Sparks Electrical News July 2018

STANDBY AND EMERGENCY POWER

17

FREQUENTLY ASKED UPS QUESTIONS

STANDBY POWER SYSTEM FOR AFRICAN BANK A n uninterruptible power supply or uninter- ruptible power source (UPS) is an electri- cal apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery runtime of most uninterruptible power supplies is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment. Q What is a UPS? A UPS is a device that allows your computer, tel- ephone or critical equipment to keep running when the primary power source is lost. It also provides protection from power surges, spikes, brownouts, interference and other unwanted problems on the supported equipment. Q How long will a UPS run when power goes? You can choose a UPS that is rated for pretty much the full VA you need, so it will run at 100% of capa- bility and thus last ‘x’ minutes. You can pick a UPS rated at a much higher VA value than you need so, for example, is running at 50% of capability and will thus last for longer than the UPS from Option 1. Or you can use extra external battery packs to run for longer. If charging capability allows, the more and the bigger the batteries, the longer the UPS runs. Q What is the lifetime of a UPS? Most plug-in UPSs are workable for at least five CUMMINS has supplied a power solution based around four of its 630 kVA generator sets to Standard Chartered Bank in Ghana. The system will provide the bank’s head office in Accra with standby power whenever interruptions to the grid supply require it. CKR Consulting Engineers, the electrical consultant to the project, has been a Cummins customer since 2015. The main contractor for the project was WBHO/MBS of South Africa. Cummins was selected for the work thanks to a combination of pricing and established brand reputation. The four generator sets have been installed in a purpose-built room on the ground floor of the 35 000 m 2 building, owned by RMB Wesport, where the bank has its headquarters. Start-up time and noise levels when operating were key considerations for the project. The units were required to be synchronised to come online within three seconds of utility failure, and the noise level requirement was 69 dB at 7 m. The Cummins generator sets supplied are open C700D5 units equipped with rugged VTA28 diesel engines, designed for reliable power with low emissions and fast response to load changes. The installed system features synchronising and ATS panels, louvres, a fully clad stainless steel exhaust system, a 20 000 litre tank with piping and cleaning systems, and four 1 000 litre day tanks with piping and pumps, float switches and other accessories to connect to the bulk tank.

Q What is Li-ion/lithium-ion? A lithium-ion battery or Li-ion battery (ab- breviated as LIB) is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, com- pared to the metallic lithium used in a non- rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the constituent components of a lithium-ion battery cell.

current is created by devices such as batteries and solar panels. When connected, an inverter allows these devices to provide electric power for small household devices. The inverter does this through a complex process of electrical adjustment. From this process, ac electric power is produced. This form of electricity can be used to power an electric light, a microwave oven, or other electronic devices/ma- chines. An inverter usually also increases the volt- age. To increase the voltage, the current must be decreased, so an inverter will use a lot of current on the dc side when only a small amount is being used on the ac side. Inverters are made in many different sizes. They can be as small as 150 W, or as large as one megawatt (one million W).

years, although it is advisable to change the batteries every three to four years. Q How do you maintain a UPS? There are three simple methods: never overload a UPS; never connect any home electronic devices such as cooling fans to the UPS (these may cause a malfunction of the UPS); and discharge the bat- tery at consistent intervals, i.e. once a month or once every two months. This is done by turning on the UPS without connecting the mains. Q What is an inverter? An inverter is an electric apparatus that changes direct current (dc) to alternating current (ac). Direct

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SPARKS ELECTRICAL NEWS

JULY 2018