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TRANSCRIPT
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UPS PRESENTATION
BMARC2-7-2010
Chuck VK2SS
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What does UPS stand for ?
1 . Useless pile of shite ?
2. United parcel service ?
3. Uninterruptible power supply ?
Yes its Uninterruptible power supply .
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Why do we need a UPS ?
1. To keep critical systems running during mainsdisturbances .
What are some examples of a critical system ?
1. Security companies .
2. Financial institutions .
3. Military installations .
4. Hospital operating theatres .
5. Government .
6. Telcos
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Mains Disturbances
1. Sags and surges .
When the mains voltage goes outside of the normal tolerance of + -10 % for more than a few seconds .
2. BrownoutsWhen the mains voltage dips below 10 % of the nominal for
a few seconds .
3. Impulses .
A short duration pulse which can be of a very high amplitude .
4. Outage .When the mains voltage drops to a very low level or to zero .
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How do we protect against thesedisturbances ?
1. Older systems used power conditioners whichwere basically A/C voltage regulators with spike andnoise suppression . There were two basic types,
Tap changers and ferro resonant .The tap changer switched taps using triacs on atransformer. Ferro used a capacitor in conjunction
with a transformer winding to create a resonant circuit. Regulation and noise rejection was excellent butthey were inefficient .
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Static UPS
Rated up to about 800kVA per unit .
Can be setup as a single or stand aloneUPS .
Or parallel redundant N+1
Or parallel for capacity N+N .
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Protection by UPS
Nearly all modern power protection is done byUPS .
There are basically two types of static UPS :
On line or double conversion .Standby or NBPS or single conversion .
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30kVA IndustrialUPS
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200kVA with 3 X40 batteries .
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6 Kvasinglephase
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Rotary UPS
Rated to 1.5 Mva per unit .
Is basically a motor with a 4 tonne flywheelwhich stores mechanical energy that powers agenerator . During a power outage the rotatingflywheel starts a diesel engine to power thesystem .
Sony in Japan has a site using 40 x 1.5mVAunits .
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Standby or single conversion.
If mains is within tolerance the critical load issupplied via the mains with some power conditioning .
If mains is out of tolerance the inverter isswitched on and takes the load after a smallbreak . Another version is called line
interactive which can boost or buck themains voltage with say a 5% variation .Outside this the inverter will run .
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Standby UPS
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Line interactive UPS
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On Line UPS
The inverter is on line all the time .
Being double conversion AC/DC then DC/ACit gives very good immunity to mainsdisturbances .
When mains goes outside of tolerance theinverter runs on battery power .
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UPS Modules
Rectifier
Uncontrolled bridge .
SCR phase controlled bridge .
Active rectifier which is basically an inverter in reverse .
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Rectifier Types
A single phase half wave rectifier is a 1 pulsecircuit .
A single phase full wave rectifier is a 2 pulsecircuit .
A three phase full wave rectifier is a 6 pulse .
A 3 phase full wave with a 30 deg tx is a 12pulse circuit .
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Full Wave Rectifier
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Rectifier
Click to edit Master text stylesSecond level Third level
Fourth level Fifth level Draws current from
the mains in narrow
pulses to charge thecapacitor .
This creates reflected
harmonics back intothe mains .
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3 Phase 12 Pulse Rectifier
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Has much lower reflectedTHDi asthe 2 rectifiers combine toproduces 12 pulse operation. This rect. is shifted 30
deg due to the star
delta transformer .
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Power Device Symbols
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Active Rectifier
Uses IGBTs and looks like an inverter inreverse .
Can work at power factor of unity andgenerates very low THD figures .
More acoustic noise than a conventionalrectifier .
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Active Rectifier
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Inverter
Square and quasi square . Has poor THD asa square wave contains all frequencies.
Not compatible with all loads and willproduce a buzz in speakers .
Sine wave is much more compatible with allloads . Normally generated by PWM .
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Square Wave Inverter
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Inverter
Older types operated into an outputtransformer ,which offers some isolation fromthe load but theres a weight penalty.
Newer types are transformer less so are moreprone to load related issues such as DCfeedback . They also require a boost circuitafter the rectifier as the rectified mainsvoltage is not quite high enough to give 240Vout .Smaller footprint and lighter
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H Bridge Inverter
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Inverter PWM
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PWM Generation
Older versions used analogue methods.Basically a triangular waveform called thecarrier , typically 6kHZ is compared in acomparator with a 50hZ sine wave .
Newer versions use DSP with jee wizalgorithms and give excellent sine wave A/Coutput .
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Inverter Power Devices .
SCRs were used in the older inverters but werenoisy and inefficient .
BJTs are a current fed device so the base driverequirements are difficult . Parallel transistors hadto be matched so they would load share .Switching frequency was limited.
Mosfets are still used in small UPS .
IGBTs are a voltage fed device so much easier to drive and do not need to be matched for parallel operation .
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500A IGBT
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300A BJT
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70uF 3PhaseFilter
Capacitor
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315ASemiconductor fuse .
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500ABlade
fuse
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Static Switch
Is a solid state A/C switch using back toback SCRs . One SCR conducts on the Poshalf cycle and the other on the neg half cycle .
Its used to switch the reserve supply or theinverter supply to the load without a break .
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IN/OUT
IN/OUT
STATIC SWITCH
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Bottom trace indicates transfer point .
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130A Double
SCR
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Batteries
Supply the power to the A/C load during amains outage .
UPS mostly use VRLA batteries . There asome wet cell sites .
Wet cells are rarely used as they requirespecial site conditions such as vent fans andemergency showers .
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A voltage is produced due to the reaction of the sulphuric acid , which forms theelectrolyte , and the spongy lead plates .
During charge the acid is driven from theplates into the electrolyte and the s.g. of theelectrolyte rises to around 1280 .
During discharge the acid is driven from theelectrolyte into the plates reducing the s.g .down to 1100 or so .
Batteries
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Battery Capacity
CCA
Is the current that the battery can deliver for 15seconds while maintaining at least 9 terminalvolts . Its for starter applications .
Amp hrs .Is the amps that a batt can give at either the10hr or 20hr rate . 10A for 10hrs = 100Ah
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Battery Capacity
Watts/cell
This is more related to UPS applications asthe load has a constant power characteristic .
Manufacturers produce charts of dischargecharacteristics , which are for constantpower , or current , versus time .
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Sizing Batteries
In UPS applications battery loading is calculated onthe Kw not the Kva load .
From the A/C Kw load add the UPS efficiency figure. Eg :1000W+ 8%=1080W
Calculate the W/cell eg: 1080/(6cells per batt X 8batts) 1080/48= 23 w/cell .
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Sizing Batteries
From the eg:
GP12-72 disch chart lookup the autonomyrequired time .
This gives 20 mins discharging to 1.65 v/cell .
If 60 mins was required we find that a GP12-340disch to 1.65v/cell is suitable .
If 180 mins was required we find that a GP12-650 disch to 1.7v/cell is suitable .
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Sizing Batteries
Wet cell car batteries are mainly designedfor starter application as once the motor isstarted the alternator takes the load .
Theyre not designed to be discharged toless than 50% capacity and rarely get to90% capacity .
This only leaves 40% available capacity soa 100aH batt becomes a 40aH batt .
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Sizing Batteries
Deep cycle and VRLA batteries are designed to bedischarged to a lower level.
Repeated deep discharges will still reduce thebatterys life .
VRLA batteries are rated under normal use and
normal temperatures to have an end of life capacityof 80 % of sol capacity.
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Average Disch Cycles
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Positive Power
Positive and NegativePower
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Power Factor
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P F
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Power Factor
To keep within the output limitations mostUPS and other power generating equipmentfactor in a de rating figure depending on the
pf of the load .
Eg: A 20kVA UPS will produce 16kW at unitypf . It will produce 20kVA at 0.8 lag but only18kVA at 0.8 lead .
Si i UPS
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Sizing a UPS
What power is required kVA and kW?
Is the load of a linear nature or likely to havea high peak factor ?
Will the load have a high inrush current
Eg : motor starting ?
What battery autonomy is required with thisconnected load ?
Si i UPS
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Sizing a UPS
Small UPS do not like laser printers due tothe heating elements .
Loads that produce a DC component eg :Electric drills will upset small UPS due to theDC getting back to the load sensing circuitsas theres no output TX .
Running an online UPS from a generator islikely to cause a synch. alarm due to thefrequency variations of the generator .
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Phaserotationmeter
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Wrap aroundtong