In industrial induction heating applications the RCTi is often used to monitor both current amplitude and zero-crossing detection. Typically the RCTi provides the feedback signal to a voltage-fed medium frequency inverter, for example to an SCR firing control board. Measured currents range from 500A to 5,000A and the frequency varies from a few hundred Hz to 10kHz. The phase error of the measurement needs to be tightly controlled for accurate zero crossing detection. The RCTi has a very small and highly predictable phase error over this frequency range. In addition to its wide-band operation, the RCTi fits the application perfectly due to its easy installation, high reliability and small size.
Power Utilities and Renewable Technologies
The RCTi-3ph unit has been deployed in energy storage systems at the electrical grid distribution / residential level (120V / 240V, split-phase, 60Hz) to help mitigate the effects of high levels of penetration of PV (Photovoltaics) in neighbourhood supplies. These effects include load shifting, peak shaving and solar firming. The RCTi measures currents of 250A (RMS, sinusoidal), 60Hz nominal, 59.3 - 60.5 Hz range, with harmonics of interest up to 40th harmonic (2.5kHz). The RCTi-3ph unit is used to measure and report the grid/load current back to the controller of the storage system. The RCTi measurement allows for better control and management of power and energy flow in the system via the derivation of reported variables such as, power (active, reactive, apparent), power factor angle, as well as net energy usage.
The RCTi enables easy hook-up (particularly with the BNC option allowing easy cable installation through conduit) and has a simple output to the A/D on the data acquisition board with minimal scaling required. Finally it has an internal isolated supply in to separate control grounds which allows for reductions in EMI through simple shielded cabling and grounding.
Similar to the solar application the RCTi has been permanently installed in a sub-station connecting the electrical grid to an offshore wind-farm. The RCTi is mounted on various incoming feeds, they are all screened cables but the installations range from 132kV / 600A to 690V / 6,000A. A number of these feeds are outdoor, and PEM has supplied our RCTi transducer with suitable insulation for long term outdoor installation. The RCTi is connected to a portable power quality monitor and this in turn to a wireless transmitter which sends data about the load current on a continuous basis back to the sub-station control centre (e.g. magnitude, power factor, harmonic strength etc).
High Voltage DC (HVDC) Applications
The RCTi can be used in a wide variety of HVDC operations. Ostensibly it is used to monitor the steady state ac current inside the valve/switching enclosures. However it is also capable of monitoring large overloads with very high di/dt (over 1000A/µs) for protection purposes. The RCTi transducer is particularly suitable for this application as there is no loss of accuracy or damage when monitoring these over-load surges.
Other applications include
- VSD motor drives and generators
- Large pumps and compressors
- Building services
- Custom versions
- Rogowski coils immersed in transformer oil
- Long coils and cable runs