Independent current and voltage transformers have a long and proven history for transforming high voltages and currents to instrumentation levels for protective relaying and revenue metering.The numbers and types of HVITs used in substations depend on the substation layout configuration, substation requirement and site constraints, eg, limited space.
Besides the standard solution of independent apparatuses, there are also the so-called combined Instrument Transformers (ITs), which integrate the two functionalities in one single apparatus.
Combined ITs represent a cost-effective solution that can reduce:
- the number of transformers in a bay
- the number of supporting structures
- the number of connections leading to reduced losses
- transportation costs
- installation costs and the time required for installation
- substation footprint
Like other instrument transformers, both the oil-insulated and the SF6-insulated versions of combined ITs are available and used in substations. ABB also has two versions of combined ITs with the type designation PVA representing the oil-insulated type and the type designation TG Combi representing the SF6-insulated type.
Advantages of ABB combined ITs
ABB combined ITs have features that are suitable for being used in a wide range of environments, eg, very low temperatures including under ice and very high temperatures, high altitude areas and earthquake-prone areas. We also have worldwide experience in various kinds of environments - our service record is proof of our high reliability. In addition, our designs require minimum maintenance and have a long service life of over 30 years.
PVA - ABB oil-insulated combined Instrument Transformer
The oil-insulated combined IT-type PVA was introduced in the market in 2012. So far, close to 2000 units have been installed worldwide. Currently, the PVA has 2 versions, ie, PVA 123/145, which changes a primary current ratio using a standard method, and PVA 123a/145a, which changes a primary ratio using only a special jumper.
TG Combi - ABB SF6-insulated combined Instrument Transformer
The SF6-insulated combined IT type TG Combi is available for system voltages of 145kV and 245kV. The concept of TG Combi is based on the simple integration of two consolidated SF6 products - TG (current transformer) and TVI (voltage transformers) - both installed in thousands of substations.
TG Combi reaches the highest levels of accuracy required for instrument transformers (0.2s and 5P for current, and 0.2 and 3P for voltage). TG Combi is suitable for severe environmental conditions, eg, pollution, altitude, corrosivity, seismic areas or even ultra-low temperatures, after being filled with a gas mixture comprising SF6 and N2. TG Combi meets the highest safety requirements by means of polymeric insulators and pressure relief devices. In addition, the design is proven to provide the highest protection level against internal arc fault (class II).
TG Combi has a reliable product design: Design solutions and manufacturing processes can guarantee an admitted maximum leakage rate of 0.1% per annum, five times less than those defined in IEC Standards.