Re: UPS efficiencies

In article <1158911587.888607.42820@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, Shay writes:
Hi there all,

I'm trying to work out the efficiency of a ups system.

The USP Manufacturer has given me the following Data:

120kVA UPS System

Efficiency
Set1 Set2
25% Load 82.29% 79.84%

I'm trying to work out what my efficiency values would be for different
loading levels

How do I find the efficiencies for these different loading levels in
Both Set 1 and Set 2?

A device like this will typically have two types of losses:
1. No-load losses, sometimes called "core" losses. This type of loss is
a constant (as long as the device is energized).
2. Load losses, sometimes called "coil" losses. This type of loss varies
as the square of the load.

With these two facts, we can set up a loss model of the device:

P_t = P_n + P_l = P_n + k*(P_o)^2

Where:
P_t = Total losses
P_n = No-load losses
P_l = Load losses
P_o = Output power
k = an arbitrary constant

The first thing that you'll need to do is convert the efficiency values
that the manufacturer provided into actual power values in kW or whatever.

Assuming for the sake of an example that this is a 10kW device, 50% output
is 5kW, or 5000W. That's a value of P_o. An efficiency of 88.51% means that
the output is 0.8851 times the input. At 5000W, that's 5649W input, or
losses of 649W.

Keep in mind that you do not want to use the kVA values. You're only
interested in real power (kW) values and efficiencies.

So, for one device, we have one ordered pair: (P_o, P_t) = (5000, 649).
Repeat this for all data points for a device, and then plug those values
into your favorite curve-fitting software to see what coefficients pop
out for fitting a curve shaped like P_t = P_n + k*(P_o)^2 for those
values. With the coefficients P_n and k, you then have a function that
will model the loss characteristics of the UPS over its entire range.

This will be input and losses in terms of power, of course. If you want
to convert these back to efficiencies, Eff = P_o / (P_o + P_t).

--
Michael F. Stemper
#include <Standard_Disclaimer>
COFFEE.SYS not found. Abort, Retry, Fail?

.

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