Think of electricity as a smooth wave that flows through wires to power things like lights or machines. This wave is supposed to be clean and regular, like a steady heartbeat. But sometimes, extra “noise” or wiggles get added to this wave, making it less smooth. These wiggles are called harmonics, and they can mess with how well electrical systems work. Total Harmonic Distortion (THD) measures how much of this unwanted noise is in the wave, and it’s split into two types: THDi for current and THDv for voltage. Let’s unpack each one.

THDi (Total Harmonic Distortion of Current): Current is like the flow of electricity that powers your devices. THDi tells us how much “noise” is in that flow, caused by things like computers, LED lights, or big machines that don’t use electricity in a smooth, simple way. These devices create extra waves (harmonics) that mess up the clean flow. THDi is a percentage that compares the noisy parts of the current to the clean, main part of the current. For example, a high THDi means the current is really wobbly, which can make motors or transformers overheat or waste energy. Imagine trying to drink from a straw, but the liquid keeps pulsing unevenly—that’s what high THDi does to electrical systems.

THDv (Total Harmonic Distortion of Voltage): Voltage is like the pressure that pushes electricity through the system. THDv measures how much noise is in that pressure. When the current has a lot of harmonics (high THDi), it can mess with the voltage, making it wobbly too. THDv is also a percentage, comparing the noisy parts of the voltage to the clean, main part. If THDv is high, it can cause problems like flickering lights or sensitive equipment (like medical devices or computers) acting up. Power companies try to keep THDv low because clean voltage is critical for everything to run smoothly. Think of it like water pressure in your house—if it’s unsteady, your shower or appliances might not work right. THDi is about the flow being messy, while THDv is about the pressure being messy, and both can cause trouble if they’re not controlled.

THDv is like having unsteady pressure in the electricity that powers your devices, making the voltage “wobbly” instead of smooth. This can mess up sensitive equipment or cause lights to flicker. To fix it, you need to clean up the voltage or reduce the “noise” causing the problem. Here’s how:

• Clean Up the Current First: Most voltage issues come from messy current (high THDi) caused by devices like computers or motors. Using filters to clean the current often fixes the voltage too.
• Add Filters for Voltage: Special devices called harmonic filters can smooth out the voltage by catching the unwanted wiggles, like a filter cleaning dirty water.
• Upgrade Equipment: Use bigger transformers or wires that can handle the noise better, so the voltage stays steady.
• Spread Out Noisy Devices: Don’t plug too many noisy devices (like big machines) into one circuit. Spread them out to reduce stress on the system.
• Check the Power Supply: If the problem is coming from the power company’s supply, work with them to fix it, as their voltage might already be distorted.

THDi issues happen when devices create “noisy” electrical currents that mess up the smooth flow of power. To fix this, you can think of it like cleaning up a messy stream of water. Here are some common ways to do it:

• Add Filters: Use special devices called harmonic filters that act like strainers to catch the unwanted “wiggles” in the current, letting only the clean current pass through.
• Choose Better Equipment: Some modern devices are designed to create less noise. For example, picking power supplies or motors that are labeled as “low harmonic” can help.
• Spread Out the Load: If too many noisy devices are plugged into one circuit, try spreading them across different circuits to reduce the strain.
• Use Bigger Transformers or Wires: Sometimes, upgrading the electrical system with larger equipment can handle the noise better, like using a wider pipe to manage water flow.
• Install Special Devices: Equipment like active harmonic filters or phase-shifting transformers can actively clean up the current, kind of like a water purifier for electricity.

Passive harmonic filters are tuned circuits made of inductors, capacitors, and resistors designed to target specific harmonic frequencies (e.g., 5th harmonic at 250 Hz in a 50 Hz system). They work by providing a low-impedance path for harmonic currents, diverting them away from the main power system, which reduces both THDi and THDv. For THDi, they directly filter out harmonic currents from non-linear loads like rectifiers. For THDv, they reduce voltage distortion by limiting the harmonic currents that interact with system impedance. Passive filters are cost-effective and simple, making them suitable for smaller systems or stable loads (e.g., an office with consistent computer use). However, they are less flexible, as they’re tuned to specific harmonics and may not adapt well to changing loads. Improper design can also cause resonance issues, amplifying certain harmonics.

Active harmonic filters are advanced electronic devices that monitor harmonic currents in real-time and inject counteracting currents to cancel them out. They are highly effective for both THDi and THDv, as they dynamically address a wide range of harmonics, making them ideal for complex or variable systems (e.g., industrial plants with fluctuating motor drives). For THDi, they directly reduce harmonic currents from non-linear loads. For THDv, they mitigate voltage distortion by minimizing the harmonic currents that cause it. Active filters are more expensive and require professional setup and maintenance, but their adaptability makes them superior for large or dynamic systems. They can also improve power factor and reduce system losses, offering broader benefits than passive filters.

Replace non-linear loads with equipment designed to minimize harmonic generation, such as power supplies with power factor correction (PFC) or drives with built-in harmonic mitigation. These reduce THDi directly and, by extension, THDv. Check equipment specifications for compliance with IEEE 519, which recommends THDi limits (e.g., 5–8%) and THDv limits (e.g., below 5%).

High harmonic currents can overheat transformers and amplify THDv due to impedance. K-rated transformers (e.g., K-13 or K-20) are built to handle harmonic loads without overheating, reducing both THDi stress and THDv. Oversizing standard transformers (derating) to 150% of load capacity can achieve similar results, ensuring stable voltage and current.

High impedance (e.g., from long cables or undersized conductors) worsens THDv by amplifying the effect of harmonic currents. Using larger conductors (e.g., upgrading from 10 AWG to 8 AWG), shorter cable runs, or low-impedance transformers reduces impedance, lowering both THDi and THDv impacts.

Distribute non-linear loads (e.g., computers, LED drivers) across multiple circuits or phases to prevent harmonic currents from concentrating, which reduces THDi and THDv. Isolating sensitive equipment (e.g., medical devices) from harmonic-heavy loads protects them from distortion effects.

In systems with multiple non-linear loads, phase-shifting transformers cancel specific harmonics (e.g., 5th and 7th) by creating phase differences in currents. This reduces THDi and, consequently, THDv, particularly in industrial settings with large motor drives.

For critical systems, automatic voltage regulators (AVRs) or uninterruptible power supplies (UPS) stabilize voltage and filter harmonics. A double-conversion UPS, which converts AC to DC and back to AC, can eliminate THDv effects for sensitive loads, while also reducing the impact of THDi.

If THDv is high due to upstream harmonics in the utility’s supply, contact the provider to investigate. They may need to install filters or adjust their system to meet IEEE 519 standards (e.g., THDv below 5%).

Use a power quality analyzer to measure THDi and THDv, identifying dominant harmonic frequencies (e.g., 3rd, 5th) and their sources. Regular monitoring ensures compliance with standards and tracks improvements after implementing solutions.