Buyers 1

BUYING

U

tility power is plagued by disruptions, fluctuations, and rationing, which makes it crucial to use uninterruptible power supply (UPS) systems for computer data and industrial process applications. The market is flooded with numerous UPS systems, both indigenous and imported. For a common user selecting the right UPS is a daunting task. Before you go for buying a UPS we will suggest you to first study power characteristics in your area, such as duration, frequency, and nature of breakdowns and fluctuations. An area prone to frequent power failures requires superior power protection. If the fluctuations are drastic, you should go in for a system that can operate over a wide range of input voltages. Power cuts for longer duration dictate the need for an engine generator. The UPS in this case should also be generator-compatible.

Buying criteria Given below are some important parameters you need to consider while purchasing a UPS: Load requirements. Define power requirements of your load (computers, printers, monitors, communication equipment, process control systems, and so on) and multiply the total power rating by a factor of safety of 1.5 to obtain UPS rating. Another method to calculate the total power consumed by your system is to consider every device that will be plugged into the UPS and sum the wattage used. A norm used by the industry is to calculate the wattage at 60 per cent of the volt-ampere (VA) rating. Users must

TVS LanUPS

GUIDE

match both watts and VAs of the UPS and the loads. It is a conservative idea to utilise the UPS to only 80 per cent of its capacity. For loads like colour monitors, printers, induction motors, air-conditioners, etc, ask your dealer about short-

sis of peak load, peak failure timings, and the minimum voltage available. Different loads have different effects (high inrush current, PF, and harmonics generation) on the power system. AC motors and printers draw heavy initial currents, with exponential reduction in amplitudes. This affects the working of

match

UPSto

your load requirements R. NARAYANAN

The UPS system should match the load to ensure fast response and recovery within half a cycle. Its power rating should ensure a voltage dip of 10 per cent or less term overload rating of UPS. Typical ratings are 125 per cent overload for 10 minutes and 150 per cent for 60 seconds. Industrial applications require different design parameters compared to dataprocessing counterparts. UPS in commercial applications have become commodity items, while industrial UPS systems remain an engineered product. The selected UPS system should have better non-linear load-handling capacity with pure sinewave output. Load should be calculated on the baELECTRONICS FOR YOU ❚ MAY 2001

other equipment connected in tandem. Duration of current inrush depends on the inertia of mechanical loads driven. Inductive loads present a lagging PF, generating spikes when these are switched off. This necessitates a built-in protection to prevent damage. Decide how long the UPS must power your system. This will depend upon what exactly you would want to do once there is a power cut. If all you need to do is just save the file on the computer and shut down, you will not require more than a 31

BUYING

GUIDE

with colour monitors and a printer requires 650 VA. A network consisting of a server with up to five disk-less nodes with monitors consumes 1,600 VA, while a network consisting of a server and up to seven disk-less nodes with mono monitors requires 2200 VA. Specifications. You should understand vendor specifications correctly in order to meet your load requirements. Specifications are categorised as environmental, mechanical, and electrical. The performance of semiconductors used in a UPS system depends on enviA Mixed Load Situation ronmental conditions (like minimum/ Load kVA PF kW kVAR maximum operating conditions, relative Computer 50 0.6 30 40 humidity, dust, altitude, etc) for control Resistive 150 1.0 150 0 room applications and computer installaMotor 20 0.8 16 12 tions. Total 196 52 Standard UPS specifications include The total kVA in this case cannot be an operating temperature of 0 to 48oC. In obtained by the arithmetic sum due to an emergency, if the AC mains fails, the UPS may have to withstand higher temthe difference in power factors. perature and moisture conditions. So a Hence, kVA = (kW)2 + (kVAR)2 =1962+522 = 203.1 system specified at 40oC needs de-rating. Resultant PF = 196/203 = 0.97 The de-rating values are sometimes menThe selected UPS must satisfy 196kW tioned in specifications. and 203kVA, or higher, output capacity Sealed lead-acid batteries need opersimultaneously. Normally, PF rating for ating temperature of 25oC, so it is always a UPS is 0.8, so the required UPS rating preferable to keep UPS and SMF batteris 196/0.8=245 kVA. This will automati- ies in AC rooms. Low temperature encally meet the 203kVA requirement, with hances equipment’s life and therefore you should be careful against tall claims made load demand of 196 kW. The following table indicates power by UPS manufacturers about high-temperature operations. consumption by some standard loads: UPS creates probAC motors VA as specified Inrush current is lems when exposed to with PF 5-6 times the high temperature, dust, rated current and moisture. In rainy Pentium PC 250-300 VA Inrush current due to SMPS season a high humidity Fluorescent 70 VA — results in condensation tube (40W) inside the equipment, Laser printers, 400-500 VA High inrush currents which weakens the plotters and heavy surge currents system’s insulation. Electric heaters In kW as PF=1, no inrush current At altitudes higher specified than that specified by the For non-linear loads it is not possible manufacturer, cooling required may not to calculate the UPS rating as the data be sufficient because of low air-pressure. pertaining to their characteristics (such Datasheets might depict the UPS system as kVA, kW, PF, load crest factor, etc) is to be designed for up to 1000m height, unavailable. It is advisable to arrive at beyond which the UPS needs de-rating. Electrical characteristics include inthe UPS capacity by using industry norms. Add kVA capacity of all loads. If put supply, frequency, etc. If the input ratings are described in kW, these can be voltage is lower than the specified limit, converted into kVA by using the relation- the charger will not be able to produce ship kVA=kW/0.6, where the assumed PF sufficient DC voltage to charge the batis 0.6. The UPS capacity should be 30 per teries up to the rated voltage. Even if the cent higher than the total kVA calculated. UPS works at low mains voltage, the batA Pentium PC with colour monitor teries will remain uncharged and will not requires 500 VA, while two Pentium PCs give any backup when power fails. So batfew minutes of backup time. Also consider the total number of devices that must be kept ‘on’. During this period, ideally a printer should not be connected to the UPS, as it consumes too much power. Sizing. When calculating the UPS rating, factors to be considered include maximum kVA rating (at 0.8 PF or the supplier’s stated value), maximum kW rating, and crest factor (peak feeding capability). A typical example of a mixed load situation is depicted below:

32 CMYK

ELECTRONICS FOR YOU ❚ MAY 2001

tery charging must be ensured at the lowest limit. RFI/EMI filter protection at the input saves the UPS from malfunction due to disturbances. UPS are designed to accept a lagging PF of up to 0.8 to cater to industrial loads. For many loads the starting kVA rating should be high. Inrush currents of AC motors, incandescent lamps, power supplies, etc need to be matched with permissible short-duration overload rating of UPS. An additional load should not create a voltage dip to disturb the exisiting loads running on the same UPS. The UPS system should match the load to ensure fast response and recovery within half a cycle. Its power rating should ensure a voltage dip of 10 per cent or less. The use of PWM techniques and magnetic components in UPS generates audible noise. Since UPS systems are often located next to equipment and operators, acoustic noise should be less than 55-60 dB. Often specifications like EMI/RFI levels, I/O galvanic isolation, MTBF, and availability factor are not mentioned explicitly. These are usually provided by reputed vendors on request. There is no benefit in buying a UPS of a higher kVA rating than that required, unless more equipment are to be added in near future. Load and battery capacity dictate backup and VA rating. Depending on the backup required, batteries of requisite capacities are installed.

Instrumentation UPS

BUYING

Aplab Powerbook 700

Other aspects include the type of UPS (single or parallel), redundancy, automatic bypass (if required to normal supply or standby supply), input power-supply voltage, frequency, phase, voltage/frequency tolerance, and earthing of neutrals of the UPS and bypass supplies. Quality of output. Low output distortions, capacity to cater to non-linear loads, and output control dictate the output quality. For 0 to 100 per cent load change in steps, the output shall remain within ±5 to ±8 per cent and recover to normal value in 5 to 10 minutes. UPS with PWM techniques and sine wave as reference can meet this stipulation, so check for the technique used. Switching technique produces immense audible noise. Typical noise figure for a high-rated UPS at 1.5 m from it is

Cansoft UPS

GUIDE

60-65 dB. The noise depends on the switching frequency of devices used in the inverter section. The higher the frequency, the lesser the noise. Using BJT and IGBTs helps in reducing the noise. For a UPS with lower rating of up to 2 kVA, using MOSFET-based technology, the audible noise is as low as 45 dB, which allows the user to keep UPS system next to the computer. Do not forget to consider wider input window and efficiency aspects. The input supply window should cater to local power situations and fluctuations. It should be of 190V to 270V (–20 per cent to +15 per cent) for single-phase input systems and a minimum of 360 to 400V for three-phase supply systems. The overall efficiency of UPS should be more than 85 per cent, which reduces operating/recurring expenditure by 15 to 20 per cent a month. A UPS system with better rectification technique and higher overall efficiency can obviate oversizing of alternate backup source (such as diesel generator). A PC will reboot if the drop in voltage during switchover is below the threshold level (135V), so transfer time (the time lag when the UPS is switched from the mains to battery) should not be more than 20 ms. Ensure that the UPS features built-in AVR, fast recharging of batteries, protections, and long battery life. Online UPS is the best choice when there are some lingering doubts about transfer time. UPS efficiency is usually specified at full load (100 per cent load), but in reality most UPS are loaded at 25 per cent or 50 per cent only. So check out this feature with UPS manufacturer. High inverter efficiency increases battery backup time with the same battery ampere-hour (AH), reducing additional cost. Good AC-AC efficiency and inverter efficiency reduce heat loss and maintain the ambient temperature of UPS system. Poor efficiency results in higher power bills and higher battery AH capacity. The maximum/minimum output voltage of the UPS should be within 10 per cent of 230V, which increases regulation. The higher the range of supply voltage for which the UPS continues on mains without switching to it, the better the regulation. Also check whether the kW rating of generating set is dedicated to the UPS or shared with other building ELECTRONICS FOR YOU ❚ MAY 2001

33

BUYING

GUIDE

UPS FEATURES MAKE and model

Rating (VA)

Backup (hrs.)

Efficiency (%)

Output waveform

Output volts

Input DC volts

Input AC volts

Battery capacity (AH) 100

Protection

Output freq (Hz)

Tech.

OL,SC, BOC, BDD, SP, SU

50 ± 1%

OL RS232I,

Price (Rs)

Copper Connections UPS OL 1000E 24

1000

2

>90

Sine

220 ± 5%

24

160-290

UPS OL 1000B 120

1000

0.5

do

do

do

120

do

7

do

do

UPS OL 2000E 48

2000

2

do

do

do

48

do

100

do

do

UPS OL 2000E 120

2000

5

do

do

do

120

do

100

do

do

UPS OL 2000B 120

2000

0.33

do

do

do

120

do

7

do

do

MCB

UPS OL 3000E 120

3000

3

do

do

do

120

do

100

do

do

(Common to all)

UPS OL 5000E 120

5000

2

do

do

do

120

do

100

do

do

500

0.33

SASWO

do

170-275

OV,UV, OL, SC, LB, ADD

do

UPS 500T

do

do

do

do

do

do

do

UPS 650

650

do

do

do

do

do

do

NET UPS

600

do

do

do

150-280

do

do

UPS-1000

1000

do

do

do

do

do

do

UPS-1600

1600

do

do

do

do

do

do

Sar Slicon ECO/SOHO 500

500

(20-25) (7-10)

220(110V optional)

150-275

SP, IF, M/N

5 0 ±6%

COT 4ms,

(3700),4700

Luminous 700

700

(40-50),(20-22)

do

do

do

do

COT 3ms

8600/-

145 −270

S,SU P, SC, BL,OL

50 ± 0.5%

OFL TT 4ms, AVR RS232

17,500/-

50 ± 05%

pf0.7,OLC 300% 5 secs,

21,000/-

CCCV CHG,

Aar-em Electronics UPS - 5001

EMI/RF Filter LI

Cansoft Offline UPS

2000

95

SSW

2 3 0 ±3%

Online UPS

1000

90 IM

TSW

230 ±.5%

Domestic UPS

600

Aplab Powerbook 700

500

48

do

90 FL MSW

12

2 3 0 ±3%

160-275 or 415

HRCFP,OL, HV, BL, MCB,

116-275 220 ±2 5 %

SC, BRP, OL,

7,300/-

50 5 0 ±1%

LI, CS, B1B, CS AVR BI, TT<3ms, RS232

OY UY,BUV,SC, OL, OT,DOC

AN<55dB, TTU,TON, UFC,FAC, CS CI, RM,CBD

OL, SC, UV, OY, SS, AC/DC Fuse,

4950/-

Kirloskar Nano-AT/NT-2/3/5 KVA

2000/3000/ 5000

upto 8 hrs autonomy

144

160-270

230 ± 1.5%

50 ± 0.1%

87-92(I) 80-85(o) P S W

Penguin 7.5/10/15 KVA

7500/10000/ 15000

upto 2hrs autonomy

240

330-470(3PH)

230± 1.5%

50 ± 0.1%

90-93(I) 86-90(0) do

do

do

20,000/ 30,000/ 40,000/ 50,000/-

upto 1 hrs autonomy

336

do (3PH)

do

do

90-94(I) 87-90(o) do

do

do

SPO, SS,UV,OY,ISC, EMI/RFI,

CS, MBII, SPMDP,GC, SMB

5800/-

HV/LV, HB/LB,OL MC, OFL, 2ms, Mpc

5200/-

DOLPHIN 20/30/40/50 KVA

Wipro Eperipherals eMerge 525

160-290

525

48000/53600 65000/70600 94000/99600

128000/161000/255000/310000/400000/490000/585000/670000/-

Aldin AEI/500/12V

500

0.25 to 0.33

12

0.80

AEI/750/12V

750

do

12

do

do

do

6500/-

L E G E N D ADD - automatic deep-discharge protection AN - audible noise BDD - bty deep-discharge BL - battery low BOC - bty over-charge BPF - bypass fuses BRP - bty reverse polarity BUV - battery under-voltage CBD - custom-built design CCCV - constant-current constant-voltage charging CI - computer interface COT - changeover time CS - cold start DOC - DC over current FAL - fully automatic control

34 CMYK

GC - generator compatible HB/LB - high/low battery HV/LV - high/low voltage ICB - circuit breakers for input IF - input fuse I - inverter LB - low battery LI - line interactive MBII - microprocessor-based design with intelligent interface MC - microporcessor control MCB - microcontroller-based MF - mains fuse MP - microprocessor MP - modern protection MSW - modified sinewave

OFL - offline OLC - overload capacity OL - online OL - overload OOL - output overload O - overall OT - over temperature OUV - output undervlotage OVCO - over voltage cut-off OV - over voltage PMS - power management software PSW - pure sine wave QSW - quasi sine wave RDA - redundant parallel architecture RM - remote monitoring RS - 232I-RS-232 interface

ELECTRONICS FOR YOU ❚ MAY 2001

S - surge SASWO - stepped approximation to sinewave output SC - short circuit SMB - sleep mode for battery longevity SPMDP - software for power management and data protection SPO - surge-protected outlet SS - surge suppresion SSVVO - stablised sinewave output SSW - step sinewave TON - true on line TT - transfer time UFSC - unattended file saving capacity UVCO - under-voltage cut-off UV - under voltage

BUYING

GUIDE

UPS FEATURES Make and model

Rating (VA)

Backup (hrs)

Battery capacity (AH)

Input DC (V)

Input AC (V)

Output AC (V)

Output freq (Hz)

Start UPS Lite 500

500

0.166

7

12

140-300

230 ± 5%

Start UPS Lite 700

700

0.25

7

12

166-275

Startup UPS Lite 1000

1000

0.166

7

12

165-300

Startup UPS Lite 2000

2200

0.166

7

TVS Electronics

Wave shape

Protection

Tech.

50 ± 0-2%

MSVV

SU, MP, NP

LI, IPMS< CS, BIB, HSB, AVR, NL, NP, IP, TT<4ms, N<45dB,

do

do

do

do

do

50 ± 0.5%

do

do

do

Efficency (%)

Price

5280/-

do

LAN UPS 1000M

12

do

do

do

do

0.25

24

140-300

2 3 0 ± 2%

SVV

OP,

do do LI, NLS,NI,CS, BIB, MS, AVR,BM,PMS,IINM, TT 4ms,

8,245/12,645/28,595/-

do Lan UPS 1500M

1500

0.166

36

do

do

do

do

Lan UPS 2200M

2200

0.166

36

do

do

do

do

Lan UPS 3000M

3000

2.0

do

do

do

do

do

IL UPS PRO 300VA/ 500VA/700VA/1050

300/500/ 700/1050

0.166/0.06/ 0.10/.13

SSW

SS,LF,SP,NF,F/M/ NP,

LI, SD, BHM, HSB,RS232I, OSNF,TT2/ 3.5ms,MC,RS232I, 40dBA L, MC, HSB, SASD

IL MacroUPS 1/2 KVA

1000/2000

do

23645/-

do

34,095/71,495/-

Instrumentation Ltd

IL-MS UPS 3.6-10 KVA(3.6/6/8/10)

3600 10,000

7

12

184-300

230 ± 5%

50 ± 0.1

48/84

170-270

2 3 0 ± 2%

75 A-A 80A-A

SW

SC,OL,OH,HVCO, BLCo

CC,CS,IOD,II DB9,TIOL,TT 2ms,GC,TIOL,

230 ± 15%

2 3 0 ± 1%

95(I)85/86/87/87A-A

S

MCB,OL,SC,CB, RFI F

AN 50/51/54/ 54dB,RS232,TT<0.5 ms, MC, DC,CS,TM

The above features are indicative only, and may differ or change with time. Please check before buying.

ELECTRONICS FOR YOU ❚ MAY 2001

35

BUYING

services. Battery. Sealed maintenance-free (SMF) batteries are preferred because these do not require any maintenance. If you need to work for a long period during power outage, a high-capacity battery has to be installed. If float voltage of the battery is too low, the battery will not charge efficiently, and if float voltage is too high, the battery will overheat, resulting in reduced life. Check whether the dealer offers battery servicing and maintenance. You should know how much battery backup you would require in the case of mains failure. This aspect is important since UPS battery replacement is very expensive (as much as 30-50 per cent of the total cost of UPS). Temperature, battery charger design, float voltage settings, and ripple current affect reliability of the battery. The battery should have more chargedischarge life-cycles. A good battery management system carries out periodic tests of batteries to ensure that the backup is available when it is needed the most. Storage capacity of the battery determines the backup time that will be available in the case of power failure. If a long backup time is required, it is advisable to go in for additional batteries. SMF battery should be used to backup for up to one hour. However, using this battery costs high when backup is required for more than one hour, so tubular battery with ceramic plug should be used as the second option. The battery should be kept on charge permanently. In most cases batteries are not kept under charge when the office is closed, which results in reduced battery life. SMF batteries are suitable for any environment, while automotive/tubular batteries are generally used when proper ventilation is available. Software support. The UPS should support the concerned software environ-

Champion i-UPS 36 CMYK

GUIDE

Types of UPS You should understand the differences between online, offline, and lineinteractive UPS vis-à-vis your exact requirement of power. Online UPS uses double-conversion technique, wherein input AC is converted to DC and then AC output is regenerated. During mains failure DC power is taken from the battery in zero transfer time. Bypass feature is incorporated to transfer the load directly to the mains even if the inverter fails for a moment. Standby or offline UPS switches in a brief transfer time from the mains to inverter, which uses internal battery when the supply fails. Line-interactive UPS is a combination of online and offline UPS systems, wherein the inverter plays the dual role of charging the battery when the mains supply is present as well as regulating the output voltage. In the absence of mains supply it functions as a normal inverter. Line voltage is monitored at all times, activating the power transformer when utility supply deviates from specified parameters. Hybrids touted as line-interactive model in the market are in fact glorified offline designs with tap changer on the output transformer. Another version combines some features of online and offline versions. Power is supplied to the load normally from the mains. The inverter is kept running and synchronised to the utility line. ment. The most essential software nowadays is ‘auto shutdown’. Smart interface feature is a must for servers in networks. For individual PCs this feature is not essential. Serial communication and software features should be checked on if you intend to purchase the UPS for a PC/computer network. Better display and diagnosis system, frequency synchronisation window, better voltage regulation, and charger capacity with various types of batteries are to be considered. Power capacity (VA rating) of the UPS should be checked with a suitable load. Miscellaneous. Cold-start feature enables you to switch on the computer when there is no mains supply and work as long as the backup time allows. Thus you are able to complete emergency work during power failures. No-load cut-off feature enables the UPS to go into sleep mode when no load is connected, preventing unnecessary battery discharge. Safe shutdown of critical network servers, monitoring of UPS status, diagnostics, failure analysis, control of UPS, and self tests are some of the key aspects. Protection against shortcircuit, surges, spikes, overload, underload, battery overdischarge, etc should be ensured. Mean time between failures (MTBF) and mean time to repair (MTTR) are vital from the point of ELECTRONICS FOR YOU ❚ MAY 2001

view of reliability and simplicity in repairs. The higher the MTBF, the better is the reliability. MTBF is generally 20,000 to 30,000 hours. MTTR should be as low as possible. It is usually 2 to 4 hours. Site-wiring-fault indicator alerts you of potential wiring problems on the site, such as poor ground or reversed polarity. Front-panel indicators (low-battery indicator, replace-battery indicator, and load meter) indicate how much of the UPS capacity is being used vis-à-vis the load. UPS can catch fire due to over-heating of components inside it or high voltages reaching the input during ‘off’ hours. So it is important for ABS plastic used in some UPS cabinets to be fire-retardant. Servicing & brand. Reputation of the manufacturer, quality of after-sales service, commitment to the product, infrastructure, and staying power are some other vital factors to be considered. Price. The cost of a UPS involves not only the price of the product but also the maintenance cost, operating costs (electricity bills), and the cost of replacing the battery every 1-2 years. It should be lesser than 20 per cent of the investment you make on the computer. A high-technology UPS definitely demands higher premium than the low-technology UPS. But it pays off over a period of time. ❏