Designing Power Quality Systems for Mission Critical ...

© 2014 Eaton Corporation. All rights reserved.

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Designing Power Quality Systems for Mission Critical Applications

Michael Mallia,General Manager, Power Quality

2 2© 2014 Eaton Corporation. All rights reserved.

Agenda

• Understanding the key technology changes that are placing increasing demands on power infrastructure

• UPS Technology – Design and application techniques:• 1: Designing for Performance• 2: Designing for Efficiency• 3: Designing for Capacity, Redundancy & Scalability• 4: Designing for Reliability • 5: Designing for Safety


Section 1: Designing for Performance

Understanding the key technology changes that are placing increasing demands on power infrastructure

• Power quality application requirements and constraints

• Input distortion, power factor, crest factor

• What the customer wants• Prioritising the top 5 typical customer requirements


0 to10

30 to 40

60 to 70

12345

6-10

10-2020-50

0

1

2

3

4

5

6

Events Per Year

Voltage (% of Nominal)

Duration ( cycles)

Average of 50

Sags/Year

Interruptions

Typical Power Quality ProblemsThis image cannot currently be displayed.

Understanding the type & frequency of power problems, plus the requirements of your

loads may enable an increase in uptime and significant savings in

energy costs


Harmonics of a Data Centre

N

Load current– THD 70%

– p.f. 0.65 lag to 0.8 lead

Load neutral current (150Hz)

Harmonic currents cause problems:– Additional losses in supplying circuit

– Heat at transformer and generator windings

– Voltage distortion

– Neutral overload and N-PE voltage

– Malfunction of protective devices

– Errors in measurements

– Resonance in compensation capacitors

– Disturbances and malfunctions in IT &telecom equipment and networks

?


The IT “Power Supply”

Common Theme:Universal inputPower factor corrected (PFC)


Acc

epta

ble

Inpu

t Vol

tage

IT Equipment Power Requirements

• Modern IT Loads can handle:

• A Wide Range of Voltage

• Short Duration outages

• Common Mode Noise


The UPS as an “interface”

Important Selection/Design Criteria:• Rectifier design – choose most suitable rectifier

technology to provide lowest impact on mains with highest reliability and efficiency

• Inverter design – Able to handle non-linear loads with leading power factor

• Cabling to suit worst case conditions – i.e. Double Sized Neutrals if required

• Efficiency!


Where does that bring us?

• Need to protect against the variety of power quality problems that are seen today……. although the key need may just be power availability

• How do you prepare for those challenges?• Top 5 considerations that must be prioritised for

any size critical power application:1. Reliability2. Efficiency3. Flexibility/Scalability4. Manageability5. Serviceability


Section 2: Designing for Efficiency

• UPS Technology – Design and application techniques• UPS Topology (VFI, VI, VFD)• Designing for Efficiency

• Transformer-Free, Variable Module Management, ECO/Energy Saver Modes


IEC 62040-3 & ENV 500091-3

Passive standby

Line interactiveincl. “Delta conversion”

Double conversion

UPS topologies

Load

Load

Load


Double Conversion with various modes:

Maximum Power Control (VFI)

Maximum Energy Saving (VFD)

High Efficiency & Power Conditioning (VI)

UPS topologies


Defining a “Green” UPS

Initial cost of ownership is not so relevant.Customers must take into account…..• Savings in delivery costs• Savings in real estate requirements• Savings in installation and cabling• Savings in operating costs• Savings in life-cycle costs• Savings in maintenance costs


Transformer-free technology

• Low frequency & analogue control designs require transformers

• Advanced high frequency digitally controlled IGBT designs don’t!


Transformer-free: The result

250kW Transformer-free magnetics

assembly

250kW Transformer-based magnetics

assembly


Transformer-free benefits

TRANSFORMER-FREE UPS

Higher Efficiency at all loads

Better Output Power Performance

SmallerFootprint & Weight

The EATON Advantages

Lowest TCOHighest Efficiency

High Performance

Better Input Power Performance

Lower Total Cost of Ownership


Challenge: Increasing efficiency in real life applications

• In double conversion mode, the efficiency of any UPS varies depending on the % of load

• Highest efficiency when close to full capacity

• UPS systems rarely loaded at full capacity• This is fact in redundant systems

• How to maximise efficiency potential ofUPS systems with lighter loads

FACTS

FACTS

CHALLENGE

CHALLENGE

SOLUTIONS:1. Ensure higher “real

life” base efficiency2. Module Management3. Energy Saver Modes


• Example With Same Load Applied To Different Multi-UPS Configurations

Module Management Principles

* In “ready state,” the UPM rectifies DC-link, generates logic level PWM signals, and filters EMI and lightning spikes.

* * * * **

Thanks to power converter modularity, Module Management Automatically optimises efficiency at UPM level Concentrate the load on certain UPM’s to maximise overall system efficiency!


VMMS Efficiency9395 UPS Efficiency

78

80

82

84

86

88

90

92

94

96

Load kVA

Effic

ienc

y %

9395 275kVA9395 550kVA9395 825kVA9395 1100kVA9395 VMMS N+0

Eaton 9395 275kVA UPS




Typical Operations Range

VMMS allows to shift to higher efficiency curves (according to system’s redundancy requirements)

up to N+0 VMMSefficiency curve

- VMMS and N+0 curves using VMMS default max UPM % load level @ 80% (*)

Notes:- Scaled drawing

9395 550kVA with VMMS and N+0 configuration*9395 825kVA with VMMS and N+0 configuration*9395 1100kVA with VMMS and N+0 configuration*






Module Management Example:825kVA Units in Dual Corded Load with A & B feeds

UPS Configuration Without VMMS VMMS on N+1 Redundancy VMMS on N+0 Redundancy

Efficiency@ 440kVA load

91.2% 92.8% 94.3%

UPSEnergy Savings

Used as reference for savings calculation

56 MWh / year($6160 @ 11¢ / kWhr)

108 MWh / year($11,880 @ 11¢ / kWhr)

Additional Benefits& Comments

Industry-leadingUPS efficiency indouble conversion

Additional energy savings from reduced cooling in VMMS(typically +30-40% to UPS energy savings)

UPM’s in VMMS ready state available for redundancy

Example with 440kVA load(A 220kVA + B 220kVA)

“A”

“B”Single / Dual Source Data Center with Dual

Corded Servers

A Feed220kVA

B Feed220kVA

A Feed220kVA

B Feed220kVA

A Feed220kVA

B Feed220kVA






Energy Saving / “ECO” Modes


Acc

epta

ble

Inpu

t Vol

tage

to U

PS

Is a double conversion UPS really needed?

• Line Interactive UPS ideal for SMB applications

• On Line UPS provide constant voltage regulation, but may unnecessarily waste energy

• On Line UPS with Energy Saver or “ECO” modes work in bypass mode when mains is suitable, and in Double Conversion mode when line voltage is close to the limits of ITIC Curve

• Eaton’s transition time between Normal and Double Conversion mode should be ~2-4 ms under all line/load conditions – up to 2x faster than any Mission Critical STS


Maximum Efficiency Tracking

ECO/Energy Saver System saves even more at lower loadings

ESS Efficiency - 99% across the complete operating range

85% reduction in lossescompared to legacy transformer-based UPS

Continuous power trackingand proprietary DSP algorithms combined with transformer free design topology ensures critical loads are always protected

Additional Benefits: Increased component life: Fans,

capacitors etc. Reduced audible & electrical noise


ECO Mode – precautions:

• Critical loads require fast transfer times• >10ms is a problem

• Storm Detection modes enhance security and reliability

• Advanced Fault Detection to prevent unnecessary transfers

• Standard ECO modes can be risky….• Load mode may exposed to raw utility• Detection and transfer times are long• ….And most don’t work with parallel systems


Utility Fault Transitions - Three Phase Outage

ESS Output Response 1.2 msSource Outage


Utility Fault Transitions - Single Phase Outage

Source Outage ESS Output Response 1 ms


Energy Saver System

• ESS Response Example – 100% Outage






Energy Saving / “ECO” Modes


Solution:• ESS + Harmonic Reduction System (HRS) utilises converters for active harmonic correction• System provides 275kVAR of correction capacity• Maintains up to 98.5% efficiency whilst providing power conditioning

ECO with Harmonic Reduction System (VI)

Challenge: When operating in ESS or ECO modes, loadharmonic currents are placed directly on mains supply

UL1

IL1

UL1

IL1

UL1

IL1


Section 3: Designing for Capacity, Redundancy & Scalability

• UPS Technology – Design and application techniques• Designing for Capacity & Redundancy

• Hot Standby, distributed parallel, centralised parallel, Hot Sync


Increasing reliability

• Hardware additions to increase reliability

• Multi – corded (power supply) servers

• Redundant UPS Systems• Dual power path power

distribution (A & B design)• Dual UPS systems (2N)• Source Transfer Switches• Surge Protection Devices

(SPD)• Maintenance Bypass Switches

N + 1 Redundant UPS

SPM

LoadLoad

N + 1 Redundant UPS

SPM

LoadLoad


Medium/Large Data centre UPS, single/dual supply loads

“Redundant Central UPS”• Complete power redundancy – each module has integral static switch

and separate battery• Scalable by adding complete UPS/Battery modules to each System• Static Transfer Switches provide redundancy for single source loads


Back to Basics: UPS System Configurations

• Reverse Transfer• Isolated Redundant (Hot Standby)• Parallel Redundant• Parallel Capacity

Basic On Line configurations:


Reverse Transfer

One unit supplies reliable power to the critical load . . .

Utility

Battery

)

(

Critical

Load


Utility

Battery

)

(

Critical

Load

One unit supplies reliable power to the critical load . . .

. . . and if the unit fails, the load is supported by the bypass.

Reverse Transfer


Isolated Redundant (Hot Standby)

Utility

Battery

)

(

Battery

Utility)

(

Critical

Load

Two units are used. The output of the Standby UPSfeeds the bypass of the Primary UPS.

PrimaryUPS

StandbyUPS


If the Primary UPS is unable to support the critical loadit transfers the load to the Standby UPS.

Utility

Battery

)

(

Battery

Utility)

(

Critical

Load

Two units are used. The output of the Standby UPSfeeds the bypass of the Primary UPS.

StandbyUPS

PrimaryUPS

Isolated Redundant (Hot Standby)


Battery

Utility Critical

Load

Parallel Redundant SystemTwo or more units are paralleled together . . .

Note: Common Battery = false economy!


Paralleling for capacity/redundancy

Sys

tem

By-

pass

CRITICAL LOAD

MAINSComplete System

System Parallel Module


3+1 Redundancy or 4* Capacity

~=

~=

~=

~=

I II

I+II

LOAD

MAINS

~=

~=

~=

~=

If total system is redundant (N+1), failure of any one system does not affect critical bus

If system is full capacity, failure of any one system forces all units to static bypass


Installation rule

Total length1A + 1B = 2A + 2B =3A + 3B = 4A + 4B

Maximum variance10% combined input and output wire lengths

Requirement... to ensure approximately equal current sharing when in static bypass mode.

UPM 2

Battery

Bypass inputs to UPMs

UPM 1

Battery

UPM 3

Battery

UPM 4

Battery

Outputs from UPMs

1A

2A

3A

4A

1B

2B

3B

4B


Increasing capacity & reliability: N+1 Systems

30 kVA 30 kVA 30 kVA 30 kVA

Load 90 kVA total

Any single UPS can be taken off line for maintenance or repair

Systems that don’t rely on common control avoid single points of failure


Reliability – Modularity Vs Centralisation

• What’s more reliable………………..• Modular or Unitary UPS?• Distributed or Common battery?• Distributed or Centralised Parallel UPS?• Is Scalability required?


Unitary Vs Modular

• Scalable & Redundant• Distributed Logic• Distributed Static Bypass• Distributed Batteries• Higher Cost• Lower MTBF

• Single Static Bypass• Higher MTBF• Lower Cost• Minimal Redundancy• Fixed Rating


Unitary Vs Modular

Modular systems are an IT Manager’s dream, but an engineer’s problem!

Multiple systems in parallel become increasingly harder to manage with large kVA ratings and more than 6 modules in parallel

Issues: Common Controls, Common Batteries, Multiple Static Bypasses

Plug & Play??????


Centralised Vs Distributed Large UPS

Distributed ParallelStatic Bypass Switch within each

UPS module

Centralised ParallelSingle Static Bypass Switch in a

separate cabinet


Distributed Parallel

Redundancy & Capacity – Add as you grow

Lower Initial Cost Can provide more fault current – if all

switches operate simultaneously More components in Parallel (lower

MTBF) Impedance must be matched for

current sharing Shorted SCR in one UPS affects whole

system (unless back-feed protected) Difficult to manage with more than 4

large UPS Initial fault clearing capacity may not

be sufficient


Centralised Parallel

Single Static Bypass eliminates current sharing issues

Full fault clearing capacity available from day 1

Can enable paralleling of unlike ratings

Easy to add UPS modules Simplifies upstream switchgear –

up to 5000A rating No static switch redundancy Larger footprint Higher cost Higher initial capital investment


Section 4:

• UPS Technology – Design and application techniques• Designing for Reliability

• Supply redundancy & Maintenance Bypass• Batteries, Controls design, Serviceability,

Maintenance, Cooling


Dual feed input - Supply Redundancy

• Dual feed input means that UPS can be installed with separate input cables for rectifier and bypass

• Should the upstream fusing clear, for example in rectifier input short circuit, dual feed allows UPS to go to bypass, single feed will drop the load once batteries are drained


External Bypass Switches

Interlocking is essential to avoid disasters!

“Wraparound” Bypass

“Tail End” Bypass


Batteries need care!

Battery has limited life span !

... cost a lot of money, disposed batteries are toxic

waste !

is very sensitive to environmental factors, temperature is crucial

It’s a crucial component which maybe is seldom

needed, but you just have to be able to

count on it!

…and no battery means NO UPS!


Battery Selection – brief discussion

• Types: • Valve Regulated Lead Acid• Flooded Lead Acid• Nickel Cadmium

• Life Expectancy:• Design Life & end of life capacity• Annual degradation

• Degradation Factors:• Ambient Temperature• Ripple Current• Multiple cycles• Under charging• Over charging

• Regular Maintenance:- Post Commissioning checks- Leaks - Connection integrity- Equalisation


H+

e-e-

O2

O2

O2

+++

+++

--

--

---

H2SO4

PbO2Pb

The main sealed battery aging factor is the positive electrode corrosion attack caused by the float charging current

+– Float charging current- is a chemical reaction between the electrodes and electrolyte

Traditional battery charging• Positive electrode corrosion with float

charging


Control system design

Logic boardInterface board

Power Supply #1Power Supply #2

Power Module(Rectifier 1-2)

Power Module(Inverter 1-2)


Prioritised Redundant cooling

• Cool air is drawn in via the front door

• Warm air is exhausted out the top of the unit

• Fan tray assembly blows cool intake air up through the power modules

• Hot swappable fans with fan failure detection

• Fan redundancy


Other reliability measures……

• “You can’t manage what you don’t measure”• Monitoring UPS systems helps to avoid disasters

(overload, unbalancing, battery health etc.)• Managing energy consumption helps to make and

keep efficiency gains and also increase reliability• Measure the whole powertrain – from incoming

utility to sockets in the rack!

• Regular maintenance!!!!!!!


Section 5: Designing for Safety

• UPS Technology – Design and application techniques• Designing for Safety

• Back-feed protection


Back-feeding – what is it?

• Back-feeding of power means that the power transfer within an electrical device is towards the input terminals• This creates a safety hazard since, as a result, input terminals

may be on power even if they have been disconnected from the mains supply.

• Back-feed protection is implemented to shield the bypass line from thyristor short circuit failure in the static switch.

• Back-feed protection is implemented to prevent leakage current via the static switch snubbers and SCRs from creating upstream voltages when mains is not present


Backfeed protection requirements

• The international standard IEC 62040-1 and AS62040.1.1:2003 require that the UPS device shall prevent all hazardous voltage and energy from being transferred to the UPS input terminals after the input power has been interrupted

• The standards allows for two alternative implementations of backfeed protection• installing an internal backfeed isolation device within the UPS• installing an external backfeed isolation device with only

backfeed detection implemented within the UPS

• Note: (AS 62040.1.1-2003 Uninterruptible power systems (UPS) — General and safety requirements for UPS used in operator access areas, section 5.1.4 Back feed protection.)


Backfeed protection requirements

The Australian Standard AS62040.1.1:2003 states the following: “For permanently connected UPS without internal automatic backfeed isolation (see 5.1.4), the instructions shall require the fitting by the user of a warning label on all primary power isolators installed remote from the UPS area, to warn electrical maintenance personnel that the circuit feeds a UPS.

The warning label shall carry the following wording or equivalent.

ISOLATE UNINTERRUPTIBLE POWER SUPPLY (UPS)BEFORE WORKING ON THIS CIRCUIT”

The practical implications are that all isolators in the chain feeding the UPS must be so identified if the UPS does not have back-feed protection.


Backfeed protection in a single UPS system

• Back-feed contactor is situated in the bypass line


Back-feed protection in a single UPS system

• The internal back-feed contactor is used to automatically protect against fault situations in the static switch

• If a thyristor suffers a short-circuit failure• The inverter output to the bypass input terminal become

shorted• A back-feed contactor prevents the back-feeding of power

• The UPS can stay in double-conversion mode even in the case of a static switch failure


Backfeed protection in a parallel UPS system

• If a fault in one of the static switches were to occur, inverters would start feeding current back to the input transformer• Back-feed contactor opens

• The static bypass lines have redundancy• Failure of one static bypass does

not prevent the other bypass lines from operating


Backfeed protection in a centralised bypass system

• In a centralised bypass topology the system bypass module (SBM) provides a common bypass line for the paralleled UPS modules


Problems with external backfeed contactors

• External backfeed contactor means:• Space needs to be reserved in the input switchgear for the

UPS backfeed isolation device• Often only one backfeed contactor is installed per entire

parallel UPS system• Failure in one of the static switches results in the loss of all the

static bypass lines connected to the common backfeed contactor

• If the UPS doesn’t have a circuit for controlling an external contactor, then the only functionality that you can have is to protect against feedback through SCRs and snubbers during mains failure


Questions

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