30 TEST & MEASUREMENT
30 TEST & MEASUREMENT
component capacity to provide an alarm if these are exceeded . The thresholds can be set against the addition of a number of cabinets that are known to be connected to a common power distribution board , bus bar or UPS etc .
The final hidden vulnerability relates to phase balancing . In normal operation , UPS and other power distribution equipment shouldn ’ t be unduly affected by poorly balanced phases , except for inefficiency and in extreme cases high neutral currents , which can lead to overheating of neutral conductors . However , in the event of a utility power failure the mains 4 pole contactor , mandated by codes , opens before the 4 pole contactor from the generator closes .
While this can be only for a short period of time the UPS is still producing power with no neutral reference point , if the phases are poorly balanced the neutral potential tends to move towards the potential of the phase with the lowest power draw . If this is lower than the power draw on another phase the potential between the live and neutral on this phase can drop to a point where IT equipment sees it as a failure . For this reason , and bearing in mind that the phase loads will vary as outlined above , phase balance should be continuously monitored and corrected by moving loads if necessary .
IT equipment won ’ t have the facility to provide power monitoring information , and the sharing across IT and Facilities may create problems relating to network security .
The traditional method of monitoring power is via the rack PDU . However a number of IT solutions are now delivered in cabinets complete with power distribution from a 3 phase supply . Examples are supercomputer solutions , such as those from SGI , and the new Open Compute Project ( OCP ) IT equipment racks . In this instance , the installation of a power monitor at the rack supply provides compliance with PUE category 3 , and where bus bar power distribution is utilised this can be incorporated in the tap off . Power monitoring at the bus bar is also a good solution for colocation facilities where it provides an excellent level of monitoring for management and energy cost recovery .
Use of the information Many data centres are likely to require a combination of different power monitoring methods to suit the IT equipment configurations . The power monitoring system control software should have the capability to gather information from a range of sources , and present this in real-time and historical data , in a format that is easy to configure , read and interrogate . The information should be portable , and be able to be displayed on any web- enabled device , but the data should be secured against hacking and denial of service attacks . This will allow the Facilities team to mitigate risks and maximise the efficiency of the power infrastructure . Examples of information displays are shown in the images below .
Facilities infrastructure at rack level It ’ s becoming increasingly common to find parts of the cooling system within the cabinet row . Either as part of the overall cooling strategy or , more often , as a tactical solution for a high-density zone . This may include :
• In row air cooling units
• In rack ( rear door ) air cooling units
• Liquid cooling distribution units
The power consumed by these units mustn ’ t be included in the IT load for accurate reporting of PUE , but is often and quite reasonably fed from the same UPS or power distribution board as the IT cabinets .
Rack power monitoring options It ’ s possible to obtain power monitoring information directly from the PSUs in many types of IT equipment via the management port . If this is to be deployed as part of the power monitoring solution it ’ s essential that the information is made available in real-time to the facilities team and relationships between IT equipment and rack locations , power circuits etc . are strictly managed . It ’ s likely that some
Power monitoring is recognised to be essential for the effective and efficient management of a data centre , but to maximise the return on investment it should :
• Provide real-time information and historical data to the Facilities team as well as IT management
• Measure IT consumption at rack level separately to facilities power consumption
• Associate IT power consumption with circuits , phases and sections of the power supply infrastructure
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