 |
|
|
by Bob Walder It has to be said that the humble UPS is not the sexiest of computer-related technologies. You don’t often see the hoards of visitors at computer trade shows making a bee-line for the UPS stand – not unless they have got a good magician or juggler on the stand anyway (or free booze, of course – always a crowd-pleaser)! Like backup technology, the UPS is something that most of us take for granted that we ought to have (even if we haven’t actually got round to buying one quite yet). We pay very little attention to when we buy it, and then tend to plug it in and forget about it, hoping that it will work correctly when called upon. As the memories of the free booze and the amazing juggler fade, so does our concern for our newly acquired UPS. Then one day we get a power cut, and all the servers go down. What happened to the UPS? Did the batteries fail? Was it overloaded, providing mere seconds of backup before the batteries discharged? Or did we simply buy the wrong type of UPS in the first place? All these questions were ones I had never even considered until I met the guys from Merlin Gerin – or MGE. They started out by explaining all about UPS technology. As most of you will be aware, electricity suppliers provide Alternating Current (AC) from those three-pronged holes in the wall. In an ideal world, this current is supplied at a voltage of 230 volts and a frequency of 50 Hertz (in the UK). Electronic and computer-based equipment in industry and the service sector needs a high quality uninterrupted supply of electricity in order to function effectively. The electrical distribution systems, however, are subject to interference arising from atmospheric and industrial sources. In fact, no electrical installation is free of brown-outs, interference and variations in voltage. Many phenomena cause excess voltages (above 260 volts) or voltage drops (below 180 volts), and these can seriously jeopardise the operation of computer systems. Simply speaking a UPS is a “buffer battery” between the power socket and the computer. The only way of storing electricity – in a battery for example – is to convert the AC from the power supply into Direct Current (DC). The UPS converts the AC mains supply into DC in order to charge the battery, and then reconverts it back into AC in order to supply the load in case of mains failure. If only it were that simple! In fact, there are three main types of UPS currently available, with a few additional bells and whistles that make for a huge number of possible permutations for the unwary buyer. The most frequently-used
technology for protecting PCs in an environment with little electrical
interference is known as Off Line (or Passive Standby) technology. �
The typical delay in making this transfer to battery power is on the order of 4 milliseconds. This is not as bad as it sounds, however, since the power supply on a typical PC can support outages of up to 10 milliseconds thanks to its internal capacitors, with high-end hardware surviving power breaks of up to 100 milliseconds. Off-line technology offers the advantage of low cost, but is not suitable for use if there are frequent disturbances (such as in heavy industrial or rural environments). It is also important to realise that the application is affected by all current fluctuations outside accepted tolerance limits. �The
second type of UPS technology is known as Line Interactive (or Active
Standby), and is generally considered mid-range technology for protecting
single station servers. Line Interactive is a recent development made
possible by the appearance of microprocessors. The UPS is fully controlled
by a microprocessor which monitors the quality of the mains power supply
and reacts to any variations. This is what makes the UPS “Active” or
“Interactive”. �
In the event of a power problem, the UPS transfers the load to the batteries to supply stabilised power. It is increasingly frequent to add a voltage compensation circuit, called a “booster”, that is enabled in the event of prolonged voltage drops. �As with conventional Off Line devices, Active Standby technology is dependent on a low frequency (50 Hz) transformer, the weight and cost of which are prohibitive at ratings in excess of 2 kVA. �The top of the range technology is represented by the On Line UPS. In these devices, the protected devices are no longer connected directly to the power supply. Instead, current is always transformed to DC and then back to AC, thus guaranteeing a constant level of quality, regardless of disturbance on the mains power source. ��
Although the same DC current is also used to charge the batteries – as with the other types of UPS - the batteries themselves are still only used in the event of an outage. On-line technology is the ideal solution for protecting installations which are critical to the business, and for providing continuous protection. On-line technology also provides advantages over both Off-Line and Line Interactive in the area of long battery-backup times. Certain applications (telecommunications, for example) cannot be shut down at all even following power failure, and thus require very long battery-backup times – often in the region of 6 to 8 hours. Only an On-line UPS can guarantee proper operation under these conditions, since this operating mode places continuous demands on all UPS components, which is the normal state of affairs for an On-Line UPS. On the other hand, a Line Interactive device is not designed to operate for so long in battery mode, and this can result in overheating problems and premature wear of the UPS. The installation of our review UPS began with a site survey conducted by an MGE employee and a sub-contracted electrical engineer whose job it was to advise us on any changes or additions that may be required to our electrical installation. The other vital service that was performed during the survey was to identify exactly which items of equipment should be protected and how long they should run in case of a mains failure. This was a case of� starting with “everything running for 8 hours”, fainting at the cost, then working backwards until we achieved an acceptable balance between price and protection. We eventually settled on protecting three huge enterprise servers, two or three critical workstations with large monitors, and a whole raft of communications equipment including routers, TA’s, hubs, switches, telephones and faxes. We decided that we would need some room for expansion, and that when fully loaded we would require about 30 minutes following power failure to give ample time for the users to finish what they are doing and save their files before the servers began an orderly shut-down. Needless to say we wanted the shut-down to be completely automatic, in case the office was unattended when the power failed, and we required some way of monitoring the UPS from any point on the network. The recommendation was the Pulsar EX30, a 3kVA unit providing double-conversion On-Line technology with continuous voltage and frequency regulation. The base unit on its own provides 9 minutes standard backup time at the 100 per cent rated output of 3kVA, so added to this was an EXB extended battery module to provide 32 minutes of backup time at 100 per cent output. This provided us with our minimum of 30 minutes at full load, and there was plenty of room for expansion in this configuration. The equipment we had elected to protect took up only 40 per cent of the rated load, allowing us to add much more equipment in the future, as well as count on over an hour of battery backup in the mean time. The hardware itself is elegant in appearance, with the extended battery unit closely matching the EX30 with its stylishly curved front. However, the smooth lines and curves actually make both boxes incredibly difficult to move around, given the weight of the hardware and the lack of castors. Some recessed hand grips would be a welcome addition. Both units can be free-standing or rack mounted. The front of the EX30 sports a number of LED's doubling individually as status indicators (overload, battery fault, internal fault, etc.), or grouped together as a load level meter or battery charge meter. A push button provides the load level test capability, whilst another switches the unit on and off. One nice feature of the EX30 is the cold start capability, which allows the UPS to be powered up from scratch when there is no mains present. Being a substantial on-line UPS, the EX30 provides a couple of other features that will be welcome to the corporate user. The first is galvanic isolation, which protects an installation from accumulated leakage currents when many PCs are connected to the same power supply. Normally, every PC generates around 3mA of leakage current, meaning that as few as ten of these on the same installation could begin to cause problems with tripped circuit breakers. A galvanically isolated UPS, however, prevents these accumulated currents from affecting the installation to which it is connected, instead limiting the leakage current to the 3mA generated by the UPS itself. The other nice feature was the hot-swappable manual bypass option which was installed on the review unit. This takes the form of a large box with a rotary bypass switch, a standard kettle plug power input socket, and three standard 3-pin power outlets. This unit attaches to the rear of the UPS and in normal operation allows power to pass from the electricity supply, through the UPS circuitry, and out to the power outlets at the back Trailing sockets can be attached, supporting a large number of devices). Should you need to replace or maintain the UPS at any point, all you need to do is flick the bypass switch, and power is routed directly from the input to the output sockets, isolating the UPS. The whole switch box can then be unplugged from the back of the EX30 allowing the UPS to be removed or replaced whilst maintaining continuous power to all the protected devices. This is an extremely desirable option – after all, what good is it having a UPS if you have to power everything down to do a bit of maintenance? An additional automatic bypass option also guarantees the supply of electricity to the load in the event of a fault on the UPS. The SolutionPac software provided with the EX30 is standard across the MGE range, and can be installed either as a “personal” configuration (direct connection between the UPS and the monitoring PC), or as a WAN option, where software agents can be installed on a number of protected servers and controlled from a central management station. This provides automatic shutdown of protected servers in the event of extended power failure. The whole thing is based on SNMP, and so can be controlled via standard consoles such as HP OpenView. A simple console is also provided as part of SolutionPac. The UPS can be connected directly to the serial port of one of the protected machines for monitoring purposes, or you can use the UM-Link option, which allows up to four UPS units to be connected directly to the LAN and monitored over the network. As it happened it was a real baptism of fire for the EX30, since the start of the installation was greeted by the biggest rain storm you have ever seen in your life – we couldn’t see more then six feet from the windows. Not ten minutes after flicking the switch on the UPS we saw the lightning outside and had our first brief power failure, the second following ten minutes after that. On both occasions, though the lights flickered and other devices in the office powered down, the network and related equipment kept running. Half an hour later we suffered a real – and total - power failure, and found that we could work quite happily for the 20 minutes it took the electricity provider to get its act together. Entries were written to the NT event log and messages were sent to the supervisor. On running UM Console we verified that the mains power had failed and monitored the dwindling charge on the batteries as we continued to use the network. All in all, everything worked as it should, and you can’t ask more of your backup and UPS equipment than that! Verdict A well designed, expandable and solidly manufactured piece of kit with a range of useful options. It saved our bacon three times in one day during the review!
|
�
|
Send mail to webmaster
with questions or�
|
