Siemens Gas Turbine cable gland issue

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Thread Starter

Asok Kumar Hait

We are facing a peculiar issue with Siemens supplied gas turbines. Siemens historically in all their gas turbine uses a very thin sheath PTFE cables for their core engine thermocouples and other instruments in the turbine enclosure (http://www.habia.com/Materials/LowSmoke/PTFE-LS,FR.aspx). The cable is suitable for very high temperature i.e 260°C. Problem is the cable sheath is very thin, the cores are non-filled under the inner sheath and outer sheath non-rounded. The cables are connected to Ex e or Ex nR junction boxes and instruments in Zone 2 hazardous area. Problem is there are no suitable cable gland for such non-filled, non-round cables. Traditionally Siemens is using HAWKE 501/453/RAC cable glands. The cable gland is double compression type, Ex d e nR certified. But since the cable gland is suitable for round cable and in this application the cable is non-round, Siemens uses a rubber sleeve on the top of the cable outer sheath and install the gland on the top of the sleeve.

As far as I know the use of additional component like rubber sleeve for round/non-round cable is not technically allowed in any of the IEC standards. Siemens had submitted this arrangement to Baseefa and obtained an IP66 certificate from Baseefa. Though this fulfills only one requirement for cable gland (min. IP54 as per IEC-60079-0) there are many other requirements for cable glands which have not been tested with this rubber sleeve modification. These requirements are:

1. Explosion holding capability for Exd instruments and JBs;

2. Clamp test for minimum tensile strength requirement as per IEC

3. Ex nR certification for the whole assembly required for ExnR instruments & JBs

4. Oil resistance property of the rubber sleeve to prove that it won’t be damaged coming in contact with oils and hydrocarbons;

5.UV resistance property of the rubber sleeve etc.

Siemens is unable to furnish any such test reports. Only clarification they have given is that this arrangement they are using for many many years.

Personally I think this is not correct. Especially this is very dangerous for Exd and ExnR equipment. Traditionally if Siemens has used this non-standard technique for all their packages around the world then a disaster can happen at any time for applications in hazardous area.

My question is if anybody of our forum members has faced similar situation before? If yes, did you accept the solution used by Siemens or there is an alternative solution? Anybody using Siemens turbine in hazardous area can look into their machines and I am sure you can find this non-standard arrangement used by Siemens. I would like to know from the Ex-experts in our forum if this is technically acceptable.
 
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