Wind Turbine Transformer Startup to Avoid Grid Inrush Current
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Solution Overview
Problem
Inrush currents occur when connecting a power transformer between a wind turbine and an electrical grid due to mismatched magnetic states, leading to grid disturbances, and existing solutions either require complex monitoring or additional charging devices, increasing costs and lacking black start capability.
Innovation Solution
Gradually increase the voltage at the transformer's primary side from a low starting voltage to a target voltage using the wind turbine's inverter or auxiliary inverter, utilizing internal energy storage, and connect the secondary side to the grid after predefined conditions are met, avoiding inrush currents and enabling black start capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the transformer is connected to the electrical grid using conventional switching, then the connection is simple and fast, but inrush currents occur causing grid disturbances
Solution Approach 1:
The patent applies preliminary action by gradually increasing the voltage at the transformer primary side from zero to nominal voltage before connecting to the grid. This pre-conditioning of the transformer magnetic state prevents inrush currents when the secondary side is subsequently connected to the electrical grid, as the transformer is already in a stable magnetic state matching the grid voltage.
Solution Approach 2:
The patent changes the voltage parameter gradually over time during the startup phase. By controlling the inverter to increase voltage from 0 to nominal voltage in a controlled manner, the magnetic flux in the transformer builds up gradually, avoiding the sudden magnetic state change that causes inrush currents during conventional direct switching.
2Object-affected harmful factors
If precise monitoring of transformer disconnection is implemented to match magnetic states, then inrush currents are avoided, but the system becomes complicated and requires additional monitoring devices
Solution Approach 1:
The patent applies self-service by using the wind turbine's own inverter to generate and control the startup voltage, eliminating the need for external monitoring devices or complex synchronization systems. The inverter inherently knows the grid voltage characteristics since it is already connected to or synchronized with the grid, and it autonomously controls the voltage ramp-up process without requiring separate monitoring equipment.
3Object-affected harmful factors
If a charging device is provided to start the transformer without inrush currents, then inrush currents are reduced, but additional devices are required increasing system costs
Solution Approach 1:
The patent applies multi-functionality by using the existing inverter, which is already a necessary component for converting wind turbine power to grid-compatible electricity, to also perform the transformer startup function. The inverter serves dual purposes: power conversion during normal operation and controlled voltage generation during startup, eliminating the need for separate charging devices or startup equipment.
4Adaptability or versatility
If voltage is gradually increased from low starting voltage to target voltage using the inverter, then inrush currents are avoided and black start capability is enabled, but the inverter must handle variable voltage conditions
Solution Approach 1:
The patent applies dynamics by making the inverter operate in different modes during the startup sequence. The inverter dynamically adjusts its output voltage from zero to nominal voltage according to a controlled ramp profile, and dynamically switches between voltage control modes to accommodate the changing system conditions during startup versus normal operation.
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
This method provides a cost-effective solution to connect the transformer without inrush currents, supports the grid during startup, and allows for black start operations, stabilizing the electrical grid without disturbances.
Implementation Method 1
gradually increasing a voltage at the primary side of the transformer from a low starting voltage to a target voltage equal or close to a nominal voltage of the transformer, by means of the inverter of the wind turbine or by means of an auxiliary inverter
Implementation Method 2
wherein the gradually increasing of the voltage uses energy of an internal energy storage device
Data Source
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AI summary
The invention relates to a method (200) for connecting a power transformer (160), located between an inverter (150) of a wind turbine (100) and an electrical grid (170), to the electrical grid (170); the method comprises the steps gradually increasing a voltage at a primary side (161) of the transformer from a low starting voltage (a) to a target voltage (b) equal or close to a nominal voltage of the transformer (160), by means of the inverter (150) of the wind turbine (100) or by means of an auxiliary inverter, thereby increasing the voltage at a secondary side (162) of the transformer (160), wherein the gradually increasing of the voltage uses energy of an internal energy storage device (158), connecting the secondary side (162) of the transformer (160) to the electrical grid (170) after predefined target conditions have been reached.