WCA January 2018

As noted, the cone calorimeter data on the final selection indicates that the product will perform well on a wide variety of cable flame tests currently covered by commercially available systems with brominated fire retardant packages. The selection of the resin system and filler system has proved to be critical in balancing the properties of electrical, fire, mechanical and rheology required for a compound to satisfy requirements. 2.2 Compounding and industrial extrusion trials Compounding trials were successfully conducted on an industrial scale Buss kneader, producing the final formulation for full-scale industrial cable trials. A number of insulated conductor sizes have been produced on industrial cable lines to assess and confirm acceptable processability of the product and to produce a meaningful range of conductor sizes from 14 AWG to 350 kcmil. While low-compression ‘straight’ screws are recommended for heavily filled LSZH systems, industrial scale production indicates the chosen compound also has the flexibility for production on some typical PVC/PE screws with higher (3:1) compression ratios. Shelf life is a particular concern for moisture curable compounds in an industrial setting. Work is ongoing to assess shelf life performance, but results indicate performance well in excess of six months. 2.3 Final performance The final compound has been approved for types SIS, XHH, XHHW, XHHW-2, RHH, RHW, RHW-2 rated 600V in all colours and suitable for the optional -40ºC and Oil Res I and II requirements along with Gasoline and Oil Resistance II. Typical properties from cable core samples are shown in Table 3 . 2.4 HF approval The final compound has been tested at UL and certified as being halogen free, and certified cables are now eligible to bear the optional “HF” suffix in the cable surface print following the product name. The testing for the optional marking is based on the requirements of IEC 62831 and UL2885 standards covering determination of halogen acid gas, pH, conductivity and chemical assessment of halogens. ❍ ❍ Table 2 : Summary of cone calorimeter for the final zero halogen formulation against commercial brominated XHHW-2 systems. 40kW/m 2 heat flux 3mm samples

Long term electrical performance and filler blend

Time in weeks

❍ ❍ Figure 3 : Wet electrical performance and fire retardant filler type

Brominated XHHW-2 FT2 Brominated XHHW-2 VWI Experimental zero Halogen

Rate of heat release (Kw/m2)

Time, seconds

As noted in the introduction, while the minimum flame test requirement for XHHW-2 rated insulations is the horizontal FT2 test, it is understood that higher performance is highly desirable both in single conductors and in multi-conductor products. In screening candidate formulations a cone calorimeter and benchmarked 3mm press moulded plaques of the trial formulations were used against commercially available brominated FR insulation systems: one with FT2 performance and one with VW-1 performance. The cone calorimeter data presented in Figure 4 is for the final selected zero halogen system. This demonstrates a high level of performance over what would be typical for a brominated FT2 system and almost matching the brominated VW-1 system in peak heat release rate and time to ignition. The data is also summarised in Table 2 . The final formulation has met VW-1 on larger circuit sizes. In total, 14 series of multiple mixes were produced, being progressively improved during the development. From this work two formulas were selected for long-term wet electrical performance at 600V. An optimised product was then selected to take forward to full compounding scale up and industrial cable production trials. The product was subsequently commercialised. ❍ ❍ Figure 4 : Cone calorimeter data comparing the final zero halogen insulation system against commercially available brominated insulation systems. 40kW/m 2 heat flux 3mm thick samples

PHRR (Kw/m 2 )

T ig (Seconds)

Sample

Brominated XHHW-2 FT2

1,104

69

Brominated XHHW-2 VWI

385

84

Experimental zero halogen

449

78

PHHR – Peak Heat Release Rate T ig – Time to ignition

62

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Wire & Cable ASIA – January/February 2018