Generator Network Controller Avoiding Loss-of-Mains Non-Detection Zone
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Solution Overview
Problem
Existing methods for detecting loss-of-mains electrical supply are inadequate, particularly when there is a perfect balance between active and reactive power generation and demand, leading to potential undetection of islanding events, which poses hazards to electrical systems and hampers the deployment of distributed generators.
Innovation Solution
An electrical generator network with controllers that monitor real and reactive power flows to adjust the target reactive power output, ensuring that the power flows exceed predetermined thresholds, thereby avoiding the non-detection zone of loss-of-mains relays and enabling timely detection of islanding events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive ROCOF or Vector Shift relay detection methods are used, then loss-of-mains can be detected when there is power imbalance, but detection fails when active and reactive power are perfectly balanced within approximately 2.5% of generation capacity
Solution Approach 1:
The controller deliberately creates a reactive power imbalance before islanding can occur by adjusting the target reactive power output. This preliminary action ensures that when islanding happens, there is already a detectable power imbalance, eliminating the need for complex post-islanding detection algorithms and ensuring reliable detection within 2 seconds.
Solution Approach 2:
The system changes the reactive power parameter by adjusting the target reactive power output Qtarget beyond the normal operating range. This parameter change creates an intentional imbalance that ensures detectable frequency changes occur during islanding events, resolving the detection failure problem when power was perfectly balanced.
2Reliability
If reactive power output is adjusted to create intentional imbalance, then loss-of-mains detection reliability improves, but normal operation stability may be affected
Solution Approach 1:
The system dynamically adjusts the target reactive power output Qtarget based on operating conditions. During normal grid-connected operation, the reactive power remains stable for normal voltage support. Upon detecting islanding, the controller quickly transitions to an unstable state that creates the necessary imbalance for detection, then stabilizes again after tripping. This dynamic behavior ensures both normal operation stability and detection reliability.
Solution Approach 2:
The controller implements periodic monitoring of power flow conditions and adjusts reactive power output in response to detected islanding events. The system alternates between stable normal operation and controlled imbalance states, with the imbalance being temporary and only active during the critical detection window after islanding occurs.
3Ease of operation
If the detection system uses standard drooped control loops for governors and AVRs, then normal operation is maintained, but detection time extends to up to 12 seconds when the system is initially very well balanced
Solution Approach 1:
Instead of waiting for natural load/generation fluctuations to create detectable imbalances, the controller proactively creates the necessary reactive power imbalance before islanding occurs. This preliminary action reduces detection time from up to 12 seconds to under 2 seconds by ensuring an imbalance exists immediately when islanding happens, while maintaining ease of normal operation through standard drooped control loops.
4Reliability
If active methods using harmonic current injection are used, then loss-of-mains detection is reliable, but electrical power quality is compromised
Solution Approach 1:
Instead of using harmful harmonic current injection to achieve detection, the system converts the naturally occurring reactive power flow into a beneficial detection mechanism. By deliberately adjusting reactive power output to create controlled imbalances, the system transforms what would normally be a stability concern into a reliable detection signal, achieving detection without compromising power quality.
Data Source
AI summary
A local electrical system having an electrical generator is connected to an electrical generator network. The local electrical system has a controller to avoid the non-detection zone of loss-of-mains relays. The controller is arranged to monitor the real power flow from the electrical generator network to the local electrical system and to determine if the absolute value of the real power flow is below a first predetermined value to determine if there is a close match between the power requirements of the local electrical system and the electrical generator. If there is a close match, then the controller is arranged to monitor the reactive power flow the same way. If there is a close match also with the reactive power, then the controller is arranged to adjust the target reactive power output from the electrical generator of the local electrical system.