
3. Confirm Radiator Quantity, Dimensions and Required Heat-Dissipation Area
Cooling depends on heat-transfer surface, oil distribution and airflow. Adding more elements will not correct a restricted oil path or poor ventilation.
A custom transformer radiator drawing should define the number of banks, elements per bank, element height and pitch, header-pipe diameter, connection size and fan coverage. Adequate clearance is required from fire walls, acoustic barriers and nearby equipment to prevent hot-air recirculation.
A removable transformer radiator is practical for large GSU units because it simplifies transport and replacement. However, each removable bank introduces additional valves, flanges, gaskets and field-sealed joints.
4. Verify Flange Interfaces, Centre Distance and Oil-Flow Connections
Interface errors frequently delay final assembly. The approved drawing should identify the upper and lower transformer radiator flange centre distance, flange dimensions, bolt-hole pattern, gasket type and connection orientation.
Valve handles, air-release plugs, drain points, lifting lugs and braces must remain accessible after installation. For a replacement transformer radiator, measure the existing equipment directly; the transformer nameplate alone cannot confirm interchangeability.
Where IEC interchangeability dimensions apply, state them in the purchase specification. The purchaser's approved drawing remains the controlling document.
5. Consider Load Cycles, Ambient Temperature and Cooling Redundancy
A base-load plant may keep its GSU transformer heavily loaded for months, while peaking and renewable plants create more frequent load changes. Radiator selection should reflect the actual duty cycle.
High ambient temperature, solar radiation, dust and restricted airflow reduce cooling performance. High altitude also lowers air density. A high-ambient-temperature transformer radiator may therefore require more surface area or forced airflow than a similar unit in a moderate climate.
If the plant must continue operating with one radiator bank or fan group isolated, define that redundancy requirement before finalizing the layout.
6. Specify Materials, Welding Quality and Leak-Testing Requirements
Radiator elements are formed from relatively thin steel, making seam consistency and header welding critical. Small defects can develop into oil leaks after transport or thermal cycling.
When qualifying a transformer radiator supplier with leak testing, review material traceability, forming equipment, welding procedures, fixtures and repair controls. Every radiator should receive dimensional inspection and leakage testing before coating.
The specification must state the test medium, pressure, holding time and acceptance criteria. Nantong Zhihe Electric performs 100% radiator leak testing at 150 kPa for applicable orders, subject to the approved customer specification. Any repaired area should be retested before surface treatment.
7. Match the Coating System to the Power Plant Environment
"Outdoor paint" is not an adequate specification. Inland, coastal, desert and industrial power plants create different corrosion risks.
The transformer radiator coating system should define surface preparation, primer, intermediate coat, topcoat, dry-film thickness and inspection method. C4 or C5 protection may be suitable for coastal or polluted sites, depending on the required durability.
A hot-dip galvanized transformer radiator can be considered for severe exposure, but galvanizing must be included during design because it affects venting, drainage and dimensional control. Internal surfaces must remain clean, dry and compatible with transformer oil.
8. Evaluate Inspection, Transportation, Installation and Supplier Capability
Supplier assessment should cover the complete process, not only the price per panel. A qualified custom transformer radiator manufacturer for power plant projects should demonstrate drawing control, stable forming and welding, flange-position fixtures, 100% leak testing, coating inspection and protected export packing.
During transportation, radiators should be supported by their structural frames. Elements, flange faces, valves and coating edges need protection from impact and moisture. Before installation, check internal cleanliness, gaskets, flange alignment and valve operation. After oil filling and venting, inspect every field joint for seepage.
Nantong Zhihe Electric manufactures drawing-based radiators for power transformers and GSU projects. Our capabilities include seven automatic radiator welding lines, production capacity of approximately 100 sets per day, C3–C5 coating options and hot-dip galvanized radiator production.
For a technical review, send us the approved drawing, cooling method, flange details, test requirements, coating specification and delivery schedule.
Send Your GSU Transformer Radiator Drawing for Review
