Generators

Generators represent on-site power sources in your electrical system. They supply power independently of the utility grid, whether as primary power, standby backup, or distributed generation from renewables.

Generator types

ekx supports eight generator types. Select the type that matches your equipment to get appropriate default reactance values.

For steady-state power flow and short-circuit studies, the distinction mainly affects default reactance values. Inverter-based types (solar inverter, battery storage) have different fault contribution characteristics than rotating machines.

Creating a generator

1. Drag Generator from the component toolbar.
2. Drop on canvas.
3. Connect bottom handle to a bus.
4. Configure ratings in the edit panel.

Generators connect via their bottom handle only. Power flows downward from the generator into the bus, following standard SLD conventions.

Rated MVA and voltage

Set the generator nameplate ratings in the edit panel:

• Capacity - Nameplate apparent power rating in kVA. This is the maximum continuous output and determines reactive power limits.
• Voltage - Rated terminal voltage in kV. Must match the bus voltage where the generator connects.

These two values define the machine base for all per-unit reactance parameters.

Rated power and power factor

• Power - Active power output in kW. This is the real power the generator dispatches. Set it to the actual operating output, which may be less than nameplate capacity for partial-load scenarios.
• Power Factor - Nameplate power factor (0 to 1). Used to calculate reactive power limits for power flow analysis. A lower power factor means more reactive power capability. Typical value: 0.85.

The relationship between these values:

Power (kW) = Capacity (kVA) x Power Factor

Reactance values

Generator reactances are entered in per-unit on the machine base (rated MVA and rated voltage). These values drive both power flow and short-circuit calculations.

Direct-axis reactances

• Xd governs steady-state behavior and voltage regulation.
• Xd' determines fault current in the transient period (roughly 0.5 - 5 seconds after fault inception).
• Xd'' determines the initial fault current magnitude (first few cycles). This is the most critical value for short-circuit studies and breaker sizing.

Quadrature-axis reactances

Quadrature-axis values matter primarily for salient-pole machines (hydro generators, diesel generators). For round-rotor machines (steam turbines, gas turbines), Xq values are close to their Xd counterparts.

Leakage reactance

Xl represents flux that does not cross the air gap. It sets a lower bound for all other reactance values (Xd'' >= Xl).

Typical reactance values by generator type

> Note: Use actual nameplate or test report values when available. Defaults are for estimation only.

Time constants

Time constants define how quickly reactance transitions between subtransient, transient, and steady-state values after a disturbance.

These values are relevant for transient stability studies. For steady-state power flow and simple short-circuit calculations, they have no effect. Enter them if you plan to use the generator model for dynamic analysis or if you have the data from the manufacturer.

Operating parameters

Inertia constant (H)

The inertia constant represents stored kinetic energy in the rotating mass, expressed in seconds:

H = Stored Energy (MJ) / Rated MVA

Higher H means the machine resists frequency changes more strongly. This matters for stability studies and islanded operation.

Damping coefficient

The damping coefficient represents the machine's natural damping torque. Typical values range from 0 to 2.0. Leave at default unless you have specific machine data.

Grounding configuration

Generator neutral grounding limits ground fault current and affects zero-sequence impedance. Select the grounding type that matches your installation:

When you select resistance or reactance grounding, enter the neutral grounding impedance value in ohms.

> Important: Grounding configuration affects zero-sequence fault current calculations. An incorrect grounding type will produce inaccurate ground fault results.

Sequence impedances

Sequence impedances are needed for unbalanced fault analysis (single-line-to-ground, line-to-line, double-line-to-ground faults).

• X2 (negative sequence) is typically close to the average of Xd'' and Xq''.
• X0 (zero sequence) depends heavily on winding configuration and grounding. It can vary widely.

If you only need three-phase symmetrical fault results, these values can be left empty.

Physical and control properties

These optional fields provide additional documentation and may be used in future analysis features.

In-service toggle

Use the In Service toggle in the edit panel to take a generator out of service without deleting it. When a generator is out of service:

• It does not contribute power in power flow analysis.
• It does not contribute fault current in short-circuit analysis.
• It appears dimmed on the canvas.

This is useful for modeling scenarios where backup generators are offline or for comparing system behavior with and without a particular unit.

Generator as slack bus

In power flow analysis, the system needs one slack bus to balance real and reactive power and provide the voltage angle reference. Normally, the bus connected to a utility feed serves as the slack bus.

For islanded or microgrid systems with no utility feed, designate the bus connected to your generator as the slack bus. The generator then becomes the voltage and frequency reference for the system.

To configure this:

1. Select the bus connected to the generator.
2. Set the bus type to Slack Bus in the edit panel.

Only one bus in the system should be the slack bus. See Buses for details on bus type configuration.

Generator annotations after power flow

After running power flow analysis, generators display annotations on the canvas:

• Loading percentage (output power / rated capacity x 100%)
• Active power output (P) in MW or kW
• Reactive power output (Q) in MVAR or kVAR

Annotations are color-coded by loading level:

If power flow results become stale (you edit a component after running analysis), annotations turn grey until you rerun the analysis.

Related topics

• Buses - Connecting generators to buses and slack bus configuration
• Utility feeds - Alternate power source from the grid
• Power flow analysis - Generator loading calculations
• Short-circuit analysis - Generator fault contribution