Accuracy Class for Current Transformers

By tchenwa | Published: April 16, 2019 – 5:18 pm

The Shandong Yuanxing current transformers are designed for the accurate measurement of AC currents up to 120% of the rated primary current. The accuracy of the primary current to secondary signal transformation (either current or voltage) is stated as Accuracy Class. The Accuracy Class for the current transformers is measured in accordance with the IEC61869 standard. The IEC61869-2 standard specifies transformation accuracy for current transformers at different percentage levels of rated primary current and secondary burden levels.

IEC61869 Current Transformer Accuracy Class 0.2:

  • 0.75% ratio error @ 5% of rated primary current,
  • ±0.35% ratio error @ 20% of rated primary current,
  • ±0.20% ratio error @ 100% of rated primary current
  • ±0.20% ratio error @ 120% of rated primary current

IEC61869 Current Transformer Accuracy Class 0.5:

  • ±1.50% ratio error @ 5% of rated primary current,
  • ±0.75% ratio error @ 20% of rated primary current,
  • ±0.50% ratio error @ 100% of rated primary current
  • ±0.50% ratio error @ 120% of rated primary current

The Accuracy Class requirements as applied to a specific model of a current transformer may limit the rated primary current ranges that can meet those accuracy requirements.

CTSB0816 Split-core Current Transformer Accuracy Class 0.5:

Accurate measuring range is 5%-120% of rated primary current, for rated primary currents from 500A-2,000A (e.g. models CTSB0816-500A/ 5A to CTSB0816-2000A/ 5A).

  • CT rated primary current of 500A: Class 0.5 measurement range would be 25A to 600A.
  • CT rated primary current of 2,000A: Class 0.5 measurement range 100A to 2,400A
Accurate measuring range is 1%-120% of rated input current, for rated primary currents from 2,000A-5,000A;
  • CT rated primary current of 2,000A: Class 0.5 measurement range would be 20A to 2,400A.
  • CT rated primary current of 5,000A: Class 0.5 measurement range 50A to 6,000A



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DC Current Measurement

By tchenwa | Published: April 16, 2019 – 5:02 pm

The non-intrusive measurement of a DC current is accomplished through the use of electronic sensors that use the Hall Effect to monitor and measure electrical currents.

What is the Hall Effect

The Hall Effect is the principle that a magnetic field applied perpendicular to a current will create a proportional Hall voltage perpendicular to the two fields. In a typical application, the DC current in the primary conductor creates the magnetic field which is proportional to the amount of DC current flowing through the conductor.

This magnetic field acts on a current flowing through the Hall Effect sensor resulting in a Hall voltage proportional to the primary conductor DC current. This technology allows non-intrusive DC current and DC pulse measurements.

Open Loop Sensor

The basic Hall Effect electronic sensor is configured as an “open-loop” sensor. It measures the Hall voltage to determine the primary conductor DC current. For example, see our open-loop Hall Effect sensor: HOS-Q11 Open-loop Hall Effect Sensor

Closed Loop Sensor

A “closed-loop” sensor configuration is a more accurate Hall Effect electronic sensor. The “closed-loop” design incorporates a second magnetic field, which is used to offset the primary conductor magnetic field. The amount of power necessary to zero out the primary conductor field is then the representation of the DC primary conductor current. The zeroing of the magnetic flux provides a highly accurate representation of the primary conductor current. For example, see our closed-loop Hall Effect sensor: HCS-C5 Closed-loop Hall Effect Sensor


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AC Voltage Measurement, Intelligent Devices

By tchenwa | Published: February 7, 2019 – 12:24 pm

The accurate measurement of AC Voltage is complicated by the necessity to minimize the burden the measuring instrument places on the primary circuit. The incorporation of a 1:1 current style voltage transformer in the AC voltage measuring circuit offers several advantages.


Features

  • A minimal burden on the primary voltage circuit, with essentially zero primary circuit load,
  • Isolation of the primary AC circuit and the secondary output signal, and
  • Exceptional accuracy with a minimal phase shift.

The AC current style voltage transformer is designed with either a 1mA to 1mA or 2mA to 2mA ratio. An example of the implementation using an operational amplifier I/V (current to voltage) circuit or a resistor sampling circuit;

The input resistor R limits the current to the 1mA or 2mA input. An application note document provide additional information – Application Note 1:1 Voltage Transformer (pdf 510kb).
The TV31 with UL Recognition Certification is an example of a current style AC Voltage Transformer.


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AC Current Measurement, Intelligent Devices

By tchenwa | Published: January 14, 2019 – 8:15 pm

Toroidal, Solid-core Current Transformer - AC Current Measurement - Intelligent DevicesThe Supervisory Control and Data Acquisition (SCADA) systems used by electric utilities to manage the distribution of electric power are highly dependent upon the intelligent, micro-processor based devices installed throughout the electric power distribution grid.

These intelligent devices acquire in real time the critical performance measurements (e.g. current, voltage), transmitting that information back to the central SCADA control center.

The SCADA control center can issue operate commands (CONTROL actions) to the intelligent devices.

These CONTROL actions can operate a switch, operate equipment that adjusts voltage or current, operate equipment that adjusts phase shift or any number of actions necessary to manage the electric power distribution grid.

Intelligent Devices Measurements

The intelligent devices typically measure AC current based upon the secondary output of a primary current transformer, typically 0 to 5 ampere AC.

Transforming the 0 to 5 ampere AC signal to level appropriate to a micro-processor based circuit is handled by solid-core, toroidal current transformers.

The 0 to 5 ampere conductor is looped through the center opening of the current transformer. A solid core current transformer offers superior transformation accuracy at a very competitive component price. Solid-core current transformer can be designed to perform beyond the rated primary before magnetic core saturation offering the ability to measure AC current surges.

The advent of digital signal processors (DSP) offers high signal sampling rates, enabling the measurement of the AC base frequency and the harmonics of the base frequency. Surface Mount Technology (SMT) components offers compact designs capable of operating in harsh operating environments.

3 Phase SCADA Remote Terminal Unit

3 Phase SCADA Remote Terminal Unit A three(3) phase SCADA Remote Terminal Unit (RTU) incorporates analog input measurement of AC current and AC voltage, digital signal processing necessary for the calculation of power, power factor, harmonics amplitudes, etc. and data transmission to the SCADA control center.




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