Voltage Transformer

Voltage Transformers are induction type and are contained in their own   SF6 compartment, separated from the other parts of the installation.

The active portion consists of a rectangular core, upon which are placed the secondary windings and the high voltage winding.

Provision is made for up to two secondary windings for measurement and an additional open delta winding for earth fault detection.

A synthetic film separates the different wraps of the windings. The Transformers can be installed Any where on the substation.


Voltage Transformer Module
For rated voltage up to 145 kV inductive Transformer with cast resin coil For rated voltage of
245 kV inductive VT with SF6 gas as main insulation. For 300 kV and above, Capacitive Voltage Transformers are preferred Inductive type Voltage Transformer.
The single-pole inductive type Voltage Transformers (Fig. 1) can be mounted either vertical or horizontal. They are connected to the Switchgear with the standardized connecting flange via a barrier insulator.

The primary winding is insulated with SF6 gas and connected to the HV.  by a flexible connection. The primary winding (2) surround the core on which the secondary windings (1) are also wound.
The connection between the secondary winding and the terminals in the external terminal box is made through a gas tight multiple bushing.
The Transformers are equipped with two metering windings and one tertiary winding for earth-fault protection.


Capacitor Voltage Transformer
In Switchgear for voltage above 300 kV, Capacitor Voltage Transformers are also employed. Two systems are available:
- Transformers with high capacitance connected to an intermediate Transformer. The oil-insulated capacitor of conventional
   design is accommodated in an enclosure filled with SF6 gas. The high-voltage connection to the GIS is made through
   a barrier insulator. The low-voltage choke and the intermediate Voltage Transformer are housed separately in a cabinet
   on the earth potential side.

- Transformers with a low capacitance accommodated in the current Transformer or in a separate housing, connected to an

1 - Secondary winding

2 - Primary winding

3 - Terminal box

4 - Support insulator

5 - Filling valve

6 - Safety diaphragm

7 - Density Switch


(Fig. 1) Voltage Transformer (Make ABB)