ELECTRICAL INSULATION AND INSULATING OIL
A Guide to Use Electrical Insulation Materials and Insulating Oil
Insulating materials should be suitably ended so as to prevent deterioration of their qualities under the specified working conditions. Account should be taken of international standard the IEC 85 and IEC 505 recommendations.
Ebonite, synthetic resin-bonded laminated material and bituminized asbestos cement-bonded panels should be of suitable quality selected from the grades or types in the appropriate British Standard, IEC Standard, or approved National Standard.
All cut or machined surfaces and edges of resin-bonded laminated materials should be cleaned and then sealed with an approved varnish as soon as possible after cutting.
Linseed oil and untreated materials of fiber, leatheroid, presspahn, asbestos or other similar hygroscope types of materials should not be used for insulation purposes. Untreated leatheroid and presspahn may be used for mechanical protection of winding insulation.
Wherever practicable, instrument, apparatus and machine coil windings, including wire wound resistors, with the exception of those immersed in oil or compound, should be thoroughly dried in a vacuum or by other approved means and should then be insulating varnish. Varnish with a linseed oil base should not be used.
No material of a hygroscope nature should be used for covering coils. Where inter-leaving between windings in coils is necessary, only the best Manila paper, thoroughly dried, which permits penetration by the insulating varnish or wax, should be used.
The List of Insulating Materials
The insulating materials list may become very big, we can summarize as below:
A.B.S, ACETATE, ACRYLIC, BERYLLIUM OXIDE, CERAMIC, DELRIN, EPOXY/FIBERGLASS, GLASS, KAPTON, KYNAR, LEXAN and MERLON, MELAMINE, MICA, NEOPRENE, NOMEX, NYLON, P.E.T, P.E.T.G, PHENOLICS, POLYESTER (MYLAR), POLYOLEFINS, POLYSTYRENE, POLYURETHANE, PVC, SILICONE/FIBERGLASS, SILICONE RUBBER, TFE (TEFLON), THERMOPLASTICS etc,
How Comply the Insulating Oil (Transformer Oil) Requirements
This is denoting the requirements of insulating or transformer oil for a new project when supplying or installing plant and equipment rather than an operating an existing one.
Insulating oil should comply with the requirements of International Standard IEC 296. Insulating oil should be provided by the service provider for all oil-filled apparatus and 10% excess should be provided for topping up purposes in sealed drums. The service provider should satisfy himself that suitable oil treatment facilities are available at site for his use. If the service provider is unable to obtain written assurances to this effect he should provide such oil treatment facilities as required to meet the specification of the agreement.
How Effect Moisture on Transformer Oil Breakdown Voltage
The main purpose to use insulating transformer oil as a heat transfer and a good dielectric material. The insulating oil can act as an insulator up to a certain level of voltage. The voltage at which level fail to insulate is known as breakdown voltage.
The level of breakdown voltage depends on important factor of moisture particle into the oil like others factors such acidity, foreign particle, pressure etc.
The percentage of breakdown voltage relative to dry oil decrease as increase the percentage of relative moisture level. The typical sample graph shows the relationship between breakdown voltage and moisture saturation. This test must comply with the International Standard IEC 60156.
Short Guide to Transformer Oil Analysis
Moisture ingress into transformer oil is a big factor, along with others various factor it also cause of transformer breakdown; so keep the transformer on smooth operation, regular observation and test is required. The details test and observation for transformer oil should consider the points as below:
· Corrosive Sulphur
· Dielectric Strength
· Dielectric breakdown voltage
· Dissolved gas analysis
· Furfural and related compounds
· Interfacial tension (IFN)
· IFT-NN Relationship
· Kinematic viscosity
· Neutralization Number (NN)
· Oxidation Stability
· Sediment, sludge
· Specific gravity
· Suspended particles in oil, visual
· Trace analysis
· Water content
· Additional expertise
How Comments on Oil Classifications
How say the transformer oil is good, bad or very bad; here in some features are given below that will help to comments on transformer oil good or bad.
NN 0.00 - 0.10
IFT 30.0 - 45.0
Colour Pale Yellow
Proposition A Oils
NN 0.05 - 0.10
IFT 27.1 - 29.9
OQIN 271 – 600
NN 0.11 - 0.15
IFT 24.0 - 27.0
Colour Bright Yellow
OQIN 160 - 318
NN 0.16 - 0.40
IFT 18.0 - 23.9
OQIN 45 – 159
Very Bad Oils
NN 0.41 - 0.65
IFT 14.0 - 17.9
OQIN 22 - 44
Extremely Bad Oils
NN 0.66 - 1.50
IFT 9.0 - 13.9
Colour Dark Brown
OQIN 6 - 21
Where, OQIN = IFT/NN