Standard H₂ and H₂O alarm levels

Created by Renan Ferreira Santa Rosa, Modified on Thu, 15 Dec, 2022 at 5:51 PM by Renan Ferreira Santa Rosa

Summary

1. Introduction

This document has as its principal goal to show studies based on current norms and their editions related to the alarm values of H2 and H2O within the insulating oil, mineral, and vegetable, defining and explaining the values recommended by Treetech with their respective references.

2. Bibliography

The current technical references applied in this section are:

ABNT NBR 10576:2017 [1]
ABNT NBR 10576:2012 [2]
ABNT NBR 15422:2015 [3]
ABNT NBR 16518:2017 [4]
IEC 60422:2013 [5]
IEC 60599:2015 [6]
IEEE C57.104:2008 [7]
IEEE C57.106:2015 [8]
IEEE C57.155:2014 [9]
Article“Effective methods of assessment of insulation system conditions in power transformers: a view based on practical experience”, by Victor Sokolov [10].

It is important to point out that the norms considered above present values related to mineral and vegetable insulating oil. These values are standard and must be used in case of a lack of more representative information. The norm makes it clear that each user should have their asset knowledge and thus plan the value that best expresses the real critical limits of your equipment. As ABNT NBR 10576:2017 highlights:

ℹ️ "The pieces of information provided in this norm, are technical recommendations and are mainly aimed to provide a standard base for more specific and more complete procedures based on each local circumstance. Must be employed well construct engineering criteria, which aim the best balance between technical and economic resources.” (ABNT NBR 10576, 2017, page vii)
(translation made by the author)

2.1. Limit values of H2O

To mineral oil:

The limit values of H2O presented in the norm are pointed out in the following tables. 
2.1.1. ABNT NBR 10576Table 1 - Limit values of H2O according to the norm  ABNT NBR 10576:2017, to power transformers and reactors 

≤ 72,5 kV
> 72,5 kV ≤ 145 kV
> 145 kV
H2O values limits (ppm) 
40
30
20
Table 2- Limit values of H2O correct at 20 °C (68 °F) according to the  ABNT NBR 10576:2012, to power transformers and reactors

≤ 69 kV
> 69 kV ≤ 230 kV
> 230 kV
Limit values of H2O correct at 20 °C (68 °F)(ppm) 
10
8
6
The norm ABNT NBR 10576 from 2017 and from 2012 also presents limit of H2O to tap changer. These values can be found in the “Table 10”  from both norms (2017 and 2012).
Table 3 - H2O values limits  according to the norms ABNT NBR 10576 from 2017 and 2012, to tap changer

H2O values (ppm) 
Phase tap changer
40
Neutral tap changer
30
2.1.2 IEC 60422Table 4 - H2O limits values according to IEC 60422:2013, to power transformers and reactors 
Values of H2O (ppm) 
≤ 72,5 kV
>72,5 kV ≤ 170 kV
> 170 kV
Neutral tap changer 
30
20
15
Phase tap changer 
40
30
20
2.1.3 IEEE 57.106Table 5 - H2O limits values according to IEEE 57.106:2015, to transformers and reactors 

≤ 69 kV
> 69 kV < 230 kV
≥ 230 kV
H2O values limits (ppm) 
35
25
20
Table 6 -H2O values limits according to IEEE 57.106:2015, to tap changers 
Value of H2O (ppm)
≤ 69 kV
> 69 kV
Neutral tap changer 
40
Phase tap changer 
30
25
2.1.4  Relative SaturationRegarding relative saturation, a table is presented in ABNT NBR 10576:2017 and IEC 60422:2013 that relates the water content in oil saturation to the cellulosic insulator. The presence of water in the cellulosic insulator accelerates its deterioration, decreasing the life of the assets.
For the relative saturation alarms, the recommendations of ABNT NBR 10576:2017 were considered, available in "Table B.1" in Annex B of the standard. This table can also be found in the IEC 60422:2013 standard in annex B ("Table A.1"). Other articles also relate the water content in oil saturation to the dielectric strength [7], and other relevant values can be found.
Table 7 - Relative water content in oil saturation vs cellulosic condition
Water content in oil saturation (%) 
Cellulosic condition 
< 5
Dry isolation 
> 5 e < 20
Moderately wet isolation 
> 20 e < 30
Wet Isolation 
> 30
Extremely wet isolation 

To vegetable oil:

The limit H2O values in vegetable oil shown in the norms are displayed in the following tables. 
2.1.5 ABNT NBR 16518Table 8 - H2O values limits according to ABNT NBR 16518:2017, to in service transformers and reactors. 

≤ 36,2 kV
> 36,2 kV
≤ 72,5 kV
> 72,5 kV
≤ 145 kV
> 145 kV
H2O values limits (ppm) 
400
350
240
150
2.1.6 ABNT NBR 15422Table 9 -  H2O values limits according to ABNT NBR 15422:2015, to transformers and auxiliary equipment.
H2O values  limits (ppm) 
200

Calculus to water content 20 ºC

2.1.7. Calculus considerations to H2O @ 20 °CSome norms do not define the H2O limits corrected at 20 °C, but it is possible to calculate from correction variables. The theoretical precondition to the correction calculus, according to the norms ABNT NBR and IEC, are:
It must have balance in the thermochemical between the oil and the paper;
It cannot exist any non-predicted water entering;
The equipment must have cellulosic isolation
Must have no free water present in the oil.
Calculus criteria are the following:
Cannot be done the calculation if the oil sample temperature is below 20 °C;
Between 20 °C and 40 °C, the calculus has low reliability;
Between 40 °C and 70 °C, the calculus has moderate reliability;
Above 70 °C, the calculus is reliable with good results.
The H2O conversion to 20 °C made by any equipment can present a range of inaccuracies, as much as the difficulty in the measure the temperature ate the oil flux point, or by the oil temperature when it is bellow 70 °C. Therefore to get the values corrected at 20 °C from the absolute values proposed by the norms, it is possible to consider a standard operating temperature and do the correction following the elements described in the standard (“Annex A” from ABNT NBR 10576:2017, ABNT NBR 16518:2017 and IEC 60422:2013).

2.2. H2 limit value

Due to H2 being a gas formed in the natural oil decomposition process, the definition of an alarm can be more complex. The IEC and IEEE present loads of gas analysis methods for mineral and vegetable isolating oils, and they, also mention standard H2 concentration values in the oil. Its concentration, however, can change according to the vendor, model, and transformer type. Therefore, the norms already introduced highlight that each user should know each of their assets, be able to adjust the alarms limit, especially for each piece of equipment, and so on, and gain optimized equipment monitoring.

The following tables contain norm values of H2 presented by each norm to each piece of equipment depending on its application:

To mineral oil:

2.2.1. IEEE C57.104Table 10 - H2 recommended values, according to IEEE C57.104:2008 

H₂ (ppm)
Standard value 
100
2.2.2. IEC 60599Table 11 - H2 recommended values, according to IEC 60599:2015 

Transformer
Instruments transformers
Bushing
H2 Standard values (ppm) 
Power
Furnace
Distribution
Submersible
CT
VT
50-150
200
100
86
6-300
70-1000
140

To vegetable oil:

2.2.3. IEEE C57.155Table 12 - H2 recommended values, according to IEEE C57.155:2014 
Oil type 
H₂ (ppm)
Soy 
105-118
Sunflower 
24-45
Synthetic
52-82

3. Alarms values definition

Once introduced all the bibliography in item 2, the user feels free to choose the alarm limits recommended by the most convenient norm. It is possible to pick values from other standards, to better fit the asset situation, especially in areas where the rules do not provide a limit value but just a standard one.

The table below proposes a default minimum adjustment so that the asset does not unprotected by the lack of data that marks the alarms definitions. It is relevant to point out that the H2O values were defined aiming at the Brazilian scenario and using ABNT NBR 10576 and16518 norms as a base. Though, H2 limits were projected upon the support of IEEE C57.106 e C57.155, e IEC 60599, international norms. Therefore, the user must verify if these values suit the enterprise's politics, rules, the assets management and then make the needed changes to adjust all parameters.

To mineral oil:

3.1 Alarms values at H2O and H2 monitoring in mineral oilTable 13 -Standard limit values to applications with gas and moisture monitoring equipment, based on ABNT NBR 10576 from 2017 and 2012 

≤ 69 kV
> 69 kV ≤  72,5 kV
> 72,5 kV ≤ 145 kV
> 145 kV ≤ 230 kV
> 230 kV
High H2O alarm value (ppm)¹
30
30
20
15
15
Very high H2O alarm value(ppm)²
40
40
30
20
20
High H2O alarm value corrected at 20 °C (ppm)³  
16
12
12
12
9
Very high H2O alarm value corrected at 20 °C (ppm)⁴ 
20
16
16
16
12
High alarm value by relative saturation(%)⁵ 
30
Very high alarm value by relative saturation(%)⁶ 
50
High H2 alarm value (ppm)⁷ 
100
Very high H2 alarm value(ppm)⁸ 
150

¹Values defined by condition “Fair” from IEC 60422:2013
²Values defined by limits from ABNT NBR 10576:201
³Values defined by limits from ABNT NBR 10576:2012 added 50 %
⁴Values defined by limits from ABNT NBR 10576:2012 added 100 %
⁵Value defined by extremely wet isolation conditions from ABNT NBR 10576:201
⁶Value defined by studies of the article [7], which define this value as the critical dielectric strength point
⁷Value defined by the standard value from IEEE C57.106:200
⁸Value defined by the superior value of standard zone from IEC 60599:2015

To vegetable oil

3.2 Alarms values at H2O monitoring in vegetable oilTabela 13 - Standard limit values to applications with gas and moisture monitoring equipment, based on ABNT NBR 16518:2017 

≤ 36,2 kV
> 36,2 kV ≤ 72,5 kV
> 72,5 kV ≤ 145 kV
> 145 kV
High H2O alarm value (ppm)1
360
315
216
135
Very high H2O alarm value(ppm)2
400
350
240
150

¹Limit values defined according to ABNT NBR 16518:2017 subtracted from 10 
²Limit values defined according to ABNT NBR 16518:2017
3.3 Alarms values at H2 monitoring in vegetable oilTable 14 - Standard limit values to applications with gas monitoring, based on IEEE C57.155:2014 

Soy 
Sunflower
Synthetic 
High H2 alarm value (ppm)3 
101
32
58
Very high H2 alarm value(ppm)4
112
35
64

³Limit values defined according to IEEE C57.155:2014 subtracted from 10 
⁴Limit medium values defined according to IEEE C57.155:2014 

4. Bibliographic references

[1] Associação Brasileira de Normas Técnicas, “NBR 10576: Óleo mineral isolante de equipamentos elétricos – Diretrizes para supervisão e manutenção”, quarta edição, Rio de Janeiro, 2017.
[2] Associação Brasileira de Normas Técnicas, “NBR 10576: Óleo mineral isolante de equipamentos elétricos – Diretrizes para supervisão e manutenção”, terceira edição, Rio de Janeiro, 2012.
[3] Associação Brasileira de Normas Técnicas, “NBR 15422: Óleo vegetal isolante para equipamentos elétricos“, segunda edição, Rio de Janeiro, 2015.
[4] Associação Brasileira de Normas Técnicas, “NBR 16518: Óleo vegetal isolante para equipamentos elétricos – Diretrizes para supervisão e manutenção”, Rio de Janeiro, 2017.
[5] International Standard, “IEC 60422 – Mineral insulating oils in electrical equipment – Supervision and maintenance guidance”, ed. 4.0, 2013.
[6] International Standard, “IEC 60599 – Mineral oil-filled electrical equipment in service – Guidance on the interpretation of dissolved and free gases analysis”, ed. 3.0, 2015.
[7] International Standard, “C57.104 - IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers”, 2008.
[8] International Standard, “C57.106 - IEEE Guide for Acceptance and Maintenance of Insulating Mineral Oil in Electrical Equipment”, 2015.
[9] International Standard, “C57.155 - IEEE Guide for Interpretation of Gases Generated in Natural Ester and Synthetic Ester-Immersed Transformers”, Nova Iorque, 2014.
[10] V. Sokolov, Z. Berler, V. Rashkes, “Effective methods of assessment of insulation system conditions in power transformers: a view based on practical experience”, Proceedings in Electrical Insulation Conference and Electrical Manufacturing and Coil Winding Conference, 28-28 Oct. 1999, Cincinnati, OH.