Transmission projects include identifying and preventing wind induced conductor motion damage. Bundled conductors consisting of two to six subconductors are adopted for transmission lines with rated voltages 230 kV and above. In multiple bundle applications, engineers often specify spacer dampers for two-conductor through six-conductor bundles. Rigid spacers are most commonly engineered for two-conductor bundle applications.
Rigid spacers keep the subconductors within a span and in jumper loops at designed spacing to avoid damage caused by clashing, twisting or entwining. Where motion control is a concern, rigid spacers are used in conjunction with Stockbridge dampers to give sufficient damping and spacing results.
Rigid spacers must maintain the subconductor spacing in all operational conditions including wind, ice and short circuit. During short circuit, the spacer must withstand high dynamic loads and limit the damage of subconductors-without being permanently deformed.
There are many designs, but common rigid spacer designs have the following components: frame, breakaway hardware and elastomeric bushing inserts. Inserts can be ethylene propylene diene monomer (EPDM) rubber or silicon molded materials. Silicon is applicable for operational applications up to 482F.
The design of the spacer is critical with respect to the dimensions of the inserts and the hole location for the hardware. The relationship will change based on the conductor type. The spacer must pass a multitude of test sequences to assure reliability of performance:
• Clamp slip - longitudinal/torsional,
• Short circuit - compression/tensile, and
• Fatigue, corona, radio interference voltage (RIV) and electrical resistance.
Another key factor is analysis and placement within the spans. The number of total spacers required and the placements of spacers within the span are dependent of many variables-such as the topography and ice loading. BURNDY, a company with more than 60 years experience with vibration theory and line analysis, provides the customer with spacers and the location for proper installation. Most spacer installations are installed with line cars; the installer uses installation gauges, which provide the linemen with precise subconductor spacing and location. This information is provided to the customer in print or electronically.