An inverter duty transformer (IDT) connects one or more PV inverters to the collection or grid voltage. It looks like a distribution or power transformer, but its duty is different: the load follows the sun, inverter output contains harmonics, and the unit usually sits outdoors in hot, dusty sites. A complete specification avoids redesign later.
## Rating and voltages
- Rated power (kVA/MVA) matched to the inverter block's continuous AC output, including any planned overloading at low ambient.
- LV voltage equal to the inverter's AC output voltage. Confirm with the inverter datasheet — values differ between manufacturers and models.
- Number of LV windings. Many central-inverter blocks use a double-secondary (split LV) design so two inverters share one transformer while remaining electrically separated.
- HV voltage of the collection system or point of interconnection, and the required tapping range.
## Duty and losses
- Harmonic content. Provide the inverter's harmonic spectrum so additional eddy-current and stray losses can be accounted for in the thermal design.
- Load cycle. Daily cycling from zero to full load affects ageing; state expected loading profile and ambient temperatures.
- Loss requirements. Specify no-load and load losses or a loss-capitalisation formula. No-load losses accrue 24 hours a day even though generation happens only in daylight.
## Construction and environment
- Vector group and earthing arrangement per the grid code and protection design.
- Electrostatic shield between windings, if required by the inverter manufacturer.
- Ambient maximum, altitude, pollution/creepage class, and enclosure or cable-box requirements.
- Cooling class (for example ONAN) and preferred insulating liquid.
## Standards and documents
State the governing standards for the destination market — for example IEC 60076 series or national equivalents, any utility or grid-operator requirements, and guidance such as IEEE C57.159 for photovoltaic applications where the project follows IEEE practice. Request guaranteed technical particulars, GA drawings, and the routine and type-test plan with the quotation.
This guide is general engineering information. Final designs are always confirmed against the project specification by the manufacturer's engineering team.