#### Tahsina Hossain

Joined Jan 16, 2015
50
Hello, I am trying to understand how the equation 16500/T-22.093 was derived from the temp and life hours value. Also I dont know how the values co relate when I calculated it.

#### LowQCab

Joined Nov 6, 2012
3,948
Looks like the secret will be found in the context.
The context "should" provide the derivation of the formula.

The question is, do You really need to know that information ?
.
.
.

#### Tahsina Hossain

Joined Jan 16, 2015
50
Looks like the secret will be found in the context.
The context "should" provide the derivation of the formula.

The question is, do You really need to know that information ?
.
.
.
HI, thanks for your reply, I really need to understand it, my job depends on it.

#### Tahsina Hossain

Joined Jan 16, 2015
50
Hello, Thanks so much for the reply, my question is I see they got A is 9.8*10^-18 and B 15000, but according to the loading guide
the values are:

How do we get the 9.8*10^-18 values from here?

#### Tahsina Hossain

Joined Jan 16, 2015
50
Thanks for your help, I will keep researching and will post the solution if I can find it.

#### Delta Prime

Joined Nov 15, 2019
1,311
Thanks for your help, I will keep researching and will post the solution if I can find it.
Not if I find it first!

#### hrs

Joined Jun 13, 2014
392
<speculation>
I think the numbers in the formulas are for a different temperature than those in the tables. 110degC maybe?
log(9.8E-18) = 25.3 -39.2
</speculation>
edit calculation error.

Last edited:

#### Tahsina Hossain

Joined Jan 16, 2015
50
<speculation>
I think the numbers in the formulas are for a different temperature than those in the tables. 110degC maybe?
log(9.8E-18) = 25.3
</speculation>
I am thinking how to corelate that with the insulation class?

#### Tahsina Hossain

Joined Jan 16, 2015
50
I win. I found it! The driving factor for insulation credibility is temperature exposure, since at high temperatures insulation can lose its insulation properties. For this reason, it is necessary to establish the hottest-spot winding temperature.
If you know the maximum hottest-spot temperature to which the insulation is exposed, we know how much life is lost, allowing you to limit the overload.
According to the IEEE C57.12.00-2000 standard, power transformer are rated on a maximum ambient
temperature of 40° C, and the average ambient
temperature shall not exceed 30° C in a 24-hour period. This standard also states that an average winding rise of 65° C
shall not be exceeded when the transformer is operated at its rated load (KVA), voltage (V), and frequency (Hz).
In other words.As Mr. @LowQCab stated , it is in the context ,based on the ambient temperature criteria, the average temperature of the winding cannot exceed 65° C above ambient,when operated at rated
conditions. Maximum hottest-spot winding temperature cannot exceed a value of 80° C above ambient.
The IEEE C57.91-1995 states that under a continuous ambient temperature of 30° C, the maximum hottest-spot winding temperature should not exceed 110° C.
If the transformer is operated continuously at this temperature, the normal life expectancy of the transformer is 20.55 years,ambient temperature, the average winding temperature,and the maximum winding hottest-spot temperature.
The IEEE Guide of Loading of Mineral Oil-Immerse Transformers C57.91-1995 aids you in calculating the effect of aging
insulation and its exposure to high temperatures. But you know of course they use a microprocessor protective relay that can perform the algorithm calculations.
Thanks so much, I am doing my calculations now and trying to fit my curve according to the b and a value, wishing myself luck!

Thanks again!! appreciate it!