Introduction

The present version of this standard (1995) has raised issues which the EMCTLA working group C believe require clarification or revision. These vary from aspects of application of the surge to safety issues which have been brought to the attention of the working group. The purpose of this TGN is to provide guidance to members with the aim of achieving a more consistent application of the standard.

Note. The IEC working group (SC77 WG11 now SC77B MT12) has a draft proposal of changes to the standard (IEC61000-4-5:200X) which goes part way towards addressing some of the issues discussed below. Where relevant these are reflected in the recommendations. For instance, the working group considered the issue of decreasing the number of pulses applied but concluded that there was no technical justification for doing so.

An earlier issue of TGN 39 went some way towards clarifying the application issue but there are still found to be differences between testers in both method and procedure. This issue of the TGN also deals with other, wider aspects of the standard of concern to EMCTLA members.

The basic standard should deal with the default procedure and test method. There will always be exceptions and special cases and it may not be possible to encompass them all within the standard whilst still preserving clarity. Thus Product Committees may require specific test regimes involving differing phase angles, maximum test levels, timing, and so on. For other cases the product test plan can define the test set up and any special parameters of the testing carried out. The important point to keep in mind is the need to achieve repeatability wherever possible.

Application of Surge in the Laboratory

(section 8.2 of the Standard)

Basic Method

This reflects the EMCTLA interpretation of the standard. It does not conflict with anything written in the standard. It also reflects the most common interpretation of the standard.

Test Levels: All lower severity levels shall be tested up to the maximum specified by the product committee or test plan. The levels are 0.5kV, 1kV, 2kV, 4kV and x (special).

Note. The standard requires the test procedure to consider the non-linear I-V characteristics of the EUT and states that for testing the secondary protection, the output voltage shall be increased up to the let-through level of the primary protection. For products specified to 0.5kV maximum a lower level of 250V may be used to test protection let-through. However, for compliance testing, see the first bullet point under "Additional Application Considerations " of this TGN.

Phase Angle: For AC power ports (input or output) the surges shall be applied synchronized to the AC voltage phase at 0° or 180°, 90° and 270°.

Note 1: Product committees may select different phase angles as appropriate to the product.

Note 2: While testing at both 0° and 180° is allowed, testing at only one zero crossing point is considered to be required.

Note 3: For internally powered equipment and sub-systems without the option of a.c or d.c. external power input this test does not apply.

Number of Pulses/Polarity: The product shall be tested with at least 5 positive and 5 negative surge pulses at each test point, at each of the chosen phase angles and required levels.

Time Between Pulses: Normal minimum period is 1 minute. A shorter period may be agreed between test laboratory and manufacturer as a deviation from the standard method but it is recommended that this be not less than 20secs to avoid undue component heat stress. If the unit then fails this test it may be due to additional, unnecessary stress within the surge protection devices or other components. The manufacturer should be made aware that a re-test at 1 minute intervals on another sample may then be advised, at a further cost to be agreed as necessary.

It is appreciated that the concerns over the test time and possible component stress are not fully addressed in this TGN. These are matters which need consideration at international level and may be the subject of a request for new work initiated by the UK through the IEC SC77.

Additional Application Considerations

· When applying tests for CE marking the maximum level of surge to be applied should be that given in the product specific or generic standard. Applying additional investigative tests or examining immunity up to the primary protection level should be part of the manufacturer’s design proving work.

· When applying surges in line-to-line mode to 3-phase AC ports, testing is restricted to the combination, ³C₂ (e.g. L1-L2, L1-L3, L2-L3, but NOT L1-L2 and L2-L1, etc.). This is justified since both polarities are tested on the lines under test.

· Test operators should be aware of a possible safety hazard when applying surges to shielded cables in accordance with clause 7.5 (figures 13 and 14 of the standard). In the event of a faulty shield connection a dangerous charge may build up on the EUT (shown as EUT1 in the figures). To ensure the safety of the operator it may be necessary to allow discharge of the cabinet between pulses.

Note. This can be achieved by the connection of 2x470kW HIGH VOLTAGE rated resistors connected to the chassis of EUT1 (similar to the ESD coupling plane discharge network). Since the surge generator is not designed for continuous operation and considering the maximum rate of application to be 1 pulse per 20 secs the resistors can safely be rated at 0.5W each. It is unlikely that the high value of resistance introduced between chassis and ground will have a detrimental effect upon the waveform of the generator.

Modified Figure 13 (figure 14 similarly modified)

· The value R* in the test generator output is uncertain from the standard (0W, 10W or 40W). Annex B.1 definitions appear to conflict with the wording in clause 7.5. It is recommended that until the IEC working group is consulted that R* be 0W (i.e no additional resistor) leaving the output impedance of the generator as 2W (as given in clause 7.5).

· Clause 7.5 (shielded lines) does not clarify where on the shield the surge is to be applied. Where a hand held probe exists (e.g. as supplied by Haefely) this can be applied to the metalwork of the cabinet, but this may limit the repeatibility. Suggested guidance is to simulate real world conditions. Hence application at the usual earthing point of the chassis where provided or to a metallic connector shield may be the best way of achieving realistic conditions.

· Figures 6 and 7 do not differentiate connections or feedthrough of the mains. Test operators should ensure that the decoupling network case is connected to PE as is shown in figures 8 and 9.

The advice given above is based upon engineering judgement, comments from sources within the EMCTLA and from IEC SC77B working group 11 draft working document.