Friday, June 29, 2012
132kV Mineral Oil Circuit Breakers.
Source: K. Mitchell (pictured).
This 3-phase bank of 132 kV low oil volume circuit breakers is located at EnergyAustraia's 132kV/11kV inner suburban zone substation at Burwood. These days, SF6 switchgear is more commonly used.
Transformer Bushings
bushing. The porcelain covering added to the external half of the bushing consists of a stack of discs (referred to as 'shedding'). It is used to increase the creepage distance and break up the flashover path.
33kV/11kV Distribution Transformer
The transformer core and windings are contained in an oil filled tank. To be cooled, the oil is pumped to a separate radiator which, in this installation, is larger than the transformer tank itself. As a general rule, as the rating of transformers - and other electrical plant - increases, the cooling problem becomes more acute. The conservator is a reservoir which allows for the expansion of the oil during operation.
Source: EnergyAustralia.
A 330kV Overhead Transmission Line.
Overhead lines are suspended from strings of insulators which are in turn supported by, in this case, steel towers. The surrounding air acts as an insulating medium (at atmospheric pressure, air breaks down at 3kV/mm). Each phase in this line consists of a bundle of two conductors. The conductors are of type ACSR (see below). Bundles of conductors are used instead of a single conductor to reduce the effects of corona, the partial ionisation of the air close to the conductor surface. Bundling also reduces the inductive reactance of the line. For protection against lightning, ground wires (also called shield wires) are fitted above the phase conductors and are electrically connected to the towers and via the towers to ground.
Source: Transgrid.
A Typical ACSR Conductor
An ACSR (aluminium conductor steel reinforced) conductor consist of strands of aluminium and steel. The inner steel strands provide strength. The current is carried by the outer aluminium strands. Aluminium has a higher resitivity than copper but is lighter and more abundant.
Dual Circuit 500kV Transmission Line.
In recent years, Transgrid has been upgrading a number of its 330 kV lines to 500 kV. This is a dual circuit lines (two sets of three phase). Each phase is a bundle of four conductors.
Source: Transgrid.
Spacer for a Four Conductor Bundle
Parallel conductors carrying current in the same direction attract each other. Spacers are used to keep them apart.
Source: Electrical Power System Essentials, P. Schavemaker and L. van der Sluis.
Insulator String
Glass or porcelain insulator strings are used to suspend overhead lines. They form a set of series capacitors and have stray capacitance with the tower which causes variation in the voltage distribution. Metal tubes are added at the HV end of the string to improve the voltage distribution.
Some Single Phase Cables.
(a) 110kV cross-linked polyethylene (XLPE) cable with laminated sheath. (b) 400kV XLPE cable with corrugated aluminium sheath. (c) 400kV low pressure oil filled ILPOF) cable with corrugated aluminium sheath.
Source: Transmission and Distribution Electrical Engineering, C. Bayliss and B. Hardy.
Three Phase Oil Filled Cable.
Source: (Photo) Transmission and Distribution Electrical Engineering, C. Bayliss and B. Hardy. (Diagram) Electrical Power Systems, B. M. Weedy and B. J. Cory.
Electric Fields in Three Phase Cables.
(a) A belted cable with three phase conductors in a single sheath. (b) A Höchstädter type cable where each conductor has its own sheath. The diagram shows a snapshot of the equipotential lines in the insulating material inside the sheath, with the top phase at peak positive voltage and the other phases at half the negative peak. In the case of the belted cable, the electric field puts a higher demand on the insulation material. Belted cables are used only for the lower voltage ranges.
Source: Electrical Power System Essentials, P. Schavemaker and L. van der Sluis.
Single Phase SF6 Cable.
This is a 220kV cable which uses Sulphur Hexafluoride gas as an insulator.
Source: Transmission and Distribution Electrical Engineering, C. Bayliss and B. Hardy.
Thursday, June 28, 2012
Distribution Transformer Core and winding Photos
Typical 630kVA transformer core
Core and winding of an 800 kVA, 11 000/440 V
distribution transformer
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