Proposal of a New UVR-OCR Integrated Relay for Short Circuit Separation for Power Distribution Safety

Under voltage relays (UVR) and over-current relays (OCR) are used for protective modulation in distribution lines, contributing to the stabilization of distribution lines by separating lines in response to over-current or under-voltage conditions. These relays are capable of stabilizing and isolating the faulty line when operating at or near their rated limits. However, in extreme situations such as short-circuit accidents, grid coordination—in which all relays operate instantaneously to isolate only the faulty line—has a major disadvantage; that is, it is difficult to operate stably, causing a power outage across the entire distribution system. To solve this problem, there is a rapidly increasing demand for integrated relays that cooperate with each other in the current distribution coordination system they operate in independently. This paper proposes an integrated UVR-OCR relay for organic cooperation in the event of a short circuit in distribution lines. The proposed method demonstrates strong performance in all operations, including current sensing and short circuit judgment, and achieves a trip delay within 40 msec. The validity of the proposed method is verified through simulations and experiments.