Cases-GoLead Intelligent

A ±500 kV UHVDC Converter Station of State Grid

Overview

This project serves as a major power transmission channel for the Three Gorges Underground Power Station and is a key component of State Grid’s Gezhouba–Shanghai HVDC comprehensive retrofit project. It is also an important corridor of China’s national "West-to-East Power Transmission" strategy.

The converter station has a transmission capacity of 3,000 MW with a DC voltage level of ±500 kV, making it a critical project for implementing the West-to-East Power Transmission initiative. Its construction plays a vital role in expanding the export of hydropower from the Three Gorges and Sichuan regions, strengthening interconnection between the Central China and East China power grids, and enhancing the resilience of the East China and Shanghai power grids.

The transmission line passes through Hubei, Anhui, Zhejiang, Jiangsu, and Shanghai, with a total length of 976 km and a rated transmission power of 3,000 MW.

However, during no-load energization and fault recovery of converter transformers, severe magnetizing inrush currents may occur, with peak values reaching 6–8 times the rated current. This can lead to protection maloperations, equipment damage, and voltage transients, posing a serious threat to equipment safety and grid stability.

This issue can be effectively addressed through a solution combining residual-flux and bias-flux cancellation technology with intelligent phase-selection closing. The SID-3YL microprocessor-based inrush current suppressor provided by Shenzhen GoLead Intelligent Electric Power Technology Co., Ltd., featuring strong adaptability to multiple operating scenarios, easy installation and commissioning, and low operation and maintenance costs, significantly enhances equipment safety and the overall stability of the HVDC transmission system.

Pain Points & Solutions

Pain Point 1: High-Amplitude Inrush Caused by Magnetic Circuit Saturation

After de-energization, converter transformers retain residual magnetism. During breaker closing, the bias flux generated by sudden voltage application superimposes on the residual flux, driving the magnetic circuit into saturation. As a result, magnetizing inrush currents can reach 6–8 times the rated current, significantly increasing winding mechanical stress, accelerating insulation aging, and raising the risk of overheating in GIS equipment.
Solution 1

Residual Flux Monitoring and Reverse Bias Flux Generation: The magnitude and polarity of residual magnetism in the converter transformer are monitored in real time after de-energization. During closing, reverse bias flux is actively generated to keep the total magnetic flux below the saturation threshold. Optimized Zero-Flux Closing: Precise closing is performed at voltage angles of 90° or 270° (corresponding to zero magnetic flux), avoiding abrupt flux changes. This suppresses the closing inrush current peak from 6 p.u. to within 1.5 p.u. of the rated current.
Pain Point 2: Insufficient Closing Phase Control Accuracy

Conventional solutions require specific circuit breaker models with operating time dispersion ≤ ±1 ms, resulting in limited applicability and poor universality.
Solution 2

The solution is compatible with both three-phase gang-operated and single-pole-operated circuit breakers, allowing an operating time dispersion tolerance of up to ±2 ms. Built-in functions include disturbance recording, event logging, and GPS time synchronization.
Pain Point 3: Risk of Protection Maloperation

During inrush events, the second-harmonic component may exceed 50%, which can be misinterpreted by differential protection as an internal fault, leading to unplanned outages. When multiple transformers operate in parallel, superposition of inrush currents and sympathetic inrush may cause cascading trips, threatening the stability of HVDC transmission systems.
Solution 3

The second-harmonic blocking threshold of differential protection is set to 15%–20% to prevent maloperation. In addition, the system interfaces with the converter station SCADA system via the IEC 61850 protocol, enabling real-time inrush data analysis and dynamic adjustment of protection strategies.

Values

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