Brief Description of the Set-Up and Activities of the Power and Telecommunication Coordination Committee (ptcc)




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Note: Procedure circulated with Agenda for Central PTCC Meeting No. 81-82/3 held at Chandigarh on 26th November 1981 by Central Electricity Authority, New Delhi.
Conversion of Railway Train Wire Circuits into Metallic Return


  1. Introduction

Train wire is a single wire earth return telegraph circuit used by Railway Department. It is a non-continuous circuit working on station-to-station basis (as contrast to railway control circuit which is a continuous circuit looped at every station). Due to the short length of this circuit (the length depending upon the distance between the two consecutive Railway Stations), the Railway Department uses only 12 V operating battery.




  1. Procedure adopted for conversion of SWER Telegraph circuits to metallic return

As per the recommendations of the sub-committee for examining the conversion of SWER telegraph circuits to metallic return, the conversion should be done in the following cases.


If the interfering current from a power line under its normal working condition exceeds 1/10th of the normal operating current of the telegraph circuit, the telegraph circuit should be converted to metallic return. This should be examined for electromagnetic and electrostatic inductions.
(i) Electrostatic Induction
If the weighted separation between the power and telecom line for the total length of parallelism for the telegraph circuit under examination exceeds the separation obtained from the formula,
Separation for 50 c/s inducing frequency

Where,


E = Service voltage of the power line in volts and

S = Length of telecom line in kilometers involved in exposure,


the telegraph circuit is not required to be converted to metallic return.
In the case of railway train wire circuits generally the electrostatic induction is within safe limits.
(ii) Electromagnetic Induction
The mutual coupling of the telegraph circuit under examination (for full length of parallelism) is multiplied by the maximum residual unbalanced current of the power line. This value should not exceed 1/10th of the normal operating voltage of the telegraph circuit. (The inducing current and the operating current, if desired, can be obtained by dividing these voltages by the impedance of the telegraph circuit).
In the case of train wire circuits, metallic conversion is often required on account of electromagnetic induction.
(iii) Maximum residual unbalanced currents for different categories of power lines are given as below:


Category of

Power Line



Load

In

MW



Effective Line Current

In Amperes



Maximum Unbalance Residual Current 1.5% of Effective Line Current in Amps.

400 KV S/C

500

902

13.5

230/220 KV D/C

300

984

14.76

230/220 KV S/C

150

492

7.38

132 KV S/C

50

273

4.095

132 KV D/C

100

546

8.19

110 KV S/C

50

328

4.92

110 KV D/C

100

656

9.84

66 KV S/C

12.5

137

2.055

66 KV D/C

25

274

4.11

33 KV S/C




200

3.00

Note: In case of 33 KV S/C power line, line current in each phase is being confirmed in each individual case.

3. Some typical cases in which train wire circuits are required to be converted to metallic return are given below:


Sl. No.

Name of Power Line

Name of Train Wire Section

Length of Parallelism in Miles

Mutual Coupli-ng

Maximum un-balance Residual Current in Amps

Disturbing EM Volt on Train Wire Current

Permissible EM Volt

1.

2.


3.

Singrauli – Kanpur 400KV S/C
Ring Main line around Jallandhar 66 KV D/C

Nakodar – Nurmahal 33 KV D/C





1. Billi R/S

-Phaprakund

2. Phaprakund

-Mangardaha

3. Mangardaha

-Mirchandhri

4. Mirchandhri

-Churki


5. Jallandhar

-Pathankot

6. Nakodr

-Nurmahal



6.64
3.75
4.28
9.2
24.2

11 Km



0.216
0.658
0.471
0.793
0.448

0.8



13.5
13.5
13.5
13.5
4.11

3.0



2.916
8.883
6.358
10.705
1.841

2.4


1.2
1.2
1.2
1.2
1.2

1.2




  1. Conclusion

It will be seen that in the above cases, the maximum electromagnetic voltage is 10.7V. The cases range from 400 KV to 33 KV power lines (i.e. can occur in every category of the power line). To avoid the conversion in majority of cases, the only remedy is to increase the circuit impedance by adding a resistance between the sounder and earth and increasing the battery voltage to maintain the same operating current. The following table can illustrate the case.





Operating Battery Voltage

Working Current (15 to 25 mA Mean Value 20mA)

Initial Circuit Resistance 500 ohms for Sounder Plus 100 ohms for Line and Earth at Both Ends

In Ohms


Additional Resistance in ohms

Net Total Resistance in ohms

Permissible Electromagnetic Induction Volts for 10% of the Operating Current.

12 V


24 V

36 V


48 V

60 V

20mA

20mA


20mA

20mA


20mA

600


600

600


600

600

Nil

600


1200

1800


2400

600


1200

1800


2400

3000

1.2 V

2.4 V


2.6 V

4.8 V


6.0 V


Appendix VI to Chapter I

(Refer Para 6.1.8)
Copy of Central Electricity Authority, New Delhi Letter No. 19/109/89/PTCC

Dated 17th November 1989
Subject: Noise Sub-committee Report.
Dear Sir,
As you are all aware that the Central PTCC in its meeting held at Bhubaneshwar on 29.7.1983 set up a Sub-committee to go into the problem of noise interference due to power line on paralleling communication circuits and suggest remedial measures. The Sub-committee carried out studies and conducted a few tests during its period and submitted a report. The same is enclosed herewith for your kind perusal. Based on the report Chairman, Central PTCC, in the meeting held at Chennai on 29.10.1987 suggested that this Committee may be wound up. He further suggested that in future such problems should be sorted out directly by discussions among Central Electricity Authority, Department of Telecom and Railways as and when required.
Yours faithfully,

Sd/- (D.P. Sinha)



Director (Telecom & PTCC)
Enclosure to Central Electricity Authority, New Delhi

Letter No. 19/109/89-PTCC dated 17th September 1989
Report of the Noise Sub-Committee (1983-87)
Introduction
The problem of noise interference due to power lines on railway communication circuits was first reported from Southern Region way back in 1981. This noise was related to the two-phase operation of 11 and 22 KV power lines of Tamil Nadu Electricity Board. A study team investigated the problem and carried out tests on the affected circuits during 21st and 23rd April 1981. It was observed that the noise on communication circuits increased due to two-phase operation of the power lines. The Central PTCC, therefore, requested Tamil Nadu Electricity Board to discontinue the two-phase operation of the power lines wherever there were noise problems on communication circuits. Since then, there were representations from the Department of Telecommunication about noise interference in communication circuits due to power lines/cables and they have been insisting that some standards be laid for limiting noise due to power lines. The power side requested Department of Telecom to cite specific examples where noise interference was observed so that they could be studied, where the noise problem arose due to power line operation in the vicinity. However, no specific cases were referred for a long time even though there was increasing insistence from Department of Telecom for the study of the noise interference problem. Taking cognizance of this demand from Department of Telecom, the Central PTCC at its meeting held at Bhubaneswar on 29th July 1983 set up a Sub-Committee to go into the problem and suggest remedial measures. The constitution and terms of reference of the Sub-committee are annexed.
Meetings of the Sub-Committee
The first meeting of the Sub-committee was convened on 10th November 1983 at New Delhi to consider the cases referred by DET, PTCC, Northern Region, even though there was no noise interference in these cases except that there were some standing voltages on certain communication circuits as reported by DOT. A detailed discussion on the methods of calculations of noise interference based on the formulae enumerated in CCITT Directives was carried out and it was decided that the calculations would not yield any reliable and practicable results. However, the Committee felt that though there are no reported cases of noise interference, some appear to exist. Hence, it was decided to investigate specific cases, if any, reported to the Sub-committee.
Field Test
The Noise Sub-committee in its second meeting held on 30th July 1986 decided to carry out actual noise measurements on Janakpuri-Najafgarh junction cable where interference due to noise was reported by DET, PTCC Northern Region. Shut down from the Najafgarh Sub-station was to be arranged with the help of DESU to carry out the tests.
After making required arrangements including arrangement of shut down of 11 KV feeders actual noise measurements were carried out on certain pairs of the cable on 20th August 1987 at Najafgarh exchange. Representatives of Central Electricity Authority, TRC & DOT participated in the measurements.
It was decided to take noise measurements on the same 11 numbers of pairs on which noise was earlier noticed by DET, PTCC, Northern Region. These 11 numbers of pairs were identified by DOT for noise measurement and were got opened from Janakpuri end. To simulate terminating impedance of 600 ohms, it was decided to connect to each pair a telephone set which has a nominal impendance of 600 ohms. It was proposed to measure the psophometric noise with a psophometer and both weighted and flat noise observations were to be recorded.
Procedure
Before starting the measurement all the 11 KV feeders emanating from Najafgarh S/S were shut-off and psophometric noise was measured on the selected 11 numbers of pairs. On a pair 4/5/12, when the psophometer was connected the needle started shaking violently and no steady measurement was possible. The pair was later detected to be ‘open’. Each of the pair was accordingly checked for continuity and it was found that in all 5 pairs were open and therefore declared ‘Faulty’.Steady observations on the psophometer were recorded for remaining 6 numbers of pairs. The psophometric noise was recorded on each of the ‘healthy’ pairs again after all the 11 KV feeders had been switched ON from Najafgarh S/S.
Observations
The set of observations recorded, both weighted and flat are annexed. It may be seen that the psophometric noise on different pairs vary from 0.2to 90 mV when the 11 KV supply is OFF and 0.3 mV to 120 mV when the 11 KV supply is ON. This large variation in the psophometric noise for different pairs of the same cable indicates different characteristics of each pair of the cable under measurement.
As can be seen from the observations, the psophometric noise on the junction cable increased from 0.1 to 30 mV for different pairs and in one case it actually decreased by 0.8 mV.
Conclusion
From the observations recorded for Janakpuri-Najafgarh junction cable it is seen that the pairs under measurement are totally unbalanced. This is brought out by widely differing psophometric noise on different pairs even when the 11 KV feeders were OFF. The measurements on pair 4/6/27 are highly revealing, as the psophometric noise is observed to be 2.5 mV when the power lines were OFF and 1.7 mV when the power lines were ON. This decrease appears possible only due to the high stray capacitive effect of the pairs with respect to earth. It is suspected that water/moisture might have creped in the cable, resulting in stray earth capacitances, thus unbalancing the different pairs within the same cable. The most perfectly balanced pair comes out to be 4/5/10 pair for which measured psophometric noise when power lines are OFF is 0.2 mV and when power lines are ON is 0.3 mV, the variation being well within the permissible limits. The noise being observed appears purely due to fault in the cable pairs due to seepage of water or some similar reasons creating unbalance. It may be significant to note that the same pairs (which were tested now) were got tested for psophometric noise by DET, PTCC in December 1984 and he detected Noise. In the meeting held on 30thJuly 1986 he further stated that the Noise had disappeared after the investigation but had reappeared. Since monsoon rains do set in around that time of the year the rain water might have creped in the cable again, unbalancing the pairs, thus, creating psophometric noise. There had been no change as far as surrounding power lines are concerned to warrant any variation in the noise levels. This clearly shows that the condition of this junction cable is not good and the noise notified is only due to the faulty cables and not due to induction from power lines.
Observations Recorded at Najafgarh Exchange on 20th August 1987

from 1100 Hrs to 1500 Hrs.


BEFORE SHUT DOWN

AFTER SHUT DOWN

(only 11 KV feeder off)



Sl.No.

Cable Pair No.

Psophometer Reading

Sl.

No.


Cable Pair No.

Psophometer Reading

Weighted

Flat

Weighted

Flat

(i)

4/5/10

0.3 mV

0.3mV

(i)

4/5/10

0.2 mV

0.5 mV

(ii)

4/5/12

-faulty-

-

(ii)

4/5/10

-

--

(iii)

4/5/17

3.5 mV

3.5 mV

(iii)

4/5/17

2 mV

2.25 mV

(iv)

4/5/39

6 mV

6 mV

(iv)

4/5/39

5 mV

5 mV

(v)

4/6/2

-faulty-

-

(v)

4/6/2

-

-

(vi)

4/6/3

10 mV

10 mV

(vi)

4/6/3

6 mV

6 mV

(vii)

4/6/19

-faulty-

-

(vii)

4/6/19

-

-

(viii)

4/6/21

-faulty-

-

(viii)

4/6/21

-

-

(ix)

4/7/7

1.7 mV

2.5 mV

(ix)

4/6/27

2.5 mV

2.5 mV

(x)

4/7/7

0.12 V

0.12V

(x)

4/7/7

0.09 V

0.09 V

(xi)

4/7/12

-faulty-

-

(xi)

4/7/12

-

-

Annexure
Terms of Reference of the Noise Sub-Committee.


  1. The levels of Noise under conditions of normal operation from power lines of the open wire type on telecommunication lines and cables. The Sub-committee would study the existing international regulations in this regard particularly the CCITT directives and examine limits, which could be laid down under Indian conditions.




  1. Similar study in respect of underground power cables. The immediate problem is in regard to the limits to be tolerated from such cables.




  1. The protective measures that can be adopted on the power lines as well as telecommunication lines to bring down the existing level of noise to the specified limits.




  1. Aspects of cost sharing in regard to protective measures.



Appendix VII to Chapter 1

(Refer Para 6.2.5)
Minutes of the Sub-Committee Meeting For Information of Norms For

PTCC Clearance of HVDC Lines

(Circulated vide C.E.A., New Delhi Letter No. 19/117/87-PTCC dated 3rd February 1987)


The meeting of the Sub-committee for formation of norms for PTCC clearance of HVDC lines was held on 2nd February 1987 in the office of the undersigned. The list of the participants is enclosed.


  1. Details of the smoothing Reactors provided on each pole of the DC line (already furnished by NTPC) were discussed. It was shown from the calculations that the fault currents are limited to within 1.4 KA/m Sec. It was further clarified that the above value is much lower than the transient currents occurring during ground faults on AC transmission lines. Hence, it was logically concluded that there is no possibility of any hazard due to induced voltage during ground fault conditions.



  1. The maximum allowable levels for the longitudinal induced noise voltage due to DC line harmonics on a parallel telecom line at a lateral distance of 1 kilometer from the DC line, based on stringent requirements, was tentatively agreed as:

For Bipolar Operation 10 mV/km

Monopolar Metallic Return 20 mV/km

Monopolar Earth Return 30 mV/km


The above values were as suggested by the consultants M/s Hydro Quebec.
The above values for the bipolar and monopolar modes have also been used as a criterion in several cases as mentioned clearly in Reference (1) and have been taken as guiding values and design criteria for other HVDC lines.
3. It was decided that the actual values of induced voltage would be measured after construction of the Rihand – Delhi HVDC line and the need for relaxation of the above norms could be examined at that stage.
4. As regards the transverse voltages on the telecom line, it was decided that the same could be examined separately at a later date depending on requirements.

Sd/- (D.M. Rao)

Deputy Director (PTCC)

Reference (1): DC Filter Design Methods for HVDC Systems-R.H. Lasseter etc. at IEEE Transactions on Power Apparatus and Systems Vol. PAS-96 No. 2 March/April 1977.


Members present at the meeting of the Sub Committee to evolve norms for PTCC clearance of HVDC lines.

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