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Calculation of cable size and battery configuration in UPS 
Time：20210222 Source： Views：462 
There are many calculations about ups. Whether UPS is connected to air switch, cable or battery, it may need to calculate its current or power. Today, we will learn more about the relevant calculation of xiashante ups.
1、 Shante UPS power supply and current
1、 Difference between high frequency ups and power frequency UPS
UPS can be divided into high frequency ups and power frequency ups. High frequency UPS is small in size, light in weight and low in price. It is suitable for the protection of small power equipment at a single working point. It is not sensitive to interference and has low reliability requirements.
The power frequency machine is suitable for all equipment protection, whether it is network equipment or IDC (Data Center), with high reliability, but the power frequency machine has the disadvantages of large volume, heavy weight and high price.
The power frequency machine should be used where the power quality and reliability requirements are high. On the contrary, a high frequency machine can be used. Their air switch input current and output current calculation methods are the same.
Let's first look at how UPS calculates air switches.
2、 Calculation method of input current of Sante UPS
Let's first look at the calculation formula of the input current
Where: s: threephase UPS = 3, singlephase UPS = 1
Example 1:
Known: UPS power: 100kVA, input critical voltage: 176v, input power factor: 0.99 (high frequency machine can be approximately taken as 1, power frequency machine as 0.85), overall efficiency: 0.95, s = 3, output power factor: 0.8.
The results are as follows
100000×0.8
Input current (a) =  = 160A
176×0.95×3*1
Here, the input power factor of power frequency machine is taken as the calculation.
Example 2
Known: UPS power: 6KVA, input critical voltage: 176v, input power factor: 0.99 (high frequency machine can be approximately taken as 1, power frequency machine as 0.85), overall efficiency: 0.90, s = 1, output power factor: 0.7.
The results are as follows
6000×0.8
Input current (a) =  = 30A
176×0.9×1
3、 Calculation method of UPS output current
Let's first look at the calculation formula of the output current
S: Three phase UPS = 3, single phase UPS = 1.
give an example:
Known: UPS power: 100kVA, output voltage: 220V, s = 3 (threephase UPS).
The results are as follows
one hundred thousand
Output current (a) =  = 152A
220×3
In addition, what is the nominal power?
The nominal power is the nominal power of the manufacturer, and the maximum power is the actual maximum power of the product. The actual power of the product is generally not an integer, for example, 511.3w. The manufacturer can't mark all the decimals. It is very likely that it will mark 500W, so the nominal power is 500W, which is the nearest integer.
4、 Calculation method of cable size
The AC current is generally calculated as 35a / mm2, and the DC current is generally calculated as 24a / mm2;
For example: 100kVA, input current: 160A, output current: 152A, battery current: 200A.
Input cable (mm ~ 2) = 160 / 5 = 32 mm ~ 2 (35 mm ~ 2 can be used)
Output cable (mm2) = 152 / 5 = 30mm2 (35 mm2 can be used in practice)
Battery cable (mm2) = 200 / 4 = 50mm2 (60 mm2 can be used in practice)
2、 Calculation of UPS battery
Here are two common calculation methods of ups.
1、 Constant current method
1. Calculate the maximum discharge current of the battery
IMAX = PCOS ф / (η * e critical * n)
Note:
P → nominal output power of UPS power supply
Cos ф→ output power factor of UPS power supply
η→ the efficiency of UPS inverter, generally 0.88 ~ 0.96 (according to the specific model / power value)
E critical → critical discharge voltage of battery pack (about 10.5V for 12V battery and 1.75v for 2V battery)
N → number of batteries per group
2. According to the backup time of the selected battery pack, find out the required discharge rate value C of the battery pack,
Then according to:
Nominal capacity of battery pack = IMAX / C
Calculate the nominal capacity of the battery.
give an example
Model: three in three out high frequency series 100kVA, output power factor cos ф: 0.8, DC voltage: 480v (battery low voltage protection: 420v), efficiency: 93%, backup time: 2 hours, rated number of each battery pack n: 40.
Current method
IMAX = PCOS ф / (η * e, critical * n) = 100 * 1000 * 0.8 / 0.93 * 10.5 * 40 = 204.8a
Nominal capacity ah = IMAX / C = 204.8 / 0.42 = 487.6ah
(the value of C is taken from the corresponding table of battery discharge time and discharge rate C, and 0.42 corresponds to 2H. You can see the above table.)
Therefore, for the nominal capacity of ah487.6ah, 12V100AH, 40 units and 5 groups in parallel should be selected.
2、 Constant power method
According to the battery power, the model of battery can be selected accurately. Firstly, the constant power provided by each battery to UPS in the backup time is calculated.
The calculation formula of constant power method is as follows:
Power provided by battery pack w = load KVA of ups × power factor / efficiency of inverter
Power required to be provided by each battery = power provided by battery pack w / rated number of batteries per group
Namely:
W＝{P（VA)×1000×cos?}/（?×N）
Among them:
W  power provided by battery pack
P  rated power of UPS
Cos  power factor
?  inverter efficiency at full load of UPS
N  rated number of UPS batteries

