As power generation evolves around the world to meet demand, more smart grids require the storage of excess generated electricity to maximize peak efficiency. Battery storage systems are becoming more widely used. In order to help today's smart grids operate, smart electrical safety equipment is a must. Proper electrical safety doesn't just protect personnel - it helps protect equipment from electrical and fire damage.
For decades, electrical systems classified as critical infrastructure have utilized ungrounded and high-resistance grounded substations. In a single ground fault condition, these system configurations allow processes to continue to operate. In North America, passive three-light bulb indicator systems have been used for many years for ground-fault detection.
While NEC 250.21 (B) permits the use of three-light systems for detection, it should be noted that the NEC is a minimum design standard; ground-fault detection, location and protection technology has advanced significantly in the last 20 years. Since these passive systems are still used, however, it’s important discuss how they work and the typical issues that arise, especially when incorporating newly designed energy storage systems into existing Ungrounded, or High Resistance Grounded substations or facilities.
- Passive grounds fault detection systems are designed for operation on three-phase ungrounded, or high-resistance grounded systems. These devices will not work on any type of solidly grounded system.
- A traditional three-light ground fault detection system is wired in a “wye” configuration, with the center of the wye connected to ground, rated at the full voltage of the system. For example, a 480-V System requires 480-V pilot lights (which may include potential transformers).
(on the left is a typical “Three-Light” System)
System Advantages / Disadvantages:
Note: The Industrial Power System Grounding Design Handbook states that 95% of all electrical faults are phase-to-ground faults. IEEE141-1993 Recommended Practice for Electric Power Distribution for Industrial Plants 7.2.2 states “there is no arc flash hazard (on HRG systems) as there is with solidly grounded systems, since the current is limited to approximately 5amps.”
Solutions to these issues come in many forms. Conversion to high resistance grounding with individual feeder protection is often selected, to help alleviate the transient overvoltage potential inherent to ungrounded systems, and to make it easier to locate ground faults.
Where ungrounded systems are still utilized, insulation monitoring devices can provide critical infrastructure system-to-ground resistance monitoring to detect ground faults, and even to allow location of faults while maintaining continuity of service.
As more energy storage applications are being retrofitted into existing systems, safety and reliability of both the energy storage module and the end-user’s electrical system must be considered. Failing to do this undermines any advantages of energy storage. These best practice principles should begin during the specification stage of a project – not after a system has been deployed.
Dale Boyd has a Bachelor of Science degree in Electrical Engineering Technology degree from Old Dominion University. He spent the first (14) years in the Pulp & Paper Industry as a Project Design Engineer, and spent several years as Chairman of the Global Power Committee for a major consumer products paper company. He has also worked with various electrical manufacturers; his roles have included power consulting, national accounts manager and regional sales director. Dale is a member of IEEE, and active in the pulp & paper IEEE Group. He has developed power system solutions with many end customers, ranging from electrical distribution system upgrades to ground-fault solutions.
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