Residual/fault currents (also called ground fault currents or insulation leakage currents) can be used to determine the insulating state of machines and whether they require maintenance and repairs to prevent emergency shutdowns. Real-time monitoring of fault currents in the power supply enables the state of the electrical insulation to be evaluated based on actual measured values, while the long-term trend of the fault current value can be used for maintenance planning. This means that residual current monitors (RCMs) can detect faults in a timely manner and increase the availability of power supplies or plants at a much lower cost than conventional, expensive, and time-consuming high-voltage insulation testing.
These fault currents can originate from various sources, such as insulation faults, insulation leakage currents, capacitive displacement currents, or EMC filter leakage currents. While some of these fault currents are in a “normal” range, others are causes or signs of deteriorating insulation that can lead to abnormal heat dissipation, short circuits, and – in the worst cases – fires and personal safety hazards.
With the increasing prevalence of DC loads (e.g., LED lighting, DC motor drives, and 48 V DC bus systems), decentralized DC generation (PV systems, UPS, batteries, etc.), and high-frequency converters (e.g., SMPS and motor drives) in industrial environments, it is becoming increasingly difficult to reliably measure insulation faults with conventional RCMs designed for AC 50/60 Hz with limited measurement bandwidth. SCT5xxx differential current transformers therefore offer a measurement bandwidth of 0–100 kHz and are marked as type B/B+.