Smart Load to Reduce VT

AFR 31

The AFR 31 intelligent load is a device designed to protect voltage measuring transformers from the harmful effects of ferroresonance in medium voltage distribution networks with an unearthed or indirectly earthed neutral conductor. Ferroresonance occurs between the inductance of the transformer and the capacitance of the lines or medium voltage switching elements.

Triggers can be switching on/off, grounding, or other transient phenomena. Ferroresonance results in significant overvoltage and current peaks due to the saturation of the transformer’s magnetic circuit. This often leads to the destruction of the measuring transformer.

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Description

The AFR 31 intelligent load is a device designed to protect voltage measuring transformers from the detrimental effects of ferroresonance in medium voltage distribution networks with an unearthed or indirectly earthed neutral conductor. Ferroresonance arises from the interaction between the inductance of the transformer and the capacitance of the lines or medium voltage switching elements.

Triggers can include switching events, grounding, or other transient phenomena. Ferroresonance causes significant overvoltage and current peaks due to the saturation of the transformer’s magnetic circuit, often leading to the destruction of the measuring transformer. The AFR 31 acts as protection for voltage measuring transformers against these effects.

Unlike other methods, the AFR 31 is specifically activated only during the occurrence of ferroresonance and remains inactive during normal operation or even in asymmetric loads. It allows for the setting of the activation voltage at 20 V, 25 V, or 30 V and is supplemented with a delayed switching circuit (standardly 4 seconds) to ensure selectivity with ground connection protections. This is useful in cases where the voltage measuring transformer is also used to power protective automations (ground connection monitoring, residual current devices, etc.).

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Parameters

  • Nominal voltage Un: 3 x100/3, 3 x 110/3 nebo 3 x 120/3 VAC
  • Nominal frequency: without jumper: 20 VAC/ jumper 3+4: 25 VAC (standard)/ jumper 1+3: 30 VAC
  • Activation delay: 4,0 s (at the manufacturer, it can be set from 0 seconds to 10 seconds)
  • Overvoltage class: II
  • Protection class: IP20
  • Climatic category: 5/50/40
  • Working / storage temp.: -40 °C to 60 °C / -40 °C to 70 °C
  • Max. moisture: 95% non-condensing
  • Dimension: 69 × 86 × 58 mm / 0,05 kg
  • Enclosure material: polycarbonate.
  • Installation: on a 35 mm DIN rail according to DIN EN 50 022.
  • Wiring: terminal block, conductor cross-section 0.5–2.5 mm2.

Attached files

Data sheets
AFR-31_Manual_Czech_A4.pdf (pdf, 524.7 KB)

Drawing