| Applicable Standards | IEC 60076 is the main international series for power transformers. The GB/T 1094 series is the commonly used Chinese transformer standard series and is technically aligned with IEC requirements in many parts. | Confirm that the quotation identifies the exact standards, editions, and deviations applicable to the project and destination country. | Technical specification, standards compliance statement, approved drawings, and a deviation list. | Required |
| Rated Power and Voltage | Substation transformers are engineered for specific system conditions, such as rated capacity in kVA or MVA and high-, medium-, and low-voltage ratings in kV. | Choose a manufacturer that can design the required vector group, frequency, tap range, impedance, insulation level, and cooling method rather than offering only a standard catalog model. | Guaranteed technical schedule, nameplate data, transformer ratio, vector-group designation, and load profile confirmation. | Required |
| Transformer Type | Common substation options include oil-immersed power transformers, cast-resin dry-type transformers, and sealed or conservator-type designs. | Match the type to fire-safety rules, indoor or outdoor installation, ambient conditions, maintenance capability, and environmental requirements. | Construction drawings, cooling arrangement, enclosure rating where applicable, oil-system description, and installation requirements. | Required |
| Energy Efficiency | Transformer losses consist mainly of no-load loss and load loss. Both losses should be stated separately because they affect lifetime operating cost. | Compare guaranteed losses at the specified frequency, voltage, and reference temperature. A lower purchase price may not offset higher lifetime losses. | Guaranteed no-load loss, load loss, impedance, tolerances, loss-calculation method, and routine-test results. | High Priority |
| Insulation and Dielectric Performance | Insulation levels are selected according to the highest system voltage, lightning impulse withstand, power-frequency withstand, altitude, and overvoltage exposure. | Verify that insulation coordination matches the grid and local utility requirements, especially for outdoor substations and high-lightning areas. | Insulation-level schedule, impulse-test report, dielectric-test records, and altitude correction information where applicable. | Required |
| Temperature Rise and Cooling | Temperature-rise limits depend on transformer design, insulation system, cooling class, ambient temperature, and the applicable standard. | Check continuous-load capability, emergency loading requirements, fan or pump control, and performance at the project’s maximum ambient temperature. | Temperature-rise test report, cooling-class designation, thermal calculations, control schematic, and alarm settings. | Required |
| Short-Circuit Strength | Transformers must withstand the thermal and mechanical stresses caused by prospective short-circuit currents for the duration specified by the system design. | Confirm that the transformer impedance and mechanical design are suitable for the available fault level at the installation point. | Short-circuit withstand calculation or test evidence, winding-support details, impedance tolerance, and fault-level confirmation. | Required |
| Tap-Changer Configuration | Off-circuit tap changers are adjusted only when the transformer is de-energized. On-load tap changers permit voltage adjustment while energized, subject to the specified operating range. | Select the tap-changing method based on voltage-regulation needs, switching frequency, control philosophy, and maintenance capability. | Tap range, tap-step percentage, wiring diagram, operating sequence, interlocks, and type-test or routine-test documentation. | Project Dependent |
| Factory Testing | Typical routine tests include winding-resistance measurement, voltage-ratio and phase-displacement checks, impedance and load-loss measurement, no-load loss and current measurement, dielectric tests, and leak testing where applicable. | Make the inspection and test plan part of the purchase contract and define which tests require customer or third-party witnessing. | Approved inspection and test plan, routine-test reports, calibration certificates, and signed release documentation. | Required |
| Type and Special Tests | Depending on the design and project specification, type or special tests may include temperature-rise, lightning impulse, sound-level, partial-discharge, zero-sequence impedance, and short-circuit testing. | Do not treat a routine-test report as proof of every design capability. Request test evidence relevant to the proposed transformer family. | Independent laboratory reports, previous equivalent-design test records, test certificates, and traceability to the quoted design. | Preferred |
| Quality Management | A documented quality-management system supports controlled design, purchasing, manufacturing, inspection, nonconformance handling, and corrective action. | Evaluate whether the certificate scope covers transformer design and manufacture and whether the certificate is current and independently verifiable. | Current quality certificate, certificate scope, audit details, quality manual extracts, and corrective-action procedure. | Preferred |
| Materials and Component Traceability | Core steel, conductor material, insulation, bushings, tap changers, protective devices, and transformer oil can affect reliability and performance. | Require traceability for critical materials and clear identification of all major purchased components before production approval. | Material certificates, incoming-inspection records, component datasheets, batch numbers, and approved-vendor documentation. | High Priority |
| Oil and Environmental Protection | Oil-immersed transformers require appropriate oil containment, leak prevention, fire protection, and safe handling. Mineral oil and alternative fluids have different fire and environmental characteristics. | Check local regulations for bunds, drainage, fire separation, oil type, spill control, and end-of-life disposal. | Oil datasheet, material-safety documentation, leak-test records, tank design, fire-safety recommendations, and environmental compliance documents. | Required |
| Climate and Installation Conditions | Ambient temperature, humidity, altitude, solar radiation, pollution level, seismic conditions, and wind loads can change the required design. | Provide complete site data and confirm derating or design modifications for high altitude, coastal salt, desert dust, tropical humidity, or seismic zones. | Site-condition questionnaire, derating calculations, corrosion-protection specification, seismic calculation, and enclosure or creepage data. | Required |
| Protection and Monitoring Accessories | Depending on transformer type and rating, accessories may include temperature indicators, oil-level indicators, pressure-relief devices, gas-actuated protection, surge arresters, and online monitoring systems. | Ensure accessories are compatible with the substation protection, SCADA, alarms, trip circuits, and communication protocols. | Accessory list, alarm and trip matrix, terminal schedule, control schematic, communication protocol, and interface drawings. | Project Dependent |
| Manufacturing Capacity and Delivery | Delivery depends on transformer size, design approval, material availability, production loading, testing requirements, export packaging, and transport restrictions. | Use a milestone-based schedule covering drawing approval, long-lead procurement, assembly, testing, packing, shipment, and site support. | Detailed production schedule, capacity statement, procurement plan, factory-acceptance-test date, packing specification, and logistics plan. | High Priority |
| Warranty and After-Sales Support | A useful warranty defines the coverage period, performance guarantees, exclusions, response time, spare parts, and corrective-action process. | Prefer suppliers able to provide commissioning support, troubleshooting, replacement parts, technical documentation, and service after delivery. | Warranty terms, service-level agreement, spare-parts list, commissioning plan, training plan, and escalation contacts. | Required |
| Total Cost of Ownership | Total cost includes purchase price, transport, installation, testing, energy losses, maintenance, oil handling, outage risk, and disposal. | Compare suppliers using the same technical assumptions, loss capitalization method, warranty scope, delivery terms, and lifetime analysis period. | Itemized commercial offer, loss evaluation, maintenance schedule, spare-parts pricing, transport terms, and lifecycle-cost calculation. | High Priority |
