High Voltage Underhug BusBar System

Phase to Phase insulated short Circuit testing Project

During 2008 and 2009 Electropar has been working closely with Transmission Network Service Provider (TNSP) Transpower NZ Ltd, on a ground breaking substation project. Together, the two company’s have embarked upon a programme to mathematically validate and then short circuit test a full size bay width of phase to phase insulated 220kV 200mm OD (4000amp) busbar and interplant connections at 25kA, 31.5kA and 40kA/3s fault levels.

On the strength of a convincing commercial argument,Transpower and Electropar desired to prove that phase to phase insulation in transmission substations is not just technically possible; it is the future of design for delivering the best value Transmission Assets. The commercial argument was based on the reduction in quantity of foundations / civil works in addition to shrinking the footprint of the air insulated switchyard. Financial analysis indicated that the cost saving in civil works, electrical equipment and real estate was substantial enough to warrant the investment in a development programme.

Verify Critical Load Points
Before practical test could be considered though, the first milestone was to have the fundamental design elements examined and ratified by an independent and suitably qualified consultant. The analysis centred around the mechanical withstand of the system and was completed by Beca Carter (Auckland) in the third quarter of 2008. The Beca work was then peer reviewed by Maunsell prior to Christmas 2008. Subsequently all parties agreed that the mathematical calculations indicated the system would withstand the short circuit forces generated under Transpower’s worst case fault scenario. However, to provide an additional level of confidence a finite element analysis (FEA) was completed to further verify critical load points within the system.

Installed In A Real Substation
As a result of gaining agreement that technically the High Voltage Underhung Busbar System was feasible, Stage 2 of the project has been completed; ‘Practical short circuit testing of the busbar system’. The testing took place at Powertech Lab’s in Vancouver, Canada (http://www.powertechlabs.com) in June 2009 after a global search for laboratory’s with capability to complete this challenging scope. At Powertech Labs, Electropar built a full bay of 220kV (see photo) utilising Transpower’s standard cage type concrete foundations, steel support structures, post insulators and Electropar’s rigid bus / flexible conductor fittings so that the performance of all components of the system as would be installed in a real substation can be validated.

Under Varying Fault Conditions
The Electropar / Transpower project team were responsible for the measurement of the loads and displacements of the system under varying fault conditions, and used a combination of high speed camera’s, still camera’s video and fibre optic sensors for data acquisition. In all, 85 short circuit tests were completed over a 5 day test period between 25kA/0.3s and 63kA/1sec, including long duration tests at 40kA/3s. The system performed in accordance with expectation and as a result the High Voltage Underhung Busbar System is being seriously considered for an upcoming greenfields 220kV site.

Undergoing Detailed Analysis
Some incredible footage of HV systems under incredible short circuit loads has been collected as a result of the testing. This footage, and the strain data collected (1 Terrabyte!) is currently undergoing detailed analysis. However, in addition to verifying the performance of the High Voltage Underhung Busbar System, the testing has also verified the short circuit performance of other Asset critical components such as bus support posts, jumper/ dropper connections and rigid bus clamps and fittings. The method of calculation for short circuit performance of these asset critical components is already the subject of a CIGRE working group as calculation methodologies have historically differed between and within designers and asset owners.

Summary
The successful testing underscores the performance of Electropar’s substation systems and at the same time introduces a new concept in HV substation design and operation. The new concept has been successfully tested, and has the potential to significantly lower capital cost of building substation assets. It also offers a substantial reduction in maintenance costs and improves access within the switchyard. These outcomes are achieved with a minimal loss of operational flexibility and have the potential to result a step- change for substation primary construction in NZ and Australia.