Click each control path to see how real and reactive power are independently controlled once a generator is paralleled.

Load Sharing — Real & Reactive Power

Track 3: Synchronization & Paralleling — Module 4 of 5

What Changes the Instant the Breaker Closes

Modules 11-13 built toward one specific moment: breaker closure. This module covers what operational reality looks like immediately after that moment — specifically, how the same two control systems (governor and AVR) that worked one way before paralleling now work in a fundamentally different way afterward.

Before vs. After: The Same Controls, Different Effects

Before paralleling, an isolated generator's governor directly controls its speed (and therefore frequency), and its AVR directly controls terminal voltage. Once paralleled, the grid's effectively fixed voltage and frequency (the "grid dominance" concept from Module 11) take over both of those roles — and the same governor and AVR controls redirect their effect into two different quantities entirely.

The key mental shift: before paralleling — governor controls frequency, AVR controls voltage. After paralleling — governor controls real power (MW), AVR controls reactive power (MVAR). Nothing about the physical equipment changes; only what that equipment's adjustment actually accomplishes changes, because the grid now holds speed and voltage fixed.

Governor Control → Real Power

Since the grid prevents the generator from actually speeding up regardless of governor setpoint, any additional steam or fuel energy pushed in has nowhere to go except into additional torque against the fixed-speed shaft — which shows up entirely as additional real power (MW) delivered to the grid. This is why, operationally, adjusting load on a paralleled unit means adjusting governor setpoint, not "trying to speed it up."

AVR Control → Reactive Power

Similarly, since the grid holds terminal voltage essentially fixed, field current adjustments no longer meaningfully change voltage. Instead, increasing field current above the exact level needed to match grid voltage pushes the generator into an overexcited condition, exporting reactive power (VARs) to support grid voltage elsewhere. Decreasing field current below that matching level underexcites the generator, which then absorbs VARs from the grid instead of supplying them.

Watch for: reactive power management isn't a lower-priority afterthought to real power generation — grid voltage support has real operational and reliability value, and generators are often specifically dispatched or instructed by grid operators to run at a particular VAR output or power factor target, independent of their real power (MW) loading at the time.

Droop Control and Multi-Unit Sharing

When multiple generators are paralleled together, governor droop control settings allow load changes to be shared proportionally and automatically among units, without requiring instant communication between their individual control systems. Droop intentionally allows a small frequency deviation as system load changes, and each unit's governor responds to that shared frequency signal in proportion to its own droop setting — a coordinated, decentralized load-sharing mechanism.

What's Ahead

Module 15 wraps up Track 3 with a capstone covering reverse power protection and a realistic paralleling scenario, applying everything covered across this track's four prior modules.

Module Quiz

6 questions • 80% (5 of 6) required to pass