Static transfer switch (STS): Application solutions. Correct use of the STS in systems providing maximum power reliability

Abstract

It's now widely acknowledged at international level that the static transfer switch (STS) plays a crucial role in guaranteeing maximum electrical power reliability in environments that are extremely delicate and by their nature vital, for example internet data centres (IDCs).Careful evaluations are required regarding the numerous different pieces of equipment used (power sources, UPS systems, protective devices, electrical distribution, transformers, etc.) and the various closely related aspects. None of these can be considered of secondary importance.The experience has clearly shown the importance of considering every system as a whole system, in which each element must be co-ordinated with the others, in order to achieve the final objective, which has the maximum compatibility between equipment under any system operating conditions. This consideration becomes much more decisive in the choice of the STS, since very different types are available, each of which must be evaluated in context and with reference to the specific characteristics of each system, every one having features which mean that it could never be considered equivalent to another.The risk involved in dispensing with such evaluations is that a set of elements which are excellent if considered singly, are not always compatible one with another.This article is for all of those people devising, designing and building a system with STSs and aims to offer some practical suggestions.We increasingly see high quality, high reliability plant engineering power solutions exploiting the advantages offered by static transfer switches (STSs) to guarantee top level reliability, according to all of the parts which make up the system. Such solutions are particularly frequent in very delicate environments such as internet data centres (IDCs) which manage core business (banking, telephony, services, etc.), and in all the sectors where a quality, reliable power supply is crucial.

Safe-triggering-region control scheme for suppressing cross current in static transfer switch

“…Furthermore, according to condition (a) ωt k + Â 2 ∈ k , k + 2 k = 0, ±1, ±2· · ·. Hence, the cross current magnitude can be found explicitly substituting Estimated by (9) Estimated by (8) Simulated Fig. 13.…”

“…Operation of a sensitive load can be disturbed by the common voltage sags, swells and interruptions. Recent studies [7][8][9][10][11][12][13][14][15][16][17][18][19] identify solid-state transfer switch (STS) as a possible cost effective solution to power quality problems. STS, see Fig.…”

“…Two common control strategies of STS are the break-before-make (BBM) [9] and the make-before-break (MBB) approaches [10]. The BBM controller transfers the load to the alternative power feeder after the primary feeder current has ceased, whereas the MBB controller initiates the transfer to the alternative line before the current has expired [10].…”

“…the phase difference between the primary and alternative feeders) application of this method seems to be difficult. In attaining the maximum transfer reliability [9], overlapping transfer of the neutral wires is introduced in [19].…”