Recent developments in substation automation and wireless control have opened many applications in electrical power industry .Typical application include automated meter reading (AMR) and wireless data acquisition systems for substations etc .Most of our substation monitoring and control functions can be implemented with wireless connectivity using stand alone small units, eliminating PC based models with wires .Some unlicensed radio frequency bands are available for industrial scientific and medical (ISM) wireless applications, where short range communications can be realized using RF signal in the uhf range of 433.92 MHZ . Availability of low cost microcontrollers and RF ICs makes the practical implementations easier as compared to fifteen years back
All the substations including 110kv and 66kv are presently controlled and monitored by the conventional wired communication methods .If some of the breakers trip then audio visual indications are done using legacy alarms and light. A typical substation installations include incoming feeders/breakers, outgoing breakers/feeders each can be switched on/off and
Monitored separately .So there is an inherent limitation that monitoring is possible only inside the control room .Normally the status of breakers or feeders will be available on the control panel by the lights and alarm provided .The alarm can be manually reset after a trip message has been recorded. Substation automation improves the efficiency of monitoring and control, as control panel and metering are fully electronic with advanced displays and switching facilities .The following are the main functions enabled by substation automation
• Real-time status
• Real-time control
• Real-time metering
• Advanced protection relaying
• Equipment health monitoring
Wired substation automation has been implemented world wide using IEC61850 standard for networked communication. As it involves a single protocol for all substation communication, this standard has become very attractive for substation control, protection and monitoring
WIRELESS FOR SUBSTATION MONITORING AND CONTROL
Last 15 years have seen many developments in data communication using wireless techniques mainly because of the advancements in semiconductor industry .Also governments in various countries have de licensed more frequency bands for license free wireless applications .So Industrial, scientific and Medical (ISM) applications have come up with short range wire free networking .In India 433.92 MHZ and 2.4GHZ frequencies have been allotted for ISM wireless applications.
Wireless data communication technologies in general include older technologies such as spread spectrum, microwave point to point, satellite systems and newer systems, such as WIFI, Bluetooth, ZIGBEE, WIMAX, and GSM or CDMA based mobile phones
The locations for wireless installations can be within substations, in underground vaults, along transmission and distribution circuits, within generation and distributed generation plants, for customer electrical and metering equipment, and other electric power environments. The different types of communication functions will include high-speed, high reliability protective relaying, “real-time” monitoring within electric sites with high EMI(electromagnetic interference), control within electric sites, non-operational monitoring and control (e.g. maintenance, archival data, physical plan monitoring, etc.), mobile functions, temporary functions, and emergency functions. Traditionally Electrical power industry has been hesitating to utilize wireless for monitoring and control because of a perception that substations and surrounding are extremely noisy ,resulting in erroneous working .But recent developments have proven that wireless installations can work satisfactorily even in extremely noisy environments .So in an organization like KSEB ,with huge network of transmission and distribution lines, license free wireless network has to be utilized for the efficient monitoring and maintenance .
110KV SUBSTATION KADAVANTHRA
KADAVANTHRA substation consists of 2 NOS of 110 KV incoming feeders and 8 NOS of 11 KV outgoing feeders of which one is auxiliary .These feeder status are monitored using Two Lamp indicators on each panel, one for breaker on other for breaker off .Tripping of any breaker will initiate Hooter/alarm which is manually reset by the operator .Control room is in the ground floor while station engineers Office in the first floor
Also battery bank voltage is critical and has to be measured each time by entering the battery room
.So it becomes an added advantage if each 11kv breaker status and battery voltage are displayed in the station engineers office .This was the main design goal of the project –To display 11kv breaker status and battery bank voltage in the station engineers office or quarters wirelessly while not interfering with existing control panel circuit functions
11KV feeders /breaker on/off status can be displayed
At some distance away from the control room without wires, for the effective monitoring of substation even during night time at the residential places of the concerned officers .A wireless INSTRUMENT WITH LCD display was designed, fabricated and installed at KADAVANTHRA substation to monitor the trip status of 11 KV feeders. Battery bank voltage was also measured remotely. A total of 7nos of feeder/breakers status were to be displayed while battery voltage in volts
The system consists of a transmitter (TX) and a receiver (RX),
both operating at 433.92 MHZ ism band. Block diagrams of the system are shown in the accompanying figures
There are 7NOS of 11kv feeders and 110v control signals coming from the limit switches on the panels, and these signals are input to the microcontroller through optical couplers. Use of optical couplers avoid direct electrical contact of control panel circuit to the transmitter circuit .optical coupler also eliminates Noise coupling and ensures safety
.Depending on breaker on/off a hi/lo signal will be available from each optical coupler .Battery voltage is dropped and applied an analog to digital converter which converts the voltage into digital format .All the breaker status and battery voltage are displayed on a16x2 standard LCD Display .An 8Bit PIC microcontroller from Microchip inc encodes all the status and voltage into serial codes with security features .An RF transmitter was designed with ICs from MICREL semiconductors in the 433.92mhz band which was modulated by the data stream from microcontroller and subsequently transmitted to air by a small wire antenna
The digital RF information was received by RF receiver designed around by ism band IC from MICREL inc .Serial data output of the RFIC is decoded by the pi c microcontroller IC at the receiver and displayed on a standard 16x2 LCD display as used in transmitter .Display profile shows the breaker name, status and battery voltage in volts .Whenever a breaker is switched off or tripped LCD displays the status and alarm is activated which can be reset by the reset switch provided.
The design was implemented on two printed circuit boards
one for TX and Rx each and all feeder signals and battery voltages were wired to the unit 10 core cable .A standard plastic cabinet was used to house the PCBs and power supply transformer sand LCD display .Both the units are working satisfactorily with transmitter in the control room and receiver in the station engineers office. Photographs of the units are shown
Further modifications can be done to improve the range of communication and to incorporate more analog parameters such as currents and voltages of each incoming and outgoing feeders .Also critical component failures can be alarmed in the same way using RF data transmission .With recent de licensing of 2.4ghz spectrum for ism band usage, which allows more communication range as more power can be transmitted ,substation to town control room data Communication network can be established at low cost .