Iceland Parallel Diesel Generator Sets Run Normally Individually but Share Load Unevenly as Governor Droop and Load-Sharing Control Are Checked Beyond Injector Balance

Each Generator Worked Normally Alone

A representative parallel power-generation case in Iceland involved two diesel generator sets that operated acceptably when tested individually.

When synchronized and operated together, however, one engine consistently carried more electrical load than the other.

Because uneven load can appear as uneven engine fueling, injector balance was initially considered.

The fact that both engines performed normally alone redirected attention toward governor droop and load-sharing control.

Parallel Operation Adds a New Control Layer

A single generator mainly controls:

• engine speed;
• electrical frequency;
• voltage;
• and its own load response.

Parallel generators must also coordinate with one another.

The control relationship can include:

Speed governor → Load-sharing signal → Generator controller → Fuel command → Engine torque

A mismatch between the sets can create unequal power distribution without an injector defect.

Single-Unit Testing Created the Baseline

The workshop first confirmed that each generator could independently:

• reach rated operating speed;
• accept load;
• maintain frequency;
• and respond normally to governor demand.

This reduced evidence for a basic fuel-capacity difference.

Droop Settings Became Relevant

Depending on generator-control strategy, governor droop determines how engine speed or load command changes with applied load.

If two generators have mismatched settings, one unit may accept more of the shared load.

Technicians reviewed:

• governor mode;
• droop setting;
• isochronous configuration where applicable;
• load-sharing signals;
• speed references;
• and controller calibration.

Load-Sharing Communication Was Checked

Modern parallel systems may use analog or digital load-sharing signals.

A signal problem can cause the generators to “disagree” about how much load each should carry.

The engine with higher fuel command may simply be obeying the controller.

Why Injector Adjustment Would Be the Wrong Fix

If injector delivery is changed to compensate for a load-sharing control problem, the generator may then operate incorrectly when running alone.

The root issue is not cylinder-level fueling but unit-to-unit torque allocation.

Diagnostic Structure

The case followed:

Generator A alone normal → Generator B alone normal → Parallel operation uneven → Governor modes compared → Droop/load-share signals checked → Parallel load reassessed

Case Insight

The Iceland case demonstrates why a fault that appears only after systems are connected together should be investigated at the interaction layer.

The key question was:

Why do two healthy engines behave differently only when they are asked to share one electrical load?

FAQ

Can load-sharing settings make one generator carry more load than another?

Yes. Governor and load-sharing configuration can influence how parallel units divide power.

Does uneven generator load prove injector imbalance?

No. Control-system configuration should be checked before fuel-system adjustments.