What is insulation coordination and what is its importance?
There are many definitions of insulation coordination provided by different authorities. In this instance we wanted to use IEC 60071-1 definition which is
- insulation co-ordination
- selection of the dielectric strength of equipment in relation to the operating voltages and overvoltages which can appear on the system for which the equipment is intended and taking into account the service environment and the characteristics of the available preventing and protective devices
Note: The spelling of coordination is co-ordination as per IEC 60071-1 but in IEC 60664-1, it is spelled coordination. For purposes of this article, the spelling to be used will be coordination.
Insulation coordination involves the selection of the electric insulation characteristics of an electrical equipment considering ts application and the environment where it will be installed. Insulation coordination can be accomplished if the design and selection of the electrical equipment is based on the stresses to which it will be subjected during its operational lifetime.
The basis of insulation coordination are:
- Voltage
- Rated Voltage
- Rated Insulation Voltage
- Working Voltage
- Overvoltages
- Transient overvoltage
- Peak Voltages
- Temporary overvoltage
- Environmental Conditions
Environmental conditions for the insulation shall be taken into account as quantified by pollution degree which is a classification according to the amount of dry pollutants and condensation present in the environment
Note: Protection by enclosures provided according to the classes specified in IEC 60529 does not necessarily improve the environment with regards to pollution.
The most important environmental parameters are as follows:
- for clearances:
- air pressure,
- temperature, if it has a wide variation;
- for creepage distances:
- pollution,
- relative humidity,
- condensation;
- for solid insulation:
- temperature,
- relative humidity.
The goal of insulation coordination is not only to select the insulation strength but also to select the minimum insulation strength, or minimum clearance. Minimum strength can be equated to minimum cost. In its most basic form, the process of insulation selection should begin with a reliability criteria. Once the desired reliability is selected, a study needs to be undertaken to determine the electrical stresses on the equipment. This stress is then compared to the insulation strength characteristics, from which a strength is selected. If the insulation strength or the clearance is considered to be excessive, then the stress can be reduced by use of other measures such as surge arresters.
Insulation coordination is important in the safe operation of the equipment in its lifetime at the least capital investment and operational cost.
References:
- Insulation Coordination for Power Systems by Andrew R Hileman, CRC Press 1999
- IEC 60071-1 Insulation co-ordination – Part 1: Definitions, principles and rules
- IEC 60664-1 Insulation coordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests
- IEC 60529 Degrees of protection provided by enclosures (IP Code)