Utility companies transitioning to Smart Grid operations can significantly benefit from real-time knowledge of the internal operating state of their assets.
For power Transformers, the key parameters for optimal performance are oil and winding temperature indications (OTI/WTI). These two parameters are the key indicators of efficiency losses and constraint levels of the quantity of power that can be safely allowed to flow through the Transformer without causing it any damage.
Any transformer that is operated without an accurate knowledge of its OTI and WTI values must be utilised conservatively to avoid constraint violations of its internal temperature.
Our client, a leading Utility company had deployed legacy Transformers with in-built OTI and WTI sensors. As is the case with most conventional sensors, these sensors were connected to analogue indicator dials that disallowed digitised readings.
Furthermore, with the OTI and WTI sensors preinstalled inside the Transformer case, our client had to repeatedly initiate arduous manual operations for oil draining and commissioning and maintenance of the sensors.
Our strategic partner OrxaGrid was roped in to develop a smart solution that seamlessly indicated the Transformers’ internal temperatures and permissible loading without the need to replace the existing OTI and WTI sensors.
A six-month project was undertaken on the Utility’s grid-supply-point Transformers that had preinstalled physical OTI and WTI sensors.
OrxaGrid deployed advanced load current and ambient temperature sensors with readings automatically streamed to a database every 15 minutes. A robust Temperature Estimation Application was developed that precisely retrieved the live readings from the database and estimated accurate WTI and OTI values.
For determining the real-time spare capacity under continuously varying load and ambient temperature conditions, OrxaGrid developed iterative algorithms that did not need any initial oil temperature information. The results converged in a series of time-steps that gave an accurate estimation of OTI and WTI values.
The Temperature Estimation Application was specifically designed to optimise the temperature estimation accuracy when I2R losses dominate. This condition occurs when the load current is above the Transformer’s maximum efficiency point because it is in this region that the Transformer’s thermal limits are approached. The temperature estimation was then used to determine:
1. Maximum Permissible Operating Power: A real-time function of the permissible load on the Transformer as a function of its core design material and operating conditions.
2. Future Load: A predictive algorithm to forecast and alert the operator of violations of maximum operating power.
The project proved successful with low estimation errors (Mean error 0.59°C and standard deviation 1.49°C). A method for estimating Transformer oil and winding temperatures from load current and ambient temperature, in lieu of OTI and WTI sensors, was built and validated.
With the help of OrxaGrid’s solution, our client was able to accurately determine the real-time thermal rating of their power Transformers and obtain actionable insights on releasing spare capacity or deferring network reinforcements.