How does Active Harmonic Filter (AHF) on the main power distribution line save fuel consumption for generators

Installing an Active Harmonic Filter (AHF) on the main power distribution line can typically save fuel consumption for generators (especially diesel generators)

Here is a detailed explanation:

1. How Harmonics Increase Fuel Consumption in Generators (Especially Diesel Generators):

   • Additional Heat Losses: Harmonic currents flowing through the stator and rotor windings of the generator cause higher resistive losses (I²R losses) than the fundamental current. These losses are dissipated as heat, meaning some of the mechanical energy input to the generator is wasted.

   • Increased Iron Losses: Harmonic voltages lead to increased hysteresis and eddy current losses in the generator's iron core.

   • Damper Winding Losses: Harmonic currents are induced in the rotor's damper windings, creating additional losses and heat.

   • Reduced Efficiency: All these additional losses mean the overall efficiency of converting the mechanical energy from diesel combustion into electrical energy is reduced. To deliver the same active power (kW), the generator needs to consume more diesel to compensate for these losses.

   • Harmonic Torque Pulsations: Harmonic currents interacting with the generator's magnetic field produce pulsating torques at frequencies that are multiples of the fundamental frequency. This imposes extra mechanical stress on the diesel engine and can interfere with the stability of the engine governor. To maintain a constant speed (frequency), the governor must act more frequently to adjust the throttle, which itself can slightly reduce efficiency and potentially lead to increased instantaneous fuel consumption.

   • Increased Apparent Power Demand: Harmonic currents increase the total current (RMS) in the system, thereby increasing the generator's apparent power (kVA) output requirement. Generators (especially standby units) are often rated in kVA. Excessive harmonic currents can force a generator to operate near or beyond its rated kVA capacity while actually outputting less useful active power (kW). This is not only inefficient but may also trigger overload protection shutdowns. To avoid exceeding kVA limits, sometimes the active power load must be reduced, which also means diesel fuel is not being used effectively.

2. How an Active Harmonic Filter (AHF) Helps Save Fuel:

   • Eliminates Harmonic Currents: The core function of an AHF is to detect harmonic currents in the line and instantaneously inject a compensating current equal in magnitude but opposite in phase. This results in the upstream source (the generator in this case) seeing a current that is nearly sinusoidal.

   • Reduces Generator RMS Current: By eliminating harmonic currents, the AHF significantly reduces the total RMS current flowing through the generator.

   • Reduces Losses: The reduction in RMS current directly leads to a substantial decrease in I²R losses in the generator windings. Iron losses and damper winding losses are also reduced.

   • Improves Efficiency: The reduction in losses means the generator's efficiency in converting diesel's chemical energy into useful electrical energy (kW) is improved. For the same load active power demand, the required mechanical energy input to the generator decreases, thus the load on the diesel engine is reduced, leading to lower fuel consumption.

   • Decreases Apparent Power Demand: Eliminating harmonic currents means the generator's apparent power output demand more closely matches the load's active power demand. This avoids wasting kVA capacity due to harmonics, allowing the generator to operate at a more optimal power factor.

   • Mitigates Torque Pulsations: Reducing harmonic torque pulsations allows the diesel engine to run more smoothly, easing the burden on the governor and helping to maintain more stable operating efficiency.

3. Key Factors Influencing Fuel Savings:

   • Original Harmonic Distortion Level: The higher the original Total Harmonic Current Distortion (THDi), the greater the reduction in losses after installing an AHF, and the greater the potential fuel savings. If the original harmonics were low, the fuel savings would be negligible.

   • Generator Load Factor: The heavier the generator load, the greater the absolute losses caused by harmonics, and the greater the absolute fuel savings from the AHF. Under light load, even a percentage efficiency gain may result in a smaller absolute fuel saving.

   • Generator Design and Harmonic Tolerance: Some generators (particularly modern or specially designed ones) have better tolerance for harmonics, and their efficiency is less affected. Older or poorly designed generators are more affected.

   • AHF Performance and Compensation Effectiveness: The AHF must be correctly sized, installed, and configured to achieve optimal harmonic filtering. The higher the compensation rate, the better the results.

   • AHF's Own Losses: The AHF itself consumes a small amount of active power during operation (typically 3%-8% of its rated compensation capacity). This loss slightly offsets the saved fuel. However, in cases of severe harmonics, the improvement in generator efficiency far outweighs the AHF's own consumption.

Conclusion:

Yes, installing an Active Harmonic Filter on the main distribution line can indeed save fuel consumption for generators (diesel generators). The principle is that by eliminating the harmful harmonic currents flowing through the generator, the additional internal losses (copper losses, iron losses, etc.) are reduced, thereby improving the generator's efficiency in converting diesel chemical energy into useful electrical energy. The end result is that for the same load active power demand, the mechanical energy input required from the diesel engine is reduced, leading to lower fuel consumption.

Quantifying Fuel Savings: It is difficult to generalize the exact amount of diesel saved, as it heavily depends on the key factors mentioned above. In industrial scenarios with severe harmonic pollution (e.g., factories with extensive use of nonlinear loads like VFDs and rectifiers), achieving fuel savings in the range of 3% to 8% or even higher for the generator after installing a high-performance AHF is possible. To obtain an accurate estimate, it is recommended to conduct detailed measurements and comparative analysis of the generator's key parameters (input fuel flow rate, output active power, current, voltage, THDi, THDv, etc.) under identical load conditions, both before and after installing the AHF.

Therefore, if your factory has a significant harmonic problem and relies on diesel generator operation (whether as the main power source or backup), investing in an Active Harmonic Filter is not only a measure to improve power quality, protect equipment, and increase system reliability, but it is also an energy-saving measure with economic returns, directly reducing operating costs (diesel expenses).