Describe electrical power and its generation. ▫ Differentiate between various
power usages in a data center. ▫ Define power factor. ▫ Recognize the importance
of ...
Fundamentals of Power
Fundamentals of Power © 2008 American Power Conversion Corporation. All rights reserved. All trademarks provided are the property of their respective owners.
Learning Objectives At the completion of this course, you will be able to
Identify basic electricity concepts Describe electrical power and its generation Differentiate between various power usages in a data center
Define power factor Recognize the importance of electrical safety measures in a data center
Identify potential problem areas in the data center
Agenda
Electrical power key terms AC and DC power Power factor Volt configurations, plugs and receptacles
Circuit breakers and convenience outlets
Seven common electrical problems
Components in a data center
Introduction Power is a primary resource Many instances of downtime are the result of power problems
Power supply should be kept free of interruption or distortion
Servers should be insolated against potential electrical problems
It is important to provide a separate power source for the data center
Key Terms Volt (V) Describes the force of electricity flowing through a circuit
Ampere (Amp) Measures the amount of electrical current
flowing through a circuit during a specific time interval
Ohm (Ω) Describes the amount of resistance electricity encounters
Key Terms Hertz (Hz) Unit of frequency measurement Alternating Current (AC) The direction of current flowing in a circuit is constantly being reversed back and forth
Direct Current (DC) Current which flows in one direction
Key Terms Water will flow at a given rate dependent on the open faucet
Water pressure (Voltage) usually remains constant
Current is controlled by the faucet position (Resistance) Can also be controlled by an increase or loss of water pressure (Voltage)
Key Terms
The amount of water that moves through a hose in gallons, or liters, per second can be compared to the quantity of electrons that flow per second through a conductor as measured in amperes
Key Terms Resistance
A restricted garden hose has more resistance than an unrestricted garden hose
Materials with low resistance let electricity flow easily
Materials with higher resistance require more voltage to make the electricity flow
Electrical Load Load Computers Networking equipment Cooling equipment Power distribution equipment All equipment supported by your electrical infrastructure
+
+
+
= LOAD
Let's Review Column 1
Column 2
B Hertz
A. Unit of measurement which describes the amount of resistance electricity encounters as it flows through a circuit
C Alternating Current (AC)
D Direct Current (DC)
A Ohm
B. Unit of frequency measurement C. Current that is constantly being reversed back and forth through an electrical circuit D. Current that flows in one direction
Let's Review Column 1
Column 2
A Volt
A. Unit of measurement of potential difference or electrical pressure between two points
C Ampere
B Electrical Load
B. Sum of the various pieces of equipment in a data center which consume and are supplied with electrical power C. Measures the amount of electrical current flowing through a circuit during a specific time interval
AC and DC Power Alternating Current (AC) Direction of current flowing in a circuit reverses direction
Switched back and forth approximately 60 times each second Measured as 60 Hertz
Utility determines the frequency for the AC power that reaches the data center
AC and DC Power Alternating Current (AC)
Frequencies can range between 50 Hz – 60 Hz AC power
Combination of voltage and current AC voltage Stepped up to voltage levels that enable power to be distributed over long distances with minimal loss of energy
AC and DC Power Direct Current (DC) Often utilized with telecom loads
Not practical in data centers Heavy resistive losses Large cable sizes
Almost all data center equipment is designed for the local nominal AC supply voltages
Single-phase and 3-phase Power Single Phase Waveform
3-Phase Waveform
Single-phase and 3-phase Power Single phase electricity Usually distributed to residential and small commercial customers
Implies that power comes in with only one hot wire, along with accompanying neutral and ground
Single-phase and 3-phase Power 3-phase power More economical than distributing single phase power
The size of the wire Affects the amount of current that can pass
Determines the amount of power that can be delivered
Single-phase and 3-phase Power It would be nearly impossible to suspend the required huge heavy transmission wires from a pole
It is much more economical to distribute AC power using 3-phase voltage sources
120/240 and 208 Volt Configurations Residential customers use single phase 120V and 240V
Data centers use some single phase 120V 3-phase 208V supports commercial environments and data centers
Single Phase 120V and 3-Phase 208V
Single Phase 120V and 240V
Watts and Volt-Amps Watts Measures the real power drawn by the load equipment
Used as a measurement of both power and heat generated by the equipment
Wattage rating Typically stamped on the nameplate of the load equipment
Many data centers have metering available which allows for accurate recording of power at the site
Watts and Volt-Amps The VA rating represents the maximum load that the device can draw
VA is used in sizing and specifying
Wire sizes Circuit breakers Switchgear Transformers General power distribution equipment
VA ratings Represent the maximum power capable of being drawn by the equipment
Are always greater than or equal to the watt rating of the equipment
Watts and Volt-Amps Power supplies, wiring, and circuit breakers may need to be rated to handle more current and more power
Power Factor Volt-Amperes and the Watts used may not always be the same number
Watts / Volt-Amps = Power Factor
Power factor may be expressed as a number or as a percentage
Power Factor Corrected electronic switching power supply Watts represents real power Volt-Amps represent apparent power
Let's Review Watt 1. The _________ measures the real power drawn by the load equipment, and is used as a measurement of both power and heat generated by the equipment. Volt-Amp represents apparent power. 2. The _________ Volt-Amp rating represents the maximum 3. The _________ load that the device in question can draw. Watt 4. The _________ represents real power.
A) Watt (W) B) Volt-Amp (VA)
Power Factor Correction Power Factor Corrected Introduced in the mid-1990s Watt and VA ratings are equal Power factor of nearly 1 Method of offsetting inefficiencies created by electrical loads
UPS Size
Resolution
Small
The Watt rating of the UPS is 60% of the published VA rating
Large
Focus on the Watt rating of the UPS because the Watt and VA ratings for typical loads are equal
Plugs and Receptacles
IEC Design
NEMA Design
Typical 3-Prong Plug
Plugs and Receptacles The most common plug/receptacle combination for IT equipment is of an IEC design
Also common are plugs and receptacles of the twist lock variety
The plug is twisted to lock into the receptacle
International Electrotechnical Commission Plugs
IEC-320-C13 and C14
IEC 309
IEC-320-C19 and C20
IEC 309
International Electrotechnical Commission Plugs
IEC 309 2P 3W 208V 30A The letter P identifies the number of poles The letter W identifies the number of wires The letter V identifies volts The letter A designates the current in amperes
National Electric Manufacturers Association Plugs
5-15R
5-20R
5-30R 5-50R
L-15
L5-20
L5-30
L 5 - 15 P
Common Power System Failures Common Areas of Failure
Percentage of Failure
PDU and its respective circuit breakers
30%
All other circuit breakers
40%
UPS
20%
Balance of system
10%
Circuit Breakers A type of switch Designed to protect electrical equipment from damage caused by overload or short circuit
Designed to trip at a given current level Can be reset manually or automatically Can fail in a number of ways
Failure to close Failure to open under fault conditions Spurious trip Failure to operate with the time-current specifications of the unit
Circuit Breakers
Circuit breakers are designed to interrupt excessive current flow and come in a wide range of sizes
Circuit Breakers Circuit breaker coordination is important
Coordination of breakers is complicated and must be done carefully
Circuit Breakers Thermal Circuit Breaker
Bimetallic element
LOAD LINE
Normal Mode
Circuit Breakers Thermal Circuit Breaker
Contac t Opens
Bimetallic Strip Heats
LOAD LINE
Trip Mode
Circuit Breakers Magnetic Circuit Breaker
Electromagnetic coil forces contacts open
Spring force keeps contacts closed
Circuit Breaker Protection A circuit breaker may need to handle up to 15 times its current rating
Circuit Breaker Sizing Circuit breakers are designed to trip at 110% of their rated threshold Allows for normal short term overloads
Circuit breaker tripping thresholds vary according to design specification or safety code requirements
To avoid downtime and unnecessary tripping, a circuit breaker needs to be sized according to its Rated current Tripping current
Circuit Breaker Sizing Trip settings are adjusted so that the circuit breaker in question will trip in a timely fashion
It is advisable to choose a breaker designed for the characteristics of the load
Circuit breakers with delayed action may be needed for heavy electrical loads
The circuit breaker needs to be rated high enough to prevent an electric arc from forming
Let's Review 110% of their 1. Circuit breakers are designed to trip at _________ rated threshold. A) 50% B) 75% C) 100% D) 110%
15 2. A circuit breaker may need to handle up to _________ times its current rating. A) 5 B) 10 C) 15 D) 20
GFCI, ELCB, and RCD Ground Fault Circuit Interrupters (GFCI), Earth Leakage Circuit Breakers (ELCI), or Residual-Current Devices (RCD) trip a circuit if they detect a small amount of ground current Larger data centers use resistor banks instead of GFCI, ELCB, or RCD
Convenience Outlets Used for non-computer devices
Allows for other noncomputer equipment to be plugged in without taxing the critical load
Grounding Grounding Safety measure to protect against electric shock
A grounded wire is connected to metal appliance cases
Some wires are considered hot because they are not grounded
Ground Loops Receptacle 1
Computer is grounded
Higher ground potential
Ground 1
Receptacle 2
Printer is grounded
Lower ground potential
Ground 2
Transients Impulsive Transients Voltage
Time
Transient Voltage Surge Suppressor (TVSS)
Transients Oscillatory Transient Voltage
Time
Interruptions Interruptions Voltage
Time
Instantaneous Momentary
Temporary Sustained
Sags and Undervoltages Sag Voltage
Time
Sags and Undervoltages Undervoltage Voltage
Time
Swells and Overvoltages Swell Voltage
Time
Swells and Overvoltages Overvoltage Voltage
Time
Waveform Distortion Voltage
DC Offset
Time
Harmonic Distortion
Time
Voltage
Voltage Fluctuations Voltage Fluctuation Voltage
Time
Power Frequency Variation Frequency Variation Voltage
Time
Standby Power and Distribution Any power source available to the data center that supplies power when utility power is unavailable
Mechanical generators Provide power on large and small scales Electrochemical generation systems Provide power for smaller or temporary use How is power distributed in the data center?
Power Distribution Components Service Entrance Transformer
Automatic Transfer Switch
Primary Power Panel
Non Critical Loads
Generator
Critical Power Bus
Bypass
Computer Room Air Conditioners
UPS
PDU
One line diagram
IT Equipment
Power Distribution Components Primary power source (Utility)
Emergency power source (Generator)
Power Distribution Components Circuit/Branch Circuit
Uninterruptible Power Supply (UPS)
Automatic Transfer Switch
Power Distribution Components Power Distribution Units (PDU)
Outlet Strips
Server Plug
Let's Review Column 1
Column 2
B Automatic Transfer Switch
A. Emergency, back-up power source
C Outlet Strips
B. Switch that will automatically switch the power supply from one power source to another
D
Uninterruptible Power Supply (UPS)
A Generator
C. Strip of sockets which allows multiple devices to be plugged in at one time D. Device or system that maintains a continuous supply of electric power to essential equipment
Let's Review Column 1
Column 2
A Power Distribution Units (PDU)
A. Device that distributes electric power by usually taking high voltage and amperage and reducing it to more common and useful rates
C Server Plug
B Circuit
B. Path for electrical current to flow C. Power plug which mates with a socket or jack, and is used with electrical equipment in the data center
Summary Power infrastructure is critical to uptime Understanding basic power terms helps to better evaluate the interaction between the utility, standby power equipment, and load
Failures can occur at various points in the power infrastructure, but special care should be given to the condition and coordination of circuit breakers
Numerous power anomalies exist that can impact the uptime of data center equipment
Understanding the threats and applying practical power solutions can help to minimize risk
