What does the term 'harmonics' refer to in electrical systems?

The term 'harmonics' in electrical systems refers to sinusoidal voltages or currents that are integral multiples of a fundamental frequency. This means that if the fundamental frequency of a system, such as 60 Hz, is the primary frequency at which the system operates, the harmonics would occur at frequencies like 120 Hz, 180 Hz, and so on, corresponding to 2 times, 3 times, etc., the fundamental frequency.

Harmonics can cause various issues in electrical systems, such as overheating, equipment malfunction, and inefficiencies in operation due to non-linear loads. Understanding harmonics is crucial for effective power quality management as they can significantly impact the performance of electrical systems and devices. The presence of harmonics can distort the original waveform, resulting in inefficiencies and potential damage over time.

The other options represent different concepts unrelated to the specific definition of harmonics. Variable frequencies do not define harmonics themselves, as they focus on changes in frequency rather than multiples of a specific frequency. DC power fluctuations refer to variations in direct current supply, which is unrelated to the concept of harmonics in alternating currents. Voltage spikes are sudden increases in voltage, which are also different from the oscillatory nature of harmonics.