Megawatt Truck Charging: Coincidence and Queue Profiles for Transformer Design

A truck-charging site’s transformer duty depends on when vehicles arrive, how much energy they need and how long they can remain connected. A megawatt charger label describes equipment capability, not a universal coincidence factor. Build a fleet-based operating schedule and translate it into alternating current (AC) input demand before selecting the transformer duty envelope.

Start with the transport operation

Collect arrival and departure windows, expected energy per visit, initial state-of-charge ranges and the policy for delayed vehicles. Distinguish a scheduled depot from an open-access corridor site; their queue uncertainty and overlap can differ substantially.

The charging curve matters because vehicle demand need not remain at the charger maximum throughout a session. State whether the assumed curve comes from measured fleet data, a vehicle guarantee or a planning estimate. Do not present a rectangular maximum-power block as an observed charging session unless evidence supports it.

IEC 61851-23-3:2026 addresses megawatt charging systems within its defined scope. It does not prescribe the coincidence of a site’s fleet, and its published scope should not be stretched into a universal bidirectional-operation claim. [1]

Translate energy deadlines into feasible power schedules

An illustrative fleet requiring 12 MWh within a four-hour window needs an average of 3 MW delivered over that window before considering the precise conversion and auxiliary boundary. That average says nothing about whether arrivals cluster in the final hour or whether vehicle charge limits prevent a flat profile.

Compare the energy deadline with the permitted charging schedule and site AC cap. If the proposed transformer limit cannot deliver the required energy within the feasible vehicle windows, a lower nameplate rating has been purchased at the expense of transport performance.

This is an energy-balance check, not a final electrical design. Apparent power, terminal voltage, waveform and auxiliary loads remain separate inputs.

Test queue and control scenarios

Do not invent a universal percentage of chargers that will operate simultaneously. Use the actual fleet assumptions and test credible deviations. A sensitivity analysis should show which assumptions materially change the transformer duty or the number of vehicles served.

Direct-current (DC) supply-equipment requirements and charger input evidence remain relevant at the equipment boundary. They do not replace the transport schedule or the site’s control design. [2]

Specify the transformer from the resulting AC envelope

Request the chargers’ AC input characteristics at relevant output levels, including losses, reactive behavior and harmonic data. Add site auxiliaries and identify the measurement point used by the demand controller.

The transformer thermal assessment should use the chronological schedule, ambient conditions and available cooling. Mineral-oil loading guidance addresses one equipment class; it should not be applied indiscriminately to every charging-site transformer. [3]

The procurement package should preserve the fleet assumptions and the enforceable site limit. A future change in route schedules, vehicle battery size or charging policy can alter duty without changing the installed charger labels.

The useful outcome is a transformer operating envelope that supports a stated transport service. “Megawatt charging ready” does not establish that the site can meet its departure deadlines or remain within its electrical limits when the queue differs from the average day.