CHAPTER IV
REMOTE CONTROL EQUIPMENT
I. GENERAL 20400 Introduction
A Remote Control Centre (RCC) is set up near the Traffic Control Office on each Division having electric traction, to work in close liaison with the traffic control. The RCC includes the main control room, equipment room, Uninterrupted Power Supply (UPS) room, Remote Control Laboratory and Battery Room and is the nerve centre of the Traction Power Control.
Types Of Equipment:
The following types of Remote Control Equipment are mainly in use on Indian Railways at present:
(i) Frequency Modulated Voice Frequency Telegraph (FMVFT), Strowger type equipment for supervisory control.
(ii) Supervisory Control And Data Acquisition (SCADA) systems with Microprocessor based equipment and/or Computer based equipment.
The FMVFT equipment was in use for all electrification schemes prior to 1980. Being mainly all relay system, the equipment has become outdated although some Remote Control Centres still continue to operate on this system. Salient features of the system are indicated at paras 20401 to 20406.
The SCADA equipment based on State of the art technology has come into use after 1980. Considering the fast growth and development of computer based equipment, newer types with enhanced capabilities and new makes are being introduced. Addional facilities at each new RCC is also natural as new features get incorporated. II. FMVFT EQUIPMENT 20401 Transmission Path
For transmitting control signals from the Remote Control Centre (RCC) to the various controlled posts underground cable circuits suitable for voice frequency (VF) operation are employed. These consist of star quads with an attenuation of about 0.3 dB/km. Isolating transformers are provided on the cable circuits at intervals of 10 to 15 km to limit the build up of longitudinal induced voltage on account of induction effect of single 25kV ac traction. Line losses are made good by VF repeaters provided by the S&T Department at interval of 30 to 50 km. The maximum gain in the repeater is 20 dB. Depending upon the distance of the RCC or controlled post (TSS/SP/SSP), repeater gain is so set that signal level at any point is within prescribed limit. Impedance matching transformers of ratio 1120 : 1120 are provided at points where communication cable is tapped for taking connection to the R.C. Centre or to the controlled posts. Suitable surge arrestors are also provided inside the equipment room at the termination point of communication cable to protect the circuits.
Normally three pairs of conductors are earmarked for Remote Control System, one pair reserved for telecommand signals from RC Centre to the posts and one pair from the posts to RC centre for telesignals. The third pair is spare for use in emergency, when any one of the other two pairs become unhealthy.
20402 Remote Control Switching Equipment
The RCC switching equipment consists of the following five major in
1. Pulse Generator,
2. Send Selector Circuit,
3. Receive Selector Circuit,
4. Check Circuit and
5. Indication Circuit.
All the units are of the plug-in-type and are housed inside the steel cabinet, which is provided with dust proof front and back doors. A number of such cabinets are provided in the remote control centre depending upon the number of controlled posts in a section.
20403 Mimic Diagram Board at RCC
The mimic diagram board at the RCC comprises several control panels on which the mimic diagram is shown. Every apparatus to be remote controlled is represented on this mimic diagram board by a control discrepancy switch. Hand operated dummy switches similar to but clearly distinguishable from the control discrepancy switches are provided to represent certain non-remote controlled apparatus like sub-station isolators. The electrified tracks are represented on the mimic diagram by white perspex strips or metallic strips. Whenever the 25kV voltage on any portion of the OHE between two controlled posts fails, or is not available, the corresponding portion of the mimic diagram lights up. The mimic diagram, however, remains dark under normal working conditions.
Each control discrepancy switch includes a built-in-lamp in a central indicator bar. If the controlled equipment is in closed position, the central indicator bar shows continuity of the diagram. If it is open, the central indicator bar will be at right angles, breaking the continuity of diagram.
Besides above, fault annunciation windows on the mimic diagram board are provided for each controlled post, with suitable inscription to annunciate the following kinds of fault:
1. Station Blocked
2. R.C. Equipment Defective
3. Contact Failure
4. Low volt d.c.
5. 240V a.c. Failure
6. Transformer Alarms
7. Transformer Faults
8. Low Volt 110V/72V d.c.
Item 6,7,8 are provided only for traction sub-stations. Item 6&7 are provided separately for each individual transformer.
20404 FMVFT Equipment
The control signals from the RCC as well as indication signals from the various controlled posts are transmitted on separate channels within the voice frequency range of 420 to 2460 Hz. at a transmission speed of 50 baud, with a 120 Hz separation between the channels. Only 18 channels are thus available for use. Frequency modulation is employed. The oscillator unit on the transmitter modulates the frequency +30 Hz (for 'mark') -30 Hz (for 'space') of the channel frequency.
The transmitting level of each channel is -22dB across 1120 Ohm. The normal receiving level can be between -22 dB and a minimum level of -30 dB.
Due to availability of only 18 channels within the voice frequency range of 420 to 2460 Hz. with channel separation of 120 Hz each pair of conductor can control upto 18 independent of grouped stations, where the number of such stations exceeds 18, one more pair would be required for purposes of telesignals only.
20405 Frequency Allocation
In view of their operational importance, all the feeding and sectioning posts are controlled independently by using a separate frequency channel for transmission of telecommands and telesignals to/from each post. For purposes of telecommand only SSPs are grouped (not more than 3) in order to economize in the number of channels. Telecommands for all the posts in the same group are transmitted on the same frequency channels. However, the individual controlled post in a group is identified by inserting a code in the shape of a long pulse or a long pause in the impulse train generated by the pulse generator in the switching equipment. When posts are grouped as explained above, only one operation at a time can be carried out in the grouped posts from the RCC.
20406 Controlled Post Equipment
The switching and FMVFT equipment at each controlled post are housed in one steel cabinet with dust proof doors. The switching equipment is similar to that provided at the RCC.
The FMVFT equipment has one send channel panel and one receive channel panel. The equipment works on 24V dc battery power supply. All the panels except the termination panel are of plug-in-type. An amplifier is provided with attenuation pads for level adjustment. The channel panels are of the same type as those in the RCC. III. SCADA EQUIPMENT 20407 General
The SCADA equipment at the RCC is called Master Station while that of the controlled station is referred to as Remote Terminal Unit (RTU).
20408 Transmission Path
Underground telecommunication trunk cable is provided for transmitting the signals from and to the RCC and the controlled Remote Terminal Units (RTU). Three pairs of conductors (One pair for "Send", one pair for "receive" and the third as spare) from this cable are made available for remote control operation.
20409 Isolating Transformers
To limit the build up of longitudinal induced voltage on account of induction effects of 25 kV traction, isolating transformers are provided on the cable circuit at intervals of 10 to 15 km. The cable is tapped at the RCC and each controlled station and 3 pairs of conductors are terminated on a terminal board. Isolating transformer of impedance ratio 1120 :1120 is provided at the point of tapping.
20410 Repeater Stations
Voice frequency repeaters are provided at intervals of 40-50 km to boost the signal and to make good the line attenuation. The amplifier gain at the repeater station is about 20 dB, with an equaliser incorporated to compensate upto 0.02 dB/kHz/km. Depending upon the distance the repeater gain is set so that the signal level at any point en-route is within certain prescribed limits.
If the lead is long suitable surge arrestors are provided inside the equipment room to protect the circuits. The metallic sheath of the lead in cable shall also be kept insulated from the earth system of the switching station to prevent induction effect, the insulated conductor alone being led into control panels. For the same reason, switching station earthing, LT 240 V auxiliary transformer neutral earthing and earth of R.C. equipment are all kept separate and distinct and are NOT interconnected. In addition, the switching station structure should be solidly bonded to the track rails by two independent connections.
20411 Microwave Communication
In some of the sections on Indian Railways dedicated Microwave channel at carrier frequency of 18 GHz has been provided for the purpose of communication.
20412 Optical Fibre Cable
Optical fibre cable has also been introduced for communication in some sections of Indian Railways, which is also used for RC equipment.
Details of the interface between the latest communication systems and the RCC/RTU equipment may be seen in the relevant technical documents.
20413 Master Station Equipment
Hardware Configuration: Dual main micro-computer/mini-computer system, one main and the other hot standby, is provided at the master-station, each system interfaces with its front end processors, if any, and modem for communication with RTUs and with the man-machine interface equipment to provide up-to-date network data and to accept commands. Each system has its own system console and hard and floppy disks along with their drives. Watch dogs are provided for monitoring the health of the computer system. In case of failure of one computer system, the standby system takes over automatically.
Two data-logging printers, one on-line and other as standby, are provided, both being connected to the same online computer system. In case of failure of one printer, the other printer automatically takes over.
Man-Machine-Interface.- Work Stations
Two work-stations, one for each of the two operators, each consisting of two semi-graphic colour Visual Display Units (VDUs) and a key-board are provided at the RCC. The key board contains both functional keys for operations that are repeated frequently and alpha-numeric key for input of numerical data and text.
Both workstations are connected to the same on-line computer and meet the following requirements:
(i) Normally control pre-defined and physically demarcated sections.
(ii) In case of complete outage of one workstation, all of its functions can be transferred to the healthy workstation, so that normal operations can continue.
(iii) Normally one VDU is on line and the other acts as standby at each work station. However, if so needed, it is possible to have both VDUs of each work station on lines simultaneously, either of the two VDUs being used for viewing diagram for telecontrol purposes and the other for viewing alarm, on-demand trend curves, histograms or any other data.
20414 Mimic Diagram Board (MDB)
A mimic diagram board and its associated mimic driver is provided at the RCC. The MDB depicts the traction power supply diagram, indicating the energize/de-energize condition of the sub-sectors of the catenary, status of the interruptors and CBs at TSS & FP, SSP and SP.
Unlike in the conventional Mimic Diagram Board used in RCCs prior to introduction of SCADA system (see para 20403) all control operations are carried out from the key board (s) provided at the work station (s). The Mimic Diagram Board's sole purpose is, therefore, to give an overall view of the traction power supply system to the operator. Size of the MDB is, therefore, very much smaller. It is the intention to do away with the MDB altogether since the system can be viewed in the VDUs.
20415 Annunciations
Controlled Station
"Remote Station Defective" is annunciated by a LED.
Master Station
The following annunciations by LEDs are provided on the MDB.
(i) Main System "ON"
(ii) Standby System "ON"
(iii) Main System Defective
(iv) Standby System Defective
(v) Main UPS Failed
(vi) Standby UPS Failed
(vii) UPS battery low (below 90% of nominal voltage)
(viii) 415 V, ac, 3 ph, supply to UPS failed
20416 SCADA Software
The operating system used is suitable for multi-user, multi- tasking, net working and real time applications.
20417 VDU Display
The application software supports a large number of versatile semi-graphic coloured displays for issuing telecommands, blocking/deblocking the controlled points, viewing alarm listing, event listing or for carrying out special functions. For details of these displays, manufacturers Operating Manual may be referred to. Calling any of the VDU displays is by simple keyboard operation by the operator, with pre-defined options available for the order and manner in which displays are called.
20418 Transmission and Coding System
The master station equipment normally scans continuously all the RTUs In a pre-defined cyclic sequence, to update the equipment status, alarms, events and measurands. Exchange of Information between Master Station and RTUs takes place on interrogation by master followed by reply from RTU. The communication technique is based on Digital Address Time Division Multiplexing. Every data exchange is based on well defined transmission protocol. Each transmitted information contains sufficient parity check bits to detect transmission errors,
20419 Historical Data Storage
The SCADA system is designed to cater for historical data storage of traction power supply system data for a period of one year. This includes:
(i) All alarms /events / measurands of controlled stations and all system alarms.
(ii) Day wise storage of average feeder current and voltage during the day, maximum demand, maximum and minimum feeder voltage in the 25 kV side, total number of operations of feeder protective relays viz. OCR, DPR and WPC relays, CB trippings and maximum and minimum OHE voltage on both sides of the neutral section. A memory capacity of 40 MB is provided for this purpose in the hard disk, with provision for further expansion of the memory as required.
20420 UPS and Batteries at RCC
Dual Stand-alone UPS System of adequate capacity to supply 240 V a.c. 50 Hz single phase supply to the SCADA system at Master Station is provided.
Both the UPS work in parallel sharing the load. In case of failure of one, the entire load is automatically taken over by the healthy UPS without affecting the working of the system.
In case of outage of both the UPS at the same time, the load of SCADA equipment is directly connected to input mains through a static switch without any break.
A single battery is provided with both the UPS with adequate Ah capacity to provide 2 h supply to various equipments in case of failure of input 415 V a.c. 50 Hz supply.
20421 Remote Terminal Unit (RTU)
The RTU is microprocessor based and includes its associated digital input/output modules, alarm input modules, analog input modules, watchdog transducers, memory modules, interposting relays, summation CTs, power supply unit (s), surge arrestors and other items necessary for its proper working.
20422 Storage of Events and Alarms
All changes (one or more) in the status of the CBs/interruptors / motor-operated isolators and alarms that may occur between consecutive pollings are stored by RTU until they are reported to the master station. This is to eliminate any loss in reporting to the master station due to intermittent failures of channel or any other reason. In other words, no event is lost without its being reported to master station.
20423 SCADA Equipment Capacity
The SCADA equipment is generally designed for the following tele commands, telesignals and telemetered parameters for a typical TSS, SP & SSP of a double line section: | S.NO. | CONTROLLED STATION | TELECOMMAND | TELESIGNAL | MEASURANDS | | 1. | TSS | 24 | 64 | 8 | | 2 | SP | 8 | 12 | 4 | | 3. | SSP | 8 | 12 | . |
Number of controlled stations (TSS, SP, SSPs) to be controlled from an RCC will be as per the requirements of the section.
Speed of Transmission and Update Tune
The communication between the master station and the RTUs is at a suitable transmission speed not exceeding 600 baud. Normal polling time for updating status, alarm and measurands for the designed capacity is not more than 4 sec for 20 controlled stations and not more then 6 sec for 30 controlled stations. The actual timings may slightly vary depending on communication protocol adopted and the system design.
The RCC should be in the middle of the electrified section if the number of controlled stations exceeds 30 so that scanning on either side is possible and update time kept to the minimum.
20424 Modems
(i) The modems (modulator/ demodulators) provided for communication between the master station and the RTUs utilize frequency shift keying (FSK) modulation and include send, receive and timing functions. The send and receive functions are independently programmed as required. The modem work satisfactorily upto an input signal level of 45 dBm.
(ii) The modem also incorporates necessary amplifier having a minimum gain of 30 db to compensate for any signal variation at different points in the system. Suitable attenuation is provided within the amplifiers to adjust the level through trimpot/rotary switch. It has an output signal level adjustable between 0 and -30 d bm in steps of 1 dbm.
20425 Special Features in SCADA Equipment
The following additional features are incorporated to the SCADA equipment:
(i) Tripping of bridging interrupters on under voltage at SP in extended feed condition.
(ii) Inter lock release request facility for circuit breakers/interruptors control at boundary post (for guidelines for these inter locks see RDSO's letter No. ETI/PSI/RC/SPEC.19 dated 10.3.1989).
(iii) Control of shunt capacitor bank and monitoring of power factor.
(iv) Automatic localization of fault on OHE and isolation of faulty sub-sector.
SCADA systems on Indian Railways are being supplied by various manufacturers. Although the systems are different, the basic features of the systems are similar. For details of operating instructions and maintenance, the operating technical manuals of the makers should be referred to.
IV. OPERATION AND MAINTENANCE OF RC EQUIPMENT 20426 Duties of CTFO (RC)
He is the senior supervisor working under the control of DEE/AEE (TrD) and directly responsible for the proper operation and upkeep of the RC equipment, which are vital for the efficient operation of the electric traction system. He shall be thoroughly conversant with all the technical details of the equipment under his control. In particular, he shall perform the following duties.
1. Maintain the RC equipment at the RCC and the controlled stations in accordance with the prescribed schedules.
2. Keep close liaison with the S&T department as to the sound condition of the cable pairs allotted for RC operation.
3. Measures periodically the levels of voice frequency signals at controlled stations and arrange with the S&T department for correction, when required, at their repeater stations.
4. Keep in constant touch with the TPC on shift duty and ensure prompt rectification of defects reported in the RC system.
5. Ensure proper maintenance of UPS/battery sets for uninterrupted operation of the RC equipment and the stand by generating set in the RCC.
6. Inspect the RC equipment at every controlled post once in two months.
7. Impart necessary training to the staff under him in the special techniques of maintenance of RC equipment as well as trouble shooting.
8. Ensure that the special instruments and tools provided for maintenance of the RC equipment are properly cared for.
9. Keep a watch on stocking of spare parts and other stores required for the RC equipment and initiate timely action to recoup stocks.
10. Co-ordinate with CTFO (PSI) and CTFO (OHE) or territorial CTFOs for manning the controlled posts in the event of persisting faults in the RC equipments.
11. Submit prescribed periodical returns on RC equipment to AEE (TrD) and Sr. DEE (TrD).
12. Keep his superior officers fully informed of all important developments and seek their guidance when required.
13. Carry out such other duties as may be allotted by his superior officers.
14. Carry out minimum monthly inspections as per manufacturers recommendations.
20427 Operation of RC Equipment
The RCC is the nerve centre of the traction system, from which full control over every switching operation on the entire electrified route is exercised. It should, therefore, be kept in perfect operating condition at all times. No one, other than an authorized official, shall at any time operate the equipment. The TPC shall, at every change of shift, carry out a lamp test and, once a day give a general check for all stations and thereby ensure that the indications on the mimic panel are in order. Any defects observed in operation shall immediately be reported to the CTFO(RC) and the entry made in the log book of the time defect was reported and the time it was rectified. Any excessive delay in rectification which militates against operation shall be brought to the notice of AEE(TrD). Depending upon the nature of the defect TPC shall take adequate precautions against mal-operation until the defect noticed is rectified.
Should RC equipment of a switching station fail completely, the failure shall be reported to AEE(TrD) and Sr. DEE (TrD) and arrangements made to man the switching station with trained personnel to carry out the switching operations, observing the precautions prescribed in the Chapter VIII 'Breakdowns'.
TPC shall once a day contact on telephone the Operators of each Grid sub-station from which traction power supply is obtained and ensure that the communication facilities are intact.
20428 Investigation of Failures by CTFO
As with any other equipment, every failure of RC equipment should be separately registered, investigated and rectified, making a brief note in the failure report of the action taken as well as classifying and finally pin-pointing the exact cause of the failure. The failures should be analyzed every month and any special steps required taken to overcome the trouble and prevent recurrence should be taken. A 'history sheet' showing the faults that have occurred on different items of equipment will assist in carrying out detailed investigation of recurring troubles in consultation with the Manufacturers' of the equipment.
20429 Maintenance Schedule
The specific maintenance instructions issued by the respective suppliers of SRC/SCADA systems, should be observed and changes to be made therein may be decided in consultation with the manufacturers. For the batteries used in the remote control centre and the remote terminal units (RTUs), the instructions in Chapter II for fortnightly maintenance and quarterly maintenance shall be applicable.
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SWITCHGEAR INSPECTION AND TEST PROCEDURE PKR ELECTRICAL ENGINEERING CONFIDENTIAL TABLE OF CONTENTS 1) VISUAL INSPECTION 2) W...
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