Electrical Engineer

I work for a power generation company based in New Zealand (NZ).

We have four 3.3kV ash pump motors (Warman Frame 45 submersible motor) on our plant that utilises a special multicore, flexible EPR insulated and jacketed cable. The cable is terminated at the motor terminal box in an oil filled termination box. As the oil in the motor termination box is transformer grade oil, the cable is terminated using special oil resistant sleeves (possibly Hypalon or equivalent). An intermediate cable sealing chamber is mounted (top) adjacent to the motor termination box. The cable sealing chamber is filled with a greenish rubber like compound). The other end of the cable is terminated in an air insulated cable termination box (cable terminated using Raychem heat shrink tubing). Each motor cable length is approximately 6-7 meters.

We recently had a damage on one of the cables at the motor termination box. Two of the cable cores had damage due to corrosive effect of the transformer oil in the motor termination box. The core EPR insulation and insulating sleeve (Hypalon) were found damaged. The spare cable available on site has been used to replace the damaged cable.

Based on the cable inspection, the cable specs is believed to be 3C x 95mm2 tinned stranded copper conductors (fine strands), EPR insulated cores, textile fabric layer over individual core insulation, overall jacketed (not sure what material it is but feels like a rubber based material). The cable is not shielded/screened as there are no metallic screens visible over the individual core insulation or overall cable. There are also no visible semi conductive screens over the conductors or the core insulation. The cable is utilised on a 3.3kV system (phase to phase voltage). The cable insulation rating is not known but assumed to be 3.3kV or possibly higher. Some additional information on the cable is as follow:-

· The individual core diameter (over core insulation) - Approx 22-23mm

· The overall cable diameter - Approximately 55mm

The overall diameter of the multicore cable and diameter of the insulation cores has to be approximately the same size as existing cable due to restrictions on the cable entry to the sealing chamber / motor termination box. The space in the motor terminal box is also limited. The cable termination does not use any stress relief cone as the cable is unshielded.

The motor is located in an area where ash contamination in the atmosphere is common. The outer jacket is not only required to be flexible but also resistant to water, oil and ash.

The motor is delta connected.

We are keen to purchase approximately 50m of an equivalent cable that can be kept as spare on our site but have been having trouble finding similar unshielded / unscreened cable.

If anyone out there knows where I can source a similar cable (3.3kV non-shielded multicore cable utilising an EPR insulation), please let me know (with supplier contact particulars). I have written to and received a negative response from General Cable NZ and Olex NZ.

Note: The existing motor termination box dimensions are too small to accomodate the use of shielded cable (as this will need stress relief cone).

Additional feedback on the following would be appreciated:-

1. Do you know what type of core insulation (and sleeve) material that is suitable for use in transformer oil?

2. The motor termination box dimensions are too small to accomodate shielded cables. The motor terminal box is an integral part of the motor and hence cannot be replaced. Any suggestions as to how to utilise a shielded cable with the existing constraints?

Thank you.