The IRDH375-435 is a high‑performance insulation monitoring device from Bender, designed for unearthed power systems (IT systems). It provides continuous, real‑time insulation resistance monitoring for AC, AC/DC, and DC main circuits, making it ideal for modern power supply systems that incorporate rectifiers, converters, thyristor‑controlled DC drives, and directly connected DC components. The device complies with IEC 61557‑8 and DIN EN 61557‑8, ensuring reliable safety monitoring for demanding industrial applications.
Key Features & Functions
· Patented AMPPlus Measuring Principle
The IRDH375-435 employs Bender’s patented AMPPlus measuring technology, which delivers precise and accurate monitoring even in systems with extensive DC components and high leakage capacitances. This advanced method ensures reliable performance under challenging operating conditions.
· Automatic Adaptation to System Leakage Capacitance
Modern power systems often generate high leakage capacitances to earth due to interference suppression measures. The IRDH375-435 automatically adapts to the existing system leakage capacitance, optimising measurement time and ensuring dependable operation without manual adjustments. The maximum permissible system leakage capacitance is 500 µF.
· Two Independently Adjustable Response Values
The device features two separately adjustable alarm relays, allowing users to distinguish between pre‑warning and critical alarm. The response value ranges are independently configurable from 1 kΩ to 10 MΩ, offering flexible configuration to meet different system safety requirements.
· Backlit Two‑Line LC Display
Equipped with a clear backlit two‑line LC display, the device presents measured insulation resistance values, system leakage capacitance readings, and configuration menus in an intuitive format, facilitating easy on‑site status checks and parameter adjustments.
· Built‑In Self‑Test and Connection Monitoring
An automatic self‑test function continuously verifies the internal measuring circuits, system control components, and earth connections. Additionally, connection monitoring supervises the integrity of the measuring leads. If any fault is detected, a dedicated system fault relay and LED provide immediate indication, ensuring high functional reliability.
· External Test and Reset Functions
External push‑buttons can be connected to perform device and connection testing, or to clear stored fault messages. This remote operability enhances convenience and safety.
· Extension via Coupling Devices
The nominal voltage range can be extended using appropriate Bender coupling devices, allowing the ISOMETER® to be applied in higher‑voltage systems while maintaining accurate insulation monitoring. With coupling devices, the device can be used for voltages up to DC 0…1760 V or 3/N/AC 0…7200 V.
· De‑Energised System Monitoring
An external supply voltage allows the device to monitor systems even when the main circuit is de‑energised, ensuring continuous safety oversight during maintenance or system shutdown periods.
Technical Specifications
· Nominal system voltage (Uₙ): 3(N)AC 0…793 V / AC/DC 0…793 V; DC 0…650 V
· Frequency range (fₙ): DC, 0.1…460 Hz
· Supply voltage (Uₛ): AC 88…264 V (47…63 Hz); DC 77…286 V or 19.2…72 V
· Response value range (Rₐₙ₁ / Rₐₙ₂): 1 kΩ…10 MΩ, independently adjustable
· Maximum permissible system leakage capacitance: 500 µF
· Measuring principle: AMPPlus (patented adapted measuring pulse method)
· Display: Backlit two‑line LC display
· Alarm relays: Two independent changeover contacts (Alarm 1 and Alarm 2), configurable for N/O or N/C operation
· System fault relay: One changeover contact for device‑internal fault reporting, N/C operation
· Communication interface: None (analogue version)
· Operating temperature: –10 °C…+55 °C
· Protection class: Terminals IP30, enclosure IP20
· Mounting: DIN rail (35 mm)
· Weight: Approx. 1.0 kg
· Standards compliance: DIN EN 61557‑8, IEC 61557‑8
· Required accessories: Coupling devices for extension of nominal voltage range (when required)
Typical Applications
· Industrial IT systems – Insulation monitoring for AC, DC, and combined AC/DC unearthed systems incorporating rectifiers, converters, variable‑frequency drives, and thyristor‑controlled DC drives.
· UPS systems and battery systems – Continuous monitoring of insulation integrity in uninterruptible power supplies and battery backup installations.
· Phase‑controlled heating systems – Ensuring electrical safety in systems with phase‑angle control heating elements.
· Switch‑mode power supply installations – Monitoring insulation resistance in systems with high‑frequency switched power supplies.
· IT systems with high leakage capacitance – Installations where interference suppression filters or long cable runs generate significant leakage capacitance to earth.
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