One way of viewing a UPS is as a device that protects its critical load from power disturbances, and provides instant battery backup if the mains fails.
Another perspective shows the UPS as a network node.
While the first view is obviously more meaningful, the second has its relevance too. In today’s connected world, site operators and managers increasingly expect visibility of their equipment’s status in real time, allowing for better management and maintenance decisions. In any case, some level of communication is fundamental to UPS operation. If a UPS cannot warn its load that it is experiencing an extended power cut, its role will be nullified; the load won’t be triggered to use the battery’s autonomy to shut down safely.
Simple communications
Accordingly, modern UPSs have some level of communications capability, even if it isn’t a full network interface. The simplest communications link comprises one or more volt-free contacts that give basic signals such as ‘mains failure/good’ or ‘battery low/ok’. Although the amount of data is very limited, and only immediately available to other systems on site, such links are easy to set up and sufficient for many applications. In particular, the information is sufficient to trigger an ICT system shutdown, if appropriate.
When more information is required, without full network connectivity, RS-232 serial communications can be used. Instead of simple True/Not True flags, more detailed analogue values can be transmitted. Inverter and static bypass output conditions can be monitored, along with battery conditions and remaining time. Statistics regarding mains failures and UPS operation can also be collected. Other functions include graphical displays of UPS status, configurable responses to certain alarms, such as broadcasts to users, and scheduled diagnostics checks and data logging.
It is important to note that RS-232-based UPS shutdown software is usually specific to each manufacturer.
Networking
When communications are needed over wide areas, across multiple sites, or with remote monitoring centres, wide area networks based on an IP protocol become necessary. Inter-site communication is essential if an organisation has remote locations that are unmanned; this gives an opportunity for a network manager on a manned site to monitor the unattended remote UPSs, and respond to any conditions that need attention. It also allows operation of remote monitoring centres, often run by third parties such as the UPS supplier, as part of their maintenance support strategy.
A modern UPS’s network interface should have Simple Network Management Protocol (SNMP) compatibility. SNMP is a standard protocol and part of the TCP/IP suite which allows all network devices to transmit management variables across enterprise-wide networks. By using SNMP as a single standard, interoperability across all sites is assured. A UPS is an intelligent device that can log events, continuously monitor power quality, report on battery status, load and temperature, and perform self-diagnostics. With SNMP capability, information related to these activities becomes accessible across the network. Managers can perform immediate analyses, and detect potential problems before they create failures.
UPS communications and intelligence allows control as well as monitoring. Sections of the connected system can be de-activated for security reasons, to save power or manage redundant sections of the system. At the highest level, dozens of UPSs from multiple sites can be linked into a central network console, and managed on a system rather than modular basis. This avoids unnecessary shutdowns resulting from a single redundant module failure, and allows more efficient power protection and network control strategies.
