Fluxgate current measurement technology
Principle of the fluxgate current measurement technology
While all SCT transformers except the SCT5xxx are based on the transformer principle described above, the technology of the all-current sensitive differential current transformers is fundamentally different.
Fig.4: Principle fluxgate current measurement technologyThe measuring principle of the SCT5xxx is based on a differential current measurement of two oppositely excited cores in the transformer. For this purpose, both cores are brought into saturation with an excitation winding (red) with an internally generated 32 kHz signal, whereby the first core is driven in the positive and the second in the negative range of the y-axis. See fig.)
Fig.5: Characteristics fluxgate current measurement technologyThe detection winding now measures the induced current of the excitation winding (blue).
If the measuring current Iprim = 0, then 0 A is also measured, as no compensating current is generated for compensation.
If the exhibition current Iprim is not equal to 0, a compensating current is generated through both cores, which compensates for the imbalance of the magnetic flux density B in core 1 and core 2. Due to the compensation, Isense is 0 again.
The measured compensating current provides information about the current to be measured Iprim.
Together with a fixed excitation frequency, this leads to improved accuracy and stability.
General description of the fluxgate current measurement technology
The SCT series SCT5xxx is used for monitoring differential currents in electrical power supply systems that do not require fast system shutdown. The SCT5xxx type B/B+ can measure DC and AC residual currents at frequencies up to 100 kHz.
This makes this differential current transformer compatible with a wide range of industrial applications, loads and power sources. With its user-selectable settings, this series provides a flexible platform for differential current measurement suitable for any possible application, both at the time of industrial plant design and when expanding with new modern loads operating at DC voltages or high switching frequencies that increase the amount of leakage current in the system.
The SCT5xxx have an analog 4 - 20 mA output, which represents the real-time RMS value (TRMS) of the measured residual current for connection to a PLC, for example. In addition, a potential-free relay output (NO / NC) with a freely selectable residual current limit can be used for warning or even system shutdown if the TRMS residual current measured value has exceeded the preset value. The status of the relay output is replicated on an LED for visual indication on the device itself. A built-in test button and an external test button input are provided for periodic testing of the SCT5xxx according to the applicable product standards.