Smart transformers are an integral part of digital substations. They independently regulate voltage and maintain contact with the smart grid in order to allow remote administration and real-time feedback on power supply parameters. The use of these transformers is gaining traction at the distribution and transmission levels. These transformers are equipped with intelligent electronic devices, and intelligent monitoring and diagnostics features.
A smart transformer, a form of solid-state transformers (SSTs) with control and communication functionalities, is a collection of high-powered semiconductor components, conventional high frequency transformers and control circuitry, which is used to provide a high level of flexible control to power distribution networks. A smart transformer provides ancillary services to distribution and transmission grids in order to optimise their performance. Hence, the focus shifts from hardware advantages to functionalities. One of the most desired functionalities is DC connectivity to enable a hybrid distribution system. For this reason, the smart transformer architecture is composed of at least two power stages. The standard procedure for this kind of system is to design each power stage for the maximum load. A smart transformer covers a wide range of services such as reactive power support in MV grids and DC connectivity at medium and low voltage levels.
A smart transformer provides the accurate amount of power that is required and immediately responds to fluctuations in the power grid, acting as a voltage regulator. Further, as smart transformers consume less energy, they help in reducing greenhouse gas emissions. During instances of power supply fluctuations, a smart transformer can be monitored and controlled in real time to optimise voltage levels. These features make smart transformers ideal for power systems designed for the integration of renewable energy. For instance, the integration of SSTs with wind energy systems effectively replaces conventional transformers and reactive power compensators, thereby increasing the flexibility of the wind energy system. This equipment is able to protect the power system from load disturbances by isolating the source from load harmonics, transients and voltage sags. By providing unity power factor with sinusoidal currents under non-linear loads, this equipment has an advantage over traditional transformers.
Smart transformers help in reducing grid losses and improving power supply reliability. Such equipment provides the ability to utilise input or output impedance in AC or DC power, protect the load from power supply disturbances, eliminate the need for tap changers, ensure power backup and reduce the duration of outages.
There is an increasing trend in the uptake of digital monitoring devices and solutions for transformers. Compared to traditional transformer diagnostic methods, which are performed on site with the transformer de-energised, online monitoring devices give the asset owner access to real-time condition information, even from remote locations.
Traditional dissolved gas analysis (DGA) techniques are also paving the way for online DGA devices. Monitoring and detection devices and sensors deployed in critical transformers in the field can undertake frequent collections of DGA data and send them via a communication channel (typically wireless) to the control centre, where advanced software solutions can be used to analyse and interpret this data to assess the health of the transformer oil and come up with appropriate decisions and recommendations.
Smart DGA instruments, which work in cycles to obtain a sample of oil, detect concentrations of key gases and record the values. These are more popular for 765 kV and high voltage direct current transformers. Using software, utilities can quickly view and identify potential fault locations by monitoring key gas levels, rates and ratios, besides using diagnostic tools to evaluate the data.
Online partial discharge (PD) monitors are also seeing growing uptake. PDs are basically used to ascertain the state and health of the bushes. A PD occurs whenever there is a stressed region due to some impurity/cavity inside the insulation or when there is a protrusion outside it. Depending on the type of high voltage equipment, it successfully detects the characteristics of any PD activity, providing an early warning of incipient insulation faults.
Smart transformers are intelligent enough to meet the requirements of upcoming power systems, which is why these are expected to be highly popular in the future. The recent trend includes the use of artificial intelligence in analysis, on-site high voltage testing and low-noise transformers. There are a host of technologies available in the transformer space to meet power system requirements and address the challenges facing utilities. However, for optimal outcome, it is necessary to judiciously select the ideal technology solution through a cost-benefit analysis and identify the system requirements.