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State of Andhra Pradesh - Section

Section 5 in Andhra Pradesh Electricity Regulatory Commission (Transmission Standards of Performance) Regulation, 2007

5. Phasing of Implementation.

- 5.1 The performance standards excepting the Mandatory Standards, specified herein shall be implemented in a phased manner in three stages as follows:(a)Preliminary Stage (Level-1): The time period of two (2) years immediately after these standards come into force shall be considered as Preliminary State. During this preliminary stage, Standards marked as Level 1 shall be achieved, unless specified otherwise.(b)Transition State (Level-2): Time period spreading up to three (3) years after the Preliminary State shall be considered as Transition Stage. During this period, the licensee is expected to upgrade its systems. Standards marked as Level 2 shall be achieved during Transition State-, unless specified otherwise.(c)Final Stage (Level-3): Two years after expiry of the Transition State when substantial improvements should have been carried out and the system considered to be in satisfactory condition with necessary capability improvement. Standards marked as Level 3 shall be achieved during this Final State.
5.2In all cases, where standards are specified by appropriate authorities, for example Electricity Rules- 1956, such standards shall be required to be complied with as specified by that authority, maybe from the preliminary stage itself.Standards to be complied with:
5.3The Commission specifies the following standards for STU/ Transmission Licensees:
(a)Voltage Variation:
(i)Voltage Variation is defined as the deviation of the root-mean-square (RMS) value of the voltage from its nominal RMS value, expressed in terms of percentage. Voltage Variation may be either of short duration not exceeding one minute or of long duration for a time greater than one minute.
(ii)For the purpose of these standards, the sustained variation in steady state voltage exceeding one minute duration shall be considered. The specified permissible limits of sustained voltage variation shall not apply in the cases where the circumstances are reasonably beyond the control of State Transmission Utility/Transmission Licensee e.g. major break-down, grid failures, accidents, system distress conditions, etc.
(iii)State Transmission Utility/ Transmission Licensee shall make all possible efforts to ensure that the grid voltages remain within the following voltage levels at all points of its Transmission System:
Nominal Voltage (kV) Maximum Value (kV) Minimum Value (kV)
4002201323311* 4202451453511.67 3602001203010
* 11 kV voltages to be maintained by the transmission licensee only in those cases where 11 kV supply is extended from the EHT substation.
(b)Safety Standards:
(i)State Transmission Utility/ Transmission Licensee shall observe the general safety requirements as laid down in IE Rules, 1956, for construction, installation, protection, operation and maintenance of electric supply lines and apparatus.
(ii)Relevant rules under IE Rules, 1956 pertaining to safety standards and practices shall be followed.
(iii)State Transmission Utility/ Transmission Licensee shall develop its own Operation and Maintenance Manual (including Safety Regulations) taking into consideration the safety requirements for the construction, operation and maintenance of electrical plants and electric lines as many be specified by the Central Electricity Authority under Clause © of Section 73 read with Section 53 of the Act.
(c)Feeder Availability:
(i)The feeder availability gives the percentage fo time during which the feeder remained available for transmission. Feeder Availability shall be calculated based on following formula:
% Availability of feeders =| (No of feeders X 8760 - Feeder Annual outages in feeder-hours) X 100Total availability in feeder-hours
Here, total availability in hours is equal to the number of hours in a year i.e. 8670 (Non-leap year)
(ii)The Transmission Licensee shall achieve 99% feeder availability from the preliminary stage itself.
(d)Sub-station Availability:
(i)The sub-station availability expressed in percentage is the measure of the extent the power transmission capacity remained available from a sub-section. Sub-station availability shall be calculated based on following formula:
% Availability of SS =| (Installed in MVA X 8760-Outages in MVA X Hours) X 100Installed capacity in MVA X 8760
(ii)The Transmission Licensee shall achieve 97% Substation availability from the preliminary stage itself.
(e)Voltage Unbalance:
(i)The phase voltages of a 3-phase supply should be equal in magnitude and phase angle. The loads on each phase should be balanced. Deviations will result in decreased efficiency, negative torque, vibrations and overheating Severe unbalance could lead to malfunctioning of some equipment. The unbalance is computed as follows:
% Voltage Unbalance =| Max Deviation from Mean of {VRY, VYB, VBR}X 100{VRY, VYB, VBR}
Where, VRY is voltage between R & Y phases, VYB is Voltage between Y & B phases and VBR is voltage between B & R phases.
(ii)Subject to Distribution Licensee(s) observing the Grid Code Connection Conditions in this regard, the voltage unbalance shall not exceed the values given below:
Implementation Stage Voltage Level Limit of voltage Unbalance
PreliminaryState-Level 1Transition State-Level2Transition State-Level 2 220kV and Above132kV33 kV and 11 kV buses in EHV Substation 2%3%3%
Provided that the above limit for Voltage unbalance at the interconnection point with Distribution System arc subject to Distribution Licensee maintaining current nubalance between phases within limit of 3% applied for all feeders of one voltage class emanating from a sub-station including railway traction etc. measured at 3 sub-station in a row. The Voltage unbalance shall be measured at sub-stations provided with measuring instruments having accuracy class within 1% limit.
(f)Neutral Voltage Displacement (NVD):
(i)Unbalance in loads on three phases cause shifting of neutral from earth potential. Neutral displacement is applicable for transformers with 'Star Point' solidly ground. Under "solidly" grounded conditions, the potential of neutral should be equal to earth i.e. zero. But in actual conditions, the earthing of the star point is imperfect and so the star to ground offers small resistance. This results in flow of negative sequence currents because Ir + Iy + lb is not equal to zero, where, Ir is the current in the R-Phase, ly is the current in the Y-Phase and lb is the current in the B-Phase) through neutral to ground. The neutral therefore shifts from earth potential. This performance standard shall be achieved for star point of all EHT transformers having 33kV or 1 lkV on the low voltage side.
(ii)Unbalance voltages and displacement of neutral result in decreased efficiency, negative torque, leakage currents, vibrations and overheating. Severe unbalance and neutral displacement could lead to malfunctioning of some equipment.
(iii)The State Transmission Utility/ Transmission Licensee shall ensure that the neutral point voltage of the transformers with respect to earth will not have potential greater than 2% of the no load phase to phase voltage of the transformer.
(iv)This standard shall be implemented in the Preliminary State (Level 1) itself.
(g)Voltage Variation Index (WI): Voltage Variation Index representing the degree of voltage variation from nominal value (in %) over a specified period of time shall be computed separately by the State Transmission Utility/Transmission Licensee for higher than nominal system voltage and lower than nominal system voltage as per the following formula:
N
VVI = Square Root of {| ∑ (Vt-VN)/N²) X (1000/Vs)%}
I=1Where,Vi=RMS value of measured voltage (in kV) at hour in the period for which WI is computedVs=RMS value of the nominal system voltage i.e. 400kV, 220kV and 132kV etc. as may be applicable at the interconnection pointN=Number of hourly measurements over the specified period of time.The data from defective metering or any abnormal data shall be discarded from calculations. The VVI shall be computed on monthly basis:
Preliminary State-Level 1 = 10 To be achieved for more than 90% of buses
Transition stage Level 2 = 6 To be achieved for more than 90% of buses
Final Stage-Level 3 = 4 To be achieved for more than 90% of buses
(h)System Adequacy:
System adequacy is the ability of the electric system to receive the generated power or supply the aggregate electrical demand and energy requirements of its consumers at all times, taking into account scheduled and reasonably expected unscheduled outage of system elements. Adequacy of the power system is usually measured in terms of Loss from calculations. The WI shall be computed on monthly basis:Of Load Probability (LOLP) LOLP is the probability of transmission system capacity not being able to meet system load. LOLP can also be expressed as Loss Of Load Expectation (LOLE) in hours per year. This measure does not consider the amount or duration of the generation capacity shortfall. State Transmission Utility/Transmission Licensee is expected to achieve LOLE hours in percentage as under:
Implementation Stage Nos. of hours in year when system demand   Loss of Load Expectation
can be fully met subject to generation availability (A) can not fully met even with generation availability (B=8760-A) (LOLE) in % of hours (C=B XI00/8760)
PreliminaryState-Level 1TransitionStage-Level 2Final Stage-Level 3 744678848672.4 131487687.60 15%10%1%
(i)System Security:
Security is the ability of the electric system to withstand sudden disturbance such as electric short circuit or unanticipated loss of system element, detailed in clause 6 of "Manual on Transmission Planning Criteria" issued by CEA. The State Transmission System shall be designed for a security level of "n-1" i.e. to withstand a single contingency with little negative effect. This means the most severe fault or tripping of a critical generator, transformer or line should not result in instability of the system, overloading lines and / or transformers for more than 15 minutes, voltage drop of more than 10% when the system import is increased by 20%. State Transmission Utility/Transmission Licensee shall maintain the system security level of "n-1" (single contingency) plus spinning reserve margin for Steady State Operation.
Implementation Stage System Security Level of "n-1" (SingleContingency) plus spinning reserve margin of:
Preliminary Stage-Level 1Transition Stage-Level 2Final Stage-Level 3 No mandatoryrequirement0.5% of system peakload1% of system peak load