GB/Z 16935.2-2013Insulation coordination for equipment within low-voltage systems - Part 2-1: Application guide - Explanation of the application of the IEC 60664 series, dimensioning example and dielectric testing (English PDF)

1 Scope

This part lays down an application guide for the explanation of the application of the GB/T 16935 series and for the dimensioning requirements.

The important matters to be taken into account are: the nominal system voltage or the rated insulation voltage; the overvoltage category of the product, abbreviated OV cat.; overvoltage of any type; the frequency of the voltage; the characteristics of the solid insulating material; and the pollution degree together with the humidity level.

2 Normative references

The following documents are indispensable for the application of this document. For a dated reference, only the edition cited applies; for an undated reference, the latest edition, including all amendments, applies.

GB/T 16895.10-2010, Low-voltage electrical installations—Part 4-44: Protection for safety—Protection against voltage disturbances and electromagnetic disturbances (IEC 60364-4-44:2007, IDT).

GB/T 16935.1-2008, Insulation coordination for equipment within low-voltage systems—Part 1: Principles, requirements and tests (IEC 60664-1:2007, IDT).

GB/T 16935.3-2005, Insulation coordination for equipment within low-voltage systems—Part 3: Use of coating, potting or moulding for protection against pollution (IEC 60664-3:2003, IDT).

GB/T 16935.4-2011, Insulation coordination for equipment within low-voltage systems—Part 4: Consideration of high-frequency voltage stress (IEC 60664-4:2005, IDT).

GB/T 16935.5-2008, Insulation coordination for equipment within low-voltage systems—Part 5: Method for determining clearances and creepage distances not exceeding 2 mm (IEC 60664-5:2007, IDT). The English wording above renders the Chinese title as printed in this document.

GB/T 17045-2008, Protection against electric shock—Common aspects for installation and equipment (IEC 61140:2001, IDT).

IEC 60085:2007, Electrical insulation—Thermal evaluation and designation.

IEC 60112:2003, Method for the determination of the proof and the comparative tracking indices of solid insulating materials, together with Amendment 1 (2009).

IEC 60216 (all parts), Electrical insulating material—Property of thermal endurance.

3 Terms and definitions

The following terms and definitions apply to this document. A note states that all the definitions may be found in the various parts of the GB/T 16935 series, as shown below.

3.1 Approximately homogeneous field: a field is regarded as approximately homogeneous when its frequency is above 30 kHz and the radius of curvature of its conductive parts is greater than or equal to 20 % of the clearance. Source: GB/T 16935.4-2011, definition 3.1.

3.2 Base material: an insulating material on which a conductive pattern may be formed. Source: GB/T 16935.3-2005, 3.1.

3.3 Basic insulation: insulation applied to hazardous live parts that provides basic protection. Source: GB/T 16935.1-2008, 3.17.2. A note adds that this concept does not apply to insulation used exclusively for functional purposes.

3.4 Clearance: the shortest distance in air between two conductive parts. Source: GB/T 16935.1-2008, 3.2.

3.5 Coating: insulating material such as varnish or dry film on the surface of an assembly. Source: GB/T 16935.3-2005, 3.5. A note adds that the coating and the base material of the printed board form an insulation system with characteristics similar to those of solid insulation.

3.6 Conductor: a single conductive path within a conductive pattern. Source: GB/T 16935.3-2005, 3.3.

3.7 Creepage distance: the shortest distance between two conductive parts along the surface of a solid insulating material. Source: GB/T 16935.1-2008, 3.3.

3.8 Double insulation: insulation made up of both basic insulation and supplementary insulation. Source: as printed, GB/T 16935.3-2005, 3.17.4.

3.9 Electrical breakdown: the failure of insulation under electrical stress when the discharge completely bridges the insulation, so that the voltage between the electrodes falls to nearly zero. Source: GB/T 16935.1-2008, 3.20.

3.10 Electric field strength: the voltage gradient per unit length, usually expressed in kV/mm. Source: GB/T 16935.4-2011, 3.7. The document prints no English term for this entry.

3.11 Environment: the surrounding conditions that may affect the performance of equipment or of a system. Source: GB/T 16935.1-2008, 3.12. A note lists air pressure, temperature, humidity, pollution, radiation and vibration.

3.12 Flashover: an electrical breakdown along the surface of solid insulation in a gaseous or liquid medium. Source: GB/T 16935.1-2008, 3.20.2.

3.13 Functional insulation: insulation between conductive parts that is necessary only for the proper functioning of the equipment. Source: GB/T 16935.1-2008, 3.17.1.

3.14 Homogeneous field: a field in which the voltage gradient between the electrodes is basically constant, that is, a uniform field, for example the field between two spheres each of which has a radius greater than the distance between them. Source: GB/T 16935.1-2008, 3.14. The English term is printed on the page as homogeneous filed.

3.15 Impulse withstand voltage: the highest peak value of an impulse voltage of prescribed form and polarity that does not cause breakdown of the insulation under specified conditions. Source: GB/T 16935.1-2008, 3.8.1.

3.16 Inhomogeneous field: a field in which the voltage gradient between the electrodes is basically not constant, that is, a non-uniform field. Note 1 states that, as regards voltage withstand capability, the inhomogeneous field condition of a point-to-plane electrode arrangement is the worst case, called case A, and may be represented by a point electrode of 30 µm radius and a plane electrode of 1 m x 1 m. Note 2 states that at frequencies above 30 kHz a field is regarded as inhomogeneous when the radius of curvature of the conductive parts is less than 20 % of the clearance. Source: GB/T 16935.1-2008, 3.1.5 modified, and GB/T 16935.4-2011, 3.2.

3.17 Insulation: that which is used in an electrotechnical product to separate conductive parts at different potentials. Source: GB/T 16935.1-2008, 3.17.

3.18 Insulation coordination: the mutual relation of the insulation characteristics of electrical equipment, taking into account the expected micro-environment and other influencing conditions. Source: GB/T 16935.1-2008, 3.1 modified.

3.19 Macro-environment: the environment of the room or of the other place in which the equipment is installed or used. Source: GB/T 16935.1-2008, 3.12.1.

3.20 Micro-environment: the environment near the insulation that particularly affects the dimensioning of the creepage distance. Source: GB/T 16935.1-2008, 3.12.2.

3.21 Overvoltage: any voltage whose peak value is greater than the corresponding peak value of the maximum steady-state voltage under normal operating conditions. Source: GB/T 16935.1-2008, 3.7.

3.22 Overvoltage category: a numeral defining a transient overvoltage condition. Source: GB/T 16935.1-2008, 3.10 modified.

3.23 Partial discharge, PD: a discharge that partially bridges the insulation. Source: GB/T 16935.1-2008, 3.18.

3.24 Partial discharge inception voltage, U with subscript i: the lowest peak value of the test voltage at which, when the test voltage is raised above the value below which no discharge occurs, the apparent charge is greater than the specified discharge magnitude. A note adds that the r.m.s. value may be used for an AC test. Source: GB/T 16935.1-2008, 3.18.4.

3.25 Pollution: any combination of foreign matter, solid, liquid or gaseous, that reduces the electric strength and the surface resistivity of the insulation. Source: GB/T 16935.1-2008, 3.11.

3.26 Pollution degree: a numeral characterising the expected pollution of the micro-environment. Source: GB/T 16935.1-2008, 3.13.

3.27 Printed board: the general name for a completely processed printed circuit and printed wiring structure. Source: GB/T 16935.3-2005, 3.2. A note adds that printed boards include single-sided, double-sided and multi-layer boards with rigid, flexible or rigid-flexible base material.

3.28 Protection: any means by which the influence of the environment can be reduced. Source: GB/T 16935.3-2005, 3.4.

3.29 R.m.s. withstand voltage: the highest r.m.s. value of a voltage that does not cause breakdown of the insulation under specified conditions. Source: GB/T 16935.1-2008, 3.8.2.

3.30 Rated impulse voltage: the impulse withstand voltage value assigned by the manufacturer to the equipment or to a part of it, characterising the specified withstand capability of its insulation against transient overvoltages. Source: GB/T 16935.1-2008, 3.9.2.

3.31 Rated insulation voltage: the r.m.s. withstand voltage value assigned by the manufacturer to the equipment or to a part of it, characterising the specified long-term withstand capability of its insulation. A note adds that the rated insulation voltage is not necessarily equal to the rated voltage of the equipment, the rated voltage being related mainly to the operating performance of the equipment. Source: GB/T 16935.1-2008, 3.9.1.

3.32 Rated recurring peak voltage: the recurring peak withstand voltage value assigned by the manufacturer to the equipment or to a part of it, characterising the specified withstand capability of its insulation against recurring peak voltage. Source: GB/T 16935.1-2008, 3.9.3.

3.33 Rated temporary overvoltage: the temporary withstand overvoltage value assigned by the manufacturer to the equipment or to a part of it, characterising the specified short-term withstand capability of its insulation against AC voltage. Source: GB/T 16935.1-2008, 3.9.4.

3.34 Rated voltage: the voltage value assigned by the manufacturer to a component, an appliance or a piece of equipment, related to its operating characteristics, including operation, and to its performance. A note adds that equipment may have more than one rated voltage or may have a rated voltage range. Source: GB/T 16935.1-2008, 3.9.

3.35 Recurring peak voltage, U with subscript rp: the maximum peak voltage arising from the periodic displacement of the voltage waveform caused by distortion of an AC voltage or by an AC component superimposed on a DC voltage. A note adds that random overvoltages, for example those produced by occasional switching, are not regarded as recurring peak voltage. Source: GB/T 16935.1-2008, 3.6.

3.36 Recurring peak withstand voltage: the highest peak value of a recurring voltage that does not cause breakdown of the insulation under specified conditions. Source: GB/T 16935.1-2008, 3.8.3.

3.37 Reinforced insulation: insulation applied to hazardous live parts that provides a degree of protection against electric shock equivalent to double insulation. A note adds that reinforced insulation may consist of several layers, which cannot be tested singly as basic insulation or as supplementary insulation. Source: GB/T 16935.1-2008, 3.17.5.

3.38 Routine test: a test carried out on each appliance during and or after manufacture in order to judge whether it complies with certain criteria. Source: GB/T 16935.1-2008, 3.19.2.

3.39 Sampling test: a test carried out on a number of appliances taken at random from a batch. Source: GB/T 16935.1-2008, 3.19.3.

3.40 Solid insulation: solid insulating material inserted between two conductive parts. A note adds that where a printed board carries a coating, the solid insulation includes the printed board itself and the coating; in other cases the solid insulation means the potting material. Source: GB/T 16935.3-2005, 3.6.

3.41 Spacing: any combination of clearance, creepage distance and insulation distance through the insulation. Source: GB/T 16935.3-2005, 3.7.

3.42 Specified discharge magnitude: the apparent charge taken as the limiting value under this part. A note adds that the pulse of maximum amplitude is to be counted. Source: GB/T 16935.1-2008, 3.18.2.

3.43 Supplementary insulation: independent insulation applied in addition to the basic insulation used for fault protection. Source: GB/T 16935.1-2008, 3.17.3.

3.44 Temporary overvoltage: a power-frequency overvoltage of relatively long duration, compared with a transient overvoltage. Source: GB/T 16935.1-2008, 3.7.1.

3.45 Temporary withstand voltage: the highest r.m.s. value of a temporary overvoltage that does not cause breakdown of the insulation under specified conditions. Source: GB/T 16935.1-2008, 3.8.4.

3.46 Test: a technical operation carried out according to a specified procedure to determine one or more characteristic values of a given product, process or service. A note adds that a set of environmental and operating conditions and or requirements is applied to an entity so that its characteristics or properties are measured or classified. Source: GB/T 16935.1-2008, 3.19.

3.47 Transient overvoltage: an oscillatory or non-oscillatory overvoltage, usually highly damped, whose duration is only a few milliseconds or shorter.