— A P P L I C AT I O N N O T E CONTROL SOLUTIONS FOR INSULATION MONITORING Battery Energy Storage Systems (BESS) (UL) What is insulation monitoring? Insulation monitoring, also known as insulation resistance monitor- ing or earth fault monitoring, detects insulation faults and prevents electrical hazards, such as short circuits and electric shocks. IMDs detect real-time insulation deterioration prior to a fault occurring. Why is control important for your battery energy storage system (BESS)? Insulation monitoring devices play a crucial role in ensuring the safety and reliability of electrical installations. ABB’s insulation monitoring relays help prevent damage and electrical accidents caused by insulation faults in a BESS. Continuous operation Prevent unintended downtime with our insulation relays. By monitoring voltage free networks and providing pre- warnings, ABB’s insulation monitoring relays allow you to proactively maintain your system. Safety and protection ABB’s insulation monitoring relays deliver safe and reliable insulation fault detection in accordance with the latest standards. The portfolio extends from standard to more challenging applications and can prevent fire due to fast and reliable earth fault detection. Built-in self-diagnosis and interrupted wire detection further ensure safety. Easy to install Our insulation monitoring relays are designed to be almost maintenance free and easy to install with clear marking of the terminals, direct reading rotary switches, and a wiring diagram printed on the device. Main benefits Protect your battery energy storage system against ground faults with our insulation monitoring relays. As one of the few suppliers of insulation monitoring devices (IMDs), our reliable solutions can provide secure and continuous monitoring. 2C O N T R O L S O L U T I O N S F O R I N S U L AT I O N M O N I T O R I N G B AT T E R Y E N E R G Y S TO R A G E S Y S T E M S ( B E S S ) ( U L ) Battery energy storage systems (BESS) BESS overview As focus on decarbonization, decentralization, and digitalization increases, the battery energy storage system (BESS) market is forecasted to become a megatrend in upcoming years. The implementation of BESS is becoming increasingly imperative for the provision of reliable, clean energy. These systems source and store energy for various applications such as peak shaving, transmission and distribution congestion relief, and arbitrage. As the BESS market and its applications continue to expand, it is critical to take the proper safety measures to reduce hazards and prevent downtime. ABB’s insulation monitoring relays can help protect your system by alerting to fault-vulnerability before it occurs. Ground 3 Ground fault in BESS What is ground fault? Ground fault occurs when an energized conductor comes in contact with grounded equipment due to faulty wiring, damaged insulation, or the buildup of moisture or debris. Grounded v. ungrounded BESS In a BESS, two grounding systems can be utilized: grounded and ungrounded. A grounded system directly connects a conductor to ground to serve as a return path for current generated by a ground fault. On the other hand, an ungrounded system, most commonly used, isolates conductors from grounding. This allows the BESS to keep operating even during a first fault. Preventing system damage If your system experiences an initial fault, it is critical to clear the fault quickly as possible to avoid a short-circuit in the event of a second fault. Insulation monitoring devices are helpful in keeping you informed about insulation degradation before a first fault arises, helping you stay ahead of the problem. Ungrounded Grounded First fault → pre-warn Gained time to plan maintenance Second fault → short circuit → tip → plant interruption Insulation resistance Time First fault → pre-warn Gained time to plan maintenance trip Insulation resistance Time 4C O N T R O L S O L U T I O N S F O R I N S U L AT I O N M O N I T O R I N G B AT T E R Y E N E R G Y S TO R A G E S Y S T E M S ( B E S S ) ( U L ) Insulation monitoring An Insulation monitoring device provides pre-fault warnings, helping to prevent system disruption and safety hazards. It works by detecting deterioration of the insulation resistance and/or a first fault. This is done by generating test signals that measure the resistance to ground, establishing a resistance threshold. When an insulation monitoring device detects values outside of the threshold, it generates a pre-warning alert. These alerts paired with constant monitoring allow you to oversee insulation quality and proactively maintain your system. IMDs detect a first fault IMDs detect creeping deterioration of the insulation resistance Power supplies and monitoring relays DC breaker, contactors and/or disconnect switch Main DC breaker, contactors, and/or disconnect switch DC SPD PCS/inverter/converter CMS battery monitoring MV circuit breaker AC contactor AC main breaker AC SPD BMS battery management system Insulation monitor Inverter Battery Ground 5 BESS experience high operational stresses due to factors such as constant charge cycling and fluctuating environmental con- ditions. As a result, leaks and insulation deterioration pose sig- nificant risk to not only the BESS, but also the area surrounding Insulation monitoring devices are the optimal fault protec- tion solution for your ungrounded BESS as they measure the insulation resistance of each pole in respect to ground. When the impedance to ground of either pole drops to a lower setting, the IMD emits a pre-warning signal, allowing for maintenance to be done before a fault occurs. the system. Earth leakage can reduce the efficiency of your BESS and cause severe equipment, personnel, and fire damage if not mitigated in time. Note: Insulation monitoring devices work to detect insulation concerns before a fault occurs, while residual current devices trip at the occurrence of a primary fault. Both devices are critical for the safety and protection of your BESS 6C O N T R O L S O L U T I O N S F O R I N S U L AT I O N M O N I T O R I N G B AT T E R Y E N E R G Y S TO R A G E S Y S T E M S ( B E S S ) ( U L ) Control solutions — Advanced application insulation monitoring relays CM-IWM Features • Up to 1,500 V DC or 1,100 V AC network voltage • Up to 3,000 μF system leakage capacitance • High adjustable range up to 250 kΩ • 1 SPDT contact each for pre-warning and warning • LED status indication • Auto self test Benefits • Designed for usage in networks with connected rectifiers, inverters, thyristor controllers, or directly connected DC components • Clear visualization of device status via LED bar showing insulation resistance value in kΩ • 90 mm width • Primarily for BESS coupled systems and industrial applications — General purpose insulation monitoring relays CM-IWM Features • Up to 0–400 V AC or 0–600 V DC • Up to 20 μF system leakage capacitance • 1 SPDT contact each for pre-warning and warning • Coupling unit CM-IVN allows monitoring at 690 V AC or 1,000 V DC • LED status indication • Adjustment/DIP switches via front panel Benefits • Monitoring of voltage free networks • Clear visualization of device status via LED • Various push-in terminals • 22.5 mm to 45 mm width • Primarily used for main and battery supply networks 7 Product offering Insulation monitoring relays W E B S I T EC ATA L O G CM-IWM.10 and CM-IWM.11CM-IWS.1 and CM-IWS.2 CM-IWN.1 9AKK108469A4317 Rev. B — U.S. HQ Office: ABB 305 Gregson Drive Cary, NC 27511 United States Phone: (800) 435-7365 electrification.us.abb.com © Copyright 2026 ABB. All rights reserved. Specifications subject to change without notice. Additional information We reserve the right to make technical changes or modify the contents of this document without prior notice. With regard to purchase orders, the agreed particulars shall prevail. ABB Inc. does not accept any responsibility whatsoever for potential errors or possible lack of information in this document. We reserve all rights in this document and in the subject matter and illustrations contained therein. Any reproduction, disclosure to third parties or utilization of its contents – in whole or in parts – is forbidden without prior written consent of ABB Inc. CONTACT US Do you have a similar project and are you searching for the right application configuration? Contact us and talk to our experts!