IEC 60505 - Basic standard for estimating the ageing of electrical insulation systems

Equipment standards, for example, are based on their test and analysis methods. While IEC 60664, as the basic standard for insulation coordination, is primarily concerned with the behavior of insulating materials under environmental conditions, IEC 60505 considers entire insulation systems. These insulation systems (EIS) consist of different materials that can also interact with each other and can therefore only be considered in combination.

IEC 60505 "Evaluation and qualification of electrical insulation systems" describes its task as follows: 

"The life of electrical insulation systems (EIS) or systems often determines the life of electrical equipment and can be affected by electrical, thermal, mechanical, or environmental stresses, either individually or in combination."

The verified service life is therefore an essential parameter for categorizing electrical insulation systems. The standard shows the way to the development of EIS functional test and evaluation procedures.

Within the standard, the stresses on electrical insulation are divided into the groups "electrical", "thermal", "mechanical" and "environmental" aging. One of the main aging mechanisms is thermal aging. The rough rule of thumb "10 degrees increased temperature halves the life span" results from chemistry. There, the Arrhenius theorem describes - very abbreviated - the relationship between reaction rate and temperature.

However, direct thermal aging is now only part of the stresses that lead to a finite life of insulation materials and insulation systems.

IEC 60505 lists the following, among others, as factors to be considered for aging:

• Manufacturing defects (impurities, air inclusions, recipe defects, wrinkles and delaminations, moisture, incompatibilities, particles, fractures, etc.).

Electrical aging due to

• Surface discharges (partial discharge, corona)

• Tracking and erosion

• Build-up of space charge, consequently reduced dielectric strength

• Electric Treeing (within the material, e.g. Watertreeing)

• Electrochemical degradation (migration, depolymerization)

• Electrical losses at high frequencies in the material

Thermal aging due to

• Differences in thermal expansion (e.g. delamination)

• Melting, transition glass temperature, softening, embrittlement, etc.

• Self-heating due to electrical stress

• Oxidation, cracking

Environmental aging due to

• Chemical stress due to e.g. solvents, oils, hydrolysis

• Contact corrosion 

• Moisture absorption (reduced insulation, treeing and partial discharge)

• Dirt on the surface (as a result tracking)

• Depolymerization in aggressive environment

• UV radiation, weathering

Mechanical aging due to

• Vibration, elongation and compression, delamination, pressure

• Adhesion loss during bonding

• Breakage and tearing due to the application of mechanical force

• Creep (displacement) under shear load

• Penetration (e.g. metal chips with films)

• Abrasion

In addition to describing the various load factors, the standard also deals with test methods and evaluations of the test results. In particular, the comprehensive annex contains numerous helpful hints.

The essential standards to which IEC 60505:2011 refers include:

• IEC 60068 Environmental test methods (heat, cold, thermal cycling, thermal shock)

• IEC 60216 Determination of thermal classes of electrical insulation materials

• IEC 60664 Basic standard for insulation coordination

However, the 2011 edition of IEC 60505 does not yet take into account the increasing requirements from the area of DC technology with high voltages, as well as the increasing frequencies in the area of e.g. frequency converter applications in drive technology. These increasingly relevant load factors will only be integrated in a future new edition - or covered by other standards. The widespread use of electromobility is forcing a relatively rapid response here. 

Although the document dates back to 2010, the UL Guide "Effects of High Frequency Volage Stress on Air Insulation and Solid Insulation" is a good introduction to this topic.

Document "UL Guide

At IEC, Maintenance Team 3 of TC109 is responsible for "Voltage stress at high frequency with regard to insulation coordination of equipment in low-voltage systems".