Power Concepts: Base Power, Rating, and Max Active Power

When working with generators in PowerSystems.jl, it's important to understand the distinction between three key power concepts: base power, rating, and maximum active power. These concepts serve different purposes and are stored using different unit conventions.

Base Power

Base power is the reference power value used for per-unitization of a specific device — the denominator when converting device parameters to per-unit values, typically the nameplate capacity. It answers: "What is the natural scale of this device?"

Base power is a fundamental parameter for the per-unit system. For more details on per-unitization, see the Per-unit Conventions page.

Rating

Rating represents the maximum AC side output power rating of the synchronous machine or generator — the maximum apparent power (MVA) that the generator's electrical components can safely handle, considering constraints such as:

Stator winding thermal limits
Rotor field winding limits
Cooling system capacity

The rating is typically determined by the electrical design and thermal limits of the synchronous machine itself. It represents the maximum capability of the electrical generator, independent of the prime mover.

Maximum Active Power

Maximum active power represents the maximum real power (MW) output of the prime mover, considering constraints such as:

Turbine capacity (for steam, gas, or hydro turbines)
Combustion chamber limits (for gas turbines)
Boiler capacity (for steam generators)
Fuel flow limitations

The maximum active power is determined by the mechanical system that drives the generator. This is often less than the rating when considering only real power production.

Key Distinctions

Storage Convention Summary

Concept	Storage Units	Getter Function
Base Power	Natural units (MVA)	`get_base_power()`
Rating	Device base (p.u.)	`get_rating()`
Max Active Power	Device base (p.u.)	`get_max_active_power()`

Example

Consider a thermal generator with:

base_power = 100.0 MVA (stored in natural units)
rating = 1.0 p.u. (equals 100 MVA when converted to natural units)
max_active_power = 0.95 p.u. (equals 95 MW when converted to natural units)

In this example:

The generator's electrical components can handle up to 100 MVA
The prime mover (e.g., steam turbine) can deliver up to 95 MW of real power
The difference accounts for the fact that the turbine's mechanical power limit is slightly below the generator's electrical rating

Unit System Conversions

When you access these values through the PowerSystems.jl getter functions, they are automatically converted based on the current unit system setting. For a step-by-step guide, see Read Component Values in Different Unit Systems.