Application Note How to size Batteries for Eaton 9x55, 9390 and 9395 UPS’s
Scope This document describes the steps to follow to size a battery, considerations to take and quick calculations to make. These notes are aimed to sales personnel. Important factors The best way to start the calculation for the right UPS for a customer is by looking into 4 important things: 1. 2. 3. 4.
Load size (S) commonly in kVA Specific output power factor (pf) Desired Back-up time (Bt) in minutes or hours Recharge time required (Rt) in minutes or hours
In order to define the right UPS it is necessary to calculate: a. b. c. d. e. f.
Real Power in demand Total Real Power to be discharged Power needed to recharge the battery kWh (kilo Watts hours) Power needed in the (recharge + demand) time Recharge current Type of UPS and number of battery string required (in the case is needed)
In most of the cases, it should be calculated in this order (from a to f ) An example:
A customer is running an industrial process industrial process that demands 60 kVA. The pf (power factor) is 0.8 and it is specified a back-up time of 2 hours and a recharge time of the batteries is 20 hours (this configuration purely depends on the customer) For this example: S (Demand Power) pf (Power Factor) Bt(Backup time) Rt (Recharge Time)
60 kVA 0.8 2 hours 20 hours
Calculations: a. Real power in demand: With the load size (60kVA) is possible to obtain the a Real more accurate power in demand P (in kW) using the efficiency of the inverter (about a 94%),
P=
S × pf
Thus,
P=
0.94
How to Size Batteries
Eaton Corp.
60 kVA × 0.8 0.94
=
51.06 kW
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b. Total Power to be discharged (within back-up time) Now that we got the Real Power (51.06 kW) we can calculate the total Power to be discharge in the back-up time by multiplying it by the Back-up time (Bt), that is,
Total power discharged = P × Bt Total power discharged = 51.06 kW × 2 hours = 102.13 kWh c. Power needed to recharge the battery After the UPS battery has been discharged in the back-up time, it will start recharging in a specific time. In this example the customer demands 20hours of recharging time, that is:
Power needed to recharge battery = Power needed to recharge battery =
Total power discharged Rt 102.13kWh 20h
=
5.10 kW
d. Power needed in the (recharge + demand) time It is important to know the power needed to recharge the battery in the moment of maximum demand, this moment comes when the power from the mains is back, and the UPS is supplying the output load level in demand (51.06 kW in this example), plus the power needed to recharge the battery whilst (5.10 kW).
Power needed in (recharge + demand) time =
Power needed in (recharge + demand) time =
P + Power needed to recharge * Eff
51.06 kW + 5.10 kW 0.93
=
60.39 kW
* Eff corresponds to the system efficiency when the rectifier, inverter and charger are all together in use at the time of recharge and demand time; this value is approximately about 93%
e. Recharge current (I) It is important to know the input current limit to adjust it in the recharge + demand time, also, in order to check if our UPS model chosen (let’s say 9390 – 60kVA for now) can use that current input level of current.
As a rule: I = P/V, Therefore:
How to Size Batteries
Eaton Corp.
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I=
Total P needed for the battery V of the battery
=
5.10kW 554.4 V
=
9.21 A
This value of Voltage is constant over the battery when it i s being charged (about 2.31V/cell) and depending on the UPS model varies, for instance, for 9390 – 60kVA is 554.4 V, here is a table for other models:
Model
Voltage
9390 & 9395 models
554,4 V
9355 20 - 40kVA
498,96 V
9355 – 8kVA
443,52 V
f. Number of battery strings required To calculate battery strings needed, it is taken into account the UPS model, Battery type and backup time. Eaton 9390 uses 40 blocks of 12V batteries, 9355 (20, 30 and 40kVA) uses 36 blocks and 9355 (8 – 15kVA) uses 32 blocks . There are battery back-up time tables that we can use to size t he quantity of strings required. These tables can be found from http://pqsalesweb.eaton.com under this logic: Salesweb products & services Backup Power (UPS) e.g., Eaton 9155, 9355, 9390 or 9395 Technical Information Matrix. →
→
→
→
and then select the product Runtime chart or Runtime
→
Note: if there is no access, contact local Eaton local Marcom team. Let’s use a fragment from 9390 Runtime table for this example: (extracted from Powerware 9390 External Battery Cabinets 40 - 160 kVA / battery runtime Table 6. 1025471**) CSB HRL
Powerware 9390 UPS + Large battery cabinet(s) (part numbers 1025468* / 40 kVA
60 kVA
80 kVA
100 kVA
120 kVA
160 kVA
9390+ 1*BAT(12-500) 9390+ 2*BAT(12-500)
80 180
49 120
35 81
24 60
18 48
12 34
9390+ 3*BAT(12-500)
288
174
123
95
80
57
Note! Above run times are approx. times for batteries after several discharge cycles.
The desired back-up time in this example is 2 hours (or 120 minutes) 3 battery strings attached will enough to back-up for about 174 minutes and 2 strings exactly 120 minutes. As a conclusion we can say that a 9390 – 60kVA UPS model with 3 string batteries attached will back-up 2 hours a system load output of 60kVA and it wil l require about 5.10kW/hour or 9.21 A to recharge in a period of 20hours to 90% of the battery capacity.
How to Size Batteries
Eaton Corp.
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3
Appendix
A. Charging current and nominal voltage per string for different UPS models and loads
9x55 (kVA)
8-15
20 - 40
Nominal current (A)
3
3
Max current* (A)
30
Battery Nominal Voltage (V)
384
9390 (kVA)
9395 (kVA)
40
60
80
100
120
160
275
550
825
1100
10
20
20
30
30
40
38
76
114
152
20
40
40
60
60
80
83
166
249
332
480
480
480
480
480
480
480
480
480
480
60
432
32 battery 36 battery blocks blocks 40 battery blocks 192 cells 216 cells 240cells *May be limited by maximum UPS input current rating
40 battery blocks 240cells
This table is from Eaton 9x55, 9390 and 9 395 Datasheet (www.eaton.com/powerquality)
12V Batteries blocks:
a. For 9x55 cabinets
How to Size Batteries
b. For 9390 and 9395
Eaton Corp.
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4
B. Overall efficiency according to the load level 9155 (kVA) Efficiency input/output
8
at 100% rated load at 75% rated load at 50% rated load at 25% rated load
10
91 % 90 % 90 % 85 %
12
91 % 90 % 90 % 85 %
15
91 % 90 % 90 % 85 %
20
91 % 90 % 90 % 85 %
30
93 % 92 % 91 % 86 %
93 % 92 % 91 % 86 %
9155 (kVA) Efficiency input/output
8
at 100% rated load at 75% rated load at 50% rated load at 25% rated load
10
91 % 90 % 90 % 85 %
12
91 % 90 % 90 % 85 %
15
91 % 90 % 90 % 85 %
20
91 % 90 % 90 % 85 %
30
92 % 91 % 90 % 85 %
40
93 % 92 % 91 % 86 %
93 % 92 % 91 % 86 %
9390 (kVA) Efficiency input/output
at 100% rated load at 75% rated load at 50% rated load at 25% rated load
40
60
80
100
120
160
93,80 % 93,60 % 93,10 % 89,60 %
93,40 % 92,90 % 91,80 % 87,60 %
93,70 % 92,90 % 92,50 % 89,60 %
93,60 % 92,90 % 92,50 % 89,60 %
93,60 % 92,90 % 92,50 % 89,60 %
93,60 % 92,90 % 92,50 % 89,60 %
9395 (kVA) Efficiency input/output
225
at 100% rated load at 75% rated load at 50% rated load at 25% rated load
94 % 94 % 93 % 90 %
275
94 % 94 % 93 % 90 %
450
94 % 94 % 93 % 90 %
550
94 % 94 % 93 % 90 %
825
94 % 94 % 93 % 90 %
1100
94 % 94 % 93 % 90 %
These tables are from Eaton 9x55, 9390 and 9395 Technical Information in Salesweb. (http://pqsalesweb.eaton.com/Products/ThreePhase)
How to Size Batteries
Eaton Corp.
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