EN 50375:2002

SLOVENSKI SIST EN 50375:2004
STANDARD
april 2004
Testing methodology for wipers used in electrical insulating oil
ICS 29.040.10 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 50375
NORME EUROPÉENNE
EUROPÄISCHE NORM August 2002
ICS 29.040.10
English version
Testing methodology for wipers
used in electrical insulating oil

Méthodologie d'essai des moyens de Prüfmethoden für Putzlappen,
nettoyage utilisés dans les huiles isolantes die für Isolieröl verwendet werden
à usages électriques
This European Standard was approved by CENELEC on 2002-03-05. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 50375:2002 E
Foreword
This European Standard has been prepared by CENELEC BTWG 99-1, Insulating oil.
The text of the draft was submitted to the Unique Acceptance Procedure and was approved by
CENELEC as EN 50375 on 2002-03-05.
The following dates were fixed:

- latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-03-01

- latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-03-01

Annexes designated "normative" are part of the body of the standard.
In this standard, annexes A, B, C, D and E are normative.
Warning: This European Standard calls for the use of substances and/or procedures that may
be injurious to health if adequate precautions are not taken. It refers only to technical suitability
and does not absolve the user from legal obligations relating to health and safety at any stage.

– 3 – EN 50375:2002
Contents
Introduction. 4
1 Scope. 5
2 Normative references. 5
3 Terms and definitions . 5
4 Test methods. 6
4.1 Fibre release test (refer to annex A) . 6
4.2 Snagging test (refer to annex B). 6
4.3 Equilibrium moisture content (refer to annex C) . 6
4.4 Oil absorbency (refer to annex D and annex E) . 6
5 Test report. 7

Annex A (normative) Fibre release from wipers . 8
Annex B (normative) The snagging test. 12
Annex C (normative) Equilibrium moisture content of wipers. 14
Annex D (normative) Oil absorbency of wipers. 15
Annex E (normative) Rate of absorbency . 16

Figure A.1 – Schematic arrangement of suitable apparatus for fibre release test . 9

Figure B.1 – Test board for snagging test . 12

Figure B.2 – Schematic arrangement of scratch pattern on wiper after snagging test. 13

Introduction
Fibres and other particles have a detrimental effect on the dielectric strength of insulating oil.
During the maintenance of electrotechnical equipment it is often necessary to use a wiper or
cloth to clean components or absorb oil. To minimize contamination by fibres and resultant
degradation of oil properties, it is necessary to make a selection of the type of wiper used in this
application.
The properties required of wipers for use with insulating oil are as follows:
− low fibre release;
− fibres released from a wiper should have the least possible effect on the dielectric strength
of insulating oil;
− high tear resistance;
− should tearing occur, subsequent fibre release should be low;
− oil absorbency should ideally be high;
− the wipers should have no other effect which degrades the properties of insulating oil below
those required by IEC 60296.
– 5 – EN 50375:2002
1 Scope
This European Standard specifies testing procedures for fibrous wipers to be used with
equipment normally containing electrical insulating oil. Such testing is necessary to rank
commercial products, so that possible contamination of insulating oil and electrical equipment
with fibres during maintenance operations may be minimized.
2 Normative references
This European Standard incorporates, by dated or undated reference, provisions from other
standards. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions
of any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies.
EN 50353 Insulating oil - Determination of fibre contamination by the counting method
using a microscope
EN 60156 Insulating liquids - Determination of the breakdown voltage at power frequency -
Test method (IEC 60156)
EN 60814 Insulating liquids - Oil-impregnated paper and pressboard - Determination of
water by automatic coulometric Karl Fischer titration (IEC 60814)
IEC 60296 Specification for unused mineral insulating oils for transformers and switchgear
ISO 554 Standard atmospheres for conditioning and/or testing - Specifications
3 Terms and definitions
For the purposes of this European Standard the following terms and definitions apply.
3.1
standard atmosphere
the atmosphere in an enclosure where the temperature is (23 ± 2) ° C and the relative humidity
is (50 ± 2) %. This standard atmosphere is recommended in ISO 554. When conditioning oil, the
enclosure shall also be protected from sunlight to minimize oxidation of the oil
NOTE This atmosphere may be achieved in an enclosure containing a vessel of a saturated solution of
tetrahydrated calcium nitrate [Ca(NO ) .4H O].
3 2 2
3.2
conditioned oil
unused oil conforming to IEC 60296 which has been filtered through a membrane filter of pore
diameter 1,2 µm or less into a glass vessel cleaned as described in Clause 7 of EN 50353. This
oil is then stored in standard atmospheric conditions (3.1) for sufficient time to attain equilibrium
NOTE 1 It has been found that, if stored in a 3 litre standard tall-form beaker, 72 h is sufficient for oil to attain
equilibrium.
NOTE 2 Oil conditioned in this manner is expected to have a minimum breakdown strength of 50 kV (measured
according to EN 60156) and a maximum water content of 33 mg/kg (measured according to EN 60814).

3.3
standard wiper
a wiper of dimension 250 mm x 250 mm in the as-received condition with no cut or torn edges
made after manufacture. The wiper shall be stored in standard atmospheric conditions (3.1) for
sufficient time to attain equilibrium
NOTE Manufacturers are advised, for the purpose of testing, to produce standard size wipers
(250 mm x 250 mm) on which the edges are representative of those produced in the normal manufacturing process.
4 Test methods
The test methods for wipers are detailed in Annexes A to E and are summarized below.
NOTE Whilst wipers may perform well in these tests, in normal everyday use they may become contaminated
with fibres by contact with their environment and these fibres can then be passed on to contaminate the oil. Care
should be taken to avoid this. A particular cause for concern is the packaging. To avoid contamination, wipers should
be packaged in non-fibre shedding material and the method of dispensing should prevent excessive production of
fibres from the wipers or the container.
4.1 Fibre release test (refer to Annex A)

This test simulates the use encountered whilst wiping during maintenance operations and
measures the free fibres produced.
For the test to be comparable between different brands of wiper, it is necessary to define the
dimensions of the laboratory equipment used during the fibre release test. A standard wiper
(3.3) must be tested in standard laboratory equipment. In annex A the dimensions of suitable
apparatus are defined.
4.2 Snagging test (refer to Annex B)

Equipment being wiped often has sharp corners or edges and during use snagging or tearing of
the wiper may occur, with subsequent increased fibre release from the torn part of the wiper.
This test is designed to establish the increased number of fibres released by snagging a wiper
on a standard array of sharp points.
4.3 Equilibrium moisture content (refer to Annex C)

Reduction of the dielectric strength of oil containing fibres is lessened if these fibres have low
equilibrium moisture content. The test measures the equilibrium moisture content of a wiper.
NOTE: Natural fibres have greater equilibrium moisture contents than man-made fibres and it is for this reason that
wipers made of natural fibres such as cotton, wool or cellulose (paper) cannot be recommended for this application.
4.4 Oil absorbency (refer to Annex D and Annex E)

Wipers are mostly used for cleaning components and mopping up spillages. They should be
able to absorb sufficient quantities of oil at a rate suitable for the application. A measurement is
made of the amount of oil capable of being absorbed by a wiper and the rate at which it is
absorbed.
– 7 – EN 50375:2002
5 Test report
The test report shall contain the following information:
a) reference to this European Standard;
b) full description of sample under test, including name of wiper, manufacturer and description
of fibre type (if possible);
c) breakdown strength of the oil used to carry out test A: initial value; value after the blank
test; value after testing the fibre release from the sample;
d) number and size distribution of fibres released per square metre of wiper in the fibre
release test (Annex A);
e) number and size distribution of fibres released per square metre of wiper after the snagging
test (Annex B);
f) equilibrium moisture content of wiper (Annex C);
g) oil absorbency of wiper (Annex D);
h) rate of absorbency of two defined test samples (Annex E);
i) date of the test.
NOTE This standard comprises a variety of tests. Individual users may apply different weightings to each test to
produce a ranking or grading for their application. The suitability of any wiper for a particular application is a matter of
agreement between user and supplier.

Annex A
(normative)
Fibre release from wipers
A.1 Principle
This test simulates the use encountered whilst using a wiper during maintenance operations. A
standard wiper (3.3), conditioned in standard atmosphere (3.1) is rotated at speed of
(120 ± 2) r.p.m. in a closed, pre-cleaned glass vessel containing a quantity of conditioned fibre-
free oil (3.2), such that the wiper rubs against the walls of the vessel. A measurement is made
of the contamination of the test oil by fibres being shed by the wiper and of the effect on the
dielectric strength of the test oil due to contamination from these or other particulate material.
A.2 Apparatus
A.2.1 Glass vessel assembly, with vessel of capacity of at least 3 litres, internal diameter
130 mm and fitted with a lid containing a hole or slot for a stirrer rod. This vessel shall have a
calibrated scale denoting the volume of the contents (± 5 %).

NOTE 1 A 3 litre tall-form beaker has been found suitable.
NOTE 2 During stirring it may be necessary to stabilize the glass vessel to prevent its rotation.
A.2.2 Stirrer assembly, consisting of
− motor with rotational speed of (120 ± 2) r.p.m.,
− drive shaft with termination suitable for clamping a standard wiper (3.3),
− wiper clamping assembly.
NOTE An arrangement found to be suitable is shown in Figure A.1. The drive shaft is terminated with a disc
magnet and the wiper is clamped between this magnet and a steel disc. The clamping arrangement shall be such
that the wiper assumes a diameter of 75 mm at the clamp.
A.3 Preparation of equipment
A.3.1 All glassware, lid and stirrer rod shall be cleaned as outlined
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