Ups

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SISTEM BEKALAN KUASA TANPA GANGGUAN (UPS) 1.

PENGENALAN Bekalan kuasa bantu adalah satu perkara yang sangat mustahak bagi menjamin agar perjalanan sesuatu sistem itu tidak terganggu. Sistem bekalan kuasa tanpa gangguan (UPS) adalah salah satu sistem kuasa bantu yang amat terjamin dan berteknologi tinggi. Kegunaannya adalah berbeza iaitu mengikut keperluan beban tetapi pada kebiasaannya ianya terhad kepada beban-beban yang kritikal sahaja umpamanya komputer, PABX, dsb.

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MENGAPA SISTEM UPS ITU PERLU Untuk pengetahuan, harga bagi sesuatu UPS itu adalah jauh lebih tinggi daripada harga sebuah set janakuasa tunggusedia. Jadi kenapakah kita masih mahu menggunakan sistem UPS. Jawapan bagi soalan ini ialah keperluan kuasa bantu yang stabil dan terjamin bagi sesuatu beban yang kritikal dimana gangguan kuasa tidak boleh berlaku walau sesaat pun. Contohnya bagi sistem komputer, jika berlakunya gangguan kuasa ianya akan kehilangan isian didalam memorinya. Begitu juga dengan sistem lampu landasan kapal terbang (bagi kategori II keatas), gangguan kuasa tidak boleh melebehi satu saat.

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JENIS-JENIS SISTEM UPS Sistem UPS terbahagi kepada beberapa jenis tetapi yang biasa digunakan ialah: i) ii)

Jenis Unitary Jenis Parallel

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Jenis Unitary

Jenis Parallel

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PEMILIHAN SISTEM UPS Perkara-perkara utama yang harus diambilkira semasa membuat pemilihan sistem UPS yang sesuai dengan kehendak kita adalah: a.

Kuasa

Kuasa yang dikehendaki bagi sesuatu pemasangan hendaklah ditentukan. Ada dua cara bagi menentukan kuasa sistem UPS iaitu memilih saiz sistem UPS yang boleh menampung beban semasa dan beban tambahan dimasa akan datang. Cara ini akan melibatkan kos permulaan dan kos penyelenggaraan yang tinggi sedikit oleh kerana kemungkinan sistem UPS ini beroperasi bukan pada kecekapan yang tinggi, tetapi dalam jangkamasa panjang ianya boleh menjimatkan. Cara kedua ialah dengan menghadkan kepada beban tersambung sahaja. Ini adalah dengan menentukan saiz sistem UPS sahaja tetapi keperluan bagi membolehkan sistem UPS ini dipertingkatkan dimasa hadapan perlu diadakan. Kos permulaan dan penyelenggaraan bagi cara ini adalah lebih murah. ii)

Peraturan Voltan

Peraturan voltan keluaran dapat memberi panduan mengenai kualiti peralatan yang dicadangkan itu. Pada kebiasaannya kita hendaklah menentukan bahawa peraturan voltan adalah plus / minus 1% dalam keadaan tetap dan perubahan voltan keluaran berada dalam jeda (range) +10% hingga –2% daripada nilai terkadar keatas jumlah beban. iii)

Herotan Harmonik (Harmonic Distortion)

Aras herotan harmonik keseluruhannya hendaklah ditentukan. Ini sebenarnya mengukur kualiti gelombang bentuk sinus yang dikeluarkan oleh sistem UPS. Pihak pengeluar komputer biasanya memberikan kadar maksimumnya sebanyak 5% sahaja.

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iv)

Frekuensi

Beban komputer pada kebiasaannya boleh menerima perubahan frekuensi dalam kadar plus / minus 1% sahaja. v)

Kemuatan Beban Lebih

Oleh kerana terdapatnya beban yang boleh menyebabkan arus rempuh (inrush current) masuk yang tinggi semasa ianya dihidupkan, kemungkinan sistem UPS yang dicadangkan itu terpaksa dinaikkan saiz sebanyak 100 – 250%, tertakluk kepada jenis beban. 5.

KOMPONEN UTAMA SISTEM UPS Antara komponen utama sistem UPS ialah: a. b. c. d. e.

Penerus (rectifier)/battery charger Static transistor inverter Electronic static switch Bateri Manual maintenance by-pass circuit

Katalah satu pemasangan mempunyai beban kritikal yang berkadaran seperti berikut: 40KVA, 30KVA, 15KVA, 10KVA dan 50KVA. Beban 10KVA mempunyai selama 200ms, dihidupkan tidak menyebabkan arus pemasangan ini ialah 0.2 hadapan yang dijangkakan maksimum semasa.

arus rempuh masuk bersamaan 4 x In sekali dalam sehari. Beban-beban lain rempuh masuk. Faktur kuasa bagi menyusul. Keperluan tambahan masa adalah sebanyak 20% daripada beban

Penentuan mengenai tatarajah optimum Keadaan beban stabil P = (40+30+15+10+50) KVA = 145KVA Katalah tambahan beban akan dimasa hadapan sebanyak 20%

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P = 20% x 145 = 30KVA Pu = (145 + 30) = 175KVA Muatan terpasang tidak boleh kurang daripada Pu. Pa /175KVA Saiz sistem UPS bagi Unitary Chain piawai yang paling hampir ialah 200KVA 5.1

Kekangan (Constrains) Beban Lebih Fana (load transient) dari inductive load seperti motor dan yang seumpamanya. Kes yang paling berat ialah apabila beban 10KVA dihidupkan selepas beban-beban lain. Beban puncak akan menjadi: Pp = 40 + 30 + 15 + (4x10) + 50 + 30 = 205KVA Muatan beban lebih yang dibenarkan ialah 1.7 kali ganda iaitu 1.7 x 200 = 340KVA. Oleh itu saiz 200KVA itu adalah memadai. Sistem UPS memberi kuasa bantu selain bateri apabila bekalan kuasa terputus. Bateri ini mengeluarkan arus terus oleh itu kuasa yang dikeluarkan perlu ditukar kepada arus ulangalik. Ini diperolehi dengan adanya penyongsang (inverter). Jenis-jenis bateri yang boleh digunakan bagi tujuan ini adalah: a. b.

Sel asid plumbum (lead acid cell) Kadmium-nikel (nikel cadmium)

Jenis bateri yang lazim digunakan ialah kadmium nikel atas sebabsebab penyenggaraan yang minimum, lasak dan ketahanannya sehingga 10 tahun jika disenggara dengan baik.

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5.2

Pemilihan Saiz Bateri Untuk mendapatkan saiz bateri yang tepat, dua nilai adalah dikehendaki iaitu: i) Arus discaj atau kuasa discaj ii) Tempoh discaj dimana bateri dikehendaki membekal kuasa semasa kuasa utama terputus.

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RUMUSAN AM Penggunaan sistem UPS adalah yang terbaik bagi menjamin bekalan kuasa Bantu yang berterusan dan stabil tetapi ada beberapa perkara yang perlu diambil ingatan semasa membuat pemilihan serta keputusan bagi memesan dan memasang sistem tersebut. Diantaranya ialah: i)

ii)

Oleh kerana kos sistem UPS ini adalah tinggi, keputusan untuk memasang sistem ini perlulah mendapat justifikasi yang memuaskan. Beban-beban yang penting dan kritikal perlu dikenalpasti. Ini sangat mustahak bagi mempastikan bahawa sistem UPS yang akan dipasang itu nanti akan beroperasi pada tahap yang optimum. Selain daripada yang tersebut diatas, penggunaan set janakuasa tunggusedia sebagai bekalan kuasa Bantu kedua adalah difikirkan perlu dan mustahak agar tempoh penggunaan sistem UPS dapat dikurangkan kerana tempoh bantu sistem UPS bergantung kepada saiz dan keupayaan bateri. Tempoh yang panjang dari yang sewajarnya akan hanya menambahkan kos pemasangan.

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SENGGARAAN SISTEM UPS

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Rectifier dan Inverter System UPS jenis rectifier dan inverter tidak memerlukan senggaraan berkala secara khusus sebab ia adalah alat elektronik. Secara amnya alat elektronik hendaklah dijaga kebersihannya terutama dari habuk.

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Selain itu yang penting adalah suhu dan peredaran udara bilik UPS. Suhu yang tinggi akan mengakibatkan komponen elektronik cepat rosak. Kalau bilik UPS mempunyai alat hawa dingin itu adalah yang sebaiknya. Kalau tidak system peredaran udara hendaklah dipastikan dalam keadaan baik. Alat UPS moden mempunyai self-diagnostic system dimana ia akan memberitahu kita apa-apa masaalah yang terdapat didalam sistemnya. 7.2

Bateri Jika bateri jenis tanpa senggaraan (maintenance free battery) tiadalah senggaraan yang perlu dibuat kepada bateri kecuali pastikan caj bateri adalah baik dan masih mempunyai kuasa yang mencukupi. Jika bateri jenis lead acid, paras elektrolid hendaklah sentiasa dipastikan melebihi paras minima, ketumpatan bandingan elektrolid diantara 1.1 ke 1.2. Periksa keadaan caj bateri masih NORMAL, kalau lemah hendaklah ditukar kepada yang baru Sambungan kepada bateri-bateri hendaklah dalam keadaan bersih dan baik (good contact). Sekali sekala atau sebulan sekali ujian hendaklah dibuat untuk memastikan system UPS berfungsi dengan baik iaitu dengan memutuskan bekalan normal (TNB) dan pastikan UPS boleh berfungsi seperti yang diharapkan. Untuk trouble shooting dan pembaikan komponen elektronik didalam alat UPS selalunya pembekal dipanggil untuk kerja-kerja tersebut disebabkan kepakaran yang mereka ada serta bekalan alat ganti yang hanya boleh diperolehi dari pembekal jenama tersebut sahaja.

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8 Specification for UPS Scope The UPS shall be continuous duty, solid state, transistorized. It shall operate in conjunction with existing electrical system to provide continuous quality power for electronic equipment loads. System Description Components The UPS shall consist of the following major components -

Rectifier / battery charger Static transistor inverter Electronic static switch and reserve supply Manual maintenance by pass circuit Input, battery, reverse, output and by pass switches Battery / optional battery cubicle

Microprocessor Control and Diagnostic Operation and control of the UPS shall be provided through the use of microprocessor control logic. Indications, measurements and alarms together with power history and battery autonomy shall be shown on an eight characters liquid crystal display. Start up, shut down, manual transfer offload to reserve and retransfer back to inverter shall be by clear step by step routines shown on the display. Options a. Remote mimic to display status of remote alarm, with audible alarm, audible alarm mute, test pushbutton and mimic AC supply on/off switch b. Computer interface via a 15way ‘D’ connector to signal UPS on, reserve to load, AC input fail and battery low c. Remote terminal display up to 10 meters distance of the alpha numeric diagnostic via a RS 232C port

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d. Easy 10 – remote colour or monochrome terminal display up to 10 meters distance of the diagnostic both graphically and alpha numerically e. Easy 1000 – as (d) above except transmission by a RS 422 interface allowing a distance of up to 1000 meters f. Life – remote monitoring of the UPS status by a service center g. Remote emergency power off to STOP the inverter h. Thermal and magnetic shunt trip circuit breakers in lieu of main switches i. Input and/or output isolation transformers mounted in a matching cabinets j. Input current harmonic distortion filter mounted within the UPS, to limit the THD to less than 10% and improve input power factor to 0.9 k. 12 pulse rectifier / battery charger to limit input current THD to less than 12% l. Input current harmonic distortion filter. Mounted in a matching cubicle in conjunction with (k) above to limit input current THD to less than 5% m. Input and/or output RFI suppression filters to external to the UPS n. Battery insulation alarm dependent if isolation transformers option fitted o. Cooling air inlet dust filters to increase protection to IP40 p. Parallel operation for both a common battery and common output with up to 6 UPS MODES OF OPERATION The UPS shall be designed to operate as an on-line reserve transfer system in the following modes: Normal The critical load is supplied continuously by the inverter. The rectifier/battery charger derives power from the commercial AC source and supplies DC power to the inverter whilst simultaneously maintaining the battery in fully charged condition. The static switch monitors and ensures the inverter tracks the reserve supply frequency. This means any automatic transfer to the reserve supply due to an overload etc. is frequency synchronized and does not cause an interruption to the critical load.

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Overload In the event of an inverter overload, manual stop or failure the static switch will automatically transfer the critical load to the reserve supply, without interruption. Emergency Upon failure or reduction (-15%) of the commercial AC power the critical load is supplied, without any switching, by the inverter drawing its power from the associated battery. There shall be no interruption to the critical load upon failure, reduction or restoration of the commercial AC power. Recharge Upon restoration of the commercial AC power, the rectifier/charger powers the inverter and simultaneously recharges the battery. This shall be an automatic function and shall cause no interruption to the critical load. By-pass Mode If UPS maintenance is required or repair necessary, by manually operating the by-pass switch in the correct sequence, it shall be possible to isolate the main modules for maintenance or repair but continue to supply the load from the reserve supply. Transfer/retransfer of the critical load is accomplished by automatically synchronizing the UPS to the reserve supply and paralleling the inverter with the reserve source, before closing or opening the by-pass switch as appropriate. Battery Servicing If the battery is taken out of service for maintenance, it shall be disconnected from the rectifier/charger and inverter by means of a switch. The UPS shall continue to function and meet all the performance criteria specified except for the standby period.

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GENERAL REQUIREMENTS Applicable standards BS 2772 part 1/IEC 2041 (CE) 44-5) Electrical equipment of industrial machines BS 5486 part 1 and 2/IEC 439.2 (CEI 17-13) Low-voltage switchgear assemblies BS 4417/IEC 146 (CEI 22-1) Uninterruptible power supplies BS 5490/IEC 529 (CEI 70-1) Protection enclosure degree BS 3182/IEC 364 Building electrical installation BS 5645/IEC 76 TBA (CEI 14-4, CEI 64-8, CEI 20-22) Components All active electronic devices shall be solid-state and shall not exceed manufacturer’s recommended operating parameters for maximum reliability. Grounding The UPS output AC neutral shall be electrically isolated from the UPS chassis. The UPS chassis and signal ground system shall be connected together and to a common ground point. The UPS output AC neutral shall be connected to the commercial AC power neutral ground in the installation. EMI Suppression Electromagnetic effect shall be minimized to ensure that computer system or other similar electronic systems shall neither adversely affect nor be affected by the UPS. Materials All materials and parts comprising the UPS shall be new and of current manufacture.

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RECTIFIER/BATTERY CHARGER General / Input Incoming commercial AC power shall be converted to a regulated DC output by the rectifier/battery charger. Commercial AC normal voltage 380, 400 or 415 volts + 10% -15%, 3 phase, 3 wire, frequency 50Hz (or 60Hz option) plus minus 5%. The rectifier/battery charger shall be a 6 pulse, 3 phase fully controlled rectifier bridge with constant voltage/constant current characteristic. Voltage Regulation The rectifier/battery charger output voltage shall not deviate by more than plus minus 1% RMS under the following conditions: a. No load to 100% load variation b. Primary input voltage and frequency variations up to the stated limits c. Ambient temperature variations within specified range Walk-in/Soft Start The rectifier/battery charger shall contain a timed walk-in circuit that causes the unit to assume the load gradually over a period of 10 seconds after the input voltage is applied. Power Factor The rectifier/battery charger shall have an input power4 factor of equal or greater than 0.8 lagging with nominal input voltage and in the automatic float charge state. Ripple The rectifier/battery charger shall be provided with an output L-C filter to limit the ripple to equal or less than 2% RMS maximum in the automatic float charge state with the battery disconnected.

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Total Harmonic Distortion (THD) The maximum voltage THD on the input shall be equal or less than 15%. The maximum current THD on the input shall be equal or less than 30%. The current drawn is not sinusoidal but includes harmonics expressed in % of the fundamental as shown in Table (A) below. If a 5th harmonic trap option is specified the expected harmonics will be as shown below (B). Harmonic 5 Harmonic 7th Harmonic 11th Harmonic 13th Harmonic 17th Harmonic 19th Harmonic THD th

A 29% 5% 7% 1% 3% 1% 30%

B 5% 5% 7% 1% 3% 1% 10%

Capacity The rectifier/battery charger shall have sufficient capacity to support a fully loaded inverter and simultaneously maintain the battery in a fully charged float condition. After partial or complete discharge of the battery, the rectifier/charger powers the inverter and automatically starts recharging the battery as follows: - at constant current (set at 10% of nominal capacity at 10 hour rate) up to the recharge voltage level. - at recharge voltage level until the threshold value of the automatic return to float voltage has been reached. A pushbutton located inside the equipment shall also be provided for manually initiating a first charge or recharge boost cycle. The rectifier output voltage shall be normally adjustable up to 2.7volt per cell. An internal switch shall be provided to automatically select the correct

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float charge voltage for sealed lead-acid or vented nickel cadmium or vented lead acid cells. The recharge cycle shall be preset at 12 or 24 hours. Overvoltage Protection The rectifier/battery charger shall be automatically turned-off if the DC voltage exceeds the maximum preset value. Automatic Battery Checking The charging status of the battery shall be automatically continuously checked by monitoring the charge current ripple and if out of preset limits, an alarm shall be shown on the LCD display. Electrical Characteristic

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Battery When operated with a sealed maintenance free lead-acid battery, the preset operating parameters shall be as follows: Input Voltage Nominal voltage Float voltage Boost voltage End of battery discharge voltage

380V 384 V 435 V 441 V 320 V

400V 408 V 463 V 468 V 340 V

415V 420 V 476 V 483 V 350 V

TRANSISTOR INVERTER General/Input The inverter shall use pulse width modulation (PWM) technology to generate three phase sinusoidal AC power. The inverter shall operate within specification over the nominal rectifier/battery charger output voltage range. Output The inverter output shall be controlled by a microprocessor. Voltage 380, 400, or 415 volts and neutral 50Hz or 60Hz option, 3 phase, 4 wire. Maximum power in kVA or kW or both at 0.8 power factor lagging shall be declared. Voltage Regulation The inverter steady state output voltage shall not deviate by more than plus or minus 1% in a steady state condition for input voltage variations within quoted limits and plus 10% - 8% for 0 to 100% load step and vice versa.

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Frequency Regulations The inverter steady state output frequency when synchronized to reserve shall not deviate by more than plus minus 1% or optionally 4%. Frequency Slew Rate Frequency slew rate shall be less than 0.8Hz per second and controlled by the microprocessor controlled logic. Frequency Control The output frequency of the inverter shall be controlled by a quartz oscillator, which can be operated as a free running unit or as a slave for synchronized operation with a separate AC source. The accuracy of the frequency control shall be plus minus 0.0005% when free running and be controlled by the microprocessor controlled logic. Total Harmonic Distortion The inverter shall provide harmonic neutralization and filtering to limit the total harmonic distortion in the output voltage to less than 2% with a linear load. Voltage Transient Response The inverter transient voltage shall not exceed +105 – 8% when subjected to a load application of 0 to 100% load. Transient Recovery The output voltage shall return to within plus minus 2% within 50 miliseconds after a load step application of 100%. Overload

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The inverter shall be capable of supplying an overload of 125% for 10 minutes, 150% for 10 seconds at 0.8 PF lagging. Short circuit current for 1 second shall be 200%. Voltage Adjustment The inverter shall have the option to compensate for line voltage drop of 0%, 2%, 4% or 5%. Inverter Shut-down Upon sensing an internal failure, the inverter electronic-control shall instantaneously remove the inverter from the critical load, transfer to reserve if within limits and then shut itself down. Inverter DC Protection The inverter shall be prorected against DC overvoltage and undervoltage according to the following recommended values for the standard number of sealed lead acid cells. DC overvoltage protection: 2.5 volts per cell DC undervoltage warning: 1.8 volts per cell DC undervoltage protection: 1.67 volts per cell Output Voltage Symmetry The inverter shall guarantee the symmetry of the oiutput voltages at plus minus 1% for balanced loads or plus minus 3% for 100% unbalanced load. Phase Displacement Phase angle displacement between the three phase voltage shall be: -120 degree plus mminus 1 degree balanced load -120 degree plus minus 100% unbalanced load

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Load Fuses The inverter shall be capable of rupturing within 10milisecond the following fuse types: Extra fast semiconductor: equal or less than 50% nominal UPS output current Fast: equal or less than 30% nominal UPS output current Slow: equal or less than 10% nominal UPS output current ELECTRONIC STATIC SWITCH General The electronic static switch shall be a naturally commutated, fully rated, high speed, solid state transfer device and rated for continuous duty operation. The electronic static switch shall provide the following transfer and retransfer operations. - Uninterrupted transfer to by-pass automatically initiated by the following conditions: a. Output overload period expired b. DC voltage out of limit c. Inverter failure d. Over temperature period expired - Uninterrupted manual transfer/retransfer to/from bypass initiated from the control panel - Uninterrupted automatic transfer from bypass whenever the inverter is capable of assuming the load - Uninterrupted automatic retransfer shall be inhibited by the following conditions: a. Manual transfer to bypass b. Multiple transfers shall be limited to three transfers /retransfer operation. The fourth transfer shall leave the load on the by-pass source c. UPS failure - All transfer and retransfers are inhibited by the following conditions:

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a. By=pass voltage out of limits b. By-pass frequency synchronization out of limits Voltage The maximum operating voltage shall be 480V with a transfer inhibit voltage setting of plus minus10% of nominal. Transfer Time The switching time from inverter to reserve and vice versa shall be less than 0.5milisecond when synchronized. The automatic retransfer delay time back to inverter from reserve after a transfer from inverter to reserve shall be 10 seconds. The transfer time when out of synchronization shall be 20milisecond Overload The electronic static switch shall be capable of supplying an overload of 150% continuously. The overload capability for shorter periods shall be in the range of milliseconds. Manual Maintenance By-pass A manually initiated make-before-break transfer to bypass shall be provided for routine maintenance purposes. MIMIC PANEL The UPS shall have a mimic panel with LED to indicate the configuration of the main switches and sub-assemblies. Measurement The UPS mimic panel shall be able to display the following measurement: Frequency Phase voltages to neutral

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Phase currents Rectifier current Battery current (with polarity indicated) Battery voltage Indications: Rectifier Status: Rectifier healthy/failure DC voltage within/outside limits Battery connected/disconnected Battery charging/charged Battery discharging Battery discharged Inverter Status: Inverter voltage within limits Inverter off Inverter running Inverter in manual control mode Inverter inhibited Inverter healthy Inverter in synchronization with reserve supply Reserve Status: Reserve voltage within/outside limits Reserve frequency within/outside limits Output Status: Load on inverter Load on reserve Load on bypass Load disconnected Time on inverter Time on reserve

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Alarms Rectifier: AC mains input failure AC mains input – incorrect phase rotation AC mains input out of limits Battery charge failure Rectifier bridge fault Battery switch open Battery earth fault Battery discharging – level 1 Battery discharging – Level 2 Battery recharging Maximum battery recharge time exceeded Battery disconnected or earth fault Inverter: Over temperature Operating in overload Overload shutdown VCE saturation shutdown Current limit shutdown Over temperature inhibit DC high voltage shutdown DC low voltage shutdown Inverter out of synchronization Reserve: Input switch open Input failure Incorrect phase rotation Voltage out of limits Frequency high Frequency low Static switch transfer inhibited Static switch in manual mode

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Output: Output switch open Bypass switch closed Load on reserve Load on bypass Load not supplied REMOTE ALARMS AND CONTROL Volt-free change-over contacts rated at 125V 1A shall be provided for the following conditions: Rectifier ON Battery shutdown imminent Inverter ON Load on reserve Summary alarm Rectifier on is activated by: AC mains input present Correct input phase rotation AC mains input within tolerance Rectifier/battery charger fault Battery shutdown imminent is activated by: Battery switch closed Battery shutdown imminent Inverter on is activated by: Inverter in synchronization with reserve Inverter output voltage within tolerance Load on reserve is activated by: Reserve switch closed Output switch closed

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Bypass switch closed Load not supplied by inverter Any of the above will cause the appropriate N.O contact to close and N.C contact to open. In every case the summary alarm contacts will operate as above. In addition there shall be the following facilities: Battery fuse blown indication to UPS Emergency power off to provide an electronic stop signal to the inverter. It does NOT disconnect the AC supplies, load or battery. Auxiliary contact for diesel generator changeover inhibits the static switch when the generator is operating Battery insulation failure indication to UPS MECHANICAL SPECIFICATION Enclosure The UPS shall be housed in a free-standing modular enclosure with removable panels to the back and sides and protection as standard to IP20. Ventilation Forced redundant air-cooling shall be provided to ensure that all components are operated within specification with air entry in the base and exit in the top. The enclosure shall be mounted with 800mm of free space at the top for ventilation. Cable Entry Cable entry shall be from the bottom or side of the cabinet. Painted Surface Painted surface shall be cleaned and finished with an electrostatically applied epoxidic enamel of a minimum of 60 microns thickness of the manufacturer’s standard color.

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Access All internal subassemblies shall be accessible from the front of the unit via hinged doors. Rear access shall not be required for installation nor servicing. The UPS shall be fork liftable from the front after the removal of bottom trim panels. ENVIRONMENTAL CONDITIONS The UPS shall be capable of withstanding any combination of the following environmental conditions. It must operate without mechanical or electrical damage or degradation of operating characteristic. Ambient temperature 0 degree to +40 degree C Relative Humidity Up to 90% (non condensing) for temperature of 20 deg C Altitude Maximum altitude of 1000 meters above sea-level, without derating Audible Noise at 1 Meter Distance (dBA) Between 60 to 65 dBA ASSOCIATED BATTERY Optional matching battery cubicles complete with a battery fuse shall be available to accommodate maintenance free sealed lead-acid batteries. OPERATION WITH DIESEL GENERATOR The UPS shall have an auxiliary contact to inhibit transfer to reserve in the case of generator instability.

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Generally a generator output of at least twice the UPS rating is required because of the total harmonic distortion (