Beckhoff SCT0 Series Operator's manual

Documentation | EN
SCT0xxx
Coil current transformers
2023-08-01 | Version: 1.4

Table of contents
SCT0xxx 3Version: 1.4
Table of contents
1 Foreword....................................................................................................................................................5
1.1 Notes on the documentation .............................................................................................................5
1.2 Safety instructions.............................................................................................................................5
2 Product overview ......................................................................................................................................8
2.1 Introduction .......................................................................................................................................8
2.2 Basics current transformers ..............................................................................................................9
2.3 Product categories – SCTxxxx current transformer ........................................................................14
2.4 Notes on class accuracy SCT transformers....................................................................................23
3 Technical data .........................................................................................................................................24
3.1 SCT0xxx | General .......................................................................................................................... 24
3.2 SCT0111 | Coil current transformers for primary currents 0...1 A AC to 0...30 A AC, accuracy class
1, size 1...........................................................................................................................................26
3.3 SCT0111 | Coil current transformers for primary currents 0...1 A AC to 0...30 A AC, accuracy class
0.5, size 1........................................................................................................................................27
4 Commissioning .......................................................................................................................................28
5 Application example ...............................................................................................................................31
5.1 Power measurement at a machine .................................................................................................31
6 Appendix..................................................................................................................................................33
6.1 Documentation issue status ............................................................................................................33
6.2 Support and Service........................................................................................................................34

Table of contents
SCT0xxx4 Version: 1.4

Foreword
SCT0xxx 5Version: 1.4
1 Foreword
1.1 Notes on the documentation
Copyright
© Beckhoff Automation GmbH & Co. KG, Germany.
The reproduction, distribution and utilization of this document as well as the communication of its contents to
others without express authorization are prohibited.
Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a
patent, utility model or design.
Disclaimer
The documentation has been prepared with care. The products described are, however, constantly under
development.
We reserve the right to revise and change the documentation at any time and without prior announcement.
No claims for the modification of products that have already been supplied may be made on the basis of the
data, diagrams and descriptions in this documentation.
EtherCAT® is registered trademark and patented technology, licensed by Beckhoff Automation GmbH,
Germany.
Trademarks
Beckhoff®, TwinCAT®, TwinCAT/BSD®, TC/BSD®, EtherCAT®, EtherCATG®, EtherCATG10®, EtherCATP®,
SafetyoverEtherCAT®, TwinSAFE®, XFC®, XTS® and XPlanar® are registered trademarks of and licensed by
Beckhoff Automation GmbH. Other designations used in this publication may be trademarks whose use by
third parties for their own purposes could violate the rights of the owners.
Patent Pending
The EtherCAT Technology is covered, including but not limited to the following patent applications and
patents: EP1590927, EP1789857, EP1456722, EP2137893, DE102015105702 with corresponding
applications or registrations in various other countries.
Intended audience
This description is only intended for the use of trained specialists in control and automation engineering who
are familiar with the applicable national standards.
It is essential that the documentation and the following notes and explanations are followed when installing
and commissioning these components.
It is the duty of the technical personnel to use the documentation published at the respective time of each
installation and commissioning.
The responsible staff must ensure that the application or use of the products described satisfy all the
requirements for safety, including all the relevant laws, regulations, guidelines and standards.
1.2 Safety instructions
Description of instructions
In this documentation the following instructions are used.
These instructions must be read carefully and followed without fail!

Foreword
SCT0xxx6 Version: 1.4
DANGER
Serious risk of injury!
Failure to follow this safety instruction directly endangers the life and health of persons.
WARNING
Risk of injury!
Failure to follow this safety instruction endangers the life and health of persons.
CAUTION
Personal injuries!
Failure to follow this safety instruction can lead to injuries to persons.
NOTICE
Damage to environment/equipment or data loss
Failure to follow this instruction can lead to environmental damage, equipment damage or data loss.
Tip or pointer
This symbol indicates information that contributes to better understanding.
Exclusion of liability
All the components are supplied in particular hardware and software configurations appropriate for the
application. Modifications to hardware or software configurations other than those described in the
documentation are not permitted, and nullify the liability of Beckhoff Automation GmbH & Co. KG.
Personnel qualification
This description is only intended for trained specialists in control, automation and drive engineering who are
familiar with the applicable national standards.
Intended use
If the equipment is used in a manner not specified by the manufacturer, the protection provided by the
equipment may be impaired
Safety regulations
Please note the following safety instructions and explanations!
Product-specific safety instructions can be found on following pages or in the areas mounting, wiring,
commissioning etc.
Current transformer safety instructions
The following points must be noted:
• The applicable laws, standards and regulations.
• The state of the art at the time of installation.
• The technical rules.
• The operating instructions.
• The fact that operating instructions can only list general regulations and that these regulations must be
followed.
• Check the device carefully for transport damage prior to commissioning. The device must not be put
into operation if it is mechanically damaged.
• The devices described are intended for installation by qualified electricians and may only be installed in
electrical plant rooms or in closed housings. Any other use or the disregard of these application notes
will result in the loss of the warranty/guarantee.

Foreword
SCT0xxx 7Version: 1.4
• The devices may only be installed in dry indoor rooms.
• Do not mount on highly flammable materials.
• Operation with a higher current than the rated current specified on the name plate can lead to
overheating of the current transformer and thus to burns.

Product overview
SCT0xxx8 Version: 1.4
2 Product overview
2.1 Introduction
SCTxxxx | Current transformers for power measurement
Fig.1: SCT current transformers
The SCT current transformers allow reliable power sensor technology to be implemented directly in the field
as an integral part of the PC-based control system. Users can choose between two concepts, which are
highly scalable thanks to various designs and performance classes and are thus suitable for any application.
The SCT series portfolio is extremely diversified, ranging from the low-cost 3-phase transformer sets for
properties and standard industrial transformers for mechanical engineering, through to solutions for test
benches with particularly high requirements for accuracy.
The choice of the right product category [}14] depends on the type of usage:
Whilst the data acquisition can be implemented cost-efficiently and with high measurement accuracy using
the ring-type current transformers, particularly in new systems, the split-core current transformers are
suitable as an uncomplicated retrofit solution due to the simplicity of their attachment.
The SCT5xxx transformers occupy a special position. These are not intended for energy measurement, but
are specially designed for highly accurate detection of differential currents. In addition, unlike the other SCT
transformers, they are also suitable for DC currents and thus meet the differential current detection
according to the Type B definition. Therefore, AC as well as DC currents up to 100 kHz can be measured by
a fluxgate measuring principle.

Product overview
SCT0xxx 9Version: 1.4
2.2 Basics current transformers
Basic information on the technology area of current transformers is given in the following. The information is
of general nature; so it is imperative to check the extent to which these notes apply to your specific
application.
Function and design
A current transformer is a transforming device that transforms an input current into a processable current
signal at the output. A current transformer is mainly used to transform currents of large magnitudes to directly
measurable, smaller values in the milliampere or small ampere range. With a classic current transformer, the
input current is proportional to the output current. Due to the physical principle and the mechanical
construction, the current signal is transmitted galvanically isolated to the evaluation electronics.
A current transformer basically consists of a small number of windings on the primary side and a larger
number of windings on the secondary side. The current to be converted flows through the primary side. The
windings are usually wound on an alternating magnetic ferrite ring core.
A typical transformer type is the ring core or ring-type current transformer. The current rail or current-carrying
cable is often used as the primary winding, which is guided through the toroidal core of the transformer.
Thus, the rail or line forms the primary winding with one turn. The secondary winding is located on the ring
core. The transformation is determined by the ratio of the number of primary and secondary windings. The
classic structure of a ring-type current transformer is shown in the following figure.
Fig.2: Principle ring-type current transformer
Another classic type is the coiled current transformer. In this type of transformer, the primary winding is a
current-carrying wire which is wound around the ring core on the primary side. In this case, the primary
winding number is >1, but smaller than the secondary winding number. The principle is shown in the
following figure

Product overview
SCT0xxx10 Version: 1.4
Fig.3: Principle coil current transformer
WARNING
Dangerous voltages with secondary side not connected
The secondary winding must be connected to a current measuring device or short-circuited, otherwise high
core losses or dangerous voltages may occur on the secondary side. Before replacing the measuring
electronics in the secondary circuit, the current transformer must therefore be short-circuited at its
secondary terminals.
Grounding of secondary terminals
According to DIN VDE 0141 (01/2000) paragraph 5.3.4, current and voltage transformers for
nominal voltages from Um=3.6kV must be grounded on the secondary side. For low voltages
(Um≤1.2kV), grounding is not required if the transformer housings do not have any metal surfaces
with large contact areas.
Characteristic values and calculation
In principle, the construction, and thus also the calculation, correspond to a normal transformer. The basic
relationship between input and output current is determined by the ratio of the number of turns N of the
primary and secondary sides. An important characteristic value in the design of a current transformer is
therefore the transformer ratio.
IOut = N1/N2 * IIn

Product overview
SCT0xxx 11Version: 1.4
Technical terms of current transformers
Term Explanation
Primary rated current Ipr (alternative
symbol IN)
Value of the rated current on the primary side
Secondary rated current Isr Value of the rated current on the secondary side.
Rated power SrValue of apparent power (in [VA]) that the transformer can deliver
to the secondary circuit at secondary rated current and rated load
Rated frequency fRValue of the rated frequency.
Accuracy class Indication that the measurement deviations are within specified
limits under prescribed conditions of use.
Rated insulation level UmHighest voltage; RMS value of the highest conductor-to-conductor
voltage for which a measuring transformer is rated with respect to
its insulation
The value of the rated insulation level is given in three values:
1. maximum value of the conductor-to-conductor voltage for which
the insulation of the transformers is designed;
2. value of the rated short-duration power frequency withstand volt-
age (50Hz, 1min), with which the insulation safety of the de-
vices is tested
3. value of the surge voltage level (this specification is mostly un-
occupied here, since according to IEC61869/1 a specification is
only required for transformers with a conductor-to-conductor
voltage of >1.2kV)
Overcurrent limiting factor (FS) Ratio of rated limiting current to primary rated current.
Rated continuous thermal current Icth Value of the continuous current in the primary winding at which the
overtemperature does not exceed the value specified in the
standard, with the secondary winding loaded with the rated load.
Rated short-time thermal current Ith Value of short-time current for a limited time in the primary winding
at which the overtemperature does not exceed the value specified
in the standard, with the secondary winding loaded with the rated
load.
Rated peak current Idyn Maximum value of the primary current whose electromagnetic force
effect does not cause electrical and mechanical damage to the
current transformer with short-circuited secondary winding.
"Open voltage" of
current transformers
Current transformers which are not directly connected to a load
must be short-circuited on the secondary side for safety reasons!
A current transformer operated open on the secondary side induces
very high peak voltage values at its secondary terminals. The
magnitudes of these voltages can reach values of up to several
kilovolts, depending on the dimensioning of the current transformer,
and thus represent a danger to persons and the functional safety of
the transformer. For safety reasons, open operation should
generally be avoided in order to prevent magnetization of the core
iron during secondary open operation.
Grounding of secondary terminals According to DIN VDE0141 (01/2000) paragraph 5.3.4, current and
voltage transformers for nominal voltages from Um=3.6kV must be
grounded on the secondary side. For low voltages (Um≤1.2kV),
grounding is not required if the transformer housings do not have
any metal surfaces with large contact areas.

Product overview
SCT0xxx12 Version: 1.4
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 technology
The measuring principle of the SCT5xxx is based on a differential current measurement of two oppositely
excited cores in the transducer. 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.)

Product overview
SCT0xxx 13Version: 1.4
Fig.5: Characteristics fluxgate current measurement technology
The detection winding now measures the induced current of the excitation winding (blue). If the measuring
current Iprim is 0, then 0A is also measured, since no compensating current is generated for compensation.
If the measuring current Iprim is not equal to 0, a compensating current is generated through both cores, which
again compensates for the disproportion 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.
Only a single 24Vdc power supply should be provided for the SCT5xxx.

Product overview
SCT0xxx14 Version: 1.4
2.3 Product categories – SCTxxxx current transformer
Breakdown of the type designation of the SCT current transformer
Fig.6: Designation key of the SCT current transformers

Product overview
SCT0xxx 15Version: 1.4
Coil current transformers
Fig.7: SCT0xxx
In order to guarantee the power transmission, current transformers need a correspondingly large measuring
core volume with decreasing primary nominal currents. The dimensions of standard current transformers
would quickly hit their limits on the basis of this physical principle. The SCT0xxx coil current transformers
with electrical isolation are specially designed for these low primary nominal currents and are used in
corresponding applications.
Coil current transformers
SCT0111 Accuracy class 1,
Primary current 0...1AAC to 0...30AAC,
Secondary current 1AAC
SCT0121 Accuracy class 0.5,
Primary current 0...1AAC to 0...30AAC,
Secondary current 1AAC

Product overview
SCT0xxx16 Version: 1.4
Mini ring-type current transformer
Fig.8: SCT1xxx
The SCT1111 mini ring-type current transformer can be positioned on a DIN rail by means of snap-on
mounting and is thus suitable for measurements in very tight installation spaces, e.g. directly in the sub-
distribution unit. Two current transformers are attached to the DIN rail, while the third current transformer is
plugged into the fastened current transformers. The connection is realized via removable picoMAX®
connectors, which enables pre-wiring.
Mini ring-type current transformer
SCT1111 Accuracy class 1,
Primary current 0...32AAC to 0...64AAC,
Secondary current 1AAC,
Max. diameter round conductor 7.6mm (size 1)

Product overview
SCT0xxx 17Version: 1.4
Ring-type current transformer
Fig.9: SCT2xxx
The SCT2xxx series offers a large selection of ring-type current transformers for primary currents from 60 to
2500A in six sizes and two accuracy classes. The innovative screwless connection technology for rigid and
flexible conductors saves time – ferrules can be dispensed with here.

Product overview
SCT0xxx18 Version: 1.4
Ring-type current transformer
SCT2111 Accuracy class 1,
Primary current 0...60AAC to 0...500AAC,
Secondary current 1AAC,
Max. diameter round conductor 25.7mm (size 1)
SCT2121 Accuracy class 0.5,
Primary current 0...125AAC to 0...600AAC,
Secondary current 1AAC,
Max. diameter round conductor 25.7mm (size 1)
SCT2211 Accuracy class 1,
Primary current 0...600AAC / 750AAC,
Secondary current 1AAC,
Max. diameter round conductor 31.8mm (size 2)
SCT2221 Accuracy class 0.5,
Primary current 0...600AAC / 750AAC,
Secondary current 1AAC,
Max. diameter round conductor 31.8mm (size 2)
SCT2311 Accuracy class 1,
Primary current 0...800AAC / 1000AAC,
Secondary current 1AAC,
Max. diameter round conductor 43.7mm (size 3)
SCT2321 Accuracy class 0.5,
Primary current 0...800AAC / 1000AAC,
Secondary current 1AAC,
Max. diameter round conductor 43.7mm (size 3)
SCT2411 Accuracy class 1,
Primary current 0...1250AAC / 1500AAC,
Secondary current 1AAC,
Max. diameter round conductor 43.7mm (size 4)
SCT2421 Accuracy class 0.5,
Primary current 0...1250AAC / 1500AAC,
Secondary current 1AAC,
Max. diameter round conductor 43.7mm (size 4)
SCT2515 Accuracy class 1,
Primary current 0...2000AAC,
Secondary current 5AAC,
Max. diameter round conductor 54.7mm (size 5)
SCT2525 Accuracy class 0.5,
Primary current 0...2000AAC,
Secondary current 5AAC,
Max. diameter round conductor 54.7mm (size 5)
SCT2615 Accuracy class 1,
Primary current 0...2500AAC,
Secondary current 5AAC,
Max. diameter round conductor 70mm (size 6)
SCT2625 Accuracy class 0.5,
Primary current 0...2500AAC,
Secondary current 5AAC,
Max. diameter round conductor 70mm (size 6)

Product overview
SCT0xxx 19Version: 1.4
3-phase ring-type current transformers
Fig.10: SCT3xxx
The compact SCT3xxx 3-phase ring-type current transformers for direct mounting below commonly used
power switches measure primary currents from 3 x 50 to 3 x 600A, with secondary currents of 1 or 5A. The
SCT3xxx series is available throughout in accuracy class 1 and is supplemented by the SCT3121-0125 and
SCT3121-0150 current transformers in accuracy class 0.5.
3-phase ring-type current transformers
SCT3111 Accuracy class 1,
Primary current 3 x 0...50AAC to 3 x 0...150AAC,
Secondary current 1 A AC,
Max. diameter round conductor 13.5mm (size 1)
SCT3121 Accuracy class 0.5,
Primary current 3 x 0...125AAC / 3 x 0...150AAC,
Secondary current 1A,
Max. diameter round conductor 13.5mm (size 1)
SCT3215 Accuracy class 1,
Primary current 3 x 0...100AAC to 3 x 0...250AAC,
Secondary current 5AAC,
Max. diameter round conductor 18mm (size 2)
SCT3315 Accuracy class 1,
Primary current 3 x 0...250AAC to 3 x 0...600AAC,
Secondary current 5AAC,
Max. diameter round conductor 22 mm (size 3)

Product overview
SCT0xxx20 Version: 1.4
Ring-type current transformer for differential current measurement
Fig.11: SCT5xxx
The increasing prevalence of DC loads (e.g., LED lighting, DC motor drives, 48VDC bus systems, etc.),
distributed DC generation (e.g., PV systems, UPS, batteries, etc.), and high-frequency converters (e.g.,
SMPS, motor drives, etc.) in industrial environments makes it increasingly difficult to reliably measure
insulation faults with conventional current transformers designed for AC 50/60 Hz with limited measurement
bandwidth.
Differential current transformers of the SCT5xxx series can be used here. Monitoring residual currents with
the SCT5xxx in real-time in a power system opens up the possibility of evaluating the condition of the
electrical insulation based on the actual measured value, so that the long-term trend of the residual current
value can be used for planning maintenance to detect significant deterioration of the insulation.
This means that residual current monitors (SCT5xxx) used in a condition-based monitoring scheme Industrie
4.0-Standards, 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.
Ring-type current transformer for differential current measurement
SCT5564 Measuring ranges 400mA / 2A, type B / B+, transformer opening 70mm