Fundamentals of Power

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 C D A Hertz Alternating Current (AC) Direct Current (DC) Ohm A. Unit of measurement which describes the amount of resistance electricity encounters as it flows through a circuit 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 C B Volt Ampere Electrical Load A. Unit of measurement of potential difference or electrical pressure between two points 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 1. The Watt measures the real power drawn by the load equipment, and is used as a measurement of both power and heat generated by the equipment. 2. The Volt-Amp represents apparent power. 3. The Volt-Amp rating represents the maximum load that the device in question can draw. 4. The Watt 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 Small Large Resolution The Watt rating of the UPS is 60% of the published VA rating 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-320-C19 and C20 IEC 309 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 L5-15P

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 Bimetallic Strip Heats Contac t Opens 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 1. Circuit breakers are designed to trip at 110% of their rated threshold. A) 50% B) 75% C) 100% D) 110% 2. A circuit breaker may need to handle up to times its current rating. A) 5 B) 10 C) 15 D) 20 15

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 Receptacle 2 Computer is grounded Printer is grounded Higher ground potential Lower ground potential Ground 1 Ground 2

Transients Voltage Impulsive Transients Time Transient Voltage Surge Suppressor (TVSS)

Transients Oscillatory Transient Voltage Time

Interruptions Interruptions Voltage Time Instantaneous Temporary Momentary Sustained

Sags and Undervoltages Voltage Sag Time

Sags and Undervoltages Undervoltage Voltage Time

Swells and Overvoltages Swell Voltage Time

Swells and Overvoltages Voltage Overvoltage Time

Waveform Distortion Voltage DC Offset Time Harmonic Distortion Time Voltage

Voltage Fluctuations Voltage Voltage Fluctuation 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 Primary Power Panel Automatic Transfer Switch Generator Non Critical Loads Critical Power Bus UPS Bypass Computer Room Air Conditioners One line diagram PDU 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 C D A Automatic Transfer Switch Outlet Strips Uninterruptible Power Supply (UPS) Generator A. Emergency, back-up power source B. Switch that will automatically switch the power supply from one power source to another 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 C B Power Distribution Units (PDU) Server Plug Circuit A. Device that distributes electric power by usually taking high voltage and amperage and reducing it to more common and useful rates 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