Parallel Transformer Voltage Control for Reactive Current Stability
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Solution Overview
Problem
Conventional methods for controlling voltage in transformer systems connected in parallel lead to unstable control systems, resulting in unnecessary wear and tear on tap changers due to circulating reactive currents, poor control quality, and increased power loss.
Innovation Solution
Implementing temporal step prioritization by adjusting delay times for transformers based on voltage and reactive current deviations, using a logic unit to prioritize steps that counteract voltage deviations and setting longer delay times for transformers with opposite deviations, thereby stabilizing voltage regulation within specific bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional voltage control methods are used with parallel transformers, then voltage regulation is attempted, but circulating reactive currents cause increased power losses and transformer wear
Solution Approach 1:
The patent applies different control characteristics to different transformers in the parallel system. Each transformer is assigned a unique identifier and receives customized control parameters (bandwidth, delay times) based on its local characteristics, preventing uniform control actions that cause circulating currents while maintaining individual optimization
Solution Approach 2:
The control system dynamically adjusts delay times and bandwidths based on real-time voltage deviations and transformer states. The delay time for voltage deviation and circulating reactive current are adjusted dynamically to prevent unnecessary tapping operations while maintaining stable control, transforming a static control approach into an adaptive dynamic system
2Ease of operation
If voltage regulators independently regulate setpoint voltage, then voltage control is achieved, but compensating currents occur due to different open-circuit voltages
Solution Approach 1:
The patent implements a feedback mechanism where each voltage regulator monitors not only its own voltage deviation but also the circulating reactive current. The control deviation is calculated as a weighted sum of voltage deviation and circulating reactive current deviation, creating a closed-loop feedback system that coordinates transformers and eliminates compensating currents
Solution Approach 2:
The patent introduces asymmetric control parameters for different transformers, including different bandwidths (first bandwidth for voltage, second bandwidth for circulating current) and different delay times. This asymmetric configuration prevents symmetric opposing actions that would cause circulating currents while maintaining effective voltage control
3Measurement precision
If bandwidth is set small for precise voltage control, then voltage accuracy improves, but endless back and forth stepping occurs
Solution Approach 1:
The patent introduces delay times as preliminary actions before executing tapping operations. The delay time for voltage deviation and delay time for circulating reactive current are configured to prevent immediate responses to small deviations, allowing the system to stabilize before acting and preventing endless back-and-forth stepping
Solution Approach 2:
The patent changes the control parameters by introducing dual bandwidths and dual delay times. The first bandwidth and second bandwidth are set differently, as are the delay times for voltage deviation and circulating current deviation. This parameter differentiation allows precise control while preventing oscillatory behavior through appropriate timing and threshold settings
4Loss of energy
If circulating reactive current is used as control criterion, then power losses are minimized, but unnecessary tapping operations increase wear on tap changers
Solution Approach 1:
The patent applies partial action by using circulating reactive current as only one component of the control deviation, combined with voltage deviation. The control system does not react to every circulating current fluctuation but only when the combined deviation exceeds thresholds, preventing excessive tapping operations while still reducing power losses
Data Source
Figure 1
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AI summary
A method is provided for controlling the value of a voltage on a conductor (3) to which at least one secondary winding (5A) of a first stepable transformer (7A) and one secondary winding (5B) of a second stepable transformer (7B) are connected, wherein the method comprises: if a voltage deviation (DV) of the voltage on the conductor (3) from a voltage setpoint lies within a first bandwidth ([-BCC_DV, BCC_DV]) around the voltage setpoint, and if a total deviation (DA, DB) of a sum of the voltage deviation (DV) and a reactive current deviation (DCCA, DCCB) from the voltage setpoint lies for the first and second transformers respectively outside a second bandwidth ([-BC, B]) around the voltage setpoint, which is larger than the first bandwidth ([-BC, B]), is set a delay time (T1) for stepping the first transformer (7A) and/or the second transformer (7B) such thatthat a stage in the first or second transformer that counteracts the voltage deviation is prioritized.