400V 60Hz UPS Power - Piller

400/230 Volt 60Hz UPS Power

Using Dual Voltage standby generation and UPS in one

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Contents

1 Abstract..........................................................................................................................3 2 Introduction ...................................................................................................................4 3 Alternative Power Distribution .....................................................................................6 4 Integrating UPS in a 400 V 60 Hz distribution..............................................................8 5 Supplying Essential Loads in a 400 V distribution ...................................................10 6 Integrated power supply of Critical and Essential loads ..........................................13 7 Summary......................................................................................................................15 8 References ...................................................................................................................16

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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 PDUs, 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 UPS modules including the power distribution for the short break loads. A special kind of Dual Output Diesel Rotary UPS 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.

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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 480/277 V 3-phase or medium voltage 3-phase. In case of a medium voltage feeder the voltage needs to be transformed down to 480/277 V 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 60 Hz, like it is shown in Figure 1.

Phase 1

N

Phase 2

Phase 3

Line 1 Line 2

277 V 277 V

480 V 480 V

480 V

Line 3

277 V

Neutral

Figure 1: 480/277 V 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 Distribution Unit (PDU) where it is transformed from 480/277 V to 208/120 V 3-phase, as outlined in Figure 2.

MV-Transformer

PDU-Transformer

MV Feeder

Facility Distribution

IT Distribution

MV

3x 480/277 VAC

3x 208/120 VAC

IT-Loads

Phase X

N

Phase Y

Phase Z

Line X Line Y

120 V 120 V

208 V 208 V

208 V

Line Z

120 V

Neutral

208 V IT-Loads

120 V IT-Loads

Figure 2: 208/120 V standard power distribution for IT equipment

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From the PDU, power is typically distributed in three ways: 1. 120 VAC single-phase (line-to-neutral) 2. 208 VAC single-phase (line-to-line) 3. 208 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 100-120 V and high-line voltages 200-240 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.

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