A passive harmonic filter is an electronic device that is designed to reduce or eliminate harmonics in an electrical signal. Harmonics are additional sinusoidal components occurring at frequencies multiple of the fundamental frequency in an electrical power system. These harmonics can cause problems such as transformer overheating, waveform distortion, loss of energy efficiency and electrical interference. A passive harmonic filter is called 'passive' because it does not require an external power supply for its operation. It relies on passive components such as capacitors, inductors and resistors to reduce harmonics. The main types of passive harmonic filters include 1. Low-pass filter: This type of filter allows frequencies below a certain cut-off frequency to pass through, attenuating the higher frequencies. It is used to eliminate high-frequency harmonics, allowing only the fundamental frequency to pass through. 2. High-pass filter: A high-pass filter does the opposite of a low-pass filter, allowing frequencies above the cut-off frequency to pass through and attenuating lower frequencies. It is used to eliminate low-frequency harmonics 3. Band-pass filter: This filter allows a specific range of frequencies to pass between two cut-off frequencies. It is useful for eliminating specific harmonics. 4. Notch filter (rejection): This filter is designed to selectively attenuate or block a specific frequency, such as a specific harmonic. It is often used to eliminate particularly problematic harmonics. The effectiveness of a passive harmonic filter depends on its design, the specifications of the harmonics to be eliminated and the characteristics of the electrical load. Such filters are often used in industrial and commercial applications to improve power supply quality and reduce problems associated with harmonics, such as overloads, overheating and service interruptions.