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[Cites 0, Cited by 0] [Section 7] [Entire Act]

State of Tamilnadu - Subsection

Section 7(3) in Tamil Nadu Electricity Grid Code, 2005

(3)System Security Aspects: (i) The Tamil Nadu Electricity Grid shall be operated as a synchronized system. All State entities shall operate their respective power systems and power stations in synchronism with the Grid. Appropriate security standard will be adopted in the operation of the system. Reliability criteria will also be adopted.
(ii)No element/part of the Grid shall be deliberately isolated from the rest of the State Grid or islanded except:
• under an emergency, and conditions in which such isolation would prevent a total Grid collapse and / or enable early restoration of power supply,• when serious damage to a costly equipment is imminent and such isolation would prevent it,• when such isolation is specifically directed by SLDC or with specific prior approval from SLDC Complete re-synchronization of the Grid shall be restored as soon as the normal conditions are restored. The restoration process shall be supervised by SLDC, as per the approved operating procedures separately formulated.
(iii)The list of such important Grid link/elements on which the above stipulations apply shall be prepared and be available at SLDC / SSLDCs. In case of opening / removal of any important element of the Grid under an emergency situation, the same shall be communicated to SLDC at the earliest possible time after the event.
(iv)Any tripping, whether manual or automatic, of any of the above elements of State Grid shall be precisely intimated by the concerned entities to SLDC as soon as possible, say within ten minutes of the event. The reason (to the extent determined) and the likely time of restoration shall also be intimated. All reasonable attempts shall be made for the elements' restoration as soon as possible.
(v)All generating units, which are synchronized with the Grid, irrespective of their ownership, type and size, shall have their governors in normal, preferably at free-governor mode at all times. If any generator of over 50 MW rating is required to be operated without its governor in normal operation, the SLDC shall be immediately advised about the reason and duration of such operation. All governors shall have a droop between 3 %. and 6 % for thermal and 0 to 10 % for hydro generators.
(vi)Facilities available with load limiters, Automatic Turbine Run up System (ATRS), turbine supervisory control, coordinated control system, etc., shall not be used to suppress the normal governor action in any manner. No dead bands and / or time delays shall be deliberately introduced.
(vii)All generating units, operating at / up to 100% of their Maximum Continuous Rating (MCR) shall normally be capable of (and shall not in any way be prevented from) instantaneously picking up 5% of extra load and sustain the increase for a minimum of 5 minutes when frequency falls due to a system contingency. The generating units operating at above 100% of their MCR shall be capable of (and shall not be prevented from) going at least up to 105% of their MCR when frequency falls suddenly. After an increase in generation as above, a generating unit may ramp back to the original level at a rate of about one percent (1%) per minute, in case continued operation at the increased level is nol sustainable. Any generating unit of over fifty (50) MW size, not complying with the above requirement, shall be kept in operation (synchronized with the State Grid) only after obtaining the permission of SLDC. However, the entity can make up the corresponding shortfall in spinning reserve by maintaining an extra spinning reserve on the other generating units of the entity.
(viii)The recommended rate for changing the governor setting, i.e. supplementary control for increasing or decreasing the output (generation level) for all generating units, irrespective of their type and size, would be one (1.0) per cent per minute or as per manufacturer's limits. However, if frequency falls below 49.5 Hz, all partly loaded generating units shall pick up additional load at a faster rate, according to their capability.
(ix)Except under an emergency, or to prevent an imminent damage to personnel and equipment, no entity shall suddenly reduce his generating unit output by more than one hundred (100) MW without prior intimation to and consent of the SLDC, particularly when frequency is falling or is below 49.0. Similarly, no entity shall cause sudden increase in its load by more than one hundred (100) MW without prior intimation to and consent of the SLDC.
(x)All generating units shall normally have their Automatic Vqltage Regulators (AVR) in operation, with appropriate settings. *In particular, if a generating unit of over fifty (50) MW size is required to be opera ted without its AVR in service, the SLDC shall be immediately intimated about the reason and duration, and its permission obtained. Power System Stabilizers (PSS) in AVRs. of generating units (wherever provided), shall be got properly tuned by the respective generating unit owner as per a plan prepared for the purpose by the STU from time to time. STU will be allowed to carry out checking of PSS and suggests further tuning, wherever considered necessary.
(xi)Provision of protections and relay settings shall be coordinated periodically throughout the State Grid, as per a plan to be separately finalized by the STU in coordination with all entities.
(xii)All entities shall put in all possible efforts to ensure that the Grid is operated within the frequency limits prescribed by the implementation of Availability Based Tariff (ABT) i.e. frequency always remains within the 49.0 - 50.5 Hz band.
(xiii)All State entities shall provide automatic under-frequency load shedding, based on the operation of df/dt or constant frequency setting relay in their respective systems, to arrest frequency decline that could result in a collapse / disintegration of the Grid, as per the plan separately finalised by SLDC in consultation with STU, and shall ensure its effective application to prevent cascaded tripping of generating units in case of any contingency. All entities shall ensure that the under-frequency load shedding / islanding schemes are functional and no under-frequency relay is bv-passed or removed without prior consent of SLDC.
(xiv)Procedures shall be developed by SLDC in consultation with STU, to recover from partial / total collapse of the Grid and periodically updated in accordance with the requirements given under Code 7 (5) (f). These procedures shall be followed by all the entities to ensure consistent, reliable and quick restoration.
(xv)Each entity shall provide adequate and reliable communication facility internally and with other entities/ SLDC to ensure exchange of data / information necessary to maintain reliability and security of the Grid. Wherever possible, redundancy and alternate path shall be maintained for communication along important routes, e.g. SLDCs to SSLDCs and generating stations.
(xvi)The entities shall send information / data including disturbance recorder / sequential even recorder output etc., to SLDC for purpose of analysis of any Grid disturbance / event. No State entity shall block any data/ information required by the SLDC for maintaining reliability and security of the Grid and for analysis of an event.
(xvii)Only authorized persons as certified by STU can give/take line clear on Grid equipment and lines for maintenance/fault rectification works. For carrying out erection/ repair in the circuit above 230 kV the competent person should have a minimum operating experience of one year.
(xviii)Before undertaking hot line working/hot line washing of the insulators connected with Grid equipment, advance information should be given to SLDC and other operating personnel concerned.
(xix)All entities shall put in all possible efforts to ensure that the Grid voltage always remains within the following operating range.
Nominal Maximum Minimum
  Voltage in (kV rms)  
400 420 360
230 255 210
110 120 100
(xx)The steady state and transient stability limits of the Grid should be communicated periodically.
(xxi)There should be adequate spinning reserve in the system.
(xxii)The STU should provide power for maintenance, short term and emergency to the IPPs and other non utility generators in accordance with the connection agreement entered into.