Emerson U /400/S/12P Installation Design Considerations, Battery Installation And Maintenance

Chapter 6 Battery 47

adequate ventilation and heating of the cells. Boost charging must not be applied to valve regulated cells as this will cause them to overcharge and subsequently vent.

Similarly, valve-regulated cells cannot be regarded as maintenance-free as they must be kept clean and their connections checked periodically for tightness and lack of corrosion. Specific inspection instrument can also be used to check each battery cell periodically to learn about the variation in capacity.

Batteries are fully charged before delivery; however, storage and transportation times mean that, inevitably, some charge is lost by the time the battery is commissioned. All the cells forming the battery should be brought to the same state of charge and be recharged within 6 months of the factory charge.

It is especially important that the battery is fully charged before attempting a witness test of the autonomy time. This may require several days to complete; therefore any witness test concerning the batteries should take place only after the battery has been on uninterrupted float charge for at least one week.

Cell performance typically improves after a few weeks in service or after two or three discharge and recharge cycles.

6.4 Installation Design Considerations

Note

Full safety instructions concerning the use and maintenance of UPS batteries are provided in the appropriate battery manufacturers manuals. The battery safety information contained in this section relates to key considerations which must be taken into account during the installation design process and might affect the design outcome depending on localized conditions.

6.5 Battery Installation And Maintenance

6.5.1 Temperature Considerations

Battery performance depends on the ambient battery temperature. Capacity and autonomy times are quoted for a new battery operating at 20°C. Battery capacity is increased by 1% for every 1°C increase in temperature up to 25°C. If a battery is used at temperatures above 25°C, its life is reduced; consequently its capacity and UPS autonomy time will reduce more rapidly over a period of time. Operating below 20°C will reduce the battery capacity by approximately 1% to 1.5% per 1°C. For example, if a battery discharge test is attempted during the middle of winter when the ambient temperature is 5°C the battery capacity will be only 77.5% of its design value and will not satisfy its specified autonomy time.

Ambient temperature, ventilation, spacing, float voltage and ripple current all affect the battery temperature. Uneven temperature distribution through the battery string will cause the voltage distribution to be uneven which can also lead to problems — it is therefore important to maintain an even temperature across the whole battery chain.

Valve-regulated cells are very sensitive to temperature and should be operated at a temperature between 15°C and 25°C. To help sustain this operating temperature range the battery is normally float charged at 2.25V/cell.

When batteries are cabinet-mounted adjacent to the UPS module, it is the battery which dictates the designed maximum ambient temperature, not the UPS. That is, in the case of valve-regulated cells, the ambient room temperature should be kept between 15°C and 25°C, and not between 0°C and 40°C (which is the specified main equipment operating temperature range). Temperature excursions are permissible for short periods of time provided the average temperature does not exceed 25°C.

6.5.2 Battery Population

The nominal DC bus voltage, and therefore battery float voltage, is set according the module’s rated input and output voltages, and usually set to 432Vdc (380Vac), 446Vdc (400Vac) or 459V (415Vac). Given that the desired cell float voltage is 2.25V, this means that a different number of cells are required in each case (see Table 6-1).

Table 6-1 Battery population

Parameter	380V	400V	415V
Number of cells used (standard)	192 pcs	198 pcs	204 pcs
End-of-discharge voltage	320V	330V	340V
Float voltage	432V	446V	459V

HIPULSE U UPS Single Module And “1+N” (Expandable) 160/200/300/400kVA User Manual