KOLKATA: As solar installation becomes more affordable and homes begin to generate electricity and push it into the grid, power utilities like CESC and West Bengal State Electricity Distribution Co Ltd (WBSEDCL) face the challenge of managing their networks that are designed for one-way flow of electricity.
“Traditionally, power flow has been from generation unit to households through transmission line and distribution network. All safety devices – switch, relay, fuse – installed to protect a network are unidirectional. But when thousands of households with rooftop solar units start pushing electricity into the grid, the bidirectional flow will render the safety mechanisms redundant. When the voltage or current breaches the safety threshold, tripping of fuse, relay could be erratic. That is dangerous because it leaves the entire network in peril. The cost of a failure can then be huge,” indicated Alekhya Datta, fellow at The Energy & Resources Institute (Teri).
Teri has recently completed a load flow study, both under balanced and unbalanced conditions using a yearly time series load data-sets provided by WBSEDCL for selected feeders. The study is commissioned by state power and non-conventional energy sources department. As a short-term measure to protect network from damage, it has suggested that households install smart invertors for solar rooftop systems to maintain voltage stability. It will undertake a second study on protection coordination in which vulnerable points in the network will be identified and unidirectional relays will be replaced by bidirectional relays.
“There is also a need to limit power flow in reverse direction (from households to the grid) to prevent protection system from failing. The smart invertor is a short-term strategy to provide protection without any cost to distribution firm, But in long term, distribution transformers will have to be changed from manual tap changer to automatic/on-load tap changer,” said Datta.
The study revealed that distribution transformers are already close to overload conditions with load pattern changing rapidly due to rising incomes, economic growth rate and other variables like renewable energy and need to charge electric vehicles. To tackle this, Teri has proposed Battery Energy Storage System (BESS) at localised level, mainly downstream of distribution network.
Source: timesofindia.indiatimes
