How to Properly Do Rack Power Distribution Unit (PDU) Planning...

#CPEXPO | CHANNELPARTNERSCONFERENCE.COM#DATACENTERWORLD | DATACENTERWORLD.COM

How to Properly Do Rack Power Distribution Unit (PDU) Planning for IT

Equipment

Joe PriscoSenior Technical Staff Member

IBM

#DATACENTERWORLD | DATACENTERWORLD.COM

Data Center World – Certified Vendor Neutral

Each presenter is required to certify that their presentation will be vendor-neutral.

As an attendee you have a right to enforce this policy of having no sales pitch within a session by alerting the speaker if you feel the session is not

being presented in a vendor neutral fashion. If the issue continues to be a problem, please alert Data Center World staff after the session is complete.

#DATACENTERWORLDDATACENTERWORLD.COM

• Basic power terms and power consumption values• Variables that influence power consumption when IT

equipment is in operation • Rack PDU plugging and limitations• Review a detailed example of placing IT equipment on

rack PDUs

Agenda


• Watts• Active power or usable electricity• Heat output (BTU/hr = watts x 3.413)

• VAR (Volt Amps Reactive)• Imaginary power or wasted electricity• Stored in capacitors and inductors

• VA (Volt Amps)• Vector sum of the watts and VAR• Total power available at the line cord

of a piece of equipment

Basic Electrical Power Terms

Real Power (Watts)

Apparent Power (VA)

Reactive Power (VAR)

VA is the term most useful for electrical planning inside a data centerVA = Volts x Amps


• kWh (Kilowatt Hour)• How the utilities measure electricity

consumption• 100-watt light bulb uses 1 kWh every

10 hours (0.100 kW x 10 hours)• PF (Power Factor)

• Ratio of the real power (watts) to the apparent power (VA)

• Ranges from 0 to 1• A higher PF is better• Utilities may impose fees for low

power factor because of the need to increase their generation and transmission capacity

Other Helpful Power Terms

Phot

o is

licen

sed

unde

r CC-

BY-S

A

Low Power Factor High Power Factor

1.0 =100 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝟏𝟏𝟏𝟏𝟏𝟏 𝑽𝑽𝑽𝑽0.1 =

100 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏 𝑽𝑽𝑽𝑽


• Nameplate• Product safety rating label• Used for electrical code compliance

• Maximum measured power consumption

• Found in physical planning manuals• Worst case power consumption• Used for UPS and switchgear loading

• Benchmark• Power consumption running an industry

standard performance benchmark• Used in HPC environments to reduce the

electrical demand overhead

• Actual power consumption• Typical, every day value• Used for air conditioning heat rejection

calculations

Power Consumption Values

Nam

epla

te

Actual measured

powerBe

nchm

arkMax

measuredpower


• The nameplate includes all the mandatory legal compliance marks and information

• The most important data is about the input electrical service

• Voltage (V)• Amperage (A)

overcurrent protection• 24 amps x 125% = 30A

service• 48 amps x 125% = 60A

service• Calculate VA = V x A

• Use low-line volts• 200V x 24A = 4.8 kVA• 200V x 48A = 9.6 kVA

Nameplate – PDU (Ships Worldwide)

EMC

Compliance IDProduct Safety

Environmental

SinglePointof Contact


• Worst case power consumption• Largest configuration• Highest utilization• Abnormal conditions that affect fan

speed• Internal hardware failures (e.g., power

supply)• High ambient temperature

Maximum Measured Power Consumption• Look for published maximum VA

(Volt Amps)• If VA is not available, an alternative is

maximum watts• Convert to VA using power factor• VA = Watts / PF• For most IT equipment, power factor is

close to 1• Account for oversubscription

Normal ModeAmps per Power Supply

4200VA/200V/2 = 10.5 Amps


• Power consumption is affected by fan power, component power (leakage current), and power conversion

• If the Inlet temperature increases from 15°C to 35°C, the IT equipment power could increase in the range of 7 to 20%

• With the increase in fan speed over the range of ambient temperatures, the IT flowrates also increase

• The cubic feet per minute (CFM) demand of the IT equipment must be satisfied or else recirculation could further increase inlet temperature

Maximum Measured Power – High Ambient Temperature

Sour

ce:

2011

The

rmal

Gui

delin

es fo

r Dat

a Pr

oces

sing

Envi

ronm

ents

°C °C


• The IT equipment DC load can draw more output power than is available from a single power supply

• If a single power supply is unavailable, the IT equipment throttles the power consumption to a level that allows the machine to run on a single power supply

Oversubscription

Normal ModeAmps per Power Supply

2575VA/200V/2 = 6.4 Amps

Power Capped ModeAmps per Power Supply

1960VA/200V = 9.8 AmpsUse this amperage for PDU sizing


• Expected, steady-state typical value for a specific configuration under normal environmental operating conditions

• The values are very aggressive because they are used in TCO calculations

• The mechanical system can better handle fluctuations and spikes in heat load, even if it crosses a predetermined threshold for a short period of time

• The typical power consumption can be used for all cooling calculations (e.g., kW/rack, heat load balance, watts/square foot)

Actual Power Consumption

Maximum Measured Power Consumption = 1420 W

8286-41A


• Rack Power Distribution Unit (PDU) Definition

• Brings electrical power in from the facility and distributes it to server, storage, and networking hardware inside a rack

• Think of it as a power strip with superior features

• Primary circuit breaker protection• Optional: metering, monitoring, Ethernet

communications, relays• How to Properly Do Rack Power

Distribution Unit (PDU) Planning for IT Equipment

• Electrical specification choices for Rack PDU Planning

• IT equipment manufacturer maximum measured power consumption

• Your own facility measured data

Rack PDU Planning

Photo is licensed under CC BY-SA-NC


1. Understand the PDUA. Maximum input amperageB. Output receptacle quantity and limitations

i. Receptacle ratingsii. Circuit breaker ratings

C. Desired level of redundancy2. Identify the IT equipment to be connected to the PDU

A. Find the maximum measured power consumption from the manufacturer’s technical specification

B. Calculate the amperage3. Place the IT equipment on the PDU and check for rating

violations based on item #1

Steps to Rack PDU Planning

Phot

o by

is li

cens

ed u

nder

CC

BY-S

A


Step 1A – Maximum Input Voltage and Amperage

Step 1B – Output receptacle quantity and limitations• Each individual IEC 320-C13 receptacle (1-12) can

support up to 10 amps• Each pair of receptacles (a-f) is protected by a 20

amp circuit breaker derated to 16 amps • Every 4 outlets are on a phase (L1-N, L2-N, L3-N)

when line cord is 3 phase wye (European type electricity distribution)

Step 1 – Understand the PDU

Line Cord Plug Voltage Rated Amps

#1 NEMA L6-30 200-208 24

#2 IEC 309 332P6W 220-240 32

#3 IEC 309 360P6W 200-208 48

#4 IEC 309 363P6W 220-240 63


Step 1B Continued – Rack PDU SchematicCB = circuit breakerCR = control relay


Step 1C – Level of Facility RedundancyTypically referred to as A-side/B-side or left-side/right-side redundancy

Each AC power supply (#1 and #2) in a dual corded piece of IT equipment is connected to a separate power panel (typically for maintenance reasons)

#1 #2

The IT equipment is designed to run on a single AC power supply

This data center redundancy layout is designed to carry the IT equipment redundancy to the wall


• How many power supplies does the server, storage, or switch have installed?

• Two power supplies• Are the supplies current sharing?

• Power supplies draw approximately equal current from the utility (electrical supply) • Deliver approximately equal current to the load

• Are the power supplies operating like an automatic transfer switch (ATS)?• Four power supplies

• What is the redundancy setup?• 2+2 (N+N)• 3+1 (N+1)

• Is PDU mapping important?

Step 1C – IT Equipment Redundancy


• Dual Corded IT Equipment• Divide maximum measured VA (Volts

Amps) by “lowline” Volts (200 V)• EQ1 = 1750 VA / 200V = 8.75 amps• EQ2 = 1800 VA / 200 V = 9.00 amps

• PDU Input• Line cord #1 – 24 amps• A-side/B-side redundant

Steps 2 and 3 – PDU Calculations and Checks (I)

EQ1

EQ2

PDU1

PDU2

Equipment Amps Outlet Pair Pair Amps PDU Total Amps

EQ1 8.75 a – 1 8.75 8.75

EQ2 9.00 a – 2 17.75 17.75

PDU1&2

Pair “a” amps less than 16 – FailPDU total amps less than 24 – OK# of line cords less than 12 per PDU – OK


• Dual Corded IT Equipment• Divide maximum measured VA (Volts

Amps) by “lowline” Volts (200 V)• EQ1 = 1750 VA / 200V = 8.75 amps• EQ2 = 1800 VA / 200 V = 9.00 amps

• PDU Input• Line cord #1 – 24 amps• A-side/B-side redundant

Steps 2 and 3 – PDU Calculations and Checks (II)

EQ1

EQ2

PDU1

PDU2


EQ1 8.75 a – 1 8.75 8.75

a – 2

PDU1&2


EQ2 9.00 b – 3 9.00 17.75

b – 4

Pair “a” amps less than 16 – OKPair “b” amps less than 16 – OK

PDU total amps less than 24 – OK# of line cords less than 12 per PDU – OK


Steps 2 and 3 – PDU Calculations and Checks (III)

EQ1

EQ2

PDU1

PDU2


EQ1 8.75 a – 1 8.75 8.75

a – 2

PDU1&2


EQ2 9.00 b – 3 9.00 17.75

b – 4


EQ1 8.75 c – 5 8.75 26.50

c – 6

Pair “a” amps less than 16 – OKPair “b” amps less than 16 – OKPair “c” amps less than 16 – OK PDU total amps less than 24 – Fail# of line cords less than 12 per PDU – OK

EQ1


Steps 2 and 3 – PDU Calculations and Checks (IV)

EQ1

EQ2

PDU1

PDU2


EQ1 8.75 a – 1 8.75 8.75

a – 2

PDU1&2


EQ2 9.00 b – 3 9.00 17.75

b – 4


EQ1 8.75 a – 1 8.75 8.75

a – 2

Pair “a” amps less than 16 – OKPair “b” amps less than 16 – OKPDU total amps less than 24 – OK# of line cords less than 12 per PDU – OK

EQ1

PDU3&4


• Use maximum measured power consumption as specified by the IT equipment manufacturer

• Divide VA by low-line voltage• Is oversubscription (power capping) used when redundancy is

unavailable?• Use your own data

• Pre-production testing• Include corner conditions

• Run worst case applications• High ambient temperature and/or operate on a single power supply

• Reconfigure the electrical distribution of existing racks• US National Electrical Code (NEC) 220.87

• Continuously record the demand (loads averaged in 15-minute intervals) over a minimum 30-day period and find maximum demand

• Factor in conditions that can impact the power consumption of the equipment

Electrical specification choices for Rack PDU Planning


• More capacity doesn’t mean you can use it• Layout IT equipment on the PDU• Look for amperage bottlenecks

• Still must balance loads across the electrical distribution• Balanced means the IT equipment loads are identical on all three phases (e.g., Y =

A-N, B-N, C-N; Δ = A-B, B-C, C-A)• Balanced means all three line conductors have equal currents (e.g., A, B, C)

separated by 120°• Three-phase PDUs will be unbalanced

Single-Phase or Three-Phase?Wiring Wall Plug Rated Amps Voltage Power Capacity

VAPrimary Geography

1-phase 60 A 48 A 200-208 Vac 𝑃𝑃 = V ⋅ I9.6 kVA

North America

3-phase Delta (Δ) 60 A 48 A 200-208 Vac 𝑃𝑃 = 3 ⋅ V ⋅ I16.6 kVA

North America

3-phase Wye (Y) 32 A 32 A 220-240 Vac 𝑃𝑃 = 3 ⋅ V ⋅ I21.1 kVA

Europe


Questions

How to Properly Do Rack Power Distribution Unit (PDU) Planning...

Documents

Transcript of How to Properly Do Rack Power Distribution Unit (PDU) Planning...