Dynamic Responses under an Islanded Frequency Control Mode of Bhutan Power Grid

This paper investigates dynamic responses associated with the proposed frequency control schemes for islanding operation of Bhutan power grid after separation from Indian power grid. Since there is no complete dynamic model of Bhutan power grid being developed in the past, this dynamic model development is thus being conducted for the first time and, it entails collecting dynamic data from Bhutan power grid, building dynamic models, tuning relevant parameters for both static and dynamic simulations. The dynamic simulations were performed to understand the grid dynamic behavior in order to design appropriate frequency control arrangement of the islanded Bhutan power grid. Frequency response sensitivity analyses were conducted with a consideration of governor control, automatic generator control as well as under frequency load shedding scheme for emergency control.

I. Introduction

Bhutan generates around 1600 MW of power and all are of run-of-the-river type hydro power plants with huge seasonal variations in generation. As national peak load of the country is less than 400 MW, more than 75% of the total generation (in summer) is exported to India. Thus, Bhutan power grid is connected to Indian power grid through multiple transmission lines. As the system is connected through AC lines, any disturbance or system fluctuation in Indian side directly affects the Bhutan power grid. For instance, during Indian grid blackout on 30 and 31 July, 2012, it led to widespread blackout in Bhutan as well [1]. Although one of the most important recommendations after these blackouts was to develop a defense plan for each region including Bhutan power grid with an appropriate islanding schemes and frequency control arrangement [1], such schemes were never developed. This paper presents, for the first time, a research effort to develop frequency control schemes for islanding operation of Bhutan power grid after separation from Indian power grid. Currently, there is no complete dynamic model of Bhutan power grid to study such possibility. Thus, it requires collecting dynamic data from Bhutan power grid, building dynamic models in PowerWorld Simulator software, tuning relevant parameters for steady-state and dynamic simulations. The dynamic simulations were performed to understand the dynamic behavior of the system in order to design appropriate frequency control arrangement of the islanded Bhutan power grid. Frequency response sensitivity analyses were conducted with a consideration of both primary governor control and secondary automatic generator control. The other frequency control arrangement is through under frequency load shedding scheme as emergency control actions.