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Central Electricity Authority (Grid Standards) Regulation about Small Hydro Power

December 30, 2020

Selection and Mechanical Characteristics

Small hydro up to 5 MW is generally category-2 generators. These generators are factory assembled that are shipped to the field as two integral component parts, rotor and stator. With all turbines, a vertical or horizontal configuration is possible. The orientation becomes a function of the turbine selection and of the power plant structural and equipment costs for a specific layout. As an example, the Francis vertical unit will require a deeper excavation and higher power plant structure. A horizontal machine will increase the width of the power plant structure yet decrease the excavation and overall height of the unit. It becomes apparent that generator orientation and setting are governed by compatibility with turbine selection and an analysis of overall plant costs.



1. Short Title, Commencement and Interpretation

a) These regulations may be called the Central Electricity Authority (Grid Standards) Regulations, 2006 framed as per provisions under section 34, Section 73(d) and section 177(2) (a) of the Electricity Act,2003.


b) These regulations shall come into force on the date of their publication in the official Gazette.

c) Grid Standards for Operation and Maintenance of Transmission Lines as prescribed by the Authority are given in the "Schedule" appended to these Regulations.


d) These regulations shall be reviewed by the Authority in consultation with all the stake holders as and when considered necessary.


2. Definitions

In these Regulations, unless the context otherwise requires;

a)"Act" means the Electricity Act, 2003.


b)“Appropriate Load Despatch Centre" means the National Load Despatch Centre (NLDC),Regional Load Despatch Centre (RLDC) or State Load Despatch Centre (SLDC) or Area Load Despatch Centre as the case may be.


c)“Area Load Despatch Centre" means the centre as established by the state for load Despatch &control in a particular area of the state.


d)“Bulk consumer" means a consumer who avails supply at voltage of 33 kV or above.


e)Disaster management is the mitigation of the impact of a major breakdown on the system and bringing about restoration in the shortest possible time.


f)“Emergency Restoration System" A system comprising transmission towers/ structures of modular construction complete with associated components viz. insulators, hardware fittings, accessories,foundation plates, guys, anchors, installation tools etc. to facilitate quick restoration of damaged/failed transmission line towers/ sections.


g)“Islanding Scheme" is a scheme for separation of the grid into two or more independent systems as a last resort with a view to save healthy portion of the grid at the time of the grid disturbance.


h)“Standards" means "Grid Standards for Operation and Maintenance of Transmission Lines" set forth in the Schedule appended to these Regulations.


i)“Transient stability" means the ability of all the elements in the network to remain in synchronism following abrupt change in operating conditions like tripping of a feeder, tripping of generating unit, sudden application of a load and network switching etc.


j)“User" means a person such as a Generating Company including captive generating plant or Transmission Licensee other than the Central Transmission Utility (CTU) and State Transmission Utility (STU), Distribution Licensee or Bulk Consumer whose electrical plant is connected to the Grid at voltage level 33kV and above.


k)"Voltage Unbalance" is defined as the deviation between highest and lowest line voltage divided by Average line Voltage of the three phases. The words and expressions used and not defined in these Regulations but defined in the Electricity Act,


2003 shall have the meaning assigned to them in the said Act.

Schedule Grid Standards for Operation and Maintenance of Transmission Lines


1. Frequency

The standard frequency of system operation is 50 Hz and all efforts shall be made to operate at frequency close to nominal as possible. The frequency shall not be allowed to go beyond the range 49.0 to 50.5 Hz, except during the transient period accompanying tripping or connection of load.



2. Voltage

i)Bulk consumers shall ensure balanced load during operation.


ii)Low Voltage Single phase loads shall be balanced periodically at the distribution transformer by Distribution licensees.


4. Protection Standards

i) The Transmission Licensee and Users shall provide standard protection systems having the required 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. Protection coordination shall be done by the RFC.


ii) Fault Clearance Time:

The maximum fault clearance times are as given below:

Nominal System Voltage kVrms Maximum Time ( in milliseconds)765 and 400



220 and 132


iii) In the event of non clearance of the fault by a circuit breaker within the time limit prescribed in 4

(ii) above the Breaker Fail Protection shall initiate tripping of all other breakers in the concerned bus-section to clear the fault in next 200 milliseconds.


5. Criteria for System Security

The following minimum security criterion shall be followed for operation and maintenance planning of the elements of the grid:


The Grid System shall be capable of withstanding one of the following contingencies without experiencing loss of stability:


(a) Outage of one single largest generating unit of the system or

(b) Outage of a 132 kV Double circuit line or

(c) Outage of a 220 kV Double circuit line or

(d) Outage of a 400 kV Single circuit line or

(e) Outage of a 400 kV Single circuit line with series compensation or

(f) Outage of 765 kV Single circuit line without series compensation or

(g) Outage of one pole of HVDC Bipolar line or

(h) Outage of an Interconnecting Transformer

6. Transient Stability

Under any one of the following contingencies the system shall remain stable and sustain integrity (i.e., no generator shall lose synchronism and no part shall get isolated from the rest of the system):


a)Tripping of a single largest generating unit or


b)Transient ground fault in one phase of a 765 kV Single Circuit Line close to the bus or


c)A sustained single phase to ground fault in 400 kV single circuit line followed by 3 pole opening of the faulted line or


d)A sustained fault in one circuit of a 400 kV Double Circuit Line when both circuits were in service in the pre-contingency period or


e)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


f)A three-phase sustained fault in a 220 kV or 132 kV or


g)A sustained fault in one pole of HVDC bipolar in a HVDC Converter Station.



Insulation and Temperature

Rise:Class F/H insulation and Class B Temperature rise



1.For efficiency of turbine, the performance curves of similar turbines manufactured by the bidder (tested by independent institution) will be provided.


2.Generator will conform to IS: 4722 (2001) and single-phase induction generators to IS: 996(1979).


3.Electric load controllers shall be type tested by an independent institution for adequacy, for performance, surge protection, waveform deviation, electromagnetic interference, emissions of radio noise.


4.Micro hydro for power generation category B & C should have the following provisions:-


(i)Parallel operation in local grids whenever available.


(ii)Parallel operation with main grid whenever extended.


5.Micro hydropower generating station category B & C having more than 1 unit shall have following additional provisions:-


(i)Parallel operation between units at the station


(ii)The Governor/Load Controller, AVR should have adequate provision for adjusting the Speed Droop and Voltage Droop for facilitating the Parallel Operation of the Units.


2. Synchronous Generator and Induction Motors as Generators

i. Brand. The brand and power rating of the generator or motor should be approved by the manufacturer of the turbines and by the purchaser.


ii. Nameplate. The original manufacturer’s nameplate for the generator or motor must be retained.New nameplates can be added but must not replace the originals.


iii. Over-rating. The power rating given on the original nameplate must be at least 10% more than the scheme rated power.


iv. Generator voltage. The “power house voltage” is the voltage at the generator terminals with powerhouse-consumer isolation switch in off position. This must be between the nominal national voltage (415 V) and +10% of 415 V.


v. Generator rotational speeds to be selected shall be 1500 rpm (+slip) or lower. In cases of direct coupling 750 rpm or 1000 rpm generators should be preferred.


3. Synchronous Generator

i. Frequency. The operating frequency should be between 47.5and 52.5 Hz.

ii.Pf. The power factor rating should be 0.8 when an Electronic Load Controller (ELC) is in use except where all loads and the ELC present a unity power factor.


iii.Brushless generators shall be supplied with regulator (AVR). The unit proposed for interconnection with grid shall have in addition automatic power factor Regulator (APFR) with automatic change over from AVR to APFR when grid interconnection circuit breaker.


iv.The generator shall be capable of continuous withstand against runaway speed.


4. Induction Motor

i. Frequency. The frequency should be between 50 and 52.5 Hz. The frequency should be within this range under all operating conditions, including minimum and maximum power output, zeroconsumer load and worst-case consumer load power factor.


ii. The induction generator must be over-voltage protected to avoid excessive currents to flow through the excitation capacitors and induction machine. A protection system is required that disconnects all or some of the capacitors, to limit the currents flowing to below the limits for the induction machine windings and the capacitors. Provide MCBs of suitable current rating in the series with excitation capacitors.


iii. The generator shall be capable of continuous withstand against runaway speed.

5.Turbine/generator base-frame


i. The turbine and generator should be mounted on a single steel fabrication, the base frame, which shall be set into or fixed to the powerhouse floor (separate fixings shall be avoided in order to avoid tension stresses occurring in the concrete floor). This shall be fabricated from angle iron or channel section. A base frame may be omitted if the turbine and generator are close-coupled, that is, their own frames are rigidly connected to each other’s.


ii. The turbine and generator should be fixed securely to the base frame in a workshop before installation to achieve correct positioning. This should avoid problems with bearing alignment and belt tensions during operation. The runner must be easily removable on site.


6. Bearings

i.On larger machines, bearings must be selected and maintained to provide a service life of 10 years.On smaller machines a service life of 5 years is acceptable.


ii. Bearings must be properly aligned, either by use of self-aligning types or by adjusting of the bearing housings. There must never be more than two bearings on one shaft. Poor alignment will cause bearing failure and will be evident in the first year of operation of the turbine. The mandatory one-year warranty should be given to ensure that the manufacturer covers bearing failure costs, and to ensure that correct alignment is established.


iii. With the bearing housing open, the bearing housing should be one third full of clean grease.


A. National and International Standards and Codes Latest edition of the following standards are applicable. IEC-34-2A-1972 - Rotating Electrical Machines Methods for determining losses and efficiency of electrical machinery from tests (excluding machines for traction vehicles IEC-34-1: 1983 – Rotating Electrical Machines, Rating and Performance IEC-85-1987 - Classification of materials for the insulation of electrical machines IEC-34-5-1991 – Classification of degrees of protection provided by enclosures for rotating electrical machines (IP Code)