(1) All Entities, Appropriate Load Despatch Centres and Regional Power Committees, for the purpose of maintaining the Grid Standards for operation and maintenance of transmission lines, shall,-
(a) make all efforts to operate at a frequency close to 50 Hz and shall not allow it to go beyond the range 49.2 to 50.3 Hz or a narrower frequency band specified in the Grid Code, except during the transient period following tripping.
(b) maintain the steady state voltage within the limits specified below in Table 1:
Table 1 S.
No.
Nominal System Voltage (kV rms) Maximum (kV rms) Minimum (kV rms) 1 765 800 728 2 400 420 380 3 220 245 198 4 132 145 122 5 110 121 99 6 66 72 60 7 33 36 30 Page 4 of 19 ( c) ensure that the temporary over voltage due to sudden load rejection remains within the limits specified in Table 2,- Table 2 S. No. Nominal System Voltage (kV rms) Phase to Neutral Voltage (kV peak) 1 765 914 2 400 514 3 220 283 4 132 170
Provided that for the voltage level below 132 kV, the temporary over voltage limits as given in Table 2 shall be decided by the State Commission in the respective State Grid Code.
(d) ensure that the maximum permissible values of voltage unbalance shall be as specified in Table 3 below:- Table 3 S.No. Nominal System Voltage (kV rms) Voltage Unbalance (%) 1 765 and 400 1.5% 2 220 2% 3 33 to132 3%
Provided that Bulk consumers shall avoid unbalanced load during operation:
Provided further that the distribution licensees shall ensure that their loads are not unbalanced.
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(e) provide standard protection systems having the reliability, selectivity, speed and sensitivity to isolate the faulty equipment and protect all components from any type of faults, within the specified fault clearance time and shall provide protection coordination as specified by the Regional Power Committee.
Explanation.- For the purpose of this regulation “fault clearance time” means the maximum fault clearance times are as specified in the Table 4 below,- Table 4 S.No. Nominal System Voltage (kV rms) Maximum Time ( in milliseconds) 1 765 and 400 100 2 220 and 132 160
Provided that in the event of non clearance of the fault by a circuit breaker within the time limit specified in Table 4, the breaker fail protection shall initiate tripping of all other breakers in the concerned bus-section to clear the fault in the next 200 milliseconds.
(f) operate the system in a such a way that the Grid System is capable of withstanding one of the following contingencies without experiencing loss of stability:-
(1) outage of one single largest generating unit of the system or
(2) outage of a 132 kV Double circuit line or
(3) outage of a 220 kV Double circuit line or
(4) outage of a 400 kV Single circuit line or
(5) outage of a 400 kV Single circuit line with series compensation or
(6) outage of 765 kV Single circuit line without series compensation or
(7) outage of one pole of HVDC Bipolar line or
(8) outage of an Interconnecting Transformer Page 6 of 19
(g) operate the system in a such a way that under any one of the following contingencies, the system remains stable and sustains integrity so that no generator loses synchronism and no part gets isolated from the rest of the system:
(1) tripping of a single largest generating unit; or
(2) transient ground fault in one phase of a 765 kV Single Circuit Line close to the bus; or
(3) a permanent single phase to ground fault in 400 kV single circuit line followed by 3 pole opening of the faulted line; or
(4) a permanent fault in one circuit of a 400 kV Double Circuit Line when both circuits were in service in the pre-contingency period; or
(5) a transient single phase to ground fault in one circuit of a 400 kV Double Circuit Line when the second circuit is already under outage;
or
(6) a three-phase permanent fault in a 220 kV or 132 kV line; or
(7) a permanent fault in one pole of HVDC bipolar in a HVDC Converter Station.
(h) observe the following permissible limits of voltage fluctuation :-
(i) the permissible limit of voltage fluctuation for step changes which may occur repetitively is 1.5 percent:
(ii) for occasional fluctuations other than step changes the maximum permissible limit is 3 percent:
Provided that the standard on voltage fluctuations shall come into force concurrently with clause 4 of Part IV of the Schedule to the Central Electricity Authority (Technical Standards for Connectivity to the Grid) Regulations, 2007.
(2) The transmission licensee shall ensure that the voltage wave-form quality is maintained at all points in the Grid by observing the limits given in Table 5 below,- Page 7 of 19 Table 5 S.No. System Voltage (kV rms) Total Harmonic Distortion (%) Individual Harmonic of any particular Frequency (%) 1 765 1.5 1.0 2 400 2.0 1.5 3 220 2.5 2.0 4 33 to 132 5.0 3.0
Provided that the standard on Harmonic Distortion shall come into force concurrently with clause 3 of Part IV of the Schedule to the Central Electricity Authority (Technical Standards for Connectivity to the Grid) Regulations, 2007.
Explanation : For the purpose of this regulation, Total Harmonic Distortion (VTHD) expressed as percentage, shall be calculated as under,- 100 40 2 2 1 2 X V V V n n n THD ∑ = = = ‘1’ refers to fundamental frequency (50 Hz) ‘n’ refers to the harmonic of nth order (corresponding frequency is 50 x n Hz)