KERALA STATE ELECTRICITY BOARD

23/08/2018 tak save energy 1

TO

KERALA STATE ELECTRICITY BOARD


T A Kuriyakose

Assistant Executive Engineer

9446008482

Power & TelecommunicationCo-ordination Committee


Back ground & Importance of PTCC


Power & TelecommunicationCo-ordination Committee

Power and Telecom lines constitute two essentiallife lines to any community. Very often they willhave to follow the same road or railwayalignment and thus will have to exist close toeach other.

Any high voltage power line sets up in its vicinityelectric and magnetic fields. Communicationcircuits coming under the influence of thesefields will experience extraneous induction.


PTCC

The extraneous induction under certain conditionsmay induce noise in communication circuits and/ orcause danger to equipments / personnel.

Therefore it is very essential that whenever powerand telecom lines have to take rights of way close toeach other, suitable coordination measures areeffected to derive maximum benefits from both thesystems.


PTCC

For carrying out such coordination, the Govt.of India constituted a central standing bodycalled the Power and TelecommunicationCoordination Committee in 1949.


Various Levels of PTCC

1. Central 2. State 3. SSA or Telecom Dist. 4. Divisional 5. Sub-Divisional


Membership in Central PTCC

1. Chief Engineer (LD & T),Central Electricity Authority,New Delhi

2. Chief General Manager, T&D Circle,Bharat SancharNigamLtd ( BSNL), Jabalpur ( Chairman alternate year )

3. Director ( PTCC ),Central Electricity Authority,NewDelhi ( Secretary (Power) )

4. Deputy General Manger, T&D Circle,BSNL, Jabalpur( Secretary( Telecom)


Membership in Central PTCC

5. Director (Telecom),Railway Board,New Delhi - Member6. Jt. DDG (ML), Ministry of Communication - Member7. Chairman/ Co-Chairman 0f SLPTCC - Member8. Director (GP), Ministry of Communication - Member9. Representative of Dept. of Power - Member10. A representative from the Army Headquarters -

Member11. DDG(NE), TEC, BSNL, Hyderabad - Member12. DET (PTCC), T & D Circle, BSNL - Associate Member


State Level PTCC

After its inception in 1949 all cases for PTCC clearancewere being referred to the Central PTCC. The work at theCentral level increased enormously due to the enormousspurt in both the Power and Communication sectors. Theclearance of 11 KV lines was entrusted to DEs(T) of theTelecom Department on the basis of guidelines prepared bythe Central PTCC. It was necessary to further decentralizethe work relating to lines up to 33 KV. Accordingly, StateLevel Committees were set up in 1968 with representationfrom the Power and Telecom sides. A ‘Simplified Procedure’for issue of clearance in such cases was prepared by theCentral PTCC.


Frequency of SLPTCC meeting

As per the decision taken in 58th Central PTCCmeeting held at Darjeeling on 25.2.1992 theState Level PTCC meetings should be held asfrequently as possible but not later than aquarter/3 months. In Telecom Circles wherelarge number of unguarded power crossings arepending and more electrocution accidentsoccurred, the meetings in those circles shouldbe convened more frequently In order todecide any emergency cases, special State LevelPTCC meetings can also be requisitioned andthe power of requisition of such meetings isvested with Chairman State Level PTCC.


Functions of SLPTCC

(i) To review the progress of route approvalcases of 11 KV lines dealt with by TelecomDivisional Engineers.

(ii)To consider route approval cases up toservice voltages of 33 KV.


Functions of SLPTCC …..

(iii)To consider re-engineering schemes forcases where induction exceeds the protectionlimit for GD tubes.

(iv)To co-ordinate and watch the progress ofinstallation of protective measures and re-engineering works and issue of energizationcertificates on completion of protective works.


Functions of SLPTCC …..

(v) To consider violation of PTCC regulationsand take suitable corrective measures.

(vi) To discuss cases of power lines of 33 KVand above held up for PTCC clearance.


CODE OF PRACTICE FOR OVER-HEAD TELECOM LINES

Rule 87 of Indian electricity rules ensuresstatutory obligation for both power andtelecom authorities to follow PTCC code ofpractice at the crossings to avoid contacthazard. ( Refer Central Electricity Authority (Measures relating toSafety and Electricity Supply) Regulations, 2007.Section 23. Safetyrequirements pertaining to overhead lines, under ground cablesand generating stations Page 14 :-SCHEDULE-V Safetyrequirements for overhead lines, under ground cables andgenerating stations Page 53 )

The power lines should always cross over thetelecom lines and the angle of crossing shouldbe as nearly a right angle as possible.



The protection envisaged for negotiating the crossings is based on the voltage category of the power line involved

Wherever guarding is done, it should beearthed at both ends and the earthresistance for this purpose should be < 3ohms and in no condition it should be >10 ohms.



Power Contact Protectors (PCPs) should beprovided on all top telecom conductors at thepower crossings with power lines of categoryfrom 3 KV up to and including 33 KV. This is inaddition to the guarding arrangementrecommended above. The earth resistance forPCPs should be preferably 1 ohm and in nocondition it should be > 10 ohms for theirsatisfactory performance.


SAFE SEPARATIONS FOR CROSSINGS BETWEEN TELECOM & POWER LINES

Sl.No

Voltage Category of Power Line

Minimum Recommended Safe Separation

1 Low & Medium ( < 650 V )

a With Insulated Power wires >0.75 m

b With bare Power wires

(i)With guarding on PowerPost > 0.915 m

(ii)Guarding onTelecompost >1.22 m



Sl.No



2 High Voltage Lines ( HT ) ( 650 to 36KV)

a For 7.2 KV and below >1.07 m

b For 7.2 KV upto 36 KV > 1.22 m



Sl.No



3 EHT Lines

a 36 KV to 72.5 KV >2.44 m

b 72.5 KV to 145 KV >2.74 m

c 145 KV to 245 KV > 3.05 m

d Above 245 KV >3.05 m +0.305m for every addl 33 KV


GUIDELINES FOR CROSSING OF

POWER AND TELECOM CABLES

Minimum Depth of laying of UG Cables

3.3KV to 11 KV - 0.9 M

11 KV to 33 KV - 1.05 M

LT & Control Cable - 0.75 M

At road & railway crossing – 1.00 M


GUIDELINES FOR CROSSING OF POWER AND TELECOM CABLES

CLEARANCES POWER CABLES TO POWER CABLES: Not necessary

POWER CABLES TO CONTROL CABLES: 0.2 M

POWER CABLES TO COMMUNICATIONS CABLES: 0.6 M

( Preferably 0.6 M but not less than 0.3 M )

POWER CABLES TO GAS/WATER MAINS: 0.3 M


Protection of Telecom systems

In spite of the Growing sophistication intelecommunication equipments and technologicaladvancements, the DANGER perception continuesfor the electronic equipments in the telecomnetwork because of their vulnerability to voltagesand current induction.

While the voltage transients can damage or destroythe equipment, over current poses a far greaterpotential hazard i.e., Fire, and the voltages &currents continuously induced longitudinally resultin disturbances which can affect the performance oftelecommunications systems.


Reasons for over voltage & over current in telecom lines

(i). CONTACT

(ii). INDUCTION- Both Electro Static & Electro

Magnetic

(iii). EARTH POTENTIAL RISE

(iv). LIGHTNING


ELECTOMAGNETIC INDUCTION:

Electromagnetic induction on to a telecomline/cable from nearby power line ispredominant only under the faulty condition ofthe power line.

Single line to ground fault condition on powerline is considered, in view of possiblemaximum current flow to earth, for decidingthe protection on paralleling telecomconductors.


ELECTOMAGNETIC INDUCTION:

As the duration of dangerous voltages on aparalleling telecom conductor is limited to theduration of fault on the inducing power line,human safety can be ensured if these voltagesare limited to the CCITT limits. *430v for lowreliability power lines ( uto 33 KV)

* 650 V for high reliability power lines (>33KV) respectively.


INDUCED VOLTAGE

The quantum of voltage induced dependsupon the following:

(a) Length of parallelism

(b) Fault current

(c) Mutual coupling

(d) Soil Resistivity


SOIL RESISTIVITY Soil Resistivity is an important factor which determines the

magnitude of electromagnetic induction between the power

and telecom circuits. When an earth fault occurs on anyone

phase of the power line, large fault currents flow in the power

conductors and return through earth. Under such conditions,

the power line and the neighboring , telephone line form

two parallel earth return circuits with a high degree of mutual

coupling. The mutual coupling increases with soil resistivity.

Since the induced voltage in the communication circuit is the

product of fault current and mutual impedance, the value of

the induced voltage increases with increase in soil resistivity.







IV Calculation

Details required : Soil resistivity in cm, Fault current in A, Data from Curson Curves .

Calculated values :

Mutual Coupling between power lines and Telecom lines ( MC ) in , Length of parallelism ( LOP ) in metres, Induced Vottage ( IV ) in Volts


Protection - Methods

Gas discharge (GD) tubes should be usedon the paralleling telecom conductors inthe length of parallelism, one each at theend and the remaining in between atequidistance intervals.


The number of GD-tubes to be providedcan be arrived at by dividing the inducedvoltage with 300 and rounding off theresult to the next higher digit, ifnecessary. This procedure is adoptedwhen the induced voltages are in therange of 430 to 2000 volts.


When the induced voltages are 2000 V ormore, the 20-GD-tube formula, given below, isused in order to arrive at the number of GD-tubes and these are limited to (twenty) due tonoise considerations.

(i).FOR HIGH RELIABILITY POWER LINES (i.e.>33KV) ______

650 ≥ E/N [ 1 + l 10N ]

[ √ Z ]


(ii). FOR LOW RELIABILITY POWER LINES,(i.e. up to 33KV) _____

430 ≥ E/N [ 1 + l 10N ]

[ √ Z ]

Where,

E is the Induced Voltage in Volts

N is the number of GD-Tubes required

Z is the Total Impedance of effected portion oftelecom line in Ohms,

And Z= Z0 X L, Where Z0 is the Impedance per kmof telecom line in Ohms and L is Length ofparallelism in kms.


By applying this formula, the maximumnumber of GD-tubes that can be installedon telecom line is limited to 20. If thenumber arrived at is more than 20, itbecomes a case of re-engineering, whenseparation is increased or telecomcircuits are changed to another media.


ABOUT GD TUBE

The gas discharge tube essentiallyconsists of three tungsten electrodessealed in a special glass envelopecontaining a mixture of inert gases,mainly neon. Two of the electrodes arefor connections to the lines and the thirdis connected to the earth electrodes.


ABOUT GD TUBE

If the potential difference across theelectrodes rises to a certain critical value(the striking value) the gas is ionizedand becomes conducting. This conditionwill continue till the potential differenceacross the electrodes falls to theextinction voltage value.


EARTH POTENTIAL RISE

When an earth fault occurs in a powersystem, some of the fault current returnsvia the earth through the earthingsystem, and this current raises thepotential of the earthing system withrespect to a remote earth for theduration of the fault.


EPR LIMITS


EPR LIMITSType of Telecom Plant

Power lines upto 33 KV

Power lines >33KV

Terminal Apparatus, Joints,Cabinets, Pillars,

Manholes,Pits, Poles

430 V 650 V

Telephone Exchanges 430 V 430 V

Metal Sheathed cable 430 V 650 V

Plastic Insulated cable 7 KV 7 KV

PIJF Cable 10 KV 10 KV


HAZARD ZONE

The hazard zone near an earthingsystem varies from some tens to somethousands of metres, depending on soilresistivity, layout of the earth mat,power network, fault current and otherlocal conditions.


The EPR zone or the distance ‘X’ in metres at whichthe EPR may rise to a value ‘Ex’ can be determinedfrom the formula:

(i). For Simple Earthing System such as singleelectrode earthing system:

ρ l

X = ------ Metres

2 π Ex

Where, ρ is the Soil Resistivity in Ohm metre

I is the Fault Current in Amps and

Ex is the EPR voltage Limit as specified in the Code ofPractice above.


(ii).For large earthing systems:

Emax x D IR x D

Ex = ------------------ = -------------

(d + D) (d + D)

Where, Ex is the Potential at radial distance of ‘d’ fromthe perimeter of the earth mat in volts.

I is the maximum fault current through theearth mat in Amps.

R is the measured Resistance of the earthmat in ohm.

D is the diagonal distance of the mat inmetres

d is the distance in metres from theperimeter of the earth mat.


GENERAL PRECAUTIONS IN EPR

ZONE

The telecom circuits should be provided in plasticinsulated and unscreened plastic sheathed cable laid inrigid PVC conduit.

Location of cable joints, pillars, cabinets andterminations, which require personnel to attend, shouldbe avoided in EPR zone.

While working in EPR zone, the staff should insulatethemselves from the earth by standing on an insulatingmat having a specified insulation, withstanding voltage ofat least 15 KV for one minute. Insulated tools, gloves andfootwear should also be used.


THE PTCC PROPOSAL

THE ROUTE MAP

SCALE OF MAP AS PER PTCC NORMS

THE QUESTIONNAIRE

THE SINGLE LINE DIAGRAM

THE SOIL RESISTIVITY DATA

TOWER CONFIGURATION WITH DATA OF GENERATORS,TRANSFORMERS, REACTORS


THE ROUTE MAP

THE POWER LINE ON ROUTE MAP MAY BE MARKEDWITH RED COLOUR ONLY

THE SCALE OF THE ROUTE MAP MAY BE SENT AS PERPTCC NORMS SUCH AS 1CM.=1/2 KM. (1:50000) OR 1INCH=1 MILE

THE ROUTE MAP SHOULD SHOW ALL TOPOGRAPHICALDETAILS SUCH AS ROADS,RAIL,RIVERS,FOREST AREAUPTO 5 KMS/ 8KMS. ON EITHER SIDE OF THEPROPOSED POWER LINE


THE NOS. OF CROSSINGS FROM THE TELECOM/RAILWAYLINES SHOULD BE GIVEN.

RAILWAY LINE SHOULD BE MARKED IN YELLOW

INDICATE THE SOIL RESISTIVITY OF THE AREA ALONG THEPOWER LINE.THE SOIL RESISTIVITY SHOULD BEMEASURED BY FOUR ELECTRODE METHOD USING ANINTER ELECTRODE SPACING OF 50M. THE MEASUREMENTMAY BE MADE AT EVERY 2 OR 3 Km. ALONG THE LENGTHOF THE LINE. ALWAYS MEASURE SOIL RESISTIVITY IN DRYSEASON

THE SINLE LINE DIAGRAM MAY BE SENT FOR BOTH OF THESUB-STATIONS


Route Approval & Energisation Approval

Power line Approval Issued by

33 KV S/C Route SLPTCC

Energisation GM,SSA

33 KV D/C & Route Central

Above Energisation CGMT


THANK YOU

KERALA STATE ELECTRICITY BOARD

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