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IS 14353 (1996): Guide for determining compatibilitybetween enamelled winding wires and impregnating compounds[ETD 2: Solid Electrical Insulating Materials andInsulation Systems]

IS 14353 : 1996

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GUIDE FOR DETERMINING COMPATIBILITY BETWEEN ENAMELLED

WINDING WIRE AND IMPREGNATING COMPOUNDS

ICS 29.060.10; 29.080

0 BIS 1996

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MA3AG

NEW DELHI 110002

May 1996 Price Group 1

Electrical Insulation System Sectional Committee, ETD 4

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Electrical Insulation System Sectional Committee had been approved by the Electrotechnical Division Council.

Enamelled winding wire and impregnating compound are important components of the insulation systems of.electrical rotating and static machines. Experience has shown that the majority of difficulties arises when an enamelled wire is used in combination with an impregnating compound which causes chemical reaction between the cured enamelled film and impregnating compounds. These reactions are accelerated by the effect of temperature and may cause alteration of the electrical and/or mechanical properties of the impregnated enamelled wire.

This standard suggests two short term methods to determine relative compatibility of combinations:

a) Twisted pair ageing, and

b) Twisted pair cyclic ageing.

These methods should be considered as pre-selection methods to choose a wire enanielled/impregnating compound combination from amongst many available to an insulation designer. The compatibility of combinations not accepted by these methods should be confirmed by the well experienced thermal endurance procedure according to IS 5825 : 1993 ‘Guide for evaluation of thermal endurance of enamelled wire (first revision)‘.

Attention is drawn to the fact that both methods may not lead to same results while selecting the combination.

Whereas the method a) Twisted pair ageing is confirmed by extensive experience in India and other countries, not enough experience is available by method b) Twisted pair cyclic ageing. Due to this, the end point criteria for method b) is not included.

The method to determine compatibility between enamelled wire and impregnating compound is by no means methods to test insulation system of an electrical machine. Environmental factors such as, humidity, chemical contamination, mechanical vibration, etc, which may cause failure of insulation system are not covered in this guide. The combined effect of such factors on the insulation system need to be evaluated by other methods, for example, motorette testing.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing~the result of a test or analysis, shall be founded off in accordance with IS 2 : 1960 ‘Rules for rounding off numerical ‘values (revised)‘. The number of significant values retained in the rounded off value should be the same as that of the specified value in this standard.

IS 14353 : 1996

Indian Standard

GUIDE FOR DETERMINING COMPATIBILITY BETWEEN ENAMELLED

WINDING WIRE AND IMPREGNATING COMPOUNDS

1 SCOPE

1.1 This standard covers suggested test methods to determine compatibility of enamelled winding wires and impregnating compounds (impregnating varnishes and solventless resins). 1.2 The standard does not cover test methods to determine compatibility of other types of winding wires such as, enamelled rectangular wires, fibrous covered round and rectangular wires, etc.

2 REFERENCES

The following Indian Standards are necessary adjuncts to this standard:

IS No.

13730 (Part 0)

(Set 1) : 1993

(Set 2) : 1993

(Set 3) : 1994

(Set 4) : 1993

13778

Title

Particular type of winding wires: Part 0 General requirements

Enamelled round copper wire

Enamelled rectangular copper wire

Enamelled round aluminium wire

Glass fibre wo~und bare or enamelled rectangular copper wire

Methods of tests for winding wires: (Part 5) : 1993 Part 5 Electrical properties

3 TERMINOLOGY

3.0 For the purpose of this standard, the following definitions, in addition to those given in IS 13730 (Part O/Section 1,2,3 and 4) shall apply.

3.1 Enamelled Wire

A wire coated with an insulation of cured resins.

3.2 Twisted Pair

Two wires laid side by side and one end of the pair rotated while the other is held, imparting a spiral form.

3.3 Compatibility

Ability possessed by two or more materials to be associated with each other without the association causing degradation of one or more materials.

4 COMPATIBILITY TEST METDODS

4.1 Twisted Pair Ageing

4.1.1 Twivted Pair Heat Ageing - Test Method

In this method, the change-in dielectric strength of the twisted pair impregnated enamelled wire specimens after exposure to accelerated thermal ageing~is determined.

The enamelled wire test specimen is the specimen prescribed for breakdown voltage tests, BDV [see 4 of IS 13778 (Part 5) : 19931. Six series of eleven specimens each are prepared. Impregnate three series of specimens selected, once by immersing in the impregnating compound at room temperature for 10 minutes (any other temperature of impreg- nating compound or immersion time shall be selected as specified by impregnating compound supplier). For preparation of twisted pair, it shall be pre-heated for 10 minutes at 130°C and cooled for one hour at room temperature. The impregnat- ing compound shall be left for atleast 30 minutes in impregnated container to remove air bubbles. The twisted pair after impregnating shall be withdrawn at a rate of 10 cm/min from the impregnant. Curing of the specimens was done according to cure schedule recommended by impregnating com- pound supplies. Remaining three series are unimpregnated.

The impregnated (0 and non-impregnated (Nr) specimens are divided into following three groups:

- The set GO undergoes no heat ageing

- The set Gl undergoes heat ageing of 168 h at temperature (T)

- The set G2 undergoes heat ageing of 336 h at temperature (T)

The ageing takes place in an air circulated electric oven. The ageing temperature (T) is selected according to temperature class of enamelled wire and impregnant raised by 40°C. For example:

For temperature class 155 T = 195°C

1

IS 14353 : 1996

After ageing, the specimens are cooled to room : 1993. Average BDV values of eleven specimens temperature and breakdown voltage shall be are reported and the following ratios of dielectric measured in accordance with 4 of IS 13778 (Part 5) strength determined:

RO= IGO Average BDV of impreganted, unaged

NIGO Average BDV of unimpreganted, unaged

Rl = IGl Average BDV of impreganted and aged for 168h

NE1 Average BDV of unimpreganted and aged for 168h

R2 = IG2 Average BDV of impreganted specimen aged for 336h

NIG2 Average BDV of unimpreganted specimen aged for 336h

R3 = NIG2 Average BDV of unimpreganted specimen aged for 336h NIGO Average BDV of unimpreganted specimen unaged

4.1.2 Test Result and Assessment of Compatibility

Compare the breakdown voltage ratio RO, Rl, R2 and R3 obtained for a combination with the ex- pected values of BDV ratios as given in Table 1. If the ratio-R2 for combination tested is more than 0.8,’ the combination is considered to be com- patible. The ratios RO, Rl and R3 to be used for guidance only, to study the ageing behaviour of the winding wire or the combination.

4.2 Twisted Pair Cyclic Ageing

4.2.1 Cyclic Ageing Test Method

In this method, the change in dielectric strength of the twisted pair enamelled wire specimens after exposure to cyclic ageing is determined.

Seven sets of five specimens each (total 35 specimens) of twisted pair enamelled wire as described in 4.1.1 shall be prepared. Impregnate all specimens in impregnating compound at room temperature and cure as per the schedule recom- mended by impregnating compound supplier.

First series of five specimens shall be tested for break down voltage as per 4 of IS 13778 (Part 5) : 1993 and determine average BDV.

Subject the remaining six sets of BDV specimens (total 30 specimens) to cyclic ageing.

Each cycle of ageing shall consist of:

a)

b)

cl

After

heating the specimen for two and half hours at T ‘C (T = Temperature class of the com- bination +4O”C), cooling for 30 min at temperature 15 - 25°C and removal of the samples from oven and exposing them to ambient temperature.

such 32 cycles of ageing, 5 specimens .are -_ _ . tested for breakdown voltage. The remaining specimens are continued for cyclic ageing. Similarly 5 specimens shall be drawn and tested for BDV after cyclic ageing of 64,96,128,160 and 192 cycles.

4.2.2 Physical examination tests must be per- formed at the end of 192 cycles. Each sample is observed under a microscope for the presence of cracks or any other surface flaws to qualitatively assess the degree of degradation.

4.2.3 Reporting Test Result and Assessment of Compatibilily

By comparing the retained BDV after 192 cycles, relative performance of enamelled wire and im- pregnant combinations can be judged.

Table 1 Breakdown Voltage Ratios - Twisted Pair Heat Ageing Method

(Clause 4.1.2)

Ratio

IGO

IX0 = NIGO

Expeckil Value Signlllcance of spined Ratio Value

>l Measures ‘immediate chemical action of varnish during impregnation

IGl R1 = NIGl

z 0.65 Measures action of varnish after 168h heat age@. Wider dispersion in results is caused by non-stability. Value below 0.65 indicates unsatisfactory compatibility

IG2 R2 = NIG2

r 0.8 Measures action of varnish after 336h heat ageing. This is most significant ratio.

NIG2 R3 = NIGG

2 0.8 Establisheswhetherenamelled wirealone (impregnated) hassatisfactory heatageing. This has no direct significance for compatibility with impregnant. If the ratio is 0.8, the conclusion about compatibility can be misleading.

2

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This Indian Standards has been developed from Dot : No. ETD 04 ( 3405 ).

Amendments Issued Since Publication.

Amend. No. Date of Issue Text Affected

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