12.- COMPROBACIONES GEOMÉTRICAS Y DE RESISTENCIA

High voltage power cable design must meet the requirements of the following Standards:  SS-1-1.4 Substation Design Requirements

 SS-1-4.4 Substation Cables and Cabling

 AS2067 Substations and High Voltage Installations Exceeding 1 kV AC  Ergon Energy Underground Manual

When designing a HV power cable installation the Designer must also consider the following:

Brownfield Site Considerations

When an extension is required to an existing switchboard, it is recommended that baseline

electrical testing in the form of partial discharge testing and insulation resistance is undertaken prior to any construction work.

Switchboard busbar extensions generally involve the design, manufacture and installation of a suitable “joggle” (adaptor) panel to match the existing busbar height and position to the new circuit breaker cubicle, and as such it is recommended that this design and supply is undertaken by a switchboard manufacturer.

The switchgear building must be structurally assessed for the new installation, including the

footprint and weight of the new cubicles, additional floor and/or wall penetrations for HV and control cabling, and installation of arc venting as required.

Protection and control panels for new circuit breaker extensions to existing switchboards must be installed remote from the switchboard and be in accordance with the Ergon Energy Zone substation standards.

 The Thermal Resistivity (TR) of the native soil along the cable route must be tested and the thermal performance of the bedding and backfill materials must be known. Testing TR of native soil will determine whether it is suitable to be used as backfill material or imported backfill will be needed. Soil TR testing can be undertaken by Ergon Energy Ratings and Capability Group.  Current ratings of HV power cables must be determined by using software (eg Cymcap), which

is the preferred method, or from cable manufacturers data and hand calculations in accordance with IEC60287. A list of the software parameters for the Cymcap software to meet the Ergon Energy Cable Design Standards is included in ANNEX H – CYMCAP SOFTWARE

PARAMETER TABLE.

 Cables must be designed to meet the required continuous current and emergency current ratings. HV power cables must be rated to supply the substation Transformer Emergency Cyclic Capacity (Long Term Emergency Rating) of the transformer, which is normally 125% of rated transformer current, and Short Term Emergency Capacity (Two Hour Emergency Capacity), which is normally 150% of rated transformer current.

 Cables connected to capacitor banks must have a rating of at least 143% of the capacitor bank continuous current to allow for harmonic currents and 1.1 pu overvoltage.

 Cables connected to station services transformers that are piggy-backed off Distribution

Feeders must have a rating for the continuous rating of the station services transformer and the short circuit capability rating of the Distribution Feeder.

 All cable screens must be brought out under the termination and bonded to earth in accordance with the Ergon Energy Standard SS-1-4.4 Substation Cables and Cabling. The Designer must ensure that mitigation measures are in place, including the design and installation of voltage limiters, to ensure the voltage on single bonded cable screens does not exceed 25V. For single point bonded cables the earth bond must be at the transformer end for substation transformer cables, and at the distribution feeder pole for distribution exit cables. The cable screen at the unbonded end must be suitably insulated and protected against inadvertent contact during fault conditions.

 The substation designer must liase with the civil design group to ensure the cable route is coordinated with all underground services, and modifications to existing footings, and/or additional building or wall penetrations are assessed and certified.

 The Designer must clearly indicate the cable location on a cable route drawing. This drawing must include all trench section details (including conduit sizes, dimensions, backfill type, backfill compaction, protective covers), design rating data, and cable earth bonding detail.

 The Designer must ensure minimum cable depths for a substation cable trench design are in accordance with Ergon Energy Standard SS-1-4.4 Cables and Cabling which specifies: - 800mm for 11kV & 22kV rated cables

- 900mm for 33kV and above rated cables

Additional design requirements including backfill, conduit separations, separation to other services, and protective covers can be found in the Ergon Energy Underground Construction Manual.

 The cable trench design and associated cable configuration for single core cables must minimise the EMF.

 HV power cables must be supported and clamped as the cables rise into the control building or onto the transformer, and on the floor or support structures in cable basements or ducts. Cable clamps must be two piece clamp style and manufactured from non-ferrous material. Clamps must be installed at no more than 1.5m intervals to prevent excessive movement under fault conditions.

 The division of responsibility between SDTaP Substation Design and Distribution Operations design is as follows:

- Substation Design will design all feeder cable exit trenches and conduits as far as the substation fence, and must take into account the required feeder minimum cable ratings. - Distribution Operations Design will design the cable trenches and conduits beyond the

substation fence and is responsible for the supply of all feeder cables and terminations to the substation switchboard.