Changing industry standards: friend or foe?

Transcription

1 Changing industry standards: friend or foe? In 1998, Google was founded, the first Apple imac was introduced and the legendary Windows 98 was released by Microsoft. In a less glamorous but equally important corner of industry, a new commission was being formed to revise the complex IEC industry standard, which governed the safety and performance of electrical switchgear assemblies. Although Windows 98 has long been consigned to history, the new industry standard BS EN will only become mandatory on November 1, Here, Pat McLaughlin Boulting Technology s Operations Director explains how original equipment manufacturers, panel builders, electrical engineers, consulting engineers and contractors can make sure they aren t caught off guard by the new BS EN standard. The good news for electrical engineers, contractors and consulting engineers looking to purchase a switchboard is that all they need to do is make sure their suppliers are compliant with the new standard, especially after November 1, Unfortunately, original equipment manufacturers and panel builders don t get off as easily. The BS EN brings a set of significant changes when it comes to the design and testing of switchboards and switchgear assemblies.

2 Why a new standard? In a market where the demand to optimise and reduce costs blends heavily with higher needs for assembly flexibility, the introduction of a new set of standards guarantee the performance of Low Voltage Switchgear Assemblies and previous ambiguities have been addressed i.e. diversity, rating of circuits and substitution In light of this, in 2009, the new BS EN standard was introduced by the International Electrotechnical Commission (IEC). The aim of the new standard was to harmonise technical specifications and clearly define the requirements for a good quality and safe assembly. of devices. The new BS EN consists of six parts, but Switchgear and Control Gear assemblies are multifaceted and have an endless number of component combinations. Testing every conceivable variant was not only time consuming only parts one and two are applicable to Switchgear and Controlgear Assemblies, where the rated voltage does not exceed 1000 V AC or 1500 V DC. and costly, but impractical. The intricate character of assemblies also meant that many did not fit into the previous two testing categories: Type Tested Assembly (TTA) and Partially Tested Assembly (PTTA). For example, panels which were too small to be covered by TTA and PTTA fell outside the standard. Finally, in the case of a PTTA, ensuring the safety and suitability of a design was often dependent strictly on the expertise and integrity of the manufacturer.

3 Design verification The major change introduced by the new BS EN standard refers to testing. It states that the capabilities of each assembly will be verified in two stages: design verification and routine verification. This means the new standard completely discards the type-tested (TTA) and partially type-tested assemblies (PTTA) categories in favour of design verification. The new standard however enable manufacturers to perform a short circuit withstand test on the smallest Busbar system that will be used at the appropriate Fault Level, the Busbars may then be increased in size or thickness increasing its current rating but making it mechanically stronger. The use of the standards designated design check list table 13 enables the uprated system to be compared with the reference design and ensure compliance with the standard. So, why is design verification a better approach to testing assemblies? The answer is simple: flexibility and alternative testing routes. Although BS EN still regards type testing as the preferred option for verifying designs, it also introduces a series of alternative routes to design verification. Temperature Rise Testing. The new standard now contains more guidance regarding the requirements surrounding temperature rise tests compared with the old standard. The options are; Testing, Derivation of The options include using an already verified design for reference, calculation and interpolation. The BS EN standard specifies that specific margins must be added to the design, when using anything other than type testing. As mentioned earlier, one of the benefits of the new design verification procedure is its flexibility, under the old BS EN specification customers would demand (often unnecessary) a Type Test certificate for each assembly particularly Incoming Air Circuit Breakers which was very the rated values of similar equipment and Calculation. There are also greater restrictions, for example heaters can now only be used to simulate the watt losses from devices up to a certain level. The use of heater resistors during tests is still allowed but only to simulate the effect of adjacent circuits on those under test. Using actual current when testing means that all the magnetic effects are taken into account, not just the heat produced due to conductor resistance which was traditionally considered. expensive and time consuming.

4 Testing with actual current is not normally destructive and can therefore be carried out on any suitable section of switchgear. Verification regardless of which method is to be used is time consuming due to effort required to connect all the circuits to be included in the test, balance the current and insert the thermocouples. Current is applied until conditions stabilise, usually around eight hours, and, in the final hours, temperatures are monitored. Critical areas for temperature measurement are covers, operating handles, insulators, cable terminals, device and/ or internal air temperatures. It also means that every time a device change is made the Switchboard is changed and a retest may be required. This however can be avoided by testing worse case scenarios and then ensuring the change has a beneficial effect on the temperature rise such as: In order to optimise testing time, the standard allows derivation of the rating of similar variants without testing, assuming the ratings of critical variants have been established by test. For example, if the acceptability of a 15KW DOL Starter circuit is verified by test, subject to rules defined in the standard, the rating of a circuit comprising of a 7.5 KW DOL starter using the same size compartment with components of lower watt losses can be derived. Normally, a special test board will be used (due to the time involved) and the results are then compared with future assemblies to ensure compliance with the standard. derating a busbar or device already tested at a higher value of current using a larger conductor to that already tested increasing the spacing of conductors increasing the size of a device enclosure When a device is enclosed in a switchboard or Motor Control Centre, some factor of de-rating usually has to be applied. By carrying out tests as described in the standard, all the other factors are taken into account at the same time and calculations are then not required.

5 Although some might interpret the new testing alternatives as even more unwanted hassle, in reality it allows users and specifiers to pertinently define the requirements of each application. In addition, the assembly manufacturer is meant to oversee the completion of the assembly and routine testing. Annex D of the BS EN standard provides a list of 13 categories or verifications required, what testing method can be used and what comparisons can be made Dividing Responsibility The second major change implemented by the new industry standard refers to the responsibilities of each party involved in the design, test and implementation of low voltage switchboard assemblies. Unlike BS EN For Innovators like Boulting Technology, the new BS EN brings more freedom and flexibility when designing switchboard assemblies. For example, Boulting Technology has worked alongside ABB to test its brand new range of low voltage switchboards, which are now available in 25kA, 50kA, 80kA and 100kA up to 6300Amp for 1 Second , which stated the original equipment manufacturer (OEM) or the system manufacturer was solely responsible throughout the testing programme, the new standard divides the responsibilities between the OEM and the assembly manufacturer, or panel builder. The new standard recognises that several parties may be involved between concept and delivery of a switchboard assembly. The OEM The Boulting Power Centre, providing innovative Power management. is responsible for the basic design verification.

6 As the saying goes, with great power comes great responsibility. The BS EN standard also means that low voltage switchboard manufacturers and assembly manufacturers need to ensure they are compliant with more severe standards. On the other hand, electrical engineers and contractors can breathe easy, knowing that all they have to do in response to the new industry standard is make sure their suppliers are BS EN compliant.. Although change is never much fun, it s what technology and industry are all about. If this wasn t the case, we would all still be using Windows 98 or the indestructible Nokia 5110.