400VDC Distribution – Deployment, Components and Best Practices for Safe Implementation

BJ Sonnenberg – Mgr Business Development Emerson Network Power David Geary – Director of Engineering Universal Electric Corp / StarLine dc Solutions Brian Davies - Director of Product Development Anderson Power Products

2

Common Perception Related to 400VDC

Perception of safety issues in higher voltage DC applications • Hazardous voltage • Arcing • No current zero crossing – difficult to break current • Grounding methods • Arc flash issue not well understood

3

Physiological Effects of DC and AC AC or DC above 30volts can be potentially dangerous and cause involuntary muscle action (tetanus)

Low frequency (50 to 60Hz) AC is 3 to 5 times more dangerous in this regard than DC of same voltage because:

• AC produces extended muscle contraction which can freeze the hand to the power source • DC produces a single contraction , which usually forces the hand away from the power source • AC can cause heart fibrillation , and once power is removed the heart is not likely to restart • DC makes heart still, once power is removed and the heart can restart

Figures are approximate and depend on individual’s body chemistry and other factors www.allaboutcircuits.com – volume1

4

Body Current/Duration Characteristics for Hand-to-Hand Pathway, IEC/TR 60479-5 - Hot Conductor to Ground

I - Normally no perception II - No dangerous physiological effect, risk of startle reactioIII - Risk of muscular reaction IV - Critical effects, risk of ventricular fibrillation

Average human body resistance =1500 ohm (200-400V)

208/230/277VAC - IV 120VAC - III

400VDC (one pole) – III

400VDC direct midpoint - III

400VDC midpoint 50kΩ - II

48VDC - II

RCD 30mA/200ms RCD –residual current device (in US and Canada also known as GFI or GFCI)

5

Safety: 400V DC Grounding High Resistance Midpoint Ground (HRMG)

• Human body current for line to ground is limited to 7.5mA (for 50kOhm resistor) IEC Zone II • No dangerous effects

• High resistance midpoint grounding (HRMG) makes 400V DC as safe as -48V DC with regard to electrical shock (line to ground)

• No arc flash to ground during single ground fault for HRMG • HRMG is widely used today in 110/220VDC networks in industrial, utility

and railway environments • Requires real-time ground fault detection

© 2011 NTT/NTT Facilities/France Telecom/Emerson Network Power Intellectual Property. All rights reserved

R=50kΩ

AC In

400V DC Power System

+200V DC

-200V DC

R

Loads

400V DC

R

200V DC

200V DC

ᴖᴖ

6

Causes of Arcing in AC and DC

Bad connection in a circuit carrying high current - AC ≈ DC (most cases) Disconnection of components and equipment in power distribution - DC is worse Unintentional short circuit of power conductor to earth or another conductor- AC=DC

Mechanism of arc ignition : If the electrical field strength created by potential difference between two separated conductors exceeds a certain threshold , the energy will be sufficient to ionize the gas in the gap. For arc ignition a potential difference as low as 30V is enough. Electric arcing occurs and is tolerated at normal load conditions in : Connectors Switches Spark gaps

7

DC arc faults were more persistent, due to the lack of a periodic zero-crossing. As such, from a local perspective, high arc currents (175A) damaged copper electrodes and support structures and may be considered a fire hazard.

AC open series faults dissipated within a few cycles of the point of discontinuity. However, fast-acting transients were observed in both the gap voltage and current waveforms. With magnitudes up to four times the bus voltage, these spikes may be cause for alarm as this would exceed voltage ratings for various passive components within system power electronics.

From the results presented herein: DC open series faults are electrically benign, but mechanically hazardous; AC open series

faults are electrically malign, but mechanically benign.

From a dc system perspective, the lack of considerable spikes in the gap voltage or current waveforms is an electrical advantage. Despite the fact open series faults persist for a much longer duration, if power electronics could effectively be utilized for fault isolation, the impact on other distribution laterals would be minimized.

Future research will explore dc arc detection, fault clearing strategies, power downstream of limiting sources, and dc arc model development. Additionally, safety considerations will remain a strong focus.

H.B. Estes, A. Kwasinski, R.E. Hebner, F.M. Uriarte, and A.L. Gattozzi Department of Electrical & Computer Engineering

The University of Texas at Austin,Center for ElectromechanicsAustin, TX 78758, USA

Open Series Fault Comparison in AC & DC Micro-grid Architectures (ref 1)

8

Elements of Safe Deployment – Designing for Safety and Reliability

• Elements of safe design • System components selection • Equipment construction –plug in approach (minimizes

installation errors ) • System architecture and best practices – hot plug-in approach • Grounding • Procedures –installation, operating, maintenance – NFPA 70E

9

Connectors for DC Powered IT Equipment

Arc breaking technologies

Saf-D-Grid connector

Other connectors

Standardization update

10

Arc Breaking Technologies 1) Fujitsu - DC circuit breaker magnetic arc quenching technology Not practical, high cost and the size are not compatible with IEC 320

2) Delta - 4th contact pair triggers “Hot Swap” secondary circuitry of the power supply to avoid breaking arc Does not support IT devices lacking “Hot Swap” capability

Cost of 4 wire cable higher than 3 wire

PDU, Cord and Power Supply must be by same manufacturer to achieve Safety Agency Listing

3) APP - Connector geometries naturally suppress arcing & contacts have sacrificial arcing area Robust contacts increase price versus IEC320 inlet

3 wire cable keeps price of power cords down

All of the above technologies allow safe disconnection of the powered load.

11

Saf-D-Grid (SDG)

2 flat surfaces have greatest resistance to arcing SDG’s flat wiping contacts dampen initiation and

continuation of arcing

Over wipe of connector housings quenches arcing Insulators eliminate line of sight between contacts upon un-

mating

Large tracking distances between contacts Prevents arcing products from developing arcing between

lines or ground

Sacrificial contact area Prevents dampened arcing damage from effecting electrical

performance

Large selection of options Flush-mount Receptacle

Mid flange Receptacle

Ultra-short Receptacle (< IEC320)

Standard Plug

Wide “T” Latch Plug

Right Angle Plug

UL, IEC, PSE or CCC approved cordage

Specialty Cords SDG to IEC320 C20

SDG to IEC320 C14

SDG to Delta (Linetek)

Approvals UL 1977 Recognized &

UL 817 Listed IEC 61984 Certified CCC Approved

12

Other Connectors Fujitsu Plug and Socket with integral

miniature DC circuit breaker Socket has switch for plug lock and

power on/off Compatible with specification in

development by IEC Socket specified for fixed installation

usage only, no portable multiple outlets or extension cords allowed

Too big for power supply connection Delta (Rong Feng, Linetek) Plug and Socket with 4th contact pair

to trigger switching off power supply 4 wire configuration not supported

by pending IEC specification or EMerge alliance standard

Rong Feng Connector

Fujitsu Connector

13

DC Connector Standards & Specifications • EMerge Alliance Data/Telecom Center Standard 1.03

• APP Saf-D-Grid approved standard connector

• UL 2695 DC Rated Attachment Plugs And Outlet Devices Intended For Use With Information Technology And Telecommunications Equipment Installed In Restricted Access Locations

• APP Saf-D-Grid internally evaluated to all specifications. APP has differed UL evaluation until UL 2695 is raised from “Investigation” to “Standard”.

• IEC TS63275 D.C. Plugs And Socket-Outlet For ICT Equipment Installed In Data Centres And Telecom Central Offices

• Draft Technical Specification covers plug and sockets for fixed installation. Fujitsu, Legrand form factor

• Work on Appliance Connector standard will begin in TC23SCG Nov 2014. Brian Davies will convene Ad Hoc committee to develop Technical Specification

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380V DC CIRCUIT PROTECTION

Tmax Molded Case

Emax DC

380VDC FUSES 20-100 Amp, 700 V dc

22 X 58 MM

Product Highlights UL 489 Listed UL 489B Listed TUV Certified IEC/EN 60947-2 Temperature stable hydraulic/magnetic overcurrent sensing technology Optional relay trip circuit, permitting remote operator system shut down

See video: https://www.youtube.com/watch?v=6---aEbkyAE

16

380V DC CIRCUIT BREAKERS

17

SYSTEM TESTING by Emerson Network Power: System Performance under Faults and Arcing

Tests performed to evaluate short circuit performance (line to line) and impact on main bus voltage recovery time under different operating conditions Difference in circuit breaker and power distribution performance

vs. 48VDC and AC Comparison of 3 different circuit breakers Impact of cable inductance and circuit breaker rating

Arcing Understanding of risk scenario Comparison of different plugs Impact on bus voltage when disconnecting the load

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Comparison of 63A Circuit Breaker Performance from 3 Suppliers at Short Circuit Test – Battery Source (AC UPS Battery) – No Load to Short (UL 1012 supplementary breakers ) Cable: 5m x 70mm²+0.5m x 25mm², each pole .Battery: 30x12V=360V/25Ah. Rectifiers disconnected

ABB Schneider Nader

400V

1250A 400V 1100A 400V 1350A

S282UC-K C60H-DC NDB2Z-63

Test results are comparable , Nader has lowest short circuit impedance Voltage recovery on main bus well within power supply hold-up time < 10ms

No major voltage overshoot on main bus. © 2013 Emerson Network Power Intellectual Property. All rights reserved

Voltage recovery on main bus 1.9ms ~2ms ~2ms

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Power Plugs in 400VDC Disconnection Tests

APP Fujitsu Molex Saf-D-Grid EXTreme LPH Power

Power Modules

Signal Module

400VDC/20A

Micro switch

400VDC/10A 250VDC/30A per contact in Power Module

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APP Saf-D-Grid plug(20A) Disconnection

380V

5A 10A

5A load, normal disconnect 10A load, normal disconnect 10A load, slow disconnect

10A

380V 380V

- The APP plug operates satisfactory up to 20A - No arcing (current transients) between the pins at distinct and ”normal” speed disconnection - No visible arcing outside the plug - Clear tendency for arcing at slow or non distinct disconnection - The plug disconnection of 5-25A loads has no impact on DC voltage on the 400V Bus

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Conclusions from Testing on Equipment and System Level

400VDC distribution vs 48V and AC 2 – pole circuit breaker in 400VDC

The same safety requirements as for 230VAC distribution

Rectifier output capacitor is the main energy source (not the battery) for ceasing circuit breaker in hard short circuit

400VDC circuit breakers Similar and stable performance

Similar ceasing times to 48V and AC circuit breakers

400VDC plugs Commercially available today and with certifications

Safe operation with regard to arcing

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400VDC Distribution System Design – Best Practices Summary • Safe design of conversion equipment • Flexible , plug in distribution – eliminates installation errors • Busway with pluggable interfaces • Minimize field terminal type connections • Use connectors to interconnect equipment • Use factory made distribution units – avoid field improvisation

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• Plug-in components • Ability to service major elements without system shutdown • Shielding and protective access • Compartmentalize serviceable components

DC UPS Constructions Principles for Safe Equipment Design 120kW Example

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Advantage of Busway Distribution

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Adding, Servicing, Changing components in an electrical system are not always easy!

• Permissible to install on energized busway. • Grounding is established prior to voltage being applied. • Busway is “finger safe”. However, there is no reason to place hands or tools up inside the access slot. • No routine maintenance required ?

Adding, Servicing, Changing circuits using is easy and safe! THE BUSWAY ARC FLASH ADVANTAGE

Busway vs Discrete Distribution

Circuit plug in

26

Busway Layout Options

27

Rack Distribution – Power Strips

• Similar construction to AC strips • Loads can be hot plugged in or disconnected

28

Distribution Implementation Strategy – System Architecture Plug and play approach Limit personnel access to live components Allow easy and live replacement of failed components through creative distribution system architecture Maintain continuous operation under multiple

faults

29 SOURCE: EMERSON NETWORK POWER 2012

Output Connectivity Options

400VDC UPS

DistrA

DistrB

Battery

Bus duct Wire in conduit

Battery

400VDC UPS

Server Rack

Server Rack

A B

A B

Bus duct

Battery

400VDC UPS

Server Rack

A B

Bus duct

800A CB limit 230kW

Distribution options: 1.Fuses – shorter clearing time 2.Breakers – easier to operate 3.Bus duct plug-ins – space, scalability

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Plug in Concept Benefits

Hot plug in maintenance concept

• 2N+ 1 UPS configuration • Busway with 2 End Feeds (Redundant) • Busway plug In units are added as racks are added (live) • Racks can be removed without system shutdown • During routine maintenance personnel is never exposed to live

parts : • Server level • Rack level

Hot plug –in point

Server

A side B side

Fixed structure

31

DC System Architectures Between BICSI Classes - Examples

32

Practical Implementation - Example

BICSI 002 Class F1,F2,F2+,F3 ? Equivalent

BICSI 002 Class F3, F4 Equivalent – using single or double DC busway

Single utility feed shown. For BICSI Class F3 and F4 two independent utility feeds would be employed.

33

Fault Characteristics in AC and DC Circuits

• In low voltage AC distribution ground faults are substantially more common than phase to phase faults – ref. 4 ,although statistics are difficult to come by and require substantial research. In statistics cited for circuit elements that involve cable conductors (IEEE Std 493-2007), 99% of failures due to arcing faults involved ground. Remaining 1% did not (ref. 4). It is generally acknowledged that ground faults constitute at least 80% of all electrical faults.

• It is reasonable to assume that the case would be similar for low voltage DC distribution, therefore preventing arcing faults to ground is the most effective strategy to eliminate majority of electrical faults (HRMG grounding and plug-in connections)

• NFPA 70E assumes that line to ground fault will ultimately evolve to L-L fault , but with HRMG that is not the case.

34

Grounding Basics

35

ETSI EN 301 605 (Grounding and Bonding)- Summary

• Both system earthing arrangement comply with relevant safety requirements

• IF the continuity of operation is placed in the forefront THEN the symmetrical IT system ±200 Vdc with earthed high-ohmic mid-point is the first choice. In cases where an IT system is used for reasons of continuity of supply, automatic disconnection is not usually required on the occurrence of a first fault (single fault) to an exposed-conductive-part or to earth. This is valid on condition that an Insulation Monitoring Device (IMD) indicates the first fault by an audible and/or visual signal which shall continue as long as the fault persists.

• IF similar system earthing arrangement as for today’s -48 Vdc system is requested THEN the TN-S system +400 Vdc may be chosen.

IT system with earthed high-ohmic mid-point TN-S system with earthed negative line terminal

Source - Ericsson

36

By ETSI ’rejected’ system earthing arrangement

Both system earthing arrangements below are extracted from IEC 60364-1

Asymmetrical, one power source: Normal operation: L+ = +400 Vdc, L- ≈ 0 V Disadvantage: Very hard to detect the difference of a correct L- ≈ 0 V (via high-ohmic resistance) and a real earth fault L- = 0 V due to a short-circuit between L- and earth.

Symmetrical, two power sources: Normal operation: L+ = +200 Vdc, L- = -200 Vdc Disadvantage: Series connection of two 200 V power sources L+ = +200 Vdc and L- = -200 Vdc

IT systems - asymmetrical and symmetrical

Source - Ericsson

37

Grounding Conclusions High resistance midpoint grounding (HRMG) makes ≈400VDC as

safe as 48VDC with regard to electrical shock (line to ground)

No arc flash to ground during single ground fault for HRMG

HRMG is widely used today in 110/220VDC networks in industrial, utility and railway environments

The HRMG technology is already well established and proven

No RCD required, but there is a need of ground fault monitoring in HRMG

No EMI problems reported from a dozen of POC sites

NTT, NTT-F, FT and Emerson Network Power have selected high resistance midpoint grounding for 400VDC

© 2011 NTT/NTT Facilities/France Telecom/Emerson Network Power Intellectual Property. All rights reserved

38

OSHA , NFPA70E Overview What is NFPA 70E?

"Standard for Electrical Safety in the Workplace," outlines the specific procedures and practices to be followed for (OSHA compliance and) safety when working on live equipment.

What is Covered?

Safety-related work practices associated with electrical energy during activities such as installation, inspection, operation, maintenance and demolition of electric equipment.

39

12

Qualified Person: A qualified person shall be trained and knowledgeable in the construction and operation of equipment or specific work method and be trained to recognize and avoid the electrical hazards that might be present with respect to that equipment or work method.

Such person shall also be familiar with the proper use of the special precautionary techniques; personal protective equipment including arc flash suit; insulating and shielding materials; and insulated tools and test equipment. A person can be considered qualified with respect to certain equipment and methods but still be unqualified for others.

NFPA -70E Safety Requirements

40

NFPA -70E Safety Requirements • DC requirements added in 2012

• For DC systems >100VDC NFPA 70 requires an arc flash hazard risk analysis and appropriate PPE (Personnel Protective Equipment) when working on energized systems (Art.130.5).It also sets worker protection boundary distances.

• Article 130.4 also requires a shock hazard analysis to be performed

• NFPA 70E refers to two methods to determine DC arc flash and PPE requirements(Art 130.5B) – calculation methods and table method . Calculation methods require calculating the incident energy. Table method is a simple determination of PPE requirement based on system voltage and available short circuit current . The calculation methods ,especially Ammerman method are much more accurate.

• Two calculated methods are referenced in Annex D :

• Maximum Power Method (per Doan)

• DC arc model (Ammermann)

41

NFPA 70E Tables for Determining DC Arc Flash

Look up method table Calculation method table

42

Sample Calculation for 120kW System 120kW system with 60 min battery Faults in locations 1-3 do not produce a significant hazard and are omitted in the analysis 4 cabinets =

1hr back-up

Fault #5 - single battery cabinet when serviced with battery breaker opened

43

Results per Ammerman Method

Risk Category 2 Risk Category 0

AC input not considered in this analysis

44

Strategies for Safety Enhancements in DC Distribution – On the Roadmap • Use inherent current limiting characteristics of electronic converters in

distribution system design • DC powered lighting and HVAC • Further improvement of rectifier efficiency • New topologies • New components (GaN , SIC) • Improved ground fault detection and location • Battery/energy storage advances , including storage located at or near

loads • Natural gas as primary power source • Electronic and hybrid breakers and switches

Euro-team to develop semiconductor-based DC circuit breaker david manners 1st July 2014 A publicly-funded European team lead by Infineon is to try and develop a semiconductor-based DC circuit breaker. Losses in power grids and electric devices are between 5% and 7% smaller with direct current than with alternating current. Direct current also makes it possible to more efficiently feed electric energy from regenerative sources into power grids and energy storage and to improve grid stability; with direct current it would be possible to build much more compact electric devices. Funded by the German Federal Ministry of Education and Research (BMBF), the research project called “NEST-DC” aims to investigate the foundations of a semiconductor-based and completely electronic circuit breaker for DC power grids and applications.

45

•Conclusions To assure safety in electrical distribution AC or DC : • Use proper components with ratings & listings selected for safe

operation

• Assure selectivity of protection scheme

• Use proper grounding methods in distribution

• Select system architecture allowing full isolation of distribution components for ease o maintenance

• Use plug-in concept where possible , minimize field installation work

• Adhere to and follow safety procedures

Under most operating and maintenance conditions a

400VDC system is safer than an equivalent AC system

46

To Continue Discussion Please , join us at Intelec 2014 , Vancouver , booth 201 You will see a fully assembled small demo of a 400VDC system and will have an opportunity to talk to leading industry experts.

47

References – Safety Related 1. Open Series Fault Comparison in AC&DC Microgrid Applications – H.B Estes et al. – 978-1-4577-1250-0/11/$26.00 2011 IEEE

2. A DC Arc Model for Series Faults in Low Voltage Microgrids – Fabian M. Uriarte et al.– IEEE Transactions on Smart Grid, Vol.3 , No. 4, December 2012 3. NFPA70E Standard 2012 4. Fault Characteristics in Electrical Equipment – Eaton white paper TP08700001E – September 2011

5 . http://www.interfire.org/features/electric_wiring_faults.asp

6. A Study of the Safety of the DC 400 V Distribution System – Masatoshi Noritake et al , Intelec 2010

7. Grounding Concept Considerations and Recommendations for 400VDC Distribution System - Keichi Hirose , Toshimitsu Tanaka , Sylvain Person , BJ Sonnenberg , Marek Szpek , Intelec 2011 8. Phillips, J. ,Chapter 8 , “DC Arc Calculations, in Complete Guide to Arc Flash Hazard Calculation Studies , Scottsdale AZ Brainfiller, Inc. , 2011 9. Case Study – DC Arc Flash and Safety Considerations in a 400 VDC Architecture Power System Equipped with VRLA Battery - Michael , M. Krzywosz

, Intelec 2015 (not released yet)

10. Arc Flash Calculations for Exposure to DC Systems - Doan D.R. ,Industry Applications , IEEE Transactions on Volume 46 , Issue 6, 2010 11. DC arc models and Incident Energy Calculations , - Ammerman R.F. , Industry Applications , IEEE Transactions on Volume 46 , Issue 5, 2010 12. AC&DC Power Distribution for Data Centers ,TGG Presentation At the Green Grid forum -2012

13. ANSI/BICSI 002-2011 , Data Center Design and Implementation Best Practices

14. 380VDC Architectures for the Modern Data Center White paper , EMerge Alliance 2013 15. ETSI EN300-132-3-1, ITU-T L1200 , Emerge Alliance Data/Telecom Center standard 16. ETSI EN 301 605 , Earthing and Bonding standard

17. IEEE Std 493 – 2007 (Gold Book) , Design of Reliable Industrial and Commercial Power System

48

Back-up

49

Agency Status / Standards

Standardization Work Closely Harmonized to Agree on Aligned Global Standards

• 400V system standards currently released or under development through international efforts UL (several products listed today) – cover all distribution system components ETSI EN 300 132 -3-0 – power interface standard – RELEASED ETSI EN 301605 – earthing and bonding for 400VDC systems - RELEASED ITU – (ITU-T l.1200) – adopted ETSI voltage levels - RELEASED IEC / IEEE – working group in place – new DC UPS standard

ATIS – voltage levels standard in development SCTE – committee started NEC – Current edition applies to both AC and DC : Wiring , protection , safety EMerge Alliance - Focus on site and system interfaces – RELEASED YD/T 2378-2011 (China Standard) 240VDC Direct Current Power Supply System for Telecommunications – RELEASED Planned update for 336V (380VDC) mid to late 2014 NEMA / EPRI – work in progress

• Standards also needed for and driven by renewable resource deployments

50

Understanding “Arc Flash”

Simply put, an arc flash is a phenomenon where a flashover of electric current leaves its

intended path and travels through the air from one conductor to another, or to ground.

The results are often violent and when a human is in close proximity to the arc flash, serious

injury and even death can occur.

Arc flash can be caused by many things including:

Dust

Dropping tools

Accidental touching

Condensation

Material failure

Corrosion

Faulty Installation

Three factors determine the severity of an arc flash injury:

Proximity of the worker to the hazard

Temperature

Time for circuit to break

OSHA Definition of Arc Flash

An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, harm, fire, or injury. Electrical arcs experience negative resistance, which causes the electrical resistance to decrease as the arc temperature increases. Therefore, as the arc develops and gets hotter the resistance drops, drawing more and more current (runaway) until some part of the system melts, trips, or evaporates, providing enough distance to break the circuit and extinguish the arc.[

OSHA definition Wikipedia definition

51

Such persons permitted to work within the limited approach boundary of exposed energized electrical conductors and circuit parts operating at 50 volts or more, shall at a minimum, be additionally trained in all of the following: Distinguish exposed live parts from other parts of electrical

equipment. Determine nominal voltage of the exposed parts. Be aware of minimum approach distances to exposed parts. Decision-making process necessary to determine the degree and

extent of the hazard and the personal protective equipment and job planning necessary to perform the task safely

NFPA 70E Article 110.2(D)(1)(b)(4)

Training requirements from OSHA and NFPA70E

11