Detailed Solution for Reactive Power Compensation with High-Capacity Collection and Low-Capacity Compensation

1. Scheme Introduction

In the current electrical industry, SVG is widely adopted for reactive power compensation in high‑voltage electrical systems such as 6kV, 10kV, 20kV and 35kV. Two compensation topologies are commonly used: direct grid‑connection type and transformer step‑up type.

For applications with relatively small compensation capacity, the transformer step‑up SVG scheme is more cost‑effective and thus widely applied. This scheme was developed to address low power factor in high‑voltage power supply systems at the lowest possible economic cost according to on‑site requirements.

A step‑up SVG reactive power compensation system mainly consists of a low‑voltage SVG compensation cabinet (400V/690V/800V), a step‑up transformer, high‑voltage side current sampling signals and other auxiliary electrical components. The low‑voltage SVG detects system voltage and current in real time, quickly outputs compensating reactive current, which is then stepped up to the high‑voltage side via the transformer to compensate high‑voltage reactive power, thereby improving the power factor of the high‑voltage busbar.

2. Primary Schematic Diagram

3. Notes and Instructions

• The primary voltage of the step-up transformer must match that of the high-voltage system, and the secondary voltage must be consistent with the rated voltage of the selected SVG.

• The connection modes of the step-up transformer can be Dyn11, Dyn0, or Yyn0.

• The step-up transformer can be newly installed dedicated for the SVG, or an existing on-site transformer can be used as the step-up transformer.

• The total system current sampling can be taken from the main incoming cabinet or the metering cabinet. The specific location shall be determined according to the on-site sampling feasibility.

• For high-voltage current sampling, some systems are equipped with one current transformer for each phase (A, B, C), while others only have CTs on phases A and C. For systems with three CTs, the current sampling wires can be directly connected to the SVG current transformer terminals. If only phase A and C CTs are available on-site, the B-phase current can be constructed synthetically, and then the three-phase current signals can be connected to the SVG. A wiring primary schematic example is shown below:

4. On-site Application System Diagram

System Main Connection Diagram (Taking 500kvar as an Example)