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    Current transformers for accurate current measurement in energy monitoring systems

    Choose the right current transformer

    Current transformers are generally used to make measurement currents greater than 5A suitable for kilowatt-hour meters and analysers. We can distinguish between 3 types of current transformers:

    • Traditional current transformers (CTs)
    • Low power current transformers (LPCTs)
    • Rogowski coils


    Traditional current transformers    , in a split core version, are ideally suited for use in existing installations without disconnecting the primary conductor. fortop has an extensive range of split core current transformers.

    Low power current transformers     are mainly used for low measurement currents with high accuracy requirements. They are cost-effective, and the use of short-circuit terminals is not necessary.

    Rogowski coils     are ideal for measuring high measurement currents and for use around copper busbars.

    On this advice page, you will find, by type of current transformer, a handy overview to easily and quickly find the right current transformer for your application or meter/analyser.

    View specifications current transformers

    TQ-series current transformers - ELEQ

    Overview current transformers with conventional ../1A output

    Overview of conventional models of current transformers
    Description Compact transformer Power sensor Split core current transformer "click and go"
    Type RM27 VCT32 TQ30 TQ40-B TQ40-C TQ50-E TQ50-L
      Current transformer RM 27 - ELEQ Current transformer VCT32 - ELEQ Current transformer TQ30 - ELEQ Current transformer TQ40-B - ELEQ Current transformer TQ40-C - ELEQ Current transformer TQ50-E - ELEQ Current transformer TQ50-L - ELEQ
    Transformer width 27 mm 32 mm 36 mm 48,8 mm 48,8 mm 66 mm 66 mm
    Transformation ratio
      35/1A 35/1A 60/1A 100/1A 200/1A 250/1A 250/1A
      64/1A 64/1A* 75/1A 125/1A 250/1A 300/1A 300/1A
      - - 100/1A 150/1A 300/1A 400/1A* 400/1A*
      - - 125/1A 200/1A 400/1A 500/1A* 500/1A*
      - - 150/1A 250/1A 500/1A* 600/1A* 600/1A*
      - - 200/1A* - - 750/1A* 750/1A*
      - - 250/1A* - - 800/1A* 800/1A*
      - - - - - 1000/1A* 1000/1A*
    Other specifications
    Type of current transformer Type of current transformer N/A Split core
    Class 1 1/0,5* 3/1* 1 1/0,5* 1/0,5* 1/0,5*
    Connection of secondary measuring line Connector 1,5 mm² 3 m kabel / 0,5 mm² 5 m kabel / 0,5 mm²
    Max. cable diameter 7,5 mm 16 mm² 18 mm 18 mm 28 mm 42 mm 2 x 42 mm

    Measuring with low-power current transformers

    In addition to conventional current transformers, it is also possible to opt for low power current transformers. Low power current transformers are safer and easier to use than standard current transformers. They contain an internal resistor that prevents the occurrence of high voltages, thereby reducing the risk of sparking and making a short-circuit block unnecessary. Additionally, they provide an output of 333mV, making the installation safer.

    Beyond the safety benefits, low power current transformers offer several other advantages. They allow the use of thinner and longer cables without affecting the measurement results. Furthermore, the use of connectors is possible, and they are cheaper and more compact.

    Specialist low power analysers or current measurement modules are required for connecting low power current transformers. Below is a clear overview of the different low power current transformers and the analysers or current measurement modules they can be connected to.

    Measuring with low-power current transformers

    Overview low power current transformers with ../333mV output

     

    For connection to:   UMG 96-PQ-L-LP    and    800-CT8-LP*
    Series TQ30 TQ40 TQ50 CT CT-BSC CT-SC
      Current transformer TQ30 Current transformer TQ40 Current transformer TQ50 Current transformer CT-009-500-50 & CT-012-500-100 Current transformer CT-019-500-250 Current transformer CT-BSC-021-000-600 Current transformer CT-BSC-050-000-1200 & CT-BSC-050-000-2500 Current transformer CT-SC-006-500-20 Current transformer CT-SC-010-500-50 & CT-SC-010-500-75 Current transformer CT-SC-012-500-75 Current transformer CT-SC-016-500-100 Current transformer CT-SC-024-500-100, CT-SC-024-500-200 & CT-SC-024-500-250 Current transformer CT-SC-036-500-400 & CT-SC-036-500-600
    Transformation ratio
      3A-300A
    /333mV    		 5A-480A
    /333mV    		 Temporarily unavailable 50A/333mV 250A/333mV 600A/333mV 1200A/333mV 20A/333mV 50A/333mV 75A/333mV 100A/333mV 100A/333mV 400A/333mV
      - - - 100A/333mV - - 2500A/333mV - 75A/333mV - - 200A/333mV 600A/333mV
      - - - - - - - - - - - 250A/333mV -
    Other specifications
    Type of current transformer Split core Split core Split core Solid core Solid core Split core Split core Split core Split core Split core Split core Split core Split core
    Secondary measurement lead connection 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 Screw
    connection    		 Screw
    connection    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed    		 5 meter
    fixed
    Max. cable diameter 18 mm 28 mm 42 mm

    0.9 mm
    (50A)

    12.3 mm
    (100A)

    		 19.3 mm 21 x 51 mm

    50 x 90 mm
    (1200A)

    80 x 120 mm
    (2500A)

    		 6.1 mm 9.5 mm 12 mm 16 mm 23.3 mm 35.3 mm
    Class 1 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5
     

    * The 800-CT8-LP current measurement module is suitable for connection to the main modules UMG 800 and UMG 801.

     

     

    Low power current transformers for:  800-CT24* current measurement module
    Series CT24-SC
      CT24-SC current transformer 25cm | fortop CT24-SC current transformer 200cm | fortop CT24-SC current transformer 25cm | fortop CT24-SC current transformer 200cm | fortop
    Transformation ratio
      50A/333mV 50A/333mV 100A/333mV 100A/333mV
      75A/333mV 75A/333mV - -
    Other specifications
    Type of current transformer Split core Split core Split core Split core
    Secondary measurement lead connection 25 cm with molex connector 200 cm with molex connector 25 cm with molex connector 200 cm with molex connector
    Max. cable diameter 10.2 mm 10.2 mm 12.5 mm 12.5 mm
     

    * The 800-CT24 current measurement module is suitable for connection to the main modules UMG 800 and UMG 801.
      To connect the 800-CT24, the 800-CON-RJ45 communication module is required.

    Rogowski coils

    Rogowski coils are a special type of current measuring device without a magnetic core. This clearly distinguishes Rogowski coils from traditional current transformers. The Rogowski coils, named after Walter Rogowski, use a wire wound in a helical structure. This coil generates a voltage corresponding to the change in current through the conductor.

    One of the advantages of Rogowski coils is that they can measure very high currents without saturating. They are therefore linear over a wide range, with an output signal that is proportional to the measured current. Other advantages include easy installation in difficult locations, the possibility of large through-hole openings, the coils being electrically isolated from the circuit being measured, and a wide frequency range.

    Despite the many advantages, Rogowski coils also have disadvantages. For example, they are sensitive to external magnetic fields, and their accuracy can depend on the exact positioning around the conductor. Additionally, their performance can be (adversely) affected by temperature fluctuations.

    The table below provides a clear overview of the Rogowski coils.

    Rogowski coils

    Overview Rogowski coils

    Overview Rogowski coils
    For connection to

    UMG 96-PQ-L-LP

    RogoTrans converter
      Rogo Coil - Rogowski coil - Flexible current transformer- Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza Rogo Coil - Rogowski coil - Flexible current transformer - Janitza
    Max. cable diameter (mm) 120 mm 200 mm 290 mm 390 mm 580 mm 70 mm 175 mm 300 mm
    Output 100mV/1kA 22,5mV/1kA
    Max. primary current 8000A 8000A
    Secondary measurement lead connection 3 meter fixed
    Article numbers
      JA901971 JA901972 JA901973 JA901974 JA901975 JA900249 JA900250 JA900251

    Current transformer for use in combination with three-phase switch (rm27)

    Current measurement at a lower level is necessary in many installations. Relatively low values are measured at this low level and the available space is minimal. In addition, the measurements must meet high accuracy (minimum class 1).

    Most compact IEC transformer for accurate current measurement

    The compact RM27 current transformer is the smallest current transformer on the market and has been specially designed for use in combination with digital measuring systems. The small current transformer is also suitable for use on a three-phase automatic switch with a 17.5 mm distance between the phases. The RM27 is supplied with a connector with terminal technology for mounting on secondary connections. Optionally, mounting on a DIN rail or clip for screw mounting is possible.

    Features RM27 compact current transformer:

    • Ideal for detailed current measurements at level 4, where no direct energy meters can be used
    • Easy to integrate with the Wago Picomax connector
    • Meets the requirements of IEC61869-2
    • Ideal for detailed flow measurements up to automatic level
    • Primary lead-through opening suitable for cable Ø7.5 mm
    • Super compact, suitable for use on a 3-phase machine
    • Accuracy class 1, suitable for energy monitoring
    • Output power tailored to modern meters such as Janitza
    • Available in 35/1A and 64/1A transfer ratios
    • Also suitable for mounting on a DIN rail with optional adaptor

     

    View specifications RM27 compact current transformer

    RM27-series current transformers - ELEQ
    Current transfer with fuse connection - ELEQ

    Current transformer with a fused voltage tap (VCT)

    To measure power, the voltage and current values of each phase must be known. The power sensor (VCT) from ELEQ combines three functions in one product: the fused voltage tap, the current transformer and the connection terminal.

    One product for voltage and current measurements

    The VCT32 from ELEQ combines accurate current measurement and fused voltage branching and a 16mm² connection terminal in one product. By applying the VCT32, the chance of connection errors is minimised, higher safety requirements are met, less installation space is required and the costs for installation are reduced.

    Characteristics of current transformer with fused connection (VCT32):

    • Minimising connection errors through three-in-one product
    • To be mounted on DIN rail or on the mounting plate
    • Easy to install
    • Specifically developed for power measurements up to 64A
    • Including specialist short-circuit proof (70kA) SIBA fuse (2A)
    • Available in transfer ratios 32 / 1A and 64 / 1A
    • Accuracy class 1 for the current transformer

     

    View specifications current transfer with fuse connection

    Compact split core current transformer for cables

    Quickly perform accurate flow measurements in small spaces or existing installations with the TQ line split core current transformers from ELEQ.

    Simple and efficient flow measurement

    Current transformers are easy to install due to the compact design, the hinge construction, and the supplied cable tie around the transformer to mount the insulated conductor. The long color-coded secondary connections ensure that the transformer is seamlessly connected to the energy meter.

    The specified power rating applies at the end of the secondary branches and is adjusted to modern energy measurement devices such as the Janitza meters. The transformers meet the requirements of IEC61869-2, which guarantees accuracy.

    Features of the TQ series split core current transformers:

    • Compact and hinged for easy installation
    • Suitable for the insulated conductor
    • Suitable for energy measurement
    • Colour-coded connections simplify assembly
    • Available in different variants and transfer ratios (see table)

     

    View specificaties TQ series current transformers

    TQ series current transformers - ELEQ

    Split core current transformers - TQ-series

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