You're on the right track, but let's clarify the concepts and the correct interpretation. Here's a breakdown

Understanding Transformer Ratings and Losses
Nameplate Rating (kVA or MVA)

This represents the apparent power the transformer is designed to deliver at its secondary terminals at its rated voltage and frequency, while operating within its specified temperature limits. This is the key point:

It's the OUTPUT power, not the input power. Transformer Losses

Transformers aren't perfectly efficient. They have losses that manifest as heat. The primary losses are:

Core Losses (Iron Losses)

These are relatively constant, independent of load, and due to hysteresis and eddy currents in the core material.

Winding Losses (Copper Losses, I²R Losses)

These losses are proportional to the square of the current flowing through the windings and therefore increase significantly with higher load.

Stray Losses

These are small losses in the tank and other parts of the transformer.

Apparent Power (S), Real Power (P), Reactive Power (Q)

S (Apparent Power) = √(P² + Q²). This is what the transformer nameplate is rated in (kVA or MVA). P (Real Power) is the power that does useful work (measured in kW or MW). Q (Reactive Power) is the power that oscillates between the source and the load, required by inductive loads (motors, etc.) to establish magnetic fields (measured in kVAR or MVAR).

The Key Distinction: Output vs. Input1. Nameplate is Output

A 10 MVA transformer is designed to deliver 10 MVA on the secondary side at its rated voltage.2.

Input > Output

Because of the transformer losses, the input apparent power (S) to the primary side must be higher than the output apparent power. Think of it as:`Input (S) = Output (S) + Losses (P + jQ)` Where: `Output (S)` is the nameplate rating. `Losses (P + jQ)` represent the combined real power losses (heat) and reactive power used by the transformer itself.

Answering Your Questions Directly "Are you actually limited to strict nameplate size on the source side such that max MVA delivery is actually nameplate minus transformer losses?" No. The delivery capability is the nameplate rating. The source side has to provide the power for that rating plus the losses. You're not limited to nameplate - losses on the source side. You're limited to nameplate on the output/delivery side. "If you wanted 10MVA on the secondary side, maybe you'd be up >10MVA on the source side, but you'd still be under the damage curve by design." Correct. If you want 10 MVA out, you'll need to supply more than 10 MVA into the transformer. The transformer is designed to handle the input power required to deliver the nameplate output, including its own losses.

Practical Considerations Overloading

Running a transformer significantly above its nameplate rating for extended periods will cause excessive heating, insulation degradation, and ultimately, failure. Short-term overloads may be permissible, but only within carefully defined limits and under specific conditions.

Cooling

The nameplate rating is based on a specific set of operating conditions, including the ambient temperature and the cooling method (e.g., oil-immersed natural cooling, forced air cooling). Higher ambient temperatures or inadequate cooling will reduce the transformer's load carrying capacity.

Voltage Regulation

As the load on a transformer increases, the voltage on the secondary side tends to drop. This "voltage regulation" is an important factor in system design. Transformer impedance affects the voltage regulation.

Transformer Selection

When selecting a transformer, you need to consider the total load (both real and reactive power) that will be connected to the secondary side. You want to select a transformer with a nameplate rating that is sufficient to meet the load demand without regularly exceeding its rating. It's also prudent to include some margin for future load growth.

In Summary

The transformer nameplate rating represents the output apparent power capability. The input* power will always be higher due to losses. You're limited by the nameplate on the delivery side (secondary), not on the source side (primary). The transformer is designed to handle the input power required to deliver the nameplate rating while staying within its thermal limits. Don't exceed the nameplate rating of the transformer for sustained periods unless specifically designed to do so (e.g., with enhanced cooling) and under the guidance of the manufacturer's specifications. Flag for review