LEGITIMACY OF OIL ANALYSIS - Laboratoire OKSMAN · thus, by analysing the fluid, we can obtain information about : o its characteristics which aim at meeting the two functions mentioned

Oil analysis legitimacy - eng - ind 4.doc - 11/2009

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LEGITIMACY OF OIL ANALYSIS FOR DIAGNOSING THE CONDITION OF IMMERSED TRANSFORMERS

LABORATOIRE OKSMAN SERAPHIN

I N D U S T R I A L A N A L Y S I S LABORATORY P R E D I C T I V E I M M E R S E D E L E C T R I C TRANSFORMER MAINTENANCE P R O D U C T Q U A L I T Y C O N T R O L


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CONTENTS

PREVENTIVE MAINTENANCE OF IMMERSED TRANSFORMERS 4

DIAGNOSIS OF STATE 5

… FOR A BETTER KNOWLEDGE OF THE VARIOUS ANALYSES CHARACTERIZING THE LIVE PARTS CONDITION….. 8

DISSOLVED GASES CHROMATOGRAPHY 9

A few examples… 10

FURANIC DERIVATIVES 11

POLYMERIZATION DEGREE 11

CORROSIVE SULFUR 12

… FOR A BETTER KNOWLEDGE OF THE VARIOUS ANALYSES CHARACTERIZING THE FLUID CONDITION….. 14

DIELECTRIC BREAKDOWN VOLTAGE 15

WATER CONTENT 15

TOTAL ACID NUMBER 15

Dissipation factor 15

Colour and appearance 15

Particles counting 15

Search for metals 15

Deposits and sediments in the fluid 16

Viscosity 16

Interfacial tension 16

Flashing point 16

Proportioning of additives 16

Search for PCBs (or Ugilec, trichlorobenzenes,...) in mineral oils 17

Search for hydrocarbons in Askarels® 17

OTHER ANALYSES 18

DIELECTRICS THE LABORATORY SPECIALIZES IN 18

SAMPLINGS - WARRANTY 18


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Having been specializing for more than 20 years in the diagnosis of transformers condition by means of fluid analyses, the LABORATOIRE OKSMAN SERAPHIN commits itself as a partner…

Our Charter of Professional Ethics : - Confidentiality - Impartiality - Independence


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PREVENTIVE MAINTENANCE OF IMMERSED TRANSFORMERS

Upstream of electric wirings, in 95% of the supply conceptions, there are one or several transformers. Power transformers carry out various functions, the main one is to lower the tension of the HTA supply network (1 to 50 kV) to a low voltage. They can also fulfil other functions such as: step-up transformers, insulating, starting (or autotransformer), homopolar…. These equipments are of three different types :

- Dry type, - Hermetic immersed type, - Breathing immersed type.

For the two latter types, all the live parts are immersed in a dielectric fluid which fulfils several functions :

- coolant, - electric insulator, - vehicle of the damage components of the transformer,

thus, by analysing the fluid, we can obtain information about : o its characteristics which aim at meeting the two functions mentioned above, o AND about the condition of the transformer live parts.

� Transformer damage causes 50% of operating losses in the

energy production industry, 10% in the chemical industry, 7% in the papermaking industry and 6% in the commercial companies1. Breakdowns can be of various origins: electric, electrodynamic, electromagnetic, dielectric, thermal or mechanical.

An effective maintenance of the transformers is one of the best solutions to : - avoid machine breaking which could generate fire or pollution to the equipments

containing PCBs, - plan an intervention which will minimize the interruption of production by optimizing

operating halt. Thus, we advise you to carry out several types of maintenance : - SYSTEMATIC : visual checking (cleanliness, corrosion, leaks), cleaning, checking of protections, ventilation system and tap changers, checking by infrared thermography…. - AND PREVENTIVE such as the oil analyses allowing to check the properties of the dielectric fluid and to detect every new default in the live parts (coil, electric and magnetic circuits, tap changer…) and in the cellulosic insulators. Knowing the global state of the transformer also appears to be a forward planning tool of the park ensuring investment programming on factual database.

1 « Transformers protection – AGF Brokerage – Engineering prevention Management.


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DIAGNOSIS OF STATE

The transformer is a strategic equipment. Its diagnosis of state is carried out :

- by a sampling of the dielectric fluid, gas or paper - by interpreting the results of the physicochemical analyses pertinently chosen.

All the analyses that can be carried out are classified in three main categories, as illustrated below :

DIELECTRIC FLUID CONDITION Measures to check its insulating and cooling characteristics :

• Breakdown voltage

• Water content

• Total acid number

POLLUTION level Analysis to check the compliance with the regulations :

• PCBs search and content

LIVE PARTS CONDITION (coil/ connections and cellulosic insulation)

Working order of the live parts :

Analyses of 13 dissolved gases indicative of thermal or electric defaults Ageing state or deterioration of the

cellulosic insulators

Analysis of furanic derivatives


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The results of these analyses are interpreted in accordance with the standards in force by our employees in charge of the diagnoses, according to the values observed, the transformer characteristics, its operations and the data history relating to the transformer kept in our data base. These diagnoses are strategic since they result in recommending : to maintain the transformer in service, to check it periodically and possibly to switch it off for inspection.

�Energy-consuming manufacturers, institutional investors of the area, transport,

professionals of the area, security and control organizations, even insurance companies acknowledge that oil analyses are an effective tool for the preventive maintenance of transformers.


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The table below establishes the relations between the types of analyses that can be carried out and the level of interpretation they give. The analytical recommendation depending on the transformer characteristics as well as on its history is a prerequisite to the making of a pertinent diagnosis.

TRANSFORMER CONDITION

� Direct relation Live parts Dielectric fluid Regulations

� Complementary relation Electric parts*

Cellulosic insulation**

Insulating role

Coolant role

Environ- -mental

Fire

Dissolved gases �

Furanic derivatives �

Polymerization degree �

Breakdown voltage �

Water content �

Total acid number �

Dissipation factor �

Interfacial tension �

Particles counting � � �

Search for metals � �

Sediments �

Corrosive sulphur � �

Viscosity �

Density � � �

Colour and appearance �

Flashing point � �

PCBs �

Hydrocarbons �

AN

AL

YS

ES

Proportioning of additives �

* Thermal or electric internal default ** General deterioration (ageing) or localized (hot point).

The following pages present in greater details the legitimacy of each type of analysis.


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… FOR A BETTER KNOWLEDGE OF THE VARIOUS ANALYSES CHARACTERIZING THE CONDITION OF LIVE

PARTS …..


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DISSOLVED GASES CHROMATOGRAPHY

Only this analysis can ensure an early detection of a malfunctioning of the transformer live parts (thermal defaults, electric defaults). Any abnormal functioning (thermal or electric default) will generate the production of characteristic gases dissolved in the dielectric fluid in proportions and concentrations known as abnormal. The fluid is considered to be the memory of events that occurred on the transformer. Thus, on the basis of a fluid sampling, by analysing the 13 characteristic gases and on the basis of their concentrations, respective proportions and their production speed, we are able to interpret the default that originated their creation.

� Even if a dielectric fluid is known to be in excellent condition concerning its dielectric or

cooling properties, it does not necessarily mean that the transformer is working properly. The laboratory systematically carries out an analysis of the dissolved gases, even the analysis of hydrocarbons in C3. An analysis limited to hydrocarbons in C2 does not necessarily give all the information needed to make an accurate diagnosis. �� On-load tap changer If the transformer is equipped with a tap changer on load, it is advisable to carry out the dissolved gases analysis both on the tap changer and on the tank itself (except if the tap changer is integrated into the tank). In addition, we remind you that a tap changer must be regularly inspected (visualization of the connexions state, cleanliness, etc…).

�� Buchholz In case of a Buchholz alarm or disconnection, it is imperative to take a sample at the Buchholz level (Buchholz oil with the usual syringe or Buchholz gas with the special phial or bag the Laboratory can supply). Another fluid sampling at lower tank level is possible, at the same time ; this would enable us to make a more pertinent diagnosis. �� Upper tank As regards upper tank sampling (rather than lower tank sampling), the sampling point will not have any effect on the diagnosis. As for the upper tank sampling technique itself, refer to our sampling instructions. �� Remark on instrument transformers As regards instrument transformers, the Laboratory advises a chromatography of the dissolved gases. For these equipments, sampling remains a very delicate step which requires you to contact the manufacturer.


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A few examples…

Hot point On a coil cross connection

Electric arc Within the coil (with electrodynamic stress : 2d

picture)

Hot point On a vacuum switch


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FURANIC DERIVATIVES

When cellulosic insulators deteriorate, there is a production of specific compounds called “furanic derivatives” dissolved in oil. Consequently, on the basis of an oil sample, it is possible to get information about the deterioration level of the insulators. This analysis makes it possible to diagnose a possible deterioration of the cellulosic material (especially coil papers). We are able to distinguish :

- an homogeneous deterioration of the paper related to the ageing of the transformer - from a localized deterioration due to a thermal default

This analysis is generally performed when transformers are at least 20 years old or when other analyses results lead us to presume there is a deterioration. POLYMERIZATION DEGREE

When cellulosic insulators deteriorate, a decomposition of the cellulose due to the breaking of intramolecular connections occurs, resulting in a drop in the polymerization degree. Consequently, on the basis of a paper sample, it is possible to get information about the deterioration level of the insulators. This analysis is generally performed when active parts of the transformer are out of the tank, given the constraints inherent in the sampling. The representativeness of the sample also constitutes a limit to the interpretation. On the other hand, this analysis is the direct measure of the deterioration level.

General deterioration of the cellulosic insulation


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CORROSIVE SULPHUR

The presence of corrosive sulphur compounds contained in some insulating oils, in contact with the metal materials of the transformer, can cause the deterioration of these metals at a level depending on their quantity, the length of the contact and the temperature. Thus, the detection of corrosive sulphur makes it possible to identify this source of failure of the transformer.

The new method for corrosive sulphur test is performed according to IEC 62535 (2008). Example of copper sheet not attacked Non-Corrosive Oil (Colour : orange)

Example of copper sheet attacked by corrosive sulphur Corrosive Oil (Colour: greyish)


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Example of copper sulphate deposits 2000 kVA - 20kV/0.41kV - 1999 - Hermetic –

Top. = 64°C Load: 80%

…

Sulphur Corrosion

Over the past 3 years, a new global failure (and even destruction) phenomenon affecting transformers and reactances has been identified and attributed to corrosion in metal components by sulphur compounds contained in mineral dielectric oils, although they meet applicable standards.

The factsThe factsThe factsThe facts

Expert assessments on units affected by this type of failure have brought to light copper corrosion with the formation of conductive surface deposits analysed as Cu2S, resulting from a reaction when sulphur compounds in the mineral oil attack the copper coils. The deposits are observed on the surface of naked components but are also known to proliferate inside the paper/oil/copper complex. In this event, the resistance of the insulation is decreased, that may lead to arcing in the units. The dielectric mineral oils used nevertheless meet the corrosiveness limits determined by the standard IEC 60 296.

This phenomenon has mainly been observed in units manufactured from 1995 onwards, in which the copper parts are neither varnished nor enamelled, sealed or oxygen-deprived free-breathing (nitrogen envelope or sheeting/bagging) and operating high load and temperature levels.

The The The The causes causes causes causes

�� MineralMineralMineralMineral oil oil oil oil ... ... ... ... starting in starting in starting in starting in 1995199519951995

The sulphur compounds present in the oil generally enhance the oxidation stability of the oil but some of them like mercaptans or disulfides can also be corrosive to metals. It is now known that major changes in oil refining processes in the past 20 years have brought about changes in sulphur compound content with an upward trend observed as from the early 90s. Research continues with the aim of identifying guilty sulphur compounds nature and the mechanisms involved.

�� Operating cOperating cOperating cOperating conditionsonditionsonditionsonditions The corrosive potential of sulphur in oil needs special conditions to express itself:

- low oxygen medium

- high temperatures.

Reviewing the standard

Faced with this issue, the initial reaction consisted in reviewing the standard used as a basis for assessing oil corrosiveness (ISO 5662). Our laboratory participated in interlab testing (Cigré – TC10 – WG A2) aimed at defining a new analysis method that is more representative of actual operating conditions. The new method is awaiting standardisation and is still known as the Cigré method.

© - Confidential document intended for the Laboratory’s clients. May not be fully or partially reproduced without permission from the Laboratory

NEWS Dec 2006

AdAdAdAdvice vice vice vice from the Laboratoryfrom the Laboratoryfrom the Laboratoryfrom the Laboratory Step 1: identify corrosive potential with the following tests performed on dielectric mineral oils made as of 1995 using the “Cigré method”,

Step 2: if the oil is corrosive, there are currently 3 solutions for strategic units, particularly if units are hermetic type operating at full load and/or high temperature:

� replace the corrosive oil with non-corrosive oil using the latest assessment method (refer to oil manufacturers) � use and oil additive with a passivator to protect naked metal surfaces (refer to oil manufacturers) � or chemically treat the fluid to eliminate the corrosive compounds (validation currently underway).

>> >> >> >> News from Laboratoire News from Laboratoire News from Laboratoire News from Laboratoire OKSMAN SERAPHIN OKSMAN SERAPHIN OKSMAN SERAPHIN OKSMAN SERAPHIN

Illustration of materials (Copper and paper)

Before and after testing

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… FOR A BETTER KNOWLEDGE OF THE VARIOUS ANALYSIS METHODS CHARACTERIZING FLUID CONDITION…..

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DIELECTRIC BREAKDOWN VOLTAGE

This analysis makes it possible to check the insulating properties of the fluid (some contaminants can affect this property). WATER CONTENT

This analysis makes it possible to quantify the concentration of water in the fluid due to the deterioration of internal components (papers, fluid itself) and to influence from outside (migration of atmospheric humidity) TOTAL ACID NUMBER

The acid number is the sign of a chemical deterioration of the fluid and possibly of the cellulosic material due to ageing by oxidation (accelerated by specific catalysts such as copper). Dissipation factor

This measure is very sensitive to polar contaminants which soil the fluid consequently to the deterioration of internal components (e.g.: particles, residue from carbon conductor, metals, incompatibility of some materials) or to influence from outside (migration of dust, etc...). Before carrying out this test in order to check the fluid quality of instrument transformers, you must take note of the dielectric breakdown voltage value, which constitutes a first discriminatory selection, i.e.: - Insufficient breakdown voltage requires a change of the fluid. - Adequate breakdown voltage requires to keep this fluid. - Average breakdown voltage requires to decide whether to change or to keep watch on this fluid, or to keep it only after examination of the dissipation factor. We consider the breakdown voltage - dissipation factor association to be an appropriate criterion to properly evaluate the fluid quality for this kind of device. Colour and appearance

Colour can show the fluid oxidation default (it can be connected to the acid number) or the incompatibility with materials. Particles counting

This analysis consists in quantifying by their size the particles due to the deterioration of internal components (papers, metals, etc…) and to influence from outside (migration of dust). Search for metals

This analysis makes it possible to quantify metals and inorganic components due to the deterioration, corrosion and fusion of internal elements and to influence from outside (migration of dust, presence of siliconized components, ...). Note : Before carrying out the metals analysis itself, we recommend to carry out a filtration which enables to examine under a microscope the possible deposit obtained and thus getting a more accurate view on the presence of metals, fibres, dust, metal splinters,...

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Deposits and sediments in the fluid

This analysis consists in valuing the mass of deposits and sediments per unit of volume of the fluid (gravimetry). A filtration is carried out and the deposit on the filter is examined under the microscope. Viscosity

Viscosity can be valued (either kinematic viscosity or dynamic viscosity) to characterize the evolution of this property of the fluid (in comparison with new fluid). This evolution has to remain compatible with the good heat exchange of the transformer. Interfacial tension

This analysis makes it possible to estimate mainly the oxidation state of the fluid (mainly applicable to oils) This is not the more appropriate test to check the fluid oxidation because, at some level, the interfacial tension stops evolving. Flashing point

This analysis makes it possible to assess the presence of volatile substances in the fluid (pollution by volatile substances or creation of volatile substances due to a deterioration of the fluid). Proportioning of additives

This analysis concerns antioxidant additives, especially in mineral oil (there are few oils with additives in France).

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Search for PCBs (or Ugilec, trichlorobenzenes,...) in mineral oils

This analysis makes it possible to quantify the possible contamination of oil by PCBs due to a handling, non appropriate supplements, an initial presence (old transformers). � A more detailed documentation including the rules and regulations is made available by the Laboratory and can be given to you on demand. Search for hydrocarbons in Askarels®

A too important presence of hydrocarbons can affect the nonflammability characteristic of the Askarel® which, beyond a certain threshold, becomes a flammable material.

We believe

Customer satisfaction goes hand in hand with

Environment-friendliness

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OTHER ANALYSES Other analyses than those mentioned above can be carried out by the Laboratory (in the electrical engineering field or other). Please contact our offices. DIELECTRICS THE LABORATORY SPECIALIZES IN Our Laboratory specializes above all in the following fluids:

•••• Mineral oils

•••• Pyralene (and Trielec or EXP3 as a complement)

•••• Ugilec (and Trielec as a complement)

•••• Silicone oils However, you can contact us for other fluids (e.g. Esters) or other dielectrics including solids. SAMPLING - WARRANTY The Laboratory supplies appropriate sampling equipment as well as sampling instructions. The Laboratory is at your disposal should you require to improve your sampling skills. Moreover, training sessions for sampling and preventive maintenance of electric transformers are organized in your premises or in our laboratory. Our diagnosis concerning the working of the transformer as well as the quality of the fluid can only be reliable if the samplings are carried out according to the regulations and sent within the deadlines. We will not fail to notice nonconformities to those regulations, which will result in a final diagnosis expressed with reservations. The reliability of our diagnosis depends entirely on the accuracy of the results but also on the information required in the specifications sheet. We will not fail to ask you for any missing information. If you cannot provide all the information we need, we will not be able to guarantee a fully reliable diagnosis. In order to provide reliable results, the analyses must be carried out as soon as possible after the samplings. As a consequence, it would be desirable to receive the samples within 8 days. If you have to send a great number of samples, please split them up into several parcels and send them separately (every 24 h or 48 h for example). If the sampling concerns a malfunctioning transformer and involves a matter of urgency, we will answer within 8 hours from receipt.

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SPECIAL KIT: THE BUCHHOLZ KIT To troubleshoot a BUCHHOLZ or gas detector relay alarm:

1- We advise you to keep a BUCHHOLZ kit onsite 2- Cary out sampling as soon as possible after the event 3- The results are returned within 8h by email or fax (and by post) 4- This kit is invoiced and remains our property, so it is exchanged after use.

[ Following a Buchholz or DGPT alert…

THE BUCHHOLZ KIT ]

�Available on site, to allow to take gas or fluid samples as soon as possible after incident.

�Results are sent within 8 HOURS by e-mail, or by fax, and post-mail.

�The kit is yours, and is replaced as soon as it has been used.

FOR RELEVANT DIAGNOSIS ON THE NATURE OF THE ORIGINAL DEFAULT :

Analysis of volatile gases, associated with those performed on gases dissolved in oil, allows to identify the default that caused the failure.

The « LOSBUCHHOLZ » analytical formula

�1 chromatogaphy of gases taken at the protection,

�2 chromatographies of gases dissolved in oil at the BOTTOM and TOP of the tank,

�1 furanic derivatives analysis.

�

�

�

�

SAMPLE RECEIVED REPORT SENT

Date < 18.00 p.m. Date +1 < 12.00 noon

Date < 12.00 noon Date >12.00 noon - 17.00 p.m.

Date > 17.00 p.m. Date +1 < 18.00 p.m.

The kit includes :

1 x Buchholz ampoule 2 x 30 ml glass syringes 1 x 30 ml glass flask 1 x 3-way extenders Plastic tubes with connections 1 pair of goggles / gloves Sampling instructions

Data sheet to be completed

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Document intended for the Laboratory customers not to convey to a third party without our prior consent

Noncontractual document without guarantee of update

LABORATOIRE OKSMAN-SERAPHIN S.A. Areva Group legal subsidiary

8, Rue Giotto

31520 RAMONVILLE ST AGNE FRANCE Tél : +33(0) 562 190 560 Fax : +33(0) 562 19 08 89

www.laboratoireoksman.com

+33 (0)562 190 560 For further information :

Offer & Recommendation Christiane Benetti Laboratory Director Catherine Molle-Epain Diagnosis & Advices Sophie Tranchart Samples kits provider Rachid Baaji, Galinier Laurent

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LEGITIMACY OF OIL ANALYSIS - Laboratoire OKSMAN · thus, by analysing the fluid, we can obtain information about : o its characteristics which aim at meeting the two functions mentioned