A conventional Power Distribution Unit (PDU) is an assembly of electrical outlets (also called receptacles) that receive electrical power from a source and distribute the electrical power to one or more separate electronic appliances. Each such unit has one or more power cords plugged in to one or more of the outlets. PDUs also have power cords that can be directly hard wired to a power source or may use a traditional plug and receptacle connection. PDUs are used in many applications and settings such as, for example, in or on electronic equipment racks. One or more PDUs are commonly located in an equipment rack (or other cabinet), and may be installed together with other devices connected to the PDU such as environmental monitors, temperature and humidity sensors, fuse modules, or communications modules that may be external to or contained within the PDU housing. A PDU that is mountable in an equipment rack or cabinet may sometimes be referred to as a Cabinet PDU, or “CDU” for short.
A common use of PDUs is supplying operating power for electrical equipment in computing facilities, such as data centers or server farms. Such computing facilities may include electronic equipment racks that comprise rectangular or box-shaped housings sometimes referred to as a cabinet or a rack and associated components for mounting equipment, associated communications cables, and associated power distribution cables. Electronic equipment may be mounted in such racks so that the various electronic devices are aligned vertically one on top of the other in the rack. One or more PDUs may be used to provide power to the electronic equipment within each rack. Multiple racks may be oriented side-by-side, with each containing numerous electronic components and having substantial quantities of associated component wiring located both within and outside of the area occupied by the racks. Such racks commonly support equipment that is used in a computing network for an enterprise, referred to as an enterprise network.
As mentioned, many equipment racks may be located in a data center or server farm, each rack having one or more associated PDUs. One or more such data centers may serve as data communication hubs for an enterprise. Many PDUs include network connections that provide for remote control and/or monitoring of the PDUs, and may include the ability to report information related to the PDU to a user or system located remotely from the PDU. A PDU may include power control relays that may be actuated by a remote user to interrupt power to one or more of the outputs of a PDU. Such relays may have a turn on and turn off delay and in addition have natural resonances in a relay armature and armature contacts that often cause the contacts to bounce for some amount of time, typically being some number of ms. During these bounces the contacts move away from each other. In the event that current is flowing through the contacts, an arc may develop. In some examples, an arc may develop that is on the order of 35 volts, depending on the temperature and pressure. The power dissipated during the arcing causes heating of the contacts, and metal may be sputtered off of contact surfaces, which may shorten the life of the contacts. Such power control relays may be a point of failure of a PDU, which may in some cases reduce the useful lifetime of a PDU. Reliable switching operation of relays for relatively long lifetimes may thus be desirable, particularly in many data center operations. Such a relay failure in a data center may result in the loss of one or more pieces of critical equipment for an organization or enterprise, causing a potentially costly disruption in service.
Some prior solutions to this issue have attempted to perform switching of relays to reduce arcing between contacts by switching relays when a voltage and/or current of the input power waveform is less than a maximum current and/or voltage. Such solutions may reduce the amount of arcing, but such arcing may continue to occur and potentially degrade the associated relay. Accordingly, improved switching for relays may be desirable to improve relay reliability.