1. Introduction

Three-phase unbalance is a prevalent power quality issue in low-voltage distribution systems, mainly caused by dispersed single-phase loads, charging piles and residential electricity consumption. Two mainstream solutions are widely used in the industry: mechanical relay phase-switching balancers and IGBT-based active compensation devices (SVG/APF/Active Load Balancer).

This article summarizes their working principles, core differences and standard technical parameters for blog publishing and professional customer communication.

2. Core Definition & Working Principle

2.1 Mechanical Relay Type Balancer

This is a passive power quality device driven by mechanical contact switching. It detects unbalanced phase loads and reallocates surplus active loads from overloaded phases to underloaded phases via contactors and relays.

Core feature: Only shifts active loads without active compensation current output, unable to rectify reactive power deviation and harmonic distortion.

2.2 IGBT Active Power Quality Devices (SVG / APF / ALB)

Equipped with high-speed IGBT inverters and DSP intelligent control chips, the device real-timely identifies negative-sequence, zero-sequence, reactive and harmonic current components, and outputs reverse compensation current to eliminate grid power quality problems.

Core feature: Contactless, fast and grid-friendly compensation, supporting integrated correction of multiple power quality issues.

3. Performance Comparison: Mechanical Balancer vs IGBT Active Device

4. Definition Relationship of SVG / APF / Active Load Balancer (ALB)

SVG, APF and ALB adopt identical IGBT voltage source inverter hardware, and their differences are reflected in built-in algorithms and application positioning:

• ALB (Active Load Balancer): A dedicated overseas-specialized device focusing on three-phase unbalance correction and neutral current elimination, with basic reactive power compensation and no harmonic filtering function.

• SVG (Static Var Generator): A versatile device dominated by dynamic reactive power compensation and grid voltage stabilization, with built-in three-phase unbalance correction function.

• APF (Active Power Filter): A professional harmonic governance device mainly filtering 2~50 order harmonics, with auxiliary functions of three-phase unbalance correction and reactive power compensation.

5. Standard Technical Parameter Calibration (35A/50A Specification)

5.1 Basic Parameter Description

• Rated phase current: ≥35A

• Rated neutral current: ≥50A

• Applicable system: 400V three-phase four-wire low-voltage system

5.2 Capacity Conversion & Standard Model

• SVG Capacity: 25kVA = 25kvar (Standard reactive power compensation rating)

• APF Rated Current: 36A (Matched with 25kVA full capacity)

• Zero-sequence Unbalance Governance Capacity: 20kVA (Support 50A maximum neutral current compensation)

5.3 Standard English Product Specification

25kVA/25kvar 4-wire SVG/APF/Active Load Balancer features 35A rated phase current and 50A maximum neutral current, delivering millisecond-level dynamic compensation for three-phase unbalance, neutral current suppression and reactive power optimization.

6. Selection Guide

• Three-phase unbalance & excessive neutral current only: ALB

• Power factor correction & grid voltage stabilization: SVG

• Harmonic suppression & comprehensive power quality improvement: APF