ESB International (ESBI) are undertaking a series of four conductor upgrades in order to cater for increased renewable energy loads. The conductor upgrades will take place on the Cullenagh-Knockraha 220kV line, Killonan-Knockraha 220kV line, Limerick-Monateen 110kV line and Knockraha-Great Island 220kV line.
Contractors for the project are TLI, Gaeltec and ESB Networks.
Procedure for Installation of HTLS Gap Type Conductor
The HTLS Conductor has a higher maximum operating temperature, which results in a corresponding increase in current carrying capacity compared to the equivalent ACSR Conductor of the same cross-section.
The construction of HTLS conductors is such that there is a gap of approximately 1.5mm between the steel core and the inner layer of the aluminium strands. This gap is filled with grease and as a result, the aluminium layers can move with respect to the steel core during sagging of the conductor.
It is critical that this gap is maintained during Pulling Out, Sagging and Terminating of the HTLS conductor to maintain the performance of these conductors.
Albeit the maximum operating temperature of HTLS conductors is much higher than that of the equivalent existing ACSR conductors of similar cross sectional area, they have reduced sags and consequently, the existing structures on each line can be used.
Critical Design Criteria that must be adhered to:
– A Maximum of 3 Drums can be used in any one pulling out process
– The Stringing out tension must not exceed 60% of the Initial Erection Tension (IET)
– The Steel Core only is used in sagging the conductor.
– At no stage in the process must the tension on the Aluminium Strands exceed 60% IET.
– The conductor needs to be broken every 5-6 spans (Semi Strain and Mid Span Joints)
A Number of steps must be taken in order to install the conductor correctly.
– The straight in question is to be earthed, the suspension clamps removed and the conductor placed into stringing wheels
– All crossings LV/MV/HV and roads must be adequately guarded
– Conductor drums are loaded into drum carriers and connected to Puller/Tensioner machinery.
– A steel stopper is compressed onto the steel core of the conductor to prevent the steel from slipping inside the Aluminium of the conductor.
– The HTLS conductor is then connected onto the existing ACSR conductor using stringing stockings and pulled out through the section in question.
– It is very important that there is no more than one Semi Strain position in any pulling section due to the difficulty of landing the stringing stocking in position.
– Once the conductor is strung out the “Standard Compression” joints (ACSR Construction) are made off and the conductor is back-hung on the allocated towers/polesets.
– The “Gap Compression” procedure is then initiated.
– The Aluminium outer layers of the conductor are unravelled up to 8m out from the structure in question, (Semi Strain or Angle Tower)
– The steel core Comealongs / guy grips are placed on the steel core and using chain hoists the conductor is sagged as per ESBI Sag Tables.
– Depending on the size of the straight and the spans in the straight up to six guy grips may be required per phase.
– Once the conductor is sagged the straight is left to settle for 12hrs.
– Following the 12hr settling period the conductor sag is checked once more and when correct the steel Deadend is compressed onto the steel core.
– Immediately after this the aluminium Deadend is compressed.
– The Deadend is then connected directly onto the Insulator and hardware.
– Jumper arrangements are created using gap type conductor at Angle Masts.
– All Stringing wheels are removed and the conductor is clipped into the Suspension clamps at all suspension locations ensuring the Insulators are in tension balance.
– Sags are then checked by the Design team using GPS and Total Station.
– These sags are input into the design programme and Sags verified.
– Line Hardware is checked by Line Inspector.
– Straight is signed off by design team and Line Inspector,