| 1 | Efficiency and Losses | Review guaranteed no-load loss, load loss, total loss, and efficiency at the expected operating load. | Compare tested or guaranteed values at the required frequency, voltage, temperature, and load. For industrial units, ask for efficiency data at 50%, 75%, and 100% load rather than relying only on a single peak figure. | Lower losses reduce electricity consumption, operating temperature, and lifetime energy cost. | Request a loss schedule and calculate total ownership cost over the expected service life. |
| 2 | Cooling System | Identify the cooling method, rated capacity, ventilation requirements, fan controls, alarms, and redundancy. | Common arrangements include natural-air cooling for lower ratings and forced-air cooling for higher thermal loads. Forced-air fans should have temperature control, overload protection, and accessible filters or guards where applicable. | Correct cooling prevents insulation aging, nuisance trips, and premature failure during continuous furnace operation. | Verify that the transformer room has adequate airflow and that the cooling rating matches the furnace duty cycle. |
| 3 | Insulation System | Check insulation class, temperature-rise rating, dielectric strength, clearances, and suitability for heat, dust, vibration, and humidity. | Dry-type industrial transformers commonly use Class F or Class H insulation systems. The selected design should provide sufficient thermal margin for the ambient temperature and the furnace's harmonic or cyclic load. | Higher thermal capability helps maintain insulation life when the transformer operates near its rated load. | Confirm the insulation system and temperature rise in the technical specification, not only in marketing literature. |
| 4 | Electrical Safety | Evaluate enclosure protection, grounding provisions, overcurrent protection, short-circuit withstand, emergency isolation, and touch-safe barriers. | The enclosure should be selected for the installation environment, such as indoor industrial service or a dusty area. Grounding terminals, clearly identified disconnects, and properly coordinated protective devices are essential. | These features reduce the risk of electric shock, arc faults, fire, and damage caused by abnormal current. | Have the protection scheme reviewed by a qualified electrical engineer before purchase and installation. |
| 5 | Voltage, Capacity, and Load Profile | Match primary voltage, secondary voltage, frequency, phase configuration, kVA rating, tap range, and furnace inrush or cyclic demand. | Allow for the actual maximum demand and foreseeable expansion. A common engineering practice is to avoid continuous operation at the absolute nameplate limit and to assess voltage drop during furnace starting or rapid load changes. | An incorrect rating can cause overheating, poor furnace performance, nuisance trips, or unstable secondary voltage. | Provide the supplier with measured demand, duty cycle, power factor, harmonic information, and starting-current data. |
| 6 | Controls, Monitoring, and Maintenance | Look for winding-temperature sensors, over-temperature alarms, fan-status feedback, power monitoring, inspection access, and spare-parts availability. | Useful monitoring includes separate warning and trip levels, remote alarm contacts, temperature indication, and accessible terminals. Maintenance intervals should be defined for cleaning, tightening, thermal inspection, and fan testing. | Early warnings help operators correct overheating or ventilation problems before an unplanned shutdown occurs. | Specify the required alarm outputs and maintenance access before the enclosure and control panel are finalized. |
| 7 | Standards, Testing, and Documentation | Confirm applicable transformer standards, routine test reports, installation drawings, wiring diagrams, nameplate data, and operating instructions. | Depending on the installation location, documentation may reference recognized requirements such as IEC 60076 or applicable national and local electrical codes. Routine tests commonly include winding resistance, turns ratio, polarity or phase relation, insulation resistance, and applied-voltage tests. | Traceable testing and complete documentation support safe commissioning, maintenance, inspections, and warranty decisions. | Make compliance documents, certified drawings, test results, and acceptance criteria part of the purchase contract. |