UTILITY OF TELECOMMUNICATION IN MANAGEMENT OF GRIDCO POWER SYSTEM

Out of variety of Telecommunication facilities available for Power Sector utilities for their Telecommunication and Telecontrol requirements, PLCC to-date continues to play a significant and dominant role. However with the passage of time, as the integrated Grid network system is becoming more and more complex, it has become necessary to change over to high-speed data transmission and Wide Band communication system. The PLCC inherently suffers for limitation of bandwidth, there by making it unsuitable for high-speed data transmission, besides attributing to poor Signals to Noise Ratio. Therefore, GRIDCO like other utilities are opting to advanced means of communication, such as Optic Fibre, Microwave and V-SAT communication looking to the need and situation of application. The ULDC project under implementation of GRIDCO, as a member constituent of Eastern Region envisages adoption of Fibre Optic and Microwave Communication as a part of restructuring the existing Telecommunication facilities. Mostly in GRIDCO system, the Fibre Optic Communication has been preferred over other modes of communication, as it outlays all other on the basis of overall weightage, on factors like cost, capacity, speed, network management and annul recurring expenditure etc. moreover technical suitability of Optic Fibre System, arises on account of its lower transmission loss, small size and weight, immunity to electro magnetic interference and capability of providing total electrical isolation added with signal security and diversification possibilities. On completion of the ULDC Project, GRIDCO shall be benefited by real time SCADA operation covering as many as sixty RTU locations reporting through four Sub-LDCs (Area Load Despatch Centres) to the State Load Despatch Centre (SLDC) at Bhubaneswar, for effective grid management. Besides, advanced Telecommunication features such as video conferencing, teleconferencing etc. can be made available through Optic Fibre in addition to routing speech and data communication (FAX). This will also enable GRIDCO to provide basic Telecommunication services by way of leasing out spare Optic Fibre channels to the service providers for revenue generation, as a part of diversification from the existing power trading business by Gridco.

TYPES OF COMMUNICATION CHANNELS ALLOCATED IN POWER SECTOR

1. Communication Channel Width is 4 kHz out of which 0-300 Hz is left vacant to avoid up to 6th harmonic of power frequency i.e. 50 Hz.
2. 300 Hz to 2200 Hz is reserved for speech channel.
3. Pilot frequency 3600 Hz ± 30 Hz is used for dialing frequency and the center frequency 3600 Hz is used for monitoring the health of the channel.
4. The frequency band from 2200 to 3570 Hz is used for Voice Frequency Telegraph (VFT) or Frequency Shift Keying (FSK) in speeds of 50 baud, 100 baud or 200 baud as per CCITT recommendation R45, R37, R38A, R38B.

The 4 kHz channel may also be used for following means of data transmission:

• 1200-baud rate Frequency Shift Keying (FSK) to CCITT Rec. V23 on a basic 4-wire, 4 kHz PLC or analogue radio channel.
• 2400-baud (9600 bit/s) phase modulated 4-wire leased telephone type circuit as CCITT Rec. V29.
• Pulse Code Modulated (RCM) 64 kbps digital data channel to CCITT Rec. C702.
• In case of facsimile (FAX) facilities CCITT Rec. T3 using vestigial side baud modulation occupy a bandwidth 800 to 2600 Hz. In this case audio channel with cut off 2200 Hz are not possible.

TYPES OF CHANNELS:

Power Line Carrier Communication PLCC:

50 kHz to 450 kHz is allocated to power sector out of which 50 to150 kHz is freely available to power sector and rest are available with the permission of Dept. of Telecommunication (DoT) and Wireless Planning Co-ordination (WPC) under Govt. of India. Frequency 500 kHz±5 kHz is used as international distress calling frequency.

Microwave/VHF Radio Link:

The power system network is allocated with latest PCM (Pulse Code Modulation), multichannel digital circuits based on multiples of 30 channel PCM multiplex operating at 2048 kbps. The modulation method used is either two level Frequency Shift Keying (FSK). WPC has assigned 2.30 to 2.50 GHz and 8.3 to 8.5 Ghz bands to the power sector for planning narrow band networks over large areas. In addition frequency bands 7.11 to 7.125 GHz, 7.725 to 7.8 GHz and 10.5 to 10.68 GHz can be used by the power sectors for short hauls and spurts.

Satellite Links:

These links will have inherent round trip delay of 280 ms. For power system where the traffic consists of medium speed data and voice, digital Single Channel Power Carrier (SCPC) is the suitable technique where technique such as either 64 kbps PCM, or 32/16 kbps delta modulation or typically 9.6/16k voice coding is used.

Fibre Optics:

Typical bandwidth available is 100 GHz per Km with repeater span typically 50 Km is used with mono mode fibre 4 to 24 cores as per CCITT Rec. G652 having 1300 nm wave length with attenuation figure of 0.5 db per Km using semiconductor laser diode as transmitter and PIN-FET receiver. A link of this type could be of 30 channels (primary multiplex)-2 Mbps, 120 channels (second order multiplex)-8Mbps, 480 channels (third order multiplex)-34 Mbps or even 1920 channels (4th order multiplex)-140-Mbps using standard PCM equipment with relevant CCITT recommendation.

Types of Leased Circuits:

• 2-wire audio cables for distance up to 20 Km.
• CCITT M1 020 and MI 040 type circuits. The M1 020 circuits are of similar characteristics as those derived from\ PLC and Microwave radio system.
• Wide Spectrum Signals on either group (60 to 108 kHz) or super group (312 to 520 kHz) leased circuits as per CCITT Rec. M900 and M910.
• Satellite leased Circuits such as SCPC, FM modulated, Analogue circuits.

POWER AND TELECOMMUNICATION CO-ORDINATION

The principle of low frequency inductive coordination involves the determination of the induced voltage of the communication circuits under single line to ground fault conditions on the power line and limiting the induced voltage in different sections to prescribed limits and it is here that the need for coordination between power and telecommunication line is felt. Considerable thought was given to this subject by both the power and telecommunication Engineers in the past. For co-ordination different committees have been formed at different levels. At present the cases up to the voltage of 132 kV power circuits and below are taken care of by the state level PTCC and the cases for voltages above 132 kV are looked after by central PTCC at Delhi.

Under the auspices of power and telecommunication co-ordination committee, the State Electricity Board and the P and T Department have come closer resulting in better understanding of each others’ codes and practices and instructions to be observed and practiced to eliminate this interference phenomena for prevention of electric shock hazards and mutual efficient working.

The co-ordination activities between the two organizations are carried out at various levels, i.e., Central, State and Division.

Limits of Induced Voltage: In our country the PTCC has fixed certain limits, which when exceeded will cause hazards as well as interference to telecom lines. These limits have been adopted from the C.C.I.T.T.’s recommendations. The C.C.I.T.T. is an advisory body operating under the control of the I.T.U. (International Telecommunication Union).

The power lines carrying large current at high voltages and telecom circuits carrying small signaling currents for transmission of messages when running closely parallel to each other, both inductive and conductive effects could be caused on the communication circuits. While inductive effects could be reduced by keeping adequate separation between two systems, the conductive effect could be minimized by providing proper guarding arrangements at the crossing points of two systems. A situation where power and telecommunication lines accidentally come into contact with each other is the most serious one and the effects could be reduced only by making elaborate guarding arrangements as per the code of practice for protection of telecom lines at crossing with over head lines. The measures for such locations are briefly given below:

(i) The angle of crossing should be as near to right angle, but not less than 600 in any case.
(ii) The specific clearance between power and telecom lines, earth wires and earth structures are to be adhered to. The minimum clearance between lines of various voltages to be maintained are as follows:

(iii) Guardings are to be provided at crossings of telecom lines with power lines up to 33kV.