Power distribution in data centres

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Power distribution in data centres

by Manuel Lotz / Matthias Ribbe

White Paper 09

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1 Introduction

Power distribution requirements differ from data centre to data centre depending on how it is equipped. Nevertheless the basic supply is identical in every case, in other words: many data centres are equipped with a mains supply from the utility, one or more uninterruptable power supplies (UPSs), and a generator.

This is a completely different story though in the server racks: many manufacturers market standard socket strips with earthed, IEC-60320, and C15 sockets. There are scarcely any variable socket strips on the market. This white paper discusses the various types of socket strips on the market.

2 Standard socket strips

In most cases it is left up to users to install power distribution in the rack where they can choose from a range of different outlet strip types. Modern devices in a server rack feature a wide range of different supply lines, so the choice of sockets must take account of these in each and every case.

The most common supply lines today are:

C13 / C14 230 V / 10 A 3 pin C19 / C20 230 V / 16 A 3 pin earthed socket 230 V / 16 A 3 pin

Fig 1 – Overview of common plug-in connectors in data centres

Earthed sockets are widespread in the European area. C14 or, in full, IEC-60320 C14 connectors are predominantly used for servers and switches.

The C20 or, in full, IEC-60320 C20 connector is very often used for high-performance servers and switches.

These connector types are scarcely possible with the standard socket strips, so each connector type is assigned its own socket strip. In this case though there is a risk of inadequate cable management that can prove detrimental to the optimal air flow. If the air is not properly drawn away from the devices in the server rack, heat can accumulate

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and the devices suffer as a result. In the case of supply lines specific to certain countries the user must even install an additional socket strip.

To boot, today’s IT equipment often features two power units, so the server rack must be fitted with a redundant power supply. This would mean that the various socket strips must be installed twice in the rack – impossible within the confines of 600 x 1000 mm. In this case the user should opt for a modular outlet system.

Fig 2 – Socket strip

(source: Rittal GmbH & Co. KG)

2.1 Intelligent standard socket strips

Many manufacturers also market intelligent socket strips. These systems feature individual activation and management for each outlet on the strip. Some manufacturers of these socket strips even offer preinstalled instrumentation that can measure the current, consumption, voltage, and the power currently drawn by the connected consumers. These measured values can then be viewed or stored either locally on a display or over a network. Power outages, fluctuations, and overload can be reported as SNMP (Simple Network

Management Protocol), email, or text alerts to the facility management or administrator.

3 Modular socket strips

Modular socket strips present the most flexible solution for data centres to adapt to changing requirements. These modular systems consist of a mounting rail installed in the enclosure and connected directly to the supply line or, if fitted, to the UPS system. This mounting rail

Fig 3 – Intelligent socket strip

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required connector sockets. Modules of this type are available with the usual C13 and C19 sockets, but also with various sockets specific to each country.

Once the mounting rail has been installed and connected in the enclosure, these modules can also be retrofitted or replaced by non-electricians or administrators during operation. This greatly enhances flexibility with respect to the various connectors and growing loads in the rack. Also the time needed to react to new requirements is cut because changes can be made by the administrator himself during operation. When more outlets are needed, an

additional module can simply be added to the mounting rail. Also mixing modules with different connector sockets is possible.

Fig 4 – Modular socket strip

3.1 Mounting rails for modular socket strips

The used mounting rails generally consist of an extruded aluminium or plastic channel section containing the entire wiring. They feature an all-insulated design and can be secured vertically to the enclosure frame to one side of the 482.6 mm (19”) level. In other words there are no height units lost that could otherwise be used for IT equipment. Once installed the rail can be fitted with connector modules over virtually all of its length. Rails of various lengths are available for the various heights of IT racks, depending on the number of modules to be fitted.

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Fig 5 – Principle of redundant supply

The mounting rail can be supplied with either three-phase (e.g. 3 x 16 A) or single-phase (e.g. 1 x 32 A) current, depending on the rack configuration. The most common form in the IT field is three-phase because of its greater adaptability. In addition three-phase supplies offer advantages with respect to the selectivity in fusing each phase. Modern mounting rail systems also feature a facility for connecting two supplies to the one rail and can therefore draw their power from two independent sources. Hence redundancy can be obtained as well on only the one rail installed in the

enclosure. 1-phase 16 A 230 V+N+PE 1-phase 32 A 230 V+N+PE 3-phase 16 A 400 V+N+PE 3-phase 32 A 400 V+N+PE

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From which of the two supplies the module draws its power depends on how it is attached to the rail. When the module is drawn off the rail, turned through 180°, and reattached, it will draw its power from the other supply. The principle of this system with A and B supplies is illustrated in Fig 5 on page 6. When greater power draws are

required in the rack, mounting rail variants are available with up to four three-phase supplies (4 x 3 x 16 A). These rails can then take up to 192 A. Not including their

supplies they are identical to the single-phase standard mounting rails. However, these rails require special connector modules.

3.2 Connector modules

Modular connectors are self-contained systems. Just like mounting rails they feature all-insulated designs, so non-electricians too can work with these modules. The modules

are simply engaged on the rail by means of a plug & play system. This cuts assembly times in the data centre and therefore the costs. As good as all of the usual connector variants are catered to, including those specific to certain countries, just as special IEC or NEMA connectors. Most of these modules feature integrated thermal overload protection, i.e. only the fuse to the

overloaded module trips, the others on the rail are unaffected. Any defect module on the rail can be very quickly replaced with a new one. The MTTR (mean time to repair), or the time between module failure and replacement, is minimised. More recent connector modules feature in addition two integrated three-colour LEDs indicating the momentary utilisation of the module’s capacity. One example is illustrated in Fig 8. The colours green, yellow, and red indicate to the user whether the module’s capacity is utilised to the full, or whether further consumers can be attached.

Fig 7 – Various designs of connector modules

Fig 8 – Modules with LEDs

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4 Intelligent power distribution systems

In a modern data centre an overview of the momentary current consumption by each consumer and the data centre as a whole is particularly important. The option of remote monitoring gains in significance in the face of the constantly growing costs to operate a data centre. SNMP-compatible mounting rails and connector modules provide this option as well as a number of other features in addition to the above advantages of modular power distribution systems. These systems considerably simplify and at the same time intensify the monitoring and control processes in the data centre. There are various options for realising an intelligent, network-compatible power distribution system.

4.1 Network-compatible mounting rails

One monitoring option takes the form of network-compatible mounting rails with

integrated measuring systems that can monitor and log all of the rail’s relevant values. These measuring rails can be monitored and configured completely over the network, including limits for current, voltage, and power per supply phase. When these are

exceeded the system activates the alarm or sends e-mail or text messages to any number of recipients. The rail features a local LED display that also presents these data, which can be scrolled through at an adjusting wheel. Moreover it allows the user to modify the configuration locally. The LCD display flashes when alarm statuses are activated.

Fig 9 – LCD display on network-compatible

mounting rail with measuring system

(source: Rittal GmbH & Co. KG)

4.2 Intelligent connector modules

Network-compatible connector modules with integrated intelligence also present an option for the remote monitoring and control of a data centre. With these systems the intelligence is independent of the mounting rail used. For instance, a normal rail can also take a mix of intelligent or active modules and passive connector modules, when

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active modules all outlets are individually switchable, i.e. the connected consumers can be actuated independently of each other. Just like network-compatible mounting rails active connector modules too allow users to set limits for alarm messages and warnings and to send e-mail and text messages. LED segment displays present locally the

module’s momentary current values. A number of manufacturers also offer these modules in 1 U designs for installation in the 482.6 mm (19”) level. This is an interesting variant above all when there is no more space available at the side of the 482.6 mm (19”) frame or only some of these controllable outlets are needed in the enclosure. When using several active modules in one enclosure users can cascade up to four identical active modules.

Fig 10 – Intelligent and network-compatible connector module

5 Accessories for modular power distribution systems

Together with the various connector modules there are also a large number of accessories available for modular socket strip systems.

For instance there is retrofit overload protection that can be optionally connected upstream of the rail. A special module can provide measuring functions on a standard mounting rail not fitted with an integrated measuring facility. This measuring module is connected on the input side upstream of the rail and likewise installed in the enclosure. Other practical accessories are special cables for connecting servers and other devices to the connector modules. Available in lengths from 50 cm these cables are kept

relatively short so that there are no excess lengths and therefore no obstructions to the air flow, and no turbulence in the enclosure. Potential hot spots that could prove

detrimental to the performance and service life of the devices installed in the enclosure are therefore eliminated. Yet other products, e.g. a light module for use as a portable lamp that recharges when attached to the mounting rail, serve to configure such a modular system precisely to the needs of the affected enclosure.

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6 Summary

Power distribution systems are mandatory in every modern data centre. In the face of ever growing energy costs and power densities these systems will gain in importance in the future as well. Owing to the wide range of different connectors on IT equipment and the growing demand for remote monitoring facilities normal socket strips come up against their limits relatively quickly. Modular and network-compatible power distribution systems enhance flexibility and scalability to a considerable degree. Mounting rails with integrated measuring instrument allow the precise monitoring of the current

consumption. Intelligent connector modules that can switch each port individually offer great potential for the remote monitoring of the data centre as a whole. With the aid of intelligent, modular power distribution systems not only the distribution of current can be adapted precisely to the required conditions, but also the power consumption can be reduced – with the corresponding reduction in the data centre’s maintenance costs. The option of realising two independent supplies on the one rail means that two distributor rails need no longer be installed in each enclosure for the purpose of supply

redundancy. This in turn saves costs in the purchase of an IT enclosure.

All these points show clearly the superiority of modern, modular current distribution systems over normal, non-modular systems, advantages that can considerably reduce costs in the data centres of tomorrow.

Power distribution in data centres

Power distribution in data centres

White Paper 09

Contents

1

Introduction

2

Standard socket strips

3

Modular socket strips

4

Intelligent power distribution systems

5

Accessories for modular power distribution systems

6

Summary