Transcript UPS - kishorekaruppaswamy

EMERGENCY POWER SUPPLIES
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Problems of Power Failure in Industries
• Primary intention of Power Utility - Provide
uninterrupted power
• Causes for interruption:
• Equipment failures and line faults
• System instability leading to tripping
• Deliberate tripping (usually automatically) to
save system collapse
• Natural causes - Hurricane, earthquake, flood
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Problems of Power Failure in Industries
• No power system can be guaranteed to be
free from interruptions
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Transmission line faults
Equipment malfunctions
Weather related failures
Failures due to other external causes in exposed
parts of system
– Human errors
– System instability due to major disturbances
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Problems of Power Failure in Industries
• Outages more likely in a system without
adequate generation reserve
• No buffer storage possible for Electrical
energy
• Frequency drop due to system overload
• Complete system collapse due to inadequate
system reserves
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Implications of Power Failure
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Accidents involving death or injury
Damage to equipment
Creation of potentially hazardous conditions
Loss of production (not only for duration of interruption, also
time required to bring process to its pre-failure state)
Accidents that can result from a sudden interruption
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Dropping of loads lifted by electromagnets
Release of toxic materials
Spillage of hot metal
Explosions
Runaway reactions
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Implications of Power Failure
Can cause Potentially Hazardous situations
• Loss of control power
• Loss of lighting in operational areas or exit
routes
• Loss of ventilation/exhaust systems
• Loss of signaling and alarms
• Loss of fire-fighting systems
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Production behavior following Interruption
of Power Supply
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Costs of Power Interruption
• Direct Costs
– Costs due to lost man-hours
– Direct expenses due to death/injury
– Cost of repairs to damaged equipment
– Lost production
• Indirect Costs
– Legal costs - Accidents involving third parties/
quality problems/ non-fulfillment of contract
commitments
– Loss of good will
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Power Failure Problem Mitigation
• Problem mitigation
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Installation and use of adequate reserves
Deliberate tripping by islanding schemes
Advance preparation during natural calamities
Proper equipment selection, maintenance
• Power supply restoration
– Auto-reclose operations (self clearing of transient faults)
– Switching to redundant feeders
– Starting standby generating sources
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Solutions for Power Failure
• Distributed generation capacity - Owned by Utility, Industries
or third parties
• Engine generators, gas turbines - Quick start, can take up
peak demands
Advantages
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Closer to load, not affected by transmission circuit problems
Capable of being started, brought up to load faster
Serve as standby sources
Provide uninterrupted power when synchronized with utility
Improve voltage profile in end-of-line distribution circuits
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Industrial Plant - Emergency Generation
• Capacity to feed critical loads only
• Break before make Switch – Brief interruption during transfer
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Tolerance for Interruptions & Voltage/Freq.
Excursions
• Electrical equipment designed with tolerances in input
voltage parameters – Can take care of limited
variations
• Desktop computers - Tolerate voltage fluctuations to
some extent
• By virtue of large capacitances
• Internal regulation circuitry
• Tolerance for voltage fluctuations - General industrial
equipment
• –10 to +6% for slow/sustained variations (sag/swells)
• Considerably more for short time disturbances
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CBEMA, ITIC and ANSI - Voltage Sensitivity
Curves
• Random data errors in computers due to
voltage variations
• Standard Curves
– Indicating voltage limits causing no ill
effects, plotted against time
– Earliest curves developed by Computer and
Business Equipment Manufacturers
Association (CBEMA)
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CBEMA Voltage Sensitivity Curves
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ITIC Voltage Sensitivity Curves
(Information technology industry council)
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Uninterrupted Power, Emergency Power
and Standby Power
• Uninterrupted Power - Guarantees continuous
power without even a momentary break to
connected loads
• Emergency Power - Minimum backup power for
emergency
applications
(emergency
lighting,
emergency shut down systems, alarm systems,
elevators, life safety and security systems). Brief
interruption can be tolerated
• Standby Power - Provision of substantial power to
maintain all production, business processes during
short/ long power outages
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Different Solutions for Different Needs
Needs of Equipment
• Careful consideration for power quality or
continuity needed
• Questions to be asked
– Can the load tolerate power interruption? If yes,
for how long?
– What is the effect of a power failure?
– Are there associated costs?
– Are there safety hazards associated with a failure?
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Static UPS Systems
• Widely used for feeding lower capacity, low voltage
loads - Instrumentation equipment, process control
computers, general computing equipment, critical
lubrication drives and emergency lighting
• Improves power quality to critical loads
• Prone to component failures like any other electronic
system
• Redundant modules for critical loads to improve
reliability
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Static UPS System - General Configuration
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Subsystems of typical Static UPS
• Backup source (storage battery)
• Rectifier (also used as charger for battery)
• DC bus (link between rectifier output, battery and
inverter input)
• Inverter for synthesis of AC output from DC
• Regulation and conditioning of mains power supply
• Static transfer switch or static bypass (optional)
• Maintenance bypass (optional)
• Isolation transformer (optional)
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Static UPS System
• Storage battery as power source - Critical
component for reliability
• Rectifier
– Converts power from mains into DC - Charges
storage battery
– Configured to cause minimum harmonics in mains
AC
– Provided with filters to ensure ripple free output
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Static UPS System
• Battery - Maintains voltage of DC bus when
mains power fails
• Voltage keeps falling as battery continues to
discharge
– Low DC voltage alarm
– Cutout to trip inverter to avoid over-discharging
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Static UPS System
• Inverter converts voltage of DC bus to synthesized
AC output
– Low capacity inverters - Partial square or trapezoidal
waveform
– Higher capacity inverters - Pulse-width modulated
sinusoidal AC output
• Input protection - Surge protection devices to protect
sensitive components
• Output protection - Fuses/MCCBs with overload
protectors, surge protection devices
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Static UPS System
• Voltage regulating device between AC mains and UPS
where very wide fluctuations of input voltage expected
– To keep battery from going into discharge mode at low
mains voltage conditions (sustained sag)
– To regulate output voltage when mains power is directly
connected to loads
• Static switch - Automatic load transfer from mains
power to inverter or vice versa
• Filter - Control communication of noise, harmonics
from power mains to loads
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Static UPS System
• Maintenance bypass
– Optional component
– Manually operated external switch
– For undertaking UPS maintenance
• Isolation transformer - To avoid surges,
common mode noise from being conveyed to
loads
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Types of Static UPS Systems
• Passive (offline)
• Line interactive
• Double conversion (online)
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Passive UPS
Power flow under normal (mains power
available) condition
Power flow under mains failure condition
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Passive UPS
• Definite delay involved in changeover - 8 to 10
ms
• Loads must be able to tolerate break of supply
• Mechanical relay instead of static switch in
cheaper designs – Slower than static switch
• Needs attention while selecting UPS
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Passive UPS
• Advantages
– Cost effective - Rectifier sized only for battery
current, Inverter sized only for short duration
– Limited losses in inverter (only during its
operation)
• Generally restricted to lower capacities (2 kVA
or less)
• Unsuitable where break in output not
acceptable
• Limited power quality improvement
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Passive UPS
• Some UPS designs - Changeover not just for
mains failure conditions, also during supply
voltage, frequency drift
Disadvantages
– Frequent battery discharge-charge cycles
Reduced battery life
– Lower backup time during actual mains failure
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Line Interactive UPS
• Static switch positioned differently from Passive
UPS
• Not involved in switching of load from mains to
inverter
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Line Interactive UPS
• Static switch connects mains supply to load when it
is present
• Inverter module connected to load in parallel
• When mains power fails, inverter module operates
as inverter, power flow direction is reversed
• Static switch opens to prevent flow of power back to
mains
• Limited to smaller ratings only
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Double Conversion UPS
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Double Conversion UPS
• Primary mode of power flow from mains to rectifier to
inverter and to loads
• Rectifier supplies power for loads, also charges
battery
• When mains power fails battery supplies power
• No break of supply at UPS output
• Higher rectifier current – Battery charging current
plus load current
• Most designs provided with static switch - Automatic
transfer of loads from inverter to mains in case of
inverter module failure
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Double Conversion UPS
• Static switch omitted in some low output UPS designs
– Reduced UPS cost
– Carries risk of power loss if inverter fails
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Double Conversion UPS
Advantages
• Harmonics, surges and noise not get reflected at
output
• Inverter can operate at own frequency independent
of mains frequency
Disadvantages
– Higher cost
• Rectifier for load current plus battery charging current
• Inverter rated for continuous operation
– Increased power losses
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Double Conversion UPS
• Standby batteries normally sized for providing
backup for short periods only - 15 minutes to 1 hour
• Higher duration power outages - Appropriate standby
power source for UPS before battery gets fully
discharged
• UPS designed for ensuring safe, orderly shutdown of
equipment in event of mains failure
• Batteries charged at high rate to ensure quick
restoration after power interruption
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Other types of UPS Systems
• Passive UPS with Ferro-resonant output
transformer
– 3-winding Ferro-resonant transformer at UPS
output
– Two windings for input (one from mains, one from
inverter) one common output winding
• Hybrid passive UPS system
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UPS with Ferro-resonant Transformer
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UPS with ferro resonant
transformer
• Similar in concept to passive UPS system
• Loads fed from mains through static switch, Ferro-resonant
transformer when mains available
• Static switch opens, inverter takes up load through
transformer when mains fails
• Ferro-resonant transformer - Acts as output filter, can regulate
slow voltage changes
• Can minimize break of output when mains fail and inverter
takes up load
• Problems
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Unstable output when load has power factor correction capacitors
Low efficiency at part loads
May interfere with fuse protection
May call for surge protection on output side
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Hybrid Passive UPS
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Hybrid passive Configuration
• Load directly connected to mains when it is present,
switched to battery when mains power fails
• Inverter always in circuit
• Switching delay between mains and
eliminated by proper setting of regulator
battery
• Behaves like double conversion UPS except there
are two different rectifiers, one for charging battery
and another for supplying load
• Disadvantage - Any failure of inverter module can
cause failure of UPS output
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Hybrid UPS System
Combines advantages Static and Rotary Systems
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Redundant UPS Configuration
• UPS systems also prone to failure just like any other
electronic equipment
• Failures also caused by battery problems
• Redundancy to prevent interruptions due to failure
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Redundant UPS Configuration
• Usually referred to as N+1 redundant configuration
• N modules can supply total power requirement by
equal load sharing
• One additional parallel module for little extra capacity
Continued operation when one module fails
• Redundancy not just for electronic components but
also for battery
• Additional static switch fed from separate source to
switch to alternate supply during multiple module
failure
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UPS - Installation
• To be done by experienced personnel
• Read, understand manufacturer’s instructions fully
before installation and commissioning
• Follow Safety procedures strictly to avoid danger to
personnel and equipment
• Batteries are heavy – Take care during handling,
transportation
• Acid is corrosive – Take care in handling, storage
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Batteries
Different Types, Pros and Cons
• Energy storage device used for UPS
• Energy stored in form of chemical energy during
charging, converted back to electrical energy during
discharge phase
• DC of battery converted to AC by UPS and delivered
to loads
• Most commonly used battery types
– Lead acid battery (Lead Calcium and Lead Antimony)
– Nickel Cadmium battery
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Lead Acid, Nickel Cadmium Batteries
• Lead Acid Battery - Use lead electrodes, Sulphuric
acid as electrolyte
– Lead Calcium Type
• Not suitable for charge-discharge cycling applications
• Can undergo 30-50 deep discharges over life
– Lead Antimony Type
• Can tolerate up to 300-500 deep discharge cycles
• Nickel Cadmium Battery - Electrodes made of nickelcadmium, potassium hydroxide as electrolyte
• Lead acid and Nickel-Cadmium batteries designed
both in flooded and valve regulated versions
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Batteries
• Flooded cell batteries - Have liquid electrolyte like
sulphuric acid
• Valve regulated type (maintenance free batteries)
– Do not have free liquid electrolyte
– Do not require specially designed room with dedicated
temperature control, dedicated exhaust and ventilation
system or hazardous area equipment
– Less maintenance intensive
– Can be oriented in any direction without electrolyte spillage
problems
– Incorporate following technologies
• AGM - Absorbed glass matte technology
• Gelled electrolyte technology
• Oxygen recombination technology
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Batteries
• AGM (Absorbed glass matte technology) Electrolyte completely absorbed in glass matte
• Gel cell - Electrolyte in gel form
• Valve regulated battery
– Smaller in size compared to flooded cell battery. Typically
AGM battery has app. 40% less electrolyte than flooded cell,
Gel cell about 15% less electrolyte
– Also use recombination technology - Gases evolved during
charging recombine to form water (eliminates need for
adding water)
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UPS Battery – Installation
• Follow battery manufacturer's instructions
• Install on specially built steel racks of bolted/
welded construction
• Connect with correct polarity. Incorrect
connection will damage incorrectly connected
battery
• Busbars, cables should be of adequate cross
section
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UPS Battery – Installation
• Ensure flooring is strong enough to carry battery
weight
• Use nickel plated lugs for cable/ busbar termination
to reduce corrosion
• Cables, bus-bars should not touch battery top.
Electrolyte splashes should not come in contact with
bus-bars, cables
• Screw vent plugs tightly. Breathing holes should be
free from blockage/ plugging
• Keep battery under trickle
commissioned for long time
charge
if
not
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UPS Battery – Troubleshooting
Battery not taking charging
current
Open circuit - Blown fuse, tripped
breaker, charger problem
Over heating of battery while
charging
 Inadequate ventilation
 Space constraints
 High charge rate for too long
periods
Over heating of battery
while discharging
•High rate of discharge for long period
•Short between plates
Electrolyte low level
•Leaking electrolyte, cracked jar
•Evaporation due to over charging/
discharging
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UPS Battery – Troubleshooting
Battery Problem
Check point, probable cause
of problem
Battery taking longer time •Loose connection, Higher resistance
for charging
in the circuit
•Low inadequate current setting in
charger
•Charger capacity less than
requirement
•Reversed connections to charger
•Diluted electrolyte
•Electrolyte level too low
•Battery plates sulphated
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UPS Battery – Troubleshooting
Unequal cell voltages
•Over charging, discharging
•Unequal level of electrolyte in all cells
•Some cells defective
•Unequal specific gravities of electrolyte in
cells
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Any questions ?
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