400/230 Volt 60Hz UPS Power

Transcription

1 olt 60Hz Power Using ual Voltage standby generation and in one Nothing protects quite like Piller

2 Contents 1 Abstract Introduction Alternative Power istribution Integrating in a 400 V distribution Supplying Essential Loads in a 400 V distribution Integrated power supply of Critical and Essential loads Summary References

3 1 Abstract Within data centers the power used for operating the facility, running IT loads and cooling is the largest expense. With power densities continuing to rise, overall efficiency is still a major issue especially as power cost increases as well. The more the power density per rack raises the more floor space needs to be allocated for power supply components like PUs, breakers and cabling. The power distribution through the building to the IT loads contains several power lines, converters and transformers. Each components losses require equivalent cooling which consumes additional power. Reducing the number of components and operating IT equipment at 400 V will save floor space and will result in greater efficiency and reduced electrical costs. The resulting alternative power distribution allows different ways of integrating modules including the power distribution for the short break loads. A special kind of ual Output iesel Rotary with two output voltages integrates the power supply of critical and essential loads in one unit and additionally reduces upfront capital costs, infrastructure and floor space. 3

4 2 Introduction To understand this new approach to power distribution inside United States data centers, it helps to look at the current standard distribution systems first. The power delivered to most large commercial buildings and IT facilities is either 3-phase or medium voltage 3-phase. In case of a medium voltage feeder the voltage needs to be transformed down to which is the typical voltage level for the facilities internal power distribution. The voltage is 480 V line-to-line and 277 V line-to-neutral with a frequency of, like it is shown in Figure 1. N Phase 1 Phase 2 Phase 3 Line 1 Line 2 Line 3 Neutral 277 V 277 V 480 V 480 V 277 V 480 V Figure 1: used for power distribution inside a facility Switch-mode power supplies inside IT equipment typically operate within a voltage range of 100 V to 240 V single-phase, so the voltage level of the power distributed inside the facility is not suitable for this type of equipment. The voltage must be stepped down before it can be fed to the power supplies inside the computer racks. This is achieved by routing the power through an isolation transformer located inside a Power istribution Unit (PU) where it is transformed from to 208/120 V 3-phase, as outlined in Figure 2. -Transformer PU-Transformer Feeder Facility istribution IT istribution 3x AC 3x 208/120 VAC Phase X Phase Z N Phase Y Line X 120 V 208 V 208 V Line Y 120 V 208 V Line Z 120 V Neutral 208 V 120 V Figure 2: 208/120 V standard power distribution for IT equipment 4

5 From the PU, power is typically distributed in three ways: VAC single-phase (line-to-neutral) VAC single-phase (line-to-line) VAC 3-phase (for further distribution before being split into single phases) In the past it was not practical to consider alternative voltage levels for the power distribution because a significant fraction of IT equipment operated from 120 V. But in modern high density data centers most switch-mode power supplies for IT devices are designed for worldwide compatibility and do accept both low-line voltages V and high-line voltages V. So having 120 V available in the rack might be useful to power some legacy devices but should be of no importance in modern data centers. Considering the fact that running the devices at the higher voltages will increase efficiencies by approximately 2 to 3.5% [1], feeding the power supplies with 208 V or higher should be the preferred solution. 5

6 3 Alternative Power istribution As mentioned before virtually all IT equipment manufactured today is designed for worldwide compatibility. This means that it can operate with the North American 208/120 V voltage system, which is also used in Japan, as well as with the European voltage system. Mentioning only two voltage systems takes into account that many derivates like 380/220 V or 415/240 V are already included within the typical tolerance of ±10% related to these standard voltage levels. It is obvious that data centers using the European voltage level of do not need any PU transformers because they can feed the 230 V line-to-neutral directly to the IT devices, like it is shown in Figure 3. -Transformer Feeder Facility + IT istribution 3x AC Line V 400 V N Phase 1 Phase 2 Line 2 Line V 230 V 400 V 400 V 230 V Phase 3 Neutral Figure 3: distribution directly feeding the IT equipment Since all kind of IT equipment uses switch-mode power supplies it operates independently of the frequency of the supply voltage and can be used in 50 Hz and voltage systems as well. Looking at the data sheets of power supplies like the HP ProLiant L380 G5 shows, that operating rack-level equipment at 230 V vs. 208 V will result in up to 1% efficiency gain, and the efficiency gain will be up to 3% compared to equipment that is still running at 120 V. 6

7 The difference between and the typical US Baseline System becomes readily apparent when the power capacity for a three-phase branch circuit is calculated. Assuming that the feeding circuit is designed for 20 A, the power capacity of a 208/120 V circuit is 7.2 kva, while the power capacity of a circuit is 13.8 kva. So based on the same circuit current rating, the distribution is able to provide 92% more power than the 208/120 V distribution. This almost doubles the power density capability per rack without the need of changing the diameter of the cabling of the distribution network. Regarding the overall cabling losses it also needs to be considered that the currents in the main distribution network rise by 20% changing the voltage from 480 V to 400 V. This slightly reduces the positive effect of the above mentioned raised power capability in the branch circuits. Even more important than the cost, size and weight savings in wiring is the elimination of the PU transformers. In a North American data center utilizing high density racks approximately 20-30% of the floor space and the total weight on the high raised floor is consumed by the PUs. Realizing that this impact is lower using racks with less density, the new power distribution system with higher voltages and no PU transformers becomes even more important as the power density of the racks increases. As important as the savings in space and weight are the savings of energy by leaving out the PU transformers. This results in an additional efficiency gain of 1.5% to 2%, based on the typical Energy Star efficiency guideline for PU transformers. Eliminating the PU transformers also leads to increased fault current levels down to the branch breaker level. The positive effect of having this high short circuit current capability is the ability to clear any fault in the branch circuits within a few milliseconds and therefore without effecting the remaining loads. But the increased short circuit currents also need to be considered regarding breaker selection and tuning to guarantee proper electrical discrimination. So considering a modern data center which devices already run at 208 V and which utilizes highly efficient PU transformers the energy savings by changing the distribution voltage to can be expected to be between 2.5% and 3%, but can raise up to 7% if devices are still running at 120 V and less efficient equipment is used. Savings in space, cabling, material and cooling need to be considered additionally and show the high potential of overall savings coming with the change to a distribution. 7

8 4 Integrating in a 400 V distribution Even though the system is very common outside Northern America, standard 400 V units can not be used in the United States. The reason for this is that the standard comes with a frequency of 50 Hz, which is significantly different to the mains frequency in the US. So the distribution voltage needed for North American data centers is, a combination of voltage and frequency which is not a standard, but which easily can be generated from the existing mains by using transformers. There are two basic ways to implement a in such a distribution system: 1. Using a standard 480 V and add an autotransformer to its output to convert the voltage to 400 V. 2. Using a special 400 V with no need for an additional transformer downstream. On the first sight solution #1 seems to be the most convenient because standard 480 V units can be used. But it adds another transformer to the distribution network, which has just been removed. Nevertheless this can still be considered to be an advantage because of the low voltage difference that allows the utilization of autotransformers. This kind of transformer has a much better efficiency and requires less space than the isolation transformers required for the PUs. But the chance to get a distribution network without additional transformers and to avoid their losses, costs and space requirements is still worth being considered. First of all this requires modules that are designed to operate with 400 V. This should not be a serious problem for the manufacturers and so the remaining question is where to get the feeding 400 V from. In case of a 480 V feeder from the utility there again an extra autotransformer is needed to convert the 480 V to 400 V. But, in contrast to place a transformer downstream the, an upstream transformer, like it is shown in Figure 4, can be designed much bigger to feed multiple units, which comes along with a much better efficiency than an autotransformer for a single unit would have. Additionally an upstream transformer has no influence on the s short circuit capability and simplifies the design of the downstream distribution network. 8

9 Figure 4: Moving the transformer upstream the can increase the overall efficiency and simplifies the downstream distribution A medium voltage feeder, like it is common for large data centers with a power consumption above 5 A, allows the generation of 400 V 60Hz without any additional transformers by just using an transformer with 400 V secondary voltage. Figure 5 shows the design simplification as a result of this. Figure 5: A 2 nd transformer becomes unnecessary in case of a 400V feeder So this would be the optimal condition to realize a highly efficient and reliable power distribution for data centers in the world. 9

10 5 Supplying Essential Loads in a 400 V distribution The term Essential Loads describes the type of equipment that is essentially necessary to run a data center but which is less sensitive to power outages than the critical IT loads. In case of a mains outage these short-break or mechanical loads like chillers and pumps for cooling purposes will typically be supplied by iesel generators after a short power interruption of approximately 15 seconds. They are normally directly fed from the common 480 V power distribution and need no additional transformers, as it is outlined in Figure 6. G PU- Transformer 208/120 V Short-Break-Loads Figure 6: Conventional istribution including IT- and Short-Break Loads It is also quite common that these loads are fed by iesel Rotary (R) with a so called ual-output, like it is shown in Figure 7. R PU- Transformer 208/120 V Short-Break-Loads Figure 7: Conventional istribution Scheme utilizing ual Output R 10

11 This type of R utilizes an energy storage which is designed to support the critical loads only, but the iesel engine is strong enough to additionally supply the short break loads once it has been started. The 2 nd output of this kind of R is either taken directly from the output or from an isolated 2 nd winding of the generator. The breaker pair feeding the short-break loads is normally controlled by the R and can be integrated in the R switchgear cabinet as well as in the main distribution switchgear. Most mechanical loads are designed to be supplied by a standard combination of voltage and frequency (i.e. 480 V or 400 V 50 Hz) and are therefore not suited to operate with the unusual combination of 400 V and. So in case of a IT distribution the 480 V for the short-break loads needs to be taken from the line which feeds the or, in case of high power applications, from a separated transformer. An example of a standard 480 V distribution including a supply line for the IT loads is shown in Figure 8. The power for the critical and the essential loads is taken from a common 480 V bus which can be fed by standard 480 V iesel generators to supply both the critical and the short break loads in case of a mains outage. To take the advantage to supply multiple with one transformer the auto-transformers feeding the 400 V IT distribution are placed upstream the. There is no difference in the supply for the essential loads compared to the conventional 208/120 V distribution. G Short-Break-Loads Figure 8: Common 480 V distribution line for and Short-Break-Loads 11

12 Figure 9 shows a solution that does not utilize additional auto-transformers. This scheme uses 2 separate -transformers, each transforming the voltage right to the level needed for the loads. Considering that the power consumption of a big data center requires more than one transformer feeding the loads, this can simply be realized without creating additional costs by splitting the necessary transformers into two groups, each supplying its dedicated distribution network. G G Short-Break-Loads Figure 9: Separated feeders for and loads Locating the iesel generators on the low voltage side a special 400 V generator is needed for the critical loads while the mechanical loads can be supplied by a standard 480 V generator. Installing the iesel generator on the side eliminates this problem but makes the solution more expensive because it utilizes generators and additional switchgear. 12

13 6 Integrated power supply of Critical and Essential loads A very economical and cost efficient solution to supply the equipment in a data center is shown in Figure 10. A ual Output R allows supplying both the critical and the short break loads by using a single generator with two separated windings. In case of a IT distribution this generator can be designed in a way that the 1 st winding generates 400 V for the no-break loads and the 2 nd winding generates 480 V for the short break loads, both with. With this ual Voltage R there is no additional transformer necessary and it is possible to supply the critical loads as well as the short break loads with one iesel engine and one single generator. R M/G INV Short-Break-Loads Figure 10: The ual Voltage R allows supplying both and Short-Break- Loads utilizing one iesel engine and one generator only This kind of compact iesel is available with batteries as well as with kinetic energy storage. Comparing the examples shown in Figure 11 and Figure 12 illustrate the advantages of a system configuration utilizing ual Voltage R. In both figures both the critical and the short break loads are supposed to need 3300 kva electrical power, distributed through 4 power path in a 3+1 redundant configuration. So each power supply line is designed to feed 1100 kva. Two 4 A medium voltage transformers, one with and one with secondary voltage, are used to supply the associated loads. The configuration in Figure 11 utilizes 4x 1100 kva R to supply the critical loads and 4x 1100 kva iesel generators to supply the short-break-loads, both with a redundancy of 3+1. So there is the need of 8 iesel generators in total comprising the ones contained in the R including their individual auxiliaries like fuel, cooling and exhaust systems. 13

14 R R R R G G G G Critical-Loads Short-Break-Loads Figure 11 Example of a separated distribution utilizing R and Gen-Sets in a 3+1 configuration In Figure 12 the power supply for the same loads is realized by using 4 ual Voltage iesel Rotary only. Each of the units is able to supply 1100 kva no-break critical load on base of and 1100 kva short-break-load with concurrently. Therefore this configuration does not need additional iesel generator to supply the mechanical loads and the total amount of engines and generators needed to supply the loads is reduced to 4. Each of the iesel engines needs to be twice as big as in the example shown in Figure 11, but needs significantly less floor space and fewer auxiliaries than the solution with 8 engines. Accordingly the costs for equipment and installation and the time needed for installation and maintenance is reduced, too. R R R R Critical-Loads Short-Break-Loads Figure 12 Example of a combined distribution utilizing ual Voltage R in a 3+1 configuration So having everything integrated in one R reduces the infrastructure which is normally necessary for this equipment to a minimum and allows a straight forward and manageable design. 14

15 7 Summary Within data centers the power used for operating the facility, running IT loads and cooling is the largest expense. Reducing the number of components and operating at a higher voltage will save floor space and will result in greater efficiency and reduced electrical costs. A solution suitable for today s IT equipment is to change the supply voltage from 208/120 V to. This voltage level reduces the currents and the losses in the distribution network significantly and makes PU transformers obsolete. A special kind of iesel Rotary allows to supply critical IT loads with and Short-Break-Loads with 480 V using one iesel engine and one generator only. This reduces the infrastructure and the space requirement for the equipment to a minimum and allows a straight forward and manageable design. So combined with a suitable technology changing the supply voltage of IT equipment to is an effective solution to significantly reduce cost for energy and cooling in a modern data center. 15

16 8 References [1] Server Technology, Power Efficiency gains by eploying 415 VAC Power istribution in North American ata Centers, White Paper STI , 31. March 2009 [2] Facilities Engineering Associates (FEA), Power istribution Voltages, by Brian T. Soucy, Spring 2009 [3] The ata Center Journal Increasing Electrical Efficiency ownstream of the, by Christopher M. Johnston 25. June 2009 Frank Herbener, Piller Group GmbH Germany White Paper No / June