The oxidation of transformer oil

Physica III. no. 10

December 1936

THE OXIDATION OF TRANSFORMER OIL by D. TH. J. TER HORST and C. KRIJGSl\IAN Communication of the Physical Laboratory of the University of Utrecht

S'urnm a ry For the experiments made by 0 r n s t c i n, Jan sse n, K r ij g sma n and t e r H ~ r s t ') another explanation of the measurements is given.

The measurements performed about the oxidation of transformer oil done in the Physical Laboratory of Utrecht have been published already in this review 1). We will quote that paper as I. These measurements could be interpretated by supposing two or more groups of hydrocarbons with a different affinity to the oxygen. The mathematical description based on this interpretation gives an explanation of the tests. Further tests concerning the situation of the characteristic point, determined from the curves in which the logarithm of the reaction constant of the reaction: oil

+ oxygen -+ oxidation

product,

is plotted against the reciprocal value of the absolute temperature, for different times of deterioration, showed that this point belongs to a temperature which is higher or lower than the temperature of the deterioration. From the mathematical description of the conception that the transformeroil consists of different groups of hydrocarbons, we can easily show that the characteristic point should always belong to a temperature which is higher than the temperature at the deterioration. In the same notation of the article of 0 r n s t e i n, Jan sse n, K r ij g sma nand t e rHo r s t 1) we have

g}

19](t =lgC t Ig](2 = 19 C2 -

g~

1082-

(1)

THE OXIDATION OF TI{Ar\SFOIOlER OIL

1083

in which T is the temperature of the deterioration. We have also: (II) in which To is the temperature belonging to the characteristic point of intersection. From (I) and (II) we find: (III) If

K2 > K I

Q2

<

KI >

QI

< Q2 so To> T 2)

1(2

QI

so To> T

So this theoretical interpretation of the experiments does not give an exact explanation about the situation of the point of intersection. It is however also possible to describe the oxidation of transformer oil with another scheme: K.

+ oxygen -+ oxidationsproduct I K, oxidationsproduct + oxygen-+ II oil

etc. which is able to give an explanation of the fact mentioned.We denote the number of particles of the products at the time t: oil: 1t1 oxygen: N oxidationproduct I:

1t2

II: 1t3 We suppose that the oil is saturated with oxygen during the deterioration (this is true for our experiments), so N is a constant. We thus get the following equations: dn, dt = - K I 1t IN

(l) (2)

THE OXlDATIO:,\ OF TRA:'\SFOR~lER OIL

1084

in which X, and ](z are the reaction constants of the two reactions. From (1) and (2) we find: 1/

1/z

= 1/0

1

= 1/0

](1

(3)

c-XK,t

[c-XK,t -

T

](Z-I\.I

c- s K

'1

(4)

if we suppose for t = 0, 1/1 = 1/0 and 1/z = o. \Vith the rule for the activation energy given in the article I:

Q = 1/IQI 1/1

we find:

Q=

uc, -

](I)QI

e-NK,t

+ 1/ZQ2 + 1/z '

+ ](1

[C-NK,t_ C-NK,t]

f{z C-NK,t - ] ( 1

so if t = 0 we find Q = QI, both if ](1

Qz (5)

e-f,'K,t

> J(z and J(z >

](1 '

If t -+

00

and K,

> f{z we find Q = Q2'

If 1-+

00

and](z

. J(1-f{Z Q Q > f{1 we fmd Q = Qz + f{z (z I)'

The experiments show that the activation energy is an increasing function of the time of deterioration, so we have

Qz +

]{I-](Z

](z

SO Qz > QI both if tc, > same, so

(QZ-QI) > QI or Qz> QI'

s, and](z >

19 ]{I = (Qz -

ic,

tc;

The formula III is the

QI) (J... __1_) J... T To R

.

If ]{I > tc, then To> T and if ]{2 > ](1, then T> t ; The temperature belonging to the point of intersection can be both higher and lower than the temperature of the deterioration which agrees with the experiments. Received October 19. 1936. REFERENCES I) ;0)

L. S. Or ns tei n, C. Jansen Czn ., C. K r ij g s man and D. Th. J. I e r H Ph ysic a 2, 2:>1. 1935. See the formulae (6al, (6bi and (8) of th e a r ticle J.

0

rs

t,