Harmonic filters in pooling substations (often used in renewable energy, industrial, or utility applications) are designed to mitigate, reduce, or eliminate harmonic distortions caused by non-linear loads like Variable Frequency Drives (VFDs), solar inverters, or wind turbine converters.

 Harmonic filters in pooling substations (often used in renewable energy, industrial, or utility applications) are designed to mitigate, reduce, or eliminate harmonic distortions caused by non-linear loads like Variable Frequency Drives (VFDs), solar inverters, or wind turbine converters. 

The components vary based on whether the filter is Passive (LC tank circuits) or Active (power electronics)

1. Passive Harmonic Filter Components

Passive filters are most common for high-voltage, high-power applications in substations. They use a combination of components tuned to a specific frequency: 

Capacitors (C): Used to produce reactive power, improve power factor, and form the tuned circuit.

Filter Reactors/Inductors (L): Usually iron-core or air-core reactors that work with capacitors to create low impedance at the unwanted harmonic frequency.

Resistors (R): Used to provide damping, specifically in C-type or high-pass filters to manage resonance.

Protection Devices:

Capacitor Fuses: Protection against capacitor unit failure.

Surge Arresters: Protection against voltage surges.

Blown Fuse Detection System: Monitors the health of capacitor fuses.

Switching/Control Gear:

Vacuum Switches/Circuit Breakers: To turn the filter on/off based on load demands.

Control Power Transformer (CPT): Provides power for the control system and instrumentation.

Filter Rack/Enclosure: Structural steel to mount the components.

2. Active Harmonic Filter (AHF) Components

Active filters use power electronics to actively detect and cancel harmonics by injecting an opposite, anti-phase current. 

Power Electronics/Inverter: Voltage Source Inverter (VSI) using high-speed switching devices like IGBTs (Insulated Gate Bipolar Transistors).

Control System: Microprocessor-based controller that measures the harmonic frequencies and calculates the necessary compensation.

Current Transformers (CTs): Sensors to detect harmonic currents in real-time.

Passive Components (DC Link): DC capacitors and inductor reactors for the inverter DC bus. 

Summary Table of Components

Type Core Components Protection/Control Purpose

Passive Reactors (L), Capacitors (C), Resistors (R) Fuses, Surge Arresters, Breakers Low impedance path for specific harmonics

Active Inverter (IGBTs), DC Capacitor, Sensors Microprocessor, CTs Real-time cancellation of harmonics

Key Design Considerations in Substations

Tuning: Filters are often tuned slightly below the target frequency (e.g., 4.7th harmonic to address the 5th).

Voltage Ratings: Capacitors must be rated for higher voltage than the system nominal voltage to handle the voltage rise caused by the harmonic currents and reactor reactance.

Detuning: In some cases, capacitors are "detuned" (detuned reactor is smaller) to avoid resonance with the network, rather than fully filtering.