When Clean Power Isn't So Clean

Modern facilities are filled with non-linear loads: variable frequency drives (VFDs), switching power supplies in computers, and LED lighting. These devices draw current in short pulses, distorting the perfect sine wave of the electrical supply. When powered by a generator set, this distortion—known as harmonic distortion—can be amplified, leading to hidden costs and failures. This Technology & Operation guide explains the risks and solutions.

What is Total Harmonic Distortion (THD)?

THD measures the percentage of distortion in the voltage or current waveform caused by harmonics (frequencies that are multiples of the fundamental 50Hz). A high THD indicates "dirty" power.

The Hidden Costs of High Generator THD

• Overheating and Damage: Harmonics cause additional losses in the generator's alternator stator and rotor windings, as well as in transformers and motor windings downstream, leading to premature failure.
• Nuisance Tripping: Can cause protective relays and circuit breakers to operate incorrectly, leading to unexplained shutdowns.
• Communication Interference: Can disrupt data networks, PLCs, and sensitive instrumentation.
• Reduced System Capacity: Harmonic currents consume capacity in cables and transformers without doing useful work, effectively derating your electrical system.

Mitigation Strategies for Reliable Operation

Proactive design is key to managing harmonics.

1. Generator Specification: Demand a generator designed for non-linear loads. Look for an alternator with a low subtransient reactance (Xd") and a dedicated PMG (Permanent Magnet Generator) or AREP (Auxiliary Winding) excitation system. These systems provide strong excitation even with highly distorted waveforms, helping to maintain voltage stability. Ensure the quoted THD voltage is less than 5% for sensitive applications.
2. Passive Harmonic Filters: These are tuned LC (inductor-capacitor) circuits installed at the main distribution board to "trap" specific harmonic frequencies (like the 5th and 7th).
3. Active Harmonic Filters (AHF): More advanced and flexible, AHFs electronically inject opposite-phase currents to cancel out harmonics in real-time. Ideal for dynamic loads with varying harmonic content.
4. Load Segregation: Separate sensitive linear loads from non-linear loads on different generator outputs or power sources where possible.

For any installation with significant VFDs, IT servers, or medical imaging equipment, a harmonic analysis should be part of the purchase guide process. Specifying the right เครื่องกำเนิดไฟฟ้า and mitigation equipment upfront is far cheaper than dealing with the aftermath of damaged assets.