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ewable (includes solar, wind, small hydro, biomass 2. Scheduled Energy charge: To reimburse the fuel
etc.). Transmission is carried out primarily by central cost for scheduled generation.
and state companies and largely remains a government
controlled activity. The transmission segment was 3. Unscheduled Interchange (UI): A payment for
separated from the central generation agency in deviation from schedule, at a rate dependent on
1989 and Power Grid Corporation of India (Powergrid) system frequency conditions.
was set up. Powergrid is responsible for the planning,
implementation, operation and maintenance of inter- Figure 1:
state transmission system, and the operation of national The 24 hours of the day is divided into 96 blocks, each of
and regional power grids. The Electricity Act, 2003 15 minutes time blocks. The generating companies and
allows for open access which enables consumers to buy Discoms has to declare their injection and drawal energy
power from any power generating plant through non- schedule respectively on day ahead basis to the nodal
discriminatory access to transmission and distribution agency (SLDC being the nodal agency for the state, RLDC
lines, in a manner specified by the respective state/state for the region and NLDC for the country) for each of the 96
regulator. The National Load Despatch Centre (NLDC) blocks. For a perfectly balanced grid operation, the actual
manages the scheduling and dispatch of electricity over injection of power by generating plants and drawal by
inter-regional links in accordance with grid standards, Discoms must match with their respective schedule in real
and monitors the national transmission grid. It is also time maintaining grid frequency to 50 Hz. Any deviation
the nodal agency providing transmission access to the from schedule would cause demand-supply mismatch
power exchanges. The Regional Load Despatch Centres resulting in deviation of grid frequency from 50 Hz.
(RLDCs) manage the operation of the power system
grid in the respective regions (five regional grids in THE UI (DSM)
India namely Eastern, North-Eastern, Northern, Western
and Southern Regional grids each interconnected to In real time situation, deviation from schedule occurs
each other forming one grid). Distribution includes to both generating companies and Discoms due to
maintenance of the distribution network and retail dynamic system demand. UI (presently DSM) is a real
supply of electricity to the consumers. It is mostly carried time pricing of this deviation from schedule, i.e. the
out by state-owned distribution companies (Discoms). unscheduled energy, at a rate inversely proportional to
However, in cities such as Delhi, Mumbai, Ahmedabad, prevailing system frequency. The energy is metered in
and Kolkata, private entities own the distribution 15-minute time blocks (since frequency keeps changing
business. Discoms (or distribution licensees) purchase and the UI rate with it). The metered energy is then
power from generation companies either through compared with the scheduled energy for that 15-minute
power purchase agreements (PPAs) (there may be LTOA, time block, and the difference (+ or -) becomes the UI
MTOA and STOA) or through power exchanges and energy, as illustrated in Figure 1. The corresponding UI
supply it to their consumers (in the area of distribution). rate is determined by taking the average frequency for
the same 15-minute time block into account.
THE SCHEDULING AND ABT
The Availability Based Tariff (ABT) comprises of three
components:
1. Capacity Charge: Towards reimbursement of the
fixed cost of the power plant, linked to the plant’s
declared capacity to supply MW
86
etc.). Transmission is carried out primarily by central cost for scheduled generation.
and state companies and largely remains a government
controlled activity. The transmission segment was 3. Unscheduled Interchange (UI): A payment for
separated from the central generation agency in deviation from schedule, at a rate dependent on
1989 and Power Grid Corporation of India (Powergrid) system frequency conditions.
was set up. Powergrid is responsible for the planning,
implementation, operation and maintenance of inter- Figure 1:
state transmission system, and the operation of national The 24 hours of the day is divided into 96 blocks, each of
and regional power grids. The Electricity Act, 2003 15 minutes time blocks. The generating companies and
allows for open access which enables consumers to buy Discoms has to declare their injection and drawal energy
power from any power generating plant through non- schedule respectively on day ahead basis to the nodal
discriminatory access to transmission and distribution agency (SLDC being the nodal agency for the state, RLDC
lines, in a manner specified by the respective state/state for the region and NLDC for the country) for each of the 96
regulator. The National Load Despatch Centre (NLDC) blocks. For a perfectly balanced grid operation, the actual
manages the scheduling and dispatch of electricity over injection of power by generating plants and drawal by
inter-regional links in accordance with grid standards, Discoms must match with their respective schedule in real
and monitors the national transmission grid. It is also time maintaining grid frequency to 50 Hz. Any deviation
the nodal agency providing transmission access to the from schedule would cause demand-supply mismatch
power exchanges. The Regional Load Despatch Centres resulting in deviation of grid frequency from 50 Hz.
(RLDCs) manage the operation of the power system
grid in the respective regions (five regional grids in THE UI (DSM)
India namely Eastern, North-Eastern, Northern, Western
and Southern Regional grids each interconnected to In real time situation, deviation from schedule occurs
each other forming one grid). Distribution includes to both generating companies and Discoms due to
maintenance of the distribution network and retail dynamic system demand. UI (presently DSM) is a real
supply of electricity to the consumers. It is mostly carried time pricing of this deviation from schedule, i.e. the
out by state-owned distribution companies (Discoms). unscheduled energy, at a rate inversely proportional to
However, in cities such as Delhi, Mumbai, Ahmedabad, prevailing system frequency. The energy is metered in
and Kolkata, private entities own the distribution 15-minute time blocks (since frequency keeps changing
business. Discoms (or distribution licensees) purchase and the UI rate with it). The metered energy is then
power from generation companies either through compared with the scheduled energy for that 15-minute
power purchase agreements (PPAs) (there may be LTOA, time block, and the difference (+ or -) becomes the UI
MTOA and STOA) or through power exchanges and energy, as illustrated in Figure 1. The corresponding UI
supply it to their consumers (in the area of distribution). rate is determined by taking the average frequency for
the same 15-minute time block into account.
THE SCHEDULING AND ABT
The Availability Based Tariff (ABT) comprises of three
components:
1. Capacity Charge: Towards reimbursement of the
fixed cost of the power plant, linked to the plant’s
declared capacity to supply MW
86
