Zhalute–Qingzhou

The Zhalute-Qingzhou HVDC project is a major ultra-high-voltage direct current (UHVDC) power transmission system in China. It operates at ±800 kV. The project has a rated transmission capacity of 10,000 MW (10 GW), making it one of the largest HVDC transmission projects in the world.

The transmission line spans approximately 1,234 kilometers, connecting the Zhalute converter station in Inner Mongolia to the Qingzhou converter station in Shandong province. This enables the transfer of electricity from energy-rich areas in the northeast to load centers in eastern China. The project was completed and entered commercial operation in December 2017.

Converter Stations

Technically, the Zhalute-Qingzhou HVDC system utilizes a bipolar configuration with two poles. Each pole consists of two series-connected 12-pulse converters, resulting in a total of four valve halls per converter station - two for positive polarity and two for negative polarity. The converter stations employ thyristor valves for AC/DC conversion.

Transformer Specifications

The system's converter transformers have significant specifications. At the Zhalute (sending) end, the transformers have a rated capacity of 501.8 MVA per single-phase unit, with a converter-side line-to-line voltage of 170.3 kV. The Qingzhou (receiving) end transformers are rated at 472.5 MVA per phase, with a converter-side line-to-line voltage of 160.4 kV. The transformers have short-circuit impedances of 18% and 17% for Zhalute and Qingzhou, respectively.

Reactive Power Compensation and Filtering

For reactive power compensation and harmonic filtering, the project incorporates AC and DC filters at both converter stations. The DC transmission line uses aluminum conductor steel reinforced (ACSR) cables with a specification of 6 × LGJ-900/40. To smooth current and reduce harmonics, the system employs smoothing reactors with an inductance of 2 × 75 mH, installed at each pole outlet and neutral point.

Operational Flexibility

The Zhalute-Qingzhou HVDC project is designed to operate in various modes, including bipolar full voltage, bipolar mixed voltage, and monopolar configurations with either metallic or ground return. This flexibility allows for efficient operation under different conditions and maintenance scenarios.

Grid Integration

An important aspect of the project is its integration with the AC power grid. The inverter station (Qingzhou) connects to both 500 kV and 1000 kV AC systems, facilitating power distribution to the regional grid. This multi-voltage integration enhances the overall stability and reliability of the power transmission system.

Environmental and Economic Impact

The project plays a significant role in China's energy strategy by enabling the long-distance transmission of renewable energy, particularly wind power from Inner Mongolia, to populous eastern regions. It helps reduce wind curtailment and improves the utilization of clean energy resources.

In terms of environmental impact, the Zhalute-Qingzhou HVDC line traverses diverse terrains across multiple provinces, including Inner Mongolia, Hebei, Tianjin, and Shandong. The project required careful planning and implementation to minimize ecological disruption along its route.