Grounding and Isolation of Sensitive Measurement Equipment for Arc Flash Testing at High-Power Laboratory

Abstract

It is often necessary to place sensitive measurement equipment in high-power laboratories when conducting tests for arc flash research. However, direct contact or induced voltage from an arcing test can have serious consequences for testing equipment, particularly for sensitive measurement equipment, and therefore, thorough consideration of grounding or isolation schemes is required to ensure accuracy of the measurement and survivability of the equipment. Traditionally, grounding and isolation systems at high-power laboratories are designed to prevent ground loops and remove mutual interference during signal transfer. However, for arc flash testing, front-end sensors such as copper slug-type calorimeters constantly experience exposure to high-voltage contacts throughout the test. Without a proper grounding and isolation scheme, kilovolt-level common-mode voltage surges inject into the data collection and control end, potentially destroying sensitive electronic devices and ruining measurement results. Essential to avoiding such scenarios is the adoption of adequate grounding/isolation schemes for data acquisition (DAQ) systems. This paper discusses the implementation of a robust grounding and isolation topology for the whole DAQ system. A high channel separation differential input signal conditioning circuit is applied on the transducer end to avoid common-mode surge signals from the high-voltage source; a common isolated ground power supply provides single-point reference for the whole DAQ system; a high-channel-separation analog-to-digital converter avoids crosstalk among measurement signals; and optical fiber communication between DAQ and personal computer (PC) avoids electromagnetic interference/radio frequency interference and provides an additional layer of protection to the PC and the personnel. The proposed grounding and isolation scheme has been verified in high-power-rating arc flash testing and can be also applied to DAQ systems in industrial and commercial power systems with similar environments.