Description
Product Introduction
In industrial power systems with unearthed conductors, an insulation fault can remain undetected until a second fault creates a more serious electrical risk. The Bender IRDH275BM-727 is an ISOMETER insulation monitoring device designed to measure insulation resistance in unearthed AC, DC, and AC/DC systems. It supports two separately adjustable alarm response values, a backlit text display, fault-history storage, and self-monitoring functions to assist maintenance teams with electrical fault diagnosis.
The Bender IRDH275BM-727, article number B91065120, is particularly relevant to installations using converters, rectifiers, and variable-speed drives where DC components are connected to an AC system. For medium-voltage applications, selection of the external coupling device is critical. Verify the system voltage, frequency, leakage capacitance, and required alarm thresholds against the Bender documentation before commissioning or replacing an existing unit.
Key Technical Specifications
| Parameter | Specification |
|---|---|
| Product Model | IRDH275BM-727 |
| Manufacturer | Bender |
| Article Number | B91065120 |
| Product Family | ISOMETER IRDH275BM-7 |
| Product Type | Insulation monitoring device |
| System Type | Unearthed AC, DC, and AC/DC IT systems |
| Supply Voltage, AC | 19.2–55 V AC |
| AC Supply Frequency | 42–460 Hz |
| Supply Voltage, DC | 19.2–72 V DC |
| Monitoring Voltage Range | Depends on the coupling device and system configuration |
| Compatible High-Voltage Coupling | AGH675S-7 series; system-specific selection required |
| Reported Monitoring Thresholds | Two separately adjustable response values, 100 kΩ to 10 MΩ |
| Measurement Method | AMPPlus |
| Communication Interface | Bender Measuring Device Interface (BMS), electrically isolated RS-485 |
| Analog Output | Electrically isolated 0(4)–20 mA, proportional to measured insulation resistance |
| Alarm Outputs | Two alarm relays with potential-free changeover contacts |
| Display | Backlit, two-line text display |
| Diagnostics | Self-monitoring, selectable automatic self-test, alarm-history memory |
| Installation | Panel or cabinet mounting; confirm required clearances |
| Protection Rating | Confirm the applicable enclosure and installation requirements |
| Manufacturer Documentation | Manual D00123 |
| Product Standards | Includes IEC 61557-8 and IEC 61326-2-4 in the cited documentation |
Specification note: The 7.2 kV and 15.5 kV figures refer to supported system configurations using suitable external coupling devices, not to the monitor’s own supply voltage. Select the coupling device according to the actual AC/DC system voltage and frequency.
IRDH275BM-727
Application Scenarios and Pain Points
- Medium-voltage drive systems: Monitors insulation conditions in systems using variable-speed drives and converters, when paired with the appropriate coupling hardware.
- Industrial DC networks: Detects declining insulation resistance in unearthed DC systems where the monitoring configuration is suitable.
- Power generation and process plants: Supports maintenance teams monitoring insulation conditions in electrical distribution and drive systems.
- Preventive electrical maintenance: Adjustable response levels and stored alarm history help technicians identify developing insulation problems and review previous fault events.
Field note: An insulation alarm does not automatically mean the monitoring device has failed. Check the connected system, cable insulation, converter filters, leakage capacitance, coupling device, and alarm settings before replacing the monitor.
Related Products
The following products are associated with the IRDH275BM-7 monitoring arrangement. They serve different functions and are not direct substitutes for the IRDH275BM-727.
| Model | Product type or role | Compatibility consideration |
|---|---|---|
| AGH675S-7-500 | External coupling device | Supports applicable systems up to 7.2 kV; 500 mm cable version. |
| AGH675S-7-2000 | External coupling device | Similar system-voltage class, with a 2000 mm cable. |
| AGH675S-7MV15-500 | External coupling device | Intended for specified systems up to 15.5 kV; verify the application and frequency. |
| 9620-1421 | External kΩ indication instrument | Used for external indication of insulation resistance in supported arrangements. |
| COM460IP | Communication and visualization accessory | Remote parameter setting requires the applicable option and compatible configuration. |
Engineer’s Guide: Three Checks Before Replacement
- Confirm the full model and article number. Match
IRDH275BM-727andB91065120. Do not assume that another IRDH275 variant has the same supply or monitoring range. - Verify the coupling device. Check the installed AGH series, rated system voltage, AC/DC operating conditions, and cable arrangement. The monitor and coupling device must be selected as a compatible pair.
- Review commissioning settings. Record both insulation alarm thresholds, relay operating modes, BMS address, and any external analog-output wiring. After installation, conduct the manufacturer’s prescribed functional checks and confirm the alarm response.
Frequently Asked Questions
Q1: What is the Bender IRDH275BM-727 used for?
It monitors insulation resistance between unearthed electrical systems and earth, providing alarms when the measured value reaches configured response thresholds.
Q2: What supply voltage does it require?
The documented supply range is 19.2–55 V AC at 42–460 Hz or 19.2–72 V DC. This is the device’s supply voltage, not the monitored system voltage.
Q3: Can it monitor medium-voltage systems?
Yes, when used with the appropriate external coupling device and within the documented system limits. The coupling device must be selected for the actual voltage and frequency.
Q4: Does it support communication with other Bender devices?
Yes. It includes an electrically isolated RS-485 Bender Measuring Device Interface (BMS). Confirm the communication settings and connected-device requirements during integration.
Q5: What outputs are available?
The documented features include two alarm relays with potential-free changeover contacts and an electrically isolated 0(4)–20 mA analog output proportional to the measured insulation value.
Q6: Can another IRDH275 model replace the ?
Not without checking the full model suffix, supply range, monitoring configuration, interface requirements, and coupling device. Similar product-family names do not establish interchangeability.
Q7: What should buyers check before ordering?
Confirm the model and article number, physical condition, terminal integrity, included accessories, and available test records. If the unit is offered as refurbished or used, request the scope of testing and verify that the proposed configuration matches the installed system.
