1. Challenges in Applying Higher Voltage Power Distribution in the Data Center Richard Draper, P.E. Data Center Power Distribution Product Manager Thomas & Betts Power Solutions Manufacturers of Cyberex

2. Utilization Voltages Overview: North American Data Centers 575V 3 phase 480V 3 phase 208V 3 phase 208V 1 phase 120V 1 phase PRIMARY DISTRIBUTION SECONDARY DISTRIBUTION - UTILIZED AT SERVER LOADS - Legacy practices borrowed from other industries 480V is typical for “long haul” power runs Transformers needed to step voltage down to the utilization level 208/120V is safe for unskilled users working with plugs and receptacles

3. The Quest for Efficiency and Power Density Chasing the “Green Dream” forces change Migration from 208/120V to 415/240V Higher Amperage, Higher Voltage Distribution Increased Power Density

4. Up to 4 Times the Power Density TREND: Increasing Power Density of Data Center Feeders

5. 415/240V Distribution Has Compelling Features Server power supplies conveniently work from 100V to 250V 240V L-N can be used in lieu of 120V or 208V L-N Branch circuits deliver twice the power at 240V 415/240V distribution eliminates the need for transformers Transformers account for a 3% loss in many data centers A C B N 208V Current Standard (208/120V) 120V A C B N 415V Emerging Standard (415/240V) 240V

6. 415/240V Distribution Has Compelling Features So What’s the Catch? High available fault currents More robu$t de$ign OCPD selectivity & coordination issues Arc flash concerns Long 4 wire feeders 415/240V distribution presents new design challenges

7. A Quick Primer on Fault Current Glossary : Fault ASCC (Available Short Circuit Current) Interrupting Capacity and AIC Rating Coordination and Selectivity Arc Flash

8. A Quick Primer on Fault Current Definition : FAULT – The term for a short circuit in an electrical system. Thermal and mechanical forces are destructive Must be stopped instantly to avoid life and property loss Circuit breakers and fuses prevent damage from faults

9. A Quick Primer on Fault Current Definition : ASCC – Available Short Circuit Current ASCC is less near the loads. Long wire distances and transformers act to limit ASCC. ASCC is greatest near the source of power. LOAD CABLE IMPEDANCE SOURCE

10. A Quick Primer on Fault Current LOW AVAILABLE

11. A Quick Primer on Fault Current HIGH AVAILABLE

12. A Quick Primer on Fault Current Definition : INTERRUPTING CAPACITY – A rating expressing the ability of a circuit breaker or fuse to stop a fault before damage occurs. Expressed as “AIC” – Amps Interrupting Capacity. A device’s AIC rating must be greater than the ASCC at the location it is applied. Interrupting Ratings 65kAIC @ 240VAC 25kAIC @ 480VAC 18kAIC @ 600VAC

13. A Quick Primer on Fault Current Definition : COORDINATION or SELECTIVITY – Describes distribution system’s ability to only trip the breaker or fuse closest to the fault. A branch breaker should never trip the main breaker. Proper coordination is a system design issue. High ASCC compromises coordination of main and branch breakers. TRIP ONLY THE BREAKER NEAREST THE FAULT

14. A Quick Primer on Fault Current Definition : ARC FLASH – The sudden release of thermal and percussive energy during a fault event emanating from the location of the short circuit or a component that fails due to the fault. Arc Flash can result in loss of life and/or destruction of equipment. The protective device hopefully limits and mitigates the energy from an arc flash. An improperly selected protective devices is in itself an arc flash hazard. The safety concerns regarding arc flash drive maintenance methods, equipment designs and the use of personnel protective equipment.

15. 415/240V Presents New Design Challenges

16. UPS SYSTEMS 208/120V 480/277V 415/240V 13.2 kV 2,500 kV, 5%Z 300 kVA, 5%Z UPS SYSTEMS 415/240V 14,360A 13.2 kV 2,500 kV, 5%Z 60,168A 69,444A 48,600A 208/120V TOPOLOGY 415/240V TOPOLOGY 415/240V Presents New Design Challenges 415/240V Transformerless Topology Increases Available Short Circuit Current

17. 415/230V Presents New Design Challenges Higher Voltage Decreases AIC Ratings of Protective Devices 240V AIC RATING 480V AIC RATING 208/120V 415/240V 480/277V AIC ratings depend on voltage AIC is high if under 240V AIC is low if above 240V 208/120V applications benefit from high AIC ratings 415/240V applications are based on the 277/480V breaker rating. Higher rated, more expensive protective devices must be used to meet the higher ASCC

18. 415/230V Presents New Design Challenges High ASCC Compromises Coordination of Protective Devices High fault conditions may prevent proper breaker selectivity Tried and true breaker combinations may not coordinate because of today’s trend toward larger transformers with high ASCC Selective Coordination, now required by NEC for life safety loads, has always been the norm for data centers and mission critical systems

19. 415/230V Presents New Design Challenges 480V UL Listed Panelboards Required for 415/240V 415/240V distribution has been the norm in Europe IEC/CE listed panelboards and breakers are not acceptable in US US requires UL listed panelboards and breakers UL listed 480V panelboards’ cost and physical size present challenges to a data center’s design Larger size drives larger equipment footprints and more panel space per pole

20. 415/230V Presents New Design Challenges 415/230V Topology Requires Longer 4 Wire Feeders Centralized large transformer – Neutral is derived in one place far from the load. Switching between sources for redundancy requires 4 pole breakers Neutral conductor adds installation cost Phase imbalance and harmonics are exacerbated by long neutrals

21. 415/230V Presents New Design Challenges N 4 WIRE LOADS N N N 3 WIRE 480V FEEDERS Neutral is derived at each PDU near the load 208/120V WHITE SPACE

22. 415/230V Presents New Design Challenges N 4 WIRE LOADS Neutral is derived at centralized PDU outside the whitespace 415/240V WHITE SPACE 13.2 kV FEEDER

23. Meeting the 415/240V Challenges High available short circuit current Lower interrupting capacity Poor coordination and selectivity Long 4 wire feeders

24. Meeting The 415/240V Challenges Dealing With High ASCC Traditional non-current-limiting breakers High let-through Slow acting Poor selectivity Current-limiting breakers and fuses Low let-through Fast acting Superior selectivity and coordination I max

25. Meeting The 415/240V Challenges Dealing With High ASCC – Conventional Circuit Breakers Panel Voltage Rating480V Panel Current Rating400 A UL Voltage & AIC Rating35 kA Max Branch Breaker Size100 amp Main/Branch Coordination3.2 kA Branch Clearing Time16 ms Finger Safeno UL 67 (panelboard)yes UL 489 (breakers)yes EXAMPLE: Sq-D NF panels and EGB main breakers

26. Meeting The 415/240V Challenges Dealing With High ASCC – Current-Limiting Devices Panel Voltage Rating240V480V Panel Current Rating225A & 400A UL Voltage & AIC Series Rating35 kA14 kA Max Branch Breaker Size100 amp25 amp Main/Branch Coordination35 kA14 kA Branch Clearing Time2.3 -2.5 ms Finger Safeyes UL 67 (panelboard)yes UL 489 (breakers)yes EXAMPLE: ABB ProLine Panelboard with Current-Limiting Breakers

27. Meeting The 415/240V Challenges Dealing With High ASCC – Current-Limiting Devices Panel Voltage Rating600V Panel Current Rating225A & 400A UL Voltage & AIC Rating200 kA Max Branch Fuse Size100 amp Main/Branch Coordination200 kA Branch Clearing Time< 3 ms Finger Safeno UL 67 (panelboard)yes UL 98 (fused switch)yes EXAMPLE: Cooper Bussmann QSCP Fused Panel

28. Meeting The 415/240V Challenges Dealing With High ASCC – Breakers vs Fuses FEATUREBREAKERSFUSES Resetable YesNo Repeatable ?N/A Requires Testing YesNo Requires Maintenance YesNo Requires Calibration YesNo Mechanical YesNo Vulnerable to Damage Yes? Current limiting * NoYes * Tested, Listed, Labeled

29. Meeting The 415/240V Challenges Solutions to Meet Your Exact Needs Cyberex offers a multitude of custom 415/240V panel board solutions for data centers: Sq-D ABB Cooper Bussmann GE Siemens

30. Meeting The 415/240V Challenges Dealing With High ASCC – Line Reactors Line Reactors Air core reactors in series with RPP mains Housed in RPP cabinet Limits fault current to about 10 kA Minimal effect on voltage drop Minimal energy loss (mostly reactive) Large and expensive ABC

31. Meeting The 415/240V Challenges Dealing With Long Neutrals: Zig-Zag Autotransformer Zig-zag Autotransformer Primary function is to derive a neutral at load Allows 3 wire feeder to be used Parallel-connected; only active during a fault or extreme phase imbalance Secondary benefit is to limit fault current to about 10 Ka Code compliance is frequently debated N 3 WIRE 4 WIRE

32. N 3 POLE STATIC SWITCH IF SIMILAR SOURCES ARE IN CLOSE PROXIMITY AND THEIR NEUTRALS ARE DERIVED AT THE SAME POINT, A 3 POLE STATIC SWITCH MAY BE USED. 3P IF SOURCES ARE DISIMILAR AND SEPARATED BY DISTANCE A 4 POLE STATIC SWITCH MAY BE REQUIRED. N 4 POLE STATIC SWITCH 4P Meeting The 415/240V Challenges Dealing With Long Neutrals: 4 Pole Static Transfer Switches 3 POLE STS4 POLE STS

33. Richard Draper, P.E. Data Center Power Distribution Product Manager Richard.Draper@tnb.com www.tnbpowersolutions.com Thomas & Betts Power Solutions Manufacturers of Cyberex Thank You!