GSU Transformer Pre-Energization Using Impedance Injection
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Solution Overview
Problem
The increasing penetration of utility-scale distributed generators with GSU transformers causes significant inrush currents, leading to voltage sags/spikes and rapid voltage changes, which can result in non-compliance with power quality requirements and economic infeasibility for distributed generation projects.
Innovation Solution
A medium voltage inrush current (MVIC) regulator and interconnection control system using a pre-insertion impedance injection transformer, low and medium voltage switches, and a controller to manage a pre-energization switching sequence, reducing the magnetic flux rate and inrush current during grid restoration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If GSU transformers are energized during grid restoration, then power generation capacity is restored, but inrush current causes voltage sags and power quality violations
Solution Approach 1:
The system performs preliminary action by pre-charging the transformer core through the secondary winding before main energization. The controller closes the secondary switch first to establish magnetic flux in the core, then closes the primary switch to complete energization. This preliminary core magnetization prevents inrush current by ensuring the transformer is already magnetically saturated when full power is applied.
Solution Approach 2:
The controller acts as an intermediary device that mediates the energization process between the grid and transformer. It sequences the closing of primary and secondary switches, controlling the magnetization process to prevent harmful inrush currents while ensuring complete energization. The controller coordinates the timing and sequence of switch operations to achieve both productivity restoration and power quality maintenance.
2Object-affected harmful factors
If traditional inrush current mitigation methods are used, then inrush current is reduced, but system complexity and cost increase
Solution Approach 1:
The controller provides multi-functionality by performing both normal switching operations and inrush current mitigation through a single device. It sequences switch closing to prevent inrush current while also managing normal transformer operation. This universal approach eliminates the need for separate mitigation devices like pre-insertion resistors or specialized circuitry, reducing overall system complexity while maintaining effectiveness.
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 system effectively reduces inrush current and undesirable power quality phenomena by controlling the magnetic flux in GSU transformers, ensuring compliance with power quality standards and reducing operational challenges.
Implementation Method 1
magnetic flux in the designated GSU transformer occurs at a reduced rate, thereby reducing inrush of current
Data Source
AI summary
A medium voltage inrush current (MVIC) regulator and interconnection control system for interposing between a distributed power generation facility and a utility grid. The facility has a designated generator step-up (GSU) transformer and is connected to the utility grid at a point of interconnect. The system includes a pre-insertion impedance injection transformer, a low voltage first switch connected between the pre-insertion transformer and secondary coils of the designated GSU transformer, a medium voltage second switch connected inline between the pre-insertion transformer and primary coils of the designated GSU transformer, and a controller. In response to restoration of the utility grid following a loss-of-grid event, the controller opens and closes the first and second switches according to an automated pre-energization switching sequence such that magnetic flux in the designated GSU transformer occurs at a reduced rate, thereby reducing inrush of current and undesirable power quality phenomena.