Electrical noise, 电磁干扰, conducted and radiated disturbances
A hospital EKG machine produced unreliable results. Signal wiring routed parallel to the power cord created inductive coupling — a classic internal EMC failure invisible to utility PQ standards. Root cause: wiring practice, not utility supply quality. 75% of medical facility PQ problems are internal wiring and grounding issues.
A steel mill with variable speed drives experienced frequent VSD tripping with “过电压在AC线路” indication despite normal steady-state voltage. Utility-induced switching surges — invisible to RMS voltmeters — were the root cause. Case demonstrates why true PQ monitoring with transient capture is essential in facilities with long cable runs and VSD loads.
A steel factory in northern Italy had all laboratory electronic equipment behaving erratically — seemingly without cause. Investigation revealed constructive defects in the earthing system creating large current loops. With heavy currents flowing through the earth return path, the potential difference between equipment earths was sufficient to cause data corruption and equipment malfunction throughout the plant.
公吨. Washington’s communication towers serving northern New England — carrying TV, 无线电, telephone, FAA air traffic control, and emergency services — were vulnerable to lightning until 1993. A comprehensive copper grounding system redesign eliminated lightning-related equipment damage and downtime, demonstrating the economic case for proper grounding in high-exposure communication infrastructure.
Conductive noise — high-frequency electrical disturbances spreading through power, signal, and ground cables from lightning surges, 静电放电, and high-order harmonics — causes equipment malfunction and radio/TV interference in neighbouring premises. HIOKI measurement techniques covering up to 100 MHz identify the noise frequency band and propagation path for targeted mitigation.
Eighteen days of monitoring on a 1-phase 100V circuit recorded 68 identical waveform distortion events, subsequently classified into two types: UPS switching transients and persistent waveform noise. The systematic waveform comparison technique demonstrates how event classification reveals root cause — the UPS was not returning to sine wave output after switching.
A building manager with widespread electrical malfunctions and three electricians who quit — none could identify the problem. A systematic approach starting with current measurement revealed a tripped GFCI with high neutral current feeding a malfunctioning medical device. Classic case demonstrating that systematic PQ investigation beats component replacement as a troubleshooting strategy.
A glass factory imported from a 60 Hz country to a 50 Hz country suffered repeated electronic control failures, reducing production capacity by 50%. Voltmeters and simple monitors failed to capture the cause. Full PQ monitoring eventually revealed voltage transients and harmonic distortion incompatible with the 60 Hz-designed electronics — a frequency migration problem compounded by poor power quality.
