Transformer assessment should identify the primary and secondary supply requirements, connected load and intended operating modes. Where a generator supplies the transformer, the review must consider that source and the downstream equipment together. A capacity conversion alone does not establish the suitability of the arrangement.
Account for events beyond steady-state demand
Energisation and downstream load changes can present requirements different from normal operation. Obtain the relevant transformer and load information for the proposed sequence. The generating set, protection and control arrangement should be assessed against the events it is expected to support.
But transformers also have inrush
That event can disturb a generator more severely than normal transformer losses suggest.
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Generator / transformer interface
Final generator suitability may require actual transformer data and generator transient modelling.
Transformer kVA tells you the steady-state scale. Energisation tells you how difficult it may be to start that electrical system.
Balanced three-phase apparent power
kVA = (√3 × VLL × I) ÷ 1000, using line-to-line voltage in volts and line current in amperes. This describes the stated balanced steady-state condition. Transformer inrush, the connected loads, impedance, connection arrangement and the generator response require separate review before the combination is selected.
Document the selection basis
Record the ratings, installation conditions and system information used in the assessment. The balanced three-phase relationship on this page supports a stated calculation; it is not a complete transformer specification. Final selection requires the applicable equipment and installation review.
Start Engineering Review
Start Engineering Review. Share the application, location and information available so the next discussion can address your actual requirement.
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Engineering intent
Transformer Sizing should be evaluated as part of the complete power system rather than as an isolated catalogue item. Operating duty, connected load, interfaces, protection, controls, installation conditions, testing requirements and lifecycle consequences determine whether the arrangement is appropriate.
Engineering considerations
Do not finalise generator kVA from this result alone. The tool should allow the user to generate: The report must state that it is preliminary and not a final engineering design. But generator capacity is often discussed in kVA, not only kW. kW tells you useful power. kVA tells you the apparent electrical capacity the generator must support. and understand how power factor affects generator capacity. installed power in kW, installed apparent power in kVA, and estimation of maximum kVA demand as core parts of electrical installation design methodology. Final generator sizing must also review load type, starting current, power factor variation, UPS loads, harmonics, derating, duty, fuel runtime,
Selection and design considerations
Actual scope should be confirmed in the commercial/project documentation. Industrial temporary power often involves high currents and substantial cable distances. At larger capacity, multiple parallel conductors per phase may be required. A long cable run can turn a manageable motor-start problem into a difficult one. Generator sizing and cable sizing therefore interact directly. Depending on voltage and plant design, transformers or additional switchgear may also be required. A temporary generator may need to interact with an industrial transformer network. Do not assume matching steady-state kVA proves successful energisation. Industrial temporary power must survive both normal operating transients and real faults. Temporary source characteristics may differ from normal utility/transformer supply.
Integration and protection considerations
The site must not rely on accidental current paths. Some generator systems may be treated as a separately derived source. Others may be integrated with an existing neutral/earthing arrangement. Do not assume one treatment applies to every generator. When the utility or transformer is the active source, the normal neutral/earthing relationship may be defined at the transformer or main supply arrangement. If a generator is present but not supplying the load, its neutral relationship must not create unintended parallel paths. The site’s normal-source earthing architecture must be understood before generator connection. When the generator supplies the load, the generator system must have a defined neutral and fault-current return philosophy.
Testing, commissioning and verification
A correct cable can be poorly installed if the room layout ignores its route. Generator feeders often connect to ATS, AMF or manual changeover equipment. The transfer system and cable system must be reviewed together. Transformer kVA alone does not define the cable requirement. Cable design should match the paralleling architecture and protection philosophy. Do not treat a multi-generator plant as one oversized single generator. At high power, cable engineering becomes a major project discipline. A load bank may become one of the largest temporary loads connected to the generator.
Operating and lifecycle considerations
What is the most demanding credible electrical event? That may not be the highest continuous kW. kW AND kVA ARE NOT THE SAME THING subject to the usual electrical definitions and actual load characteristics. Two loads with the same kW can impose different kVA requirements. For a balanced three-phase system, a common relationship is: Motor starting is one of the most important reasons simplistic generator sizing fails. A motor may run normally at a moderate current yet draw a much larger current during acceleration. The generator must support the dynamic event—not merely the motor’s running kW. is incomplete without the starting method and actual motor data.
Decision and application considerations
The final proof may require commissioning observation or controlled testing where project scope supports it. A paper calculation does not always capture every site condition. A generator that starts and runs without load has not proven a significant motor start. Motor-starting verification requires the relevant load event or an appropriate engineering substitute/test method.
Direct answer
Transformer assessment should identify the primary and secondary supply requirements, connected load and intended operating modes. Where a generator supplies the transformer, the review must consider that source and the downstream equipment together.
The practical decision for Transformer Sizing should be based on verified load, equipment, interface and site information. Where equipment-specific data, regulatory applicability or a project study is required, this guidance does not replace that verification.
Related Reddy Generators pathways
- Power Engineering Centre
- Generator Finder
- Integrated Power Systems
- Industry Power Solutions
- Application Engineering Enquiry
Transformer system role
A transformer is more than a voltage-changing device. Its impedance, thermal capability, vector group, regulation, insulation condition and protection interfaces influence fault level, motor starting, parallel operation and downstream voltage performance. Selection should therefore be coordinated with the complete electrical network.