BENDER WR Transformer Selection

BENDER WR Transformer Selection

The reliability of residual current monitoring and insulation fault location in industrial power distribution, data centers, ships, mines, rail transit, and IT ungrounded systems largely depends on the selection and installation of measuring current transformers. The BENDER WR series rectangular measuring current transformers, including WR70x175S (P), WR115x305S (P), WR150x350S (P), and WR200x500S (P), are designed as high-sensitivity measuring elements for RCM, RCMS, and EDS series evaluation devices. They convert the primary side AC current into an assessable secondary signal for residual current monitoring, insulation fault location, and system status analysis. For engineers who are replacing discontinued modules, optimizing existing monitoring systems, or building new insulation fault location solutions, understanding the structure, parameters, installation specifications, and common fault troubleshooting methods of the WR series is key to ensuring long-term stable operation of the system.

Product positioning and core applications

The WR series belongs to the rectangular open type measuring current transformer, whose main function is to proportionally convert the alternating current generated by the current carrying conductor passing through its inner hole into a measurement signal that can be recognized by the evaluator. It does not directly display residual current, but works in conjunction with RCM, RCMS series residual current monitors or evaluators to form a complete residual current monitoring system. In IT ungrounded systems, the WR series can also be used in conjunction with insulation fault location devices such as EDS470, EDS460/490, EDS440, etc. to measure the positioning current generated by PGH positioning current injectors or ISOMETER IRDH. In other words, the WR series is both a sensor for residual current monitoring and a front-end acquisition unit for insulation fault location systems.

This series of products covers a variety of inner hole sizes, ranging from 70 × 175 mm to 200 × 500 mm, and can adapt to cable, busbar, and conductor combinations of different cross-sections. For ordinary load circuits, WR... S type can be selected; For busbar systems or situations with high load currents, WR... SP type is more suitable. The SP type is equipped with integrated shielding, which can effectively suppress the misoperation of RCM, EDS and other devices caused by high load current or surge current. This feature is particularly important in large-scale industrial power distribution, bus ducts, and transformer outgoing lines.

Model, inner hole size and selection logic

The main models of the WR series are distinguished by inner hole size: WR70x175S (P) inner hole 70 × 175 mm, WR115x305S (P) inner hole 115 × 305 mm, WR150x350S (P) inner hole 150 × 350 mm, WR200x500S (P) inner hole 200 × 500 mm. The "S" in the model represents the standard type, and the "SP" represents the integrated shielding type. The internal dimensions determine the number and cross-section of conductors that can pass through. When selecting, the first step is to confirm the number of conductors, cable outer diameter, or busbar size that need to be passed through simultaneously in the monitored circuit. If the inner hole is too small, the conductor cannot pass through or the installation stress is too high; If the inner hole is too large, although it is easy to install, it may affect the measurement sensitivity. Therefore, the size of the inner hole must match the actual conductor layout.

Next, it is necessary to confirm the load current level. The standard WR... S type is suitable for general load circuits, while the WR... SP type is specifically designed for busbar systems and situations where the load current is ≥ 500 A. SP type integrated shielding can reduce the risk of false alarms caused by external magnetic field interference and high load currents. For frequency converters UPS、 The WR series, in conjunction with RCM and RCMS evaluators, can cover the monitoring needs of AC, DC, and pulsed DC residual currents for devices such as rectifiers and battery chargers that may generate DC components or high-frequency residual currents. If the system is an IT ungrounded system and insulation fault branches need to be located, a WR transformer compatible with the EDS system should be selected, and the evaluator model should be confirmed to support the corresponding positioning current measurement.

Application of SP shielding type and busbar system

In large-scale power distribution systems, busbars typically carry currents of hundreds or even thousands of amperes. High load current will form a strong magnetic field around the transformer. If the shielding is insufficient, interference signals may be induced on the secondary side, leading to false alarms from the residual current monitor or misjudgments from the EDS positioning system. The WR... SP series measuring current transformers have built-in shielding layers, which can significantly reduce such interference. Its design goal is to avoid the erroneous tripping of RCM or EDS devices connected by high load currents or surge currents in the monitored system. Therefore, WR... SP series should be given priority in applications such as bus ducts, main distribution cabinets, transformer outgoing lines, and high-power variable frequency drive cabinets.