Islanding scheme

Islanding scheme

Subject: Science and Technology

Context: In order to avoid outages in the electricity grid like the Mumbai 2020 blackout, islanding scheme is proposed to be implemented at seven new locations across India

Concept:

The Ministry of power has identified locations for islanding scheme

• Eastern region: Patna and Ranchi
• Northern region: Agra (Uttar Pradesh), one in Rajasthan for loads of Jodhpur and Barmer, Rajpura (Punjab) and another one will have loads of Pathankot, Sarna, Mamoon, Gurdaspur and Dhariwal.
• Southern region: Vijaywada is set to have an islanding scheme.

What is grid islanding scheme?

• The process of disconnecting the Plant from the Utility (during parallel operation) in case of Grid disturbances is called Grid Islanding Scheme.
• Grid Islanding scheme means as the name indicates it isolates grid from our island (Power plant) in case of any grid side disturbance or fault.
• Grid Islanding scheme is a set of protective relays, connected at the grid incomer- these relays will sense a disturbance in the grid and give a trip command to the incomer breaker whenever the grid disturbance exceeds a set limit.
• By opening the incomer breaker, the plant is isolated from the disturbed grid and we can keep our generator safe.
• . The selected protective device for grid islanding scheme shall having protection function like directional over current & earth fault Protection, Reverse power protection, voltage vector shift protection, rate of change of frequency protection, under / over voltage protection, under / over frequency protection, negative phase sequence protection, residual over voltage protection.
• It is required to have dedicated protection scheme for industrial plant which have parallel connectivity of grid with in house generator, to keep our generator safe from grid side disturbances.

The causes of disturbances in grid network may be,

• Load and Generation imbalance
• Load Fluctuation in grid
• Loss of grid power / mains power
• Large switching operation
• Symmetrical or Asymmetrical fault in infinite grid
• Voltage dip for a long duration of 1s or more or Rise in voltage above the normal value along with zero real power import from grid to the plant.

The main objective to connect grid in parallel with in-house generator are as under

• To Black start of island (Plant),
• To Exporting / Evacuating extra generated power from generator to grid,
• To Meet the extra load requirement of plant,
• To cater fluctuating load of plant,