Inductive Combined Transformer EJAF
Combined instrument transformers of type EJAF are used in high-voltage switchgear from 123 - 420 kV. They convert high voltages and currents into standardized, equivalent values for meters, measuring and protection devices.
The pressure-resistant head housing contains the voltage instrument transformer in the upper section and the current instrument transformer cores underneath. The iron core of the voltage transformer is at high voltage potential and the secondary windings are at earth potential. The current transformer cores are protected in a core shell made of aluminum, which is short-circuit proof and connected to the discharge tube. The secondary outgoing lines are routed through the air feed-through into the terminal box at the base of the insulator.
The distribution of the electric field strength along the insulator is optimized by a special control electrode arrangement inside the silicone composite insulator.
The housing parts are made of corrosion-resistant cast aluminum. All pressurized housing parts are type and unit tested in accordance with the applicable pressure vessel regulations.
The density of the synthetic air is monitored in a temperature-compensated manner by means of a density monitor with alarm contacts. Thanks to a special design, the function of the density monitor can be checked without dismantling.
At the highest point of the head housing, a corrosion-resistant metal rupture disk protected by a sheet metal cover ensures safe pressure relief in the event of a fault.
Features
The German transmission system operators have announced that they want to use gas-insulated measuring transducers with a global warming potential of <1 for outdoor installations in the future. Only non-fluorinated gases can meet these requirements. Pfiffner has opted to develop high-voltage measuring transducers with synthetic air (80% N2 and 20% O2), known as ecosAIR. The basic concept is the same as for SF6. The similar design of the components to the proven SF6 instrument transformers guarantees that Pfiffner's decades of experience will be transferred to future generations.
