N-Phase Short Circuit Protection for Permanent Magnet Generators
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Solution Overview
Problem
Permanent magnet generators in renewable energy applications face significant damage from fault currents due to short circuits, especially between less than n conductors, leading to severe overheating and vibration, as existing protection methods like fuses and contactors are inadequate at low frequencies and high costs.
Innovation Solution
An electrical machine protection system with n-phase stator windings connected to a power converter via an n-phase circuit, where each conductor is associated with a switching device that creates a full n-phase short circuit upon fault detection, using contactors or similar devices to connect conductors in parallel to a common conductor, allowing for rapid fault current elimination and reduced risk of permanent magnet de-magnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If permanent magnet generators are used in renewable energy applications, then efficiency and operational capability are improved, but vulnerability to fault current damage increases
Solution Approach 1:
The protection circuit is configured to detect fault currents and rapidly connect all n conductors together to create a balanced n-phase short circuit, preventing the unbalanced short circuit from causing severe overheating and vibration that would damage the permanent magnets. This preliminary protective action counteracts the harmful effects before they can inflict significant damage on the generator.
Solution Approach 2:
The invention converts the harmful unbalanced short circuit condition into a beneficial balanced n-phase short circuit condition. By connecting all n conductors together upon fault detection, the system transforms the damaging asymmetric fault into a symmetric condition that produces uniform magnetic forces, eliminating severe vibration and overheating while allowing controlled fault current flow.
2Reliability
If conventional protection methods like fuses and contactors are used, then some fault protection is provided, but protection effectiveness is insufficient at low frequencies and costs increase
Solution Approach 1:
The protection system uses switching devices that can dynamically respond to fault conditions by rapidly connecting all n conductors together. This dynamic reconfiguration of the circuit provides adaptive protection that is effective across different frequency ranges, including low frequencies where conventional contactors fail, without requiring expensive specialized equipment.
Solution Approach 2:
The system changes the electrical parameters of the circuit by connecting all n conductors together in a balanced configuration, transforming the fault condition from an unbalanced state to a balanced state. This parameter change allows the use of standard AC-rated contactors rather than expensive DC-rated contactors, reducing cost while maintaining protection effectiveness at low frequencies.
3Speed
If switching devices connect conductors to a common conductor upon fault detection, then fault current elimination speed increases, but device complexity increases
Solution Approach 1:
The protection circuit merges all n conductors together by connecting them to a common conductor through switching devices upon fault detection. This merging action creates a balanced n-phase short circuit that rapidly eliminates fault current by producing uniform magnetic forces, achieving fast protection while using a relatively simple circuit topology that can be implemented with standard switching devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes damage from fault currents by creating a full n-phase short circuit, allowing for quick fault current elimination and reduced risk of permanent magnet de-magnetization, enabling the use of lower-cost AC-rated contactors and preventing severe overheating and vibration, thus enhancing protection and operational safety.
Implementation Method 1
the conductors of the n-phase circuit are connected together to provide a full n-phase short circuit
Implementation Method 2
A balanced short circuit of this type will ensure that the magnetic forces generated within the generator are uniform and will eliminate the severe vibration that would otherwise be generated
Data Source
AI summary
An assembly includes an electrical machine connected to a power converter by a three-phase circuit having three conductors, e.g. cables Each conductor is associated with a switching device such as a contactor or the like that connects the conductor to a common conductor or terminal. In the event of a fault current being developed in the circuit or the power converter the switching devices are operated to close the fault current and connect together the conductors of the three-phase circuit to provide a full three-phase short circuit.