bonitron M3534-I3, Customer Reference Manual

Page: 47 / 56

User’s Manual
47
7.2.1. E
NERGY
R
EQUIRED FOR
O
UTAGE
The total energy required for the event must be calculated first.
Using the following equation, the total number of joules required for the outage
can be calculated:
J = P ∗ T
We will use a specification of 100 hp. for a 2 second outage for this example.
For instance, a 100 hp drive outage for 2 seconds would be
P = 100hp ∗ .746 kwatts horsepower = 75kW
The total number of joules required is:
J = 75kW ∗ 2s = 150kJ
7.2.2. M
INIMUM
C
APACITOR
B
ANK
V
OLTAGE
There is a minimum voltage level that must be maintained at the end of the
discharge during backup. An M3534R for a 460VAC nominal system has a
minimum input voltage of 320VDC. Therefore, the final discharge voltage of
the capacitor bank (
𝑉
) should be 320 VDC.
These data are available in the specifications for the specific M3534R by
nominal system voltage.
7.2.3. P
EAK
C
URRENT
The peak current from the capacitor bank will occur at the minimum voltage.
This can be estimated from the equation
I =
P
V
For our example,
I =
75kW
320Vdc
= 235A
7.2.4. C
APACITOR
S
PECIFICATIONS
At this point, a specific capacitor's characteristics can be used. It is best to use
the values that are listed at end of life for the capacitor to make sure that the
storage system is sized for the eventual degradation of performance over time.
The critical points to use are
𝐸𝑠𝑟 = Internal resistance at end of life, typically 150-200% of the initial
value.
𝐶
= Capacitance at end of life
𝑉 =
Maximum charge voltage for the capacitor. (A general rule is to use
95% of the value listed on the datasheet for a reasonable margin)
For our example, we will use the following values:
𝐸𝑠𝑟
= .01Ω
𝐶
= 132F
𝑉 = 46V