Generator Control System Grid Trip Overspeed Prevention
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Solution Overview
Problem
During a grid trip, the rapid change from kW mode to speed droop mode in generator sets leads to engine overspeed due to delayed load sensor measurements and grid breaker relay reactions, potentially causing shutdowns and blackouts as the droop curve adjusts to decreasing loads without proper stabilization.
Innovation Solution
A control system that includes a delaying phase to disable the droop function and maintain the speed reference at a rated speed during the transition from kW mode to speed droop mode, followed by an activation phase to enable the droop function, allowing the droop curve to be offset based on measured load and speed, preventing engine overspeed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the control mode changes rapidly from kW mode to speed droop mode during grid trip, then the system responds quickly to grid disconnection, but the engine speed becomes unstable and may overspeed due to delayed sensor measurements and relay reactions
Solution Approach 1:
The control system performs preliminary actions by detecting grid trip conditions and initiating a controlled transition sequence before the full droop mode engages. The system prepares the speed reference value in advance and implements a delaying phase that prevents immediate droop curve adjustment, thereby avoiding engine overspeed while maintaining quick response to grid disconnection
Solution Approach 2:
The control system dynamically adjusts the speed reference value based on the transition phase. During the delaying phase, the speed reference is held constant despite load changes, while in the activation phase, the droop function is gradually enabled. This dynamic adaptation allows rapid mode change while maintaining engine speed stability throughout the transition
2Adaptability or versatility
If the droop function is enabled immediately during grid trip, then the system adapts to new operating conditions quickly, but the engine overspeeds due to rapid load decrease and delayed measurement response
Solution Approach 1:
The system performs preliminary detection of grid trip conditions and initiates a controlled transition sequence. During the delaying phase, the droop function is kept disabled and speed reference is held constant, preparing the system for the upcoming load change without immediately reacting, thus preventing engine overspeed while maintaining adaptability
Solution Approach 2:
The control system provides beforehand cushioning by implementing a delaying phase that buffers the immediate impact of grid trip on engine operation. This temporary stabilization period cushions the engine against rapid load decreases and measurement delays, preventing harmful overspeed conditions while the system adapts to the new operating state
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
In an event of disconnection of a local power network (2) from a grid (1), the change of the control mode of a generator set in the local power network from a k W mode (31) to a speed droop mode (32), is provided. The phase of changing comprises a delaying phase (51) that in turn comprises parallel sub-phases to disable (53) a droop function of the speed droop mode and keeping (54) a speed reference value at a rated speed of an engine of the generator set. After the delaying phase an activation phase (52) enables the droop function.