Let's consider the method of selecting batteries for the UPS according to the discharge tables. The process is based on the power parameters, but not on the capacity indicators! The method of selecting the capacity for short discharge times can give an error in the calculations, which reaches up to 30% of the estimated time.
Initial data for the calculation:
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UPS power (Pups): 500 kVA
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Battery life /Standby time: 10 minutes
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Battery life: 10 years
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Rated voltage of the inverter: 480 V DC
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The final voltage of the inverter: 396 V DC
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Power factor cos(φ): 0.8
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Inverter efficiency (EFFICIENCYinv): 94 %
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Current and voltage at the rectifier: calculated
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Ambient temperature: 20°C
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Ventilation requirements: calculated
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Battery placement: on racks
Calculation stages:
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Conversion of the total power into the effective power of the battery:
Pbaht= (Pups * cos(φ)) / EFFICIENCYinv= (500 * 0.8) kW / 0.94 = 425.53 kW
- Calculation of the required number of battery cells N:
N = Unom/ 2 V/el-t = 480V / 2 V/el-t = 240 elements (40 batteries of 12 V – "ruler")
- Calculation of the required power per battery cell Pel-t:
Pel-t= Pbaht / N = 425.53 kW / 240 = 1773 W
- Calculation of Pe-t for parallel connection of battery lines:
1 Ruler (40): Pel-t = 1773 W
2 Rulers (40║40): Pel-t = 886.5 W
3 Rulers (40║40║40): Pel-t = 591.0 W
4 Rulers (40║40║40║40): Pe-t = 443.3 W
5 Lines (40║40║40║40║40): Pe-t = 354.6 W
- Selection of a suitable battery according to the constant power discharge table:
- Selected 5 x 40 HR 12-100.
- Current and voltage at the rectifier:
Charging current limit at 10 :
I10 = 5 * 100 Ah / 10 h = 50 A
The voltage of the "floating" charge:
Uzar = 2.25 V/e-t * 240 e-t = 540 V DC
Of course, it is difficult to select a battery in this way. And the bit tables are not always at hand. Therefore, ЭНЕРГОН specialists have developed a special calculator to help their partners and customers, which is posted on our
website.