New Intelligent Direct Transfer Trip Over Cellular Communication

The paper will discuss two installed system designs and methods used to transmit a DTT signal over cellular systems. This new approach solves the communication reliability problems and addresses application security. This paper is a case study of 3 installed DTT systems that use cellular communication - one system at Central Virginia Electric Cooperative and two at Dominion Energy. In this paper the authors will report on the design, implementation, performance and issues encountered during and post project execution. These intelligent DTT systems have been designed to increase availability of the DG by preventing the indiscriminate disconnection of the sites. Traditionally Direct Transfer Trip Signals (DTT) has been sent between substations and remote Distributed Generation (DG) sites using leased telephone lines. If DTT communication is interrupted, the DTT system will disconnect the DG site. Leased copper lines are becoming less reliable, leading to unwanted disconnection of DG sites. Installation of fiber is not always feasible due to the cost. This paper will discuss an approach to provide DTT signals using wireless communications. The paper will address the security concerns that many Utilities might face. Two new innovations to increase the DG site's availability will be discussed. 1) Automatic Direct Transfer Close If system conditions return to normal after a DTT event, the system will automatically close the DG site back in onto the feeder. 2) Dynamic Feeder State change protection function. Using cellular or wireless communication systems it must be expected that there will be communication interruptions during normal maintenance actions. During these times the DG site device activates a new protection function that will detect any anomalies that could constitute a change in the connected feeder systems (e.g. caused by a fault or the opening of a breaker) and then only disconnect the DG site.