RCTrms 3-phase

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  • Overview
  • Performance
  • Applications
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Overview

The RCTrms-3ph is a 3-channel version of the RCTrms industrial current transducer. Available as an industry standard 4-20mA output or 0-5Vdc, the RCTrms-3ph is ideal for process control, status alarming or system monitoring purposes. The RCTrms is an ac current transducer for permanent installation. Simple to install and easy to retrofit it combines the benefits of a thin, flexible, clip-around Rogowski (sense) coil with a signal conditioner providing accurate, true rms measurement, of ac current.

Typically the RCTrms is used with SCADA systems, PLCs, data loggers and protection equipment.

Standards and Approvals

  • CE marked
  • Complies with EMC EN 61326-1 2006
  • Complies with IEC61010-1:2001
  • PEM Ltd is an ISO9001:2008 registered company

Performance

Rated current (rms)

100A to 50kA

Rated output (Full scale FS)

4 to 20mA - or - 0 to 5Vdc

Output limit

150% FS (28mA or 7.5V)

Supply voltage (wide input)

12Vdc (-10%) to 24Vdc (+20%)

Maximum input power

2.1W (at rated output)

Operating temperature range

–5℃ to +65℃ (Integrator electronics)

 

–20℃ to +80℃ (Coil and cable)

Bandwidth (-3dB)

2Hz to 100kHz

Max. Response time (10 to 90%)

1000ms

Accuracy (typ.)

±1.0% of reading (0-5V)

±1.5% of reading (4-20mA)

 

(5% to 150% FS, 25℃)

Output load

< 300Ω (Current Output)

>1kΩ (Voltage Output)

Coil Length

300mm, 500mm or 700mm (Custom lengths available)

Cable Length (coil to integrator)

1m or 2.5m (Custom lengths available)

Features

  • Traceable calibration (certificate included)
  • No magnetic materials means excellent linearity < 0.2% reading
  • Fully isolated measurement
  • Isolated power supply 2kVdc
  • Coil rated at 2kVpeak (withstand test is 4kVrms / 50Hz / 60 sec)
  • Small DIN rail (or panel mount) enclosure – UL94 V-0 rated

Options

  • Isolated BNC-BNC cable split option between coil and electronics to enable ease of installation e.g. threading through existing conduit. Standard cable permanently fixed.

Applications

Power utilities

RCTrms used in Arc furnace and other large current applications for process control and monitoringFort Collins Utilities, Light and Power Department has initiated an automation project to monitor co-generation facilities and control and monitor distribution load centres (switches and fuse locations).  Various data is gathered for transmission back to the control room SCADA system using 900MHz wireless technology. All substation feeders are currently monitored by SCADA at the substation, but this only provides a total value for the entire feeder. By applying current monitoring at each 15KV distribution switch using, the RCTrms ac current transducer, exact real time currents may be obtained for long range planning studies and for switching operations during outage restoration. There are about eighty locations in total that require monitoring.

Current tap points are not available on the main feeders so current measurement devices are installed around 600A bolted T bodies and 200A elbows.  This application would be very difficult for traditional iron-cored current transformers (CTs) because of the connection points large size and ‘inconvenient shape’.  Additionally, conventional CTs have the potential for an open circuit secondary which could develop extremely large secondary voltages, the RCTms is intrinsically safe.

The flexible Rogowski coil is very easy to install saving many hundreds of dollars at each of the eighty locations.  The RCTms also offer several other advantages in this application:

  • There is no saturation because unlike conventional CTs, Rogowski transducers do not have an iron core.
  • Clip-on coils eliminate the need for extensive switch modifications (which would be cost prohibitive) or disconnection of the 600A T-bodies to install the sensors.
  • The output of RCTrms transducer is fed directly into the SCADA node (Micro Control Systems SCADA Pack).  No additional expensive signal conditioners are required.

Arc furnaces

RCTrms coils installed on 600A T-bodiesThe RCTrms is ideal for arc furnace applications where accurate measurement of large load currents, in the 10kA to 100kA range, are required. Conductors are often large and the RCTrms can be supplied with coil lengths up to 5.0m if necessary. In one such application the RCTrms is used to monitor three individual secondary currents of a 16MVA submerged arc furnace transformer.  The secondary current is 37.5kA at 60Hz on 3 secondary windings per transformer.  The output of the RCTrms 4-20mA signal is connected to a PLC for continuous monitoring.

The secondary windings of the transformer are connected via multiple contact clamps to the electrodes. Continuous monitoring of the secondary currents using the RCTrms is important to ensure that the secondary currents are all of the same magnitude.  An imbalance in the transformer secondary currents can be used to immediately identify a failure in the electrode contacts. Without current monitoring, the contact failure may not be identified and can lead to reduced transformer lifetime due to localized overheating of the transformer windings.

The paired bus tube configuration of the secondary conductors made installation of standard CT’s impractical. The RCTrms flexible sensing coil was easily installed around the bus tube pairs and provided a simple / cost effective solution for this application.

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
    • Versions with a faster response time units up to 50ms have been supplied
    • Versions with high frequency performance > 100kHz

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