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DSM REGULATION
ANUPAM BISWAS, SAIKAT DATTA, SUBHODEEP KAR
SYSTEM CONTROL
Abstract
The rated operating frequency in our Indian electricity grid is 50 Hz (cycles per second). It physically interprets
the synchronous speed of rotor of generator units and thereby its inertial stability. The frequency remains at 50
Hz as long as the supply of electricity to grid matches exactly with the system load demand. Any demand-supply
mismatch causes deviation of frequency from 50 Hz. Low frequency situations result when the total generation
available in the grid is less than the total connected load. These can be avoided by enhancing generation and/or
by reducing the connected load. High frequency is a result of insu cient backing down of generation when the
total connected load drops. Earlier in 2002, the regional grids had been operating in a very undisciplined and
haphazard manner due to supply - demand mismatch resulting in large deviations in grid frequency from the
rated one (50.0 Hz) causing instability to grid thereby causing cascade tripping of generator units, splitting of
regional grids and blackouts.
To resolve the issue, a penal and disciplinary mechanism, solely dependent inversely to frequency, was
introduced by CERC as third component of Availability Based Tari (ABT). This frequency dependent component
of tari was called ‘Unscheduled Interchange’ (UI), presently known as the ‘Deviation Settlement Mechanism’
(DSM). The earlier tari mechanisms did not provide any incentive for either backing down generation during
higher frequency or for reducing load/ enhancing generation during low frequency. UI mechanism directly
addresses this issue. If one generating plant injects less power to grid or a distribution utility draws more power
from grid than what is scheduled for it at a particular time, he has to pay for the shortfall (for generating plant) or
excess drawal (for distribution utility) at a rate inversely proportional to system frequency, the rate being lower
if the frequency is high, and is higher if the frequency is low. The DSM mechanism also provides an incentive to
the generating plant for backing down generation or to distribution utilities for enhancing load demand during
higher frequency condition. DSM thus provides a strong commercial implication for the generating plants as
well as to the distribution utilities so that they operate together to maintain the grid frequency close to 50 Hz
thereby ensuring a stable grid.
INTRODUCTION the generation plants to the distribution substations
through a grid at high voltages. Distribution utilities
There are three primary segments in the electricity sector: supply electricity from the substations to individual
generation, transmission and distribution. Generation is consumers through a distribution network. Distribution
the process of producing power using different fuels is the retail stage and operates at lower voltages. In India,
and is carried out in generating stations (generation various sources of energy are used to generate power.
plants). Transmission utilities carry bulk power from These include coal, natural gas, hydro, nuclear, and
85
ANUPAM BISWAS, SAIKAT DATTA, SUBHODEEP KAR
SYSTEM CONTROL
Abstract
The rated operating frequency in our Indian electricity grid is 50 Hz (cycles per second). It physically interprets
the synchronous speed of rotor of generator units and thereby its inertial stability. The frequency remains at 50
Hz as long as the supply of electricity to grid matches exactly with the system load demand. Any demand-supply
mismatch causes deviation of frequency from 50 Hz. Low frequency situations result when the total generation
available in the grid is less than the total connected load. These can be avoided by enhancing generation and/or
by reducing the connected load. High frequency is a result of insu cient backing down of generation when the
total connected load drops. Earlier in 2002, the regional grids had been operating in a very undisciplined and
haphazard manner due to supply - demand mismatch resulting in large deviations in grid frequency from the
rated one (50.0 Hz) causing instability to grid thereby causing cascade tripping of generator units, splitting of
regional grids and blackouts.
To resolve the issue, a penal and disciplinary mechanism, solely dependent inversely to frequency, was
introduced by CERC as third component of Availability Based Tari (ABT). This frequency dependent component
of tari was called ‘Unscheduled Interchange’ (UI), presently known as the ‘Deviation Settlement Mechanism’
(DSM). The earlier tari mechanisms did not provide any incentive for either backing down generation during
higher frequency or for reducing load/ enhancing generation during low frequency. UI mechanism directly
addresses this issue. If one generating plant injects less power to grid or a distribution utility draws more power
from grid than what is scheduled for it at a particular time, he has to pay for the shortfall (for generating plant) or
excess drawal (for distribution utility) at a rate inversely proportional to system frequency, the rate being lower
if the frequency is high, and is higher if the frequency is low. The DSM mechanism also provides an incentive to
the generating plant for backing down generation or to distribution utilities for enhancing load demand during
higher frequency condition. DSM thus provides a strong commercial implication for the generating plants as
well as to the distribution utilities so that they operate together to maintain the grid frequency close to 50 Hz
thereby ensuring a stable grid.
INTRODUCTION the generation plants to the distribution substations
through a grid at high voltages. Distribution utilities
There are three primary segments in the electricity sector: supply electricity from the substations to individual
generation, transmission and distribution. Generation is consumers through a distribution network. Distribution
the process of producing power using different fuels is the retail stage and operates at lower voltages. In India,
and is carried out in generating stations (generation various sources of energy are used to generate power.
plants). Transmission utilities carry bulk power from These include coal, natural gas, hydro, nuclear, and
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