K R Suri
Since 2015, GOI initiated awareness programs to ensure energy supply reaches every household. Significant technological changes ensued. In the Indian network, sub transmission involves a ring main system, but far ends only have radial connections, leading to low voltage and increased transmission losses, burdening the exchequer/consumer. In the current scenario, with about 100 cities declared as SMART CITIES, reliable and high-quality electric power supply is crucial for maintaining smart grid systems and ensuring security monitoring.
BACKGROUND
Revolution in Indian power transmission began in 2001 with road shows reaching end consumers, promoting efficient electrical power use with the following advantages:
* Availability at all times
* Efficient use
* Installation of energy efficient gadgets
* To have an impact of low energy bills i.e. less electricity bill on exchequer i.e end consumers
* To improve health of state utilities and helping them to perform better.
* Etc. Etc.
This brought a tremendous change in systems with implementation of:
* APDRP Phase 1
* R-APDRP
* RGGY
Power supply saw improvement, achieving 100% household connections nationwide and a rise in per capita consumption, with a minimal shortage of 0.01% during peak hours. Yet, the introduction of converters led to harmonics, causing power quality distortion at the sub transmission/distribution level. Despite this, the sources of supply have not expanded, prompting the creation of HYBRID power supply sources, combining various technologies.
* Hydro with solar
* Hydro with wind
* Solar with wind
A total combination of 3 above.
Thus, shortages persisted during peak hours, while surplus power was available during off-peak hours. However, maintaining power quality during EV charging in night hours is crucial, requiring prevention of unwanted frequencies/harmonics generated by chargers at the local level.
ALL BHARAT INSTALLED CAPACITY
As per CEA report published in July 2023, there is rise of installed capacity in which there is a good amount of role played by RE sources.
To enhance quality, POWERGRID CORPORATION OF INDIA initiated installation of about 25 SVCs/STATCOMs at various major stations nationwide. This suffices to uphold electric parameter quality for the reasons elucidated below:
* Maintaining grid discipline for EHV LEVEL ie 400kv & above.
* This discipline is must to maintained safe long life of EHV equipment.
* Filtering out unwanted frequencies.
* Maintaining dynamic stability under grid disturbing.
* To avoid distortion in equipment for a accurate response during interruptions.
* Reducing harmonics in systems for a trouble-free operation of Transformers and reactors meaning there by reduction in transformer losses.
* Obtaining correct output of measuring equipment like CT & PT/CVT.
* Etc. Etc.
Ways Adopted
Frequency control in the transmission or distribution network solely rests with generating stations. In 2013, CTU accomplished the synchronization of all grids, achieving the slogan of ONE NATION, ONE GRID, ONE FREQUENCY.
Frequency deviation is only allowed in narrow band of 49.95 c/s as per CERC. This has made life of equipment at end user level safe and elongated.
Installation of VAR Compensators
POWERGRID CORPORATION OF INDIA, a central transmission utility and transmission planner along with CEA, installed voltage cum controllers so called SVCs/STATCOMs only at on 400kv and above level like:
2×140 MVAR SVC at Kanpur — 1992
FACTS on Ballabgarh – Kanpur 400kv line
Fixed series capacitors at Muradnagar
STATCOM at Ludhiana, Wanpoh and Jaipur, Nalagarh, Hyderabad(+/- 200 MVAR)
FACTs at Raipur
Etc. Etc.
WORKING/CHARACTERSTICS OF VAR COMPENSATORS
VAR compensators, due to their inherent traits, persistently monitor voltage at one station, adequately indicating voltage supply at the receiving end. Settings are predetermined based on the actual situation regarding load and voltage.
SVC or FACTS senses voltages at set intervals, offering support through its inherent capacity by adjusting its response, adding variable capacitors or reactors. This is accomplished by TCR or TCC. Moreover, it absorbs/suppresses harmonics generated in the system due to load characteristics, providing ample support. It operates in two ways to achieve the following:
* Dynamic support during faults.
* Regular support during normal operation.
* Operates within voltage band as set.
* Provide power factor as close to 1.00.
Below is the example of STATCOMs/SVCs in Northern Region:
In spite of installation STATCOM at Wanpoh, Voltage at Rajouri and other nearby stations as below as 124 to 128kv and there is load growth as projects execution by RAPDRP/DDUDHAY schemes. One can imagine voltage of 33kv and below.
Other example is of 33kv line from MAGAM to GULMARG. Voltage on the line is as low as from 22kv to 28kv (max). Sterlite had to install voltage stabilizer of equivalent capacity at AMARGARH S/S to cater auxiliary load demand.
Unfortunate part is that Central Transmission utility plans only for 400kv and above and do think or restricted them self at that level only.
These installations have followings demerits;
* Has a limited impact up to 220kv levels connected nearby including below level voltages stations.
* Harmonics generated remains circulated in local area/circuits only.
* Relays in these stations are not very much sophisticated on account of techno economic accounts.
* Voltage remains fluctuating due to ON/OFF operations of loaded circuits.
* Frequent tripping of lines due to bare conductor used.
* Load on a line is more than design ie beyond surge loading.
* Etc. Etc.
Due to reasons above, there’s a dire need to comprehend and install SVCs/STATCOMs to control supply parameters, i.e., QUALITY POWER schemes with the slogan POWER FOR ALL. This slogan signifies continuous power availability with quality or as per required standards.
Voltage regulation for 220kv and below has been
overlooked, known to planners, now becoming an issue. Therefore, instead of installing compensators at UHV level, there’s a dire need to enhance 220 & 132kv levels for Quality power.
INDUCTION OF SMART CITIES
After 2015, when concept of smart cities started it became imperative to maintain reliable cum quality supply. By this time load on systems started reducing due to large scale replacement of LED equipment like; TV screens, Bulbs, Energy efficient machinery like motors, pumps, fridges etc.
However, a parallel problem started arouse due induction of AC/DC convertors being used in large scale in LED bulbs, AC/DC convertors, Battery chargers. These became the sources of creating Harmonics in system with poor power factor. Harmonics and poor factor are again a virus in the systems and ultimately disturbing quality with a little effecting reliability.
MERITS OF SVC/STATCOMs
* Adhering to Grid code.
* Reduction in MVAR Demand ie Improvement in power factor and reduction in harmonics.
* Reduced equipment cost
* Decreased energy charges
* Reduced Power losses
* Incentive in electricity bills
* Reduce heat loss of transformers and equipments
* Prolong the life equipment
* Stabilizes voltage levels
* Increase system’s capacity, etc.
World Wide Installation of SVC / STACOMs across world.:
MEETING CUSTOMER SATISFACTION
The very definition of quality power is:
* Adhering to Grid Code.
* No fluctuations & Constant frequency with Good Power Factor
* Voltage varies with in specified limits i.e. +/- 5 %
* Pre-determined shut downs & Periodic specified maintenance
* Equal voltage in all the three phases.
OTHER LOW VOLTAGE INSTALLATIONS AT 33KV & BELOW
EXAMPLE OF JAMMU & KASHMIR
Attached is the JKPDD sub transmission network of Jammu Region. It is suggested to install 30 to 50 MVAR SVCs to take care of supply quality at far end. In similar way can be installed at other locations also.
In spite all above there is dire need of improvement in like:
* Equal loading on transformers
* Energy auditing
* Alternate paths for availability of power Load flow monitoring through SCADA.
* Load flow monitoring through SCADA.
* Improved power factor i.e. Reducing load on conductors
To achieve improvement in supply at tail end, there are so many ways like
Frequent operation of transformer taps – up to some extent
* Capacitors at each load point.
* Using HPC/HTLS conductor in transmission
* Installation of VAR compensators at suitable ends (SVC, STATCOM etc.)
* Smart Grid i.e. Implementation of SCADA
* Fear of tap changer failure. Transformer remains in service till end but its tap changer is not used/operated.
* Due to difference in %age impedance which restricts parallel operation of transformers.
* Old transformers are provided with Off LTC. Which restricts operating agency with the fear of repeated shut downs. Etc.
In our country biggest draw back in power system is that load dispatchers never or advise for operation of transformer taps for VAR support due to the followings:
DEPLOYMENT OF ETOS
In this type of system all type of controls like :
Automatic Tap changer operations
* Oil sensors (DGA & other parameters)
* Temperature cum load monitoring etc.
* Central communication inter phase for data transfer
* Making cyber security proof.
* Etc.
This type of systems has been installed by Powergid on large scale but not by DISCOMS
USE OF CAPACITORS AT LOAD POINT
Switched capacitors provide support at end locations for a better-quality supply.
Capacitors at large has own limitations like:
* Installations at 220 or 132 kv level.
* Regular maintenance
* Causes unbalance if compromised with biasing.
* Spares availability. Etc.
USING HTLS/HPC CONDUCTORs IN SUB TRANSMISSION
This conductor has 1.6 to 2.25 times capacity to bear the load which increases with demand/time as compared to ACSR OR AAC. HTLS – It is one of the ways to improve voltage end point connectivity.
SCADA IMPLEMENTAION AS PER IEC- 61850
Digital cum Make in India plans (SMART GRIDS)
The Indian government globally expresses in world forums,
* Total load along with distributed load.
* Load forecasted visa vis Generation (Individual & Gross)
* Selection of units to loaded priority wise
* Remote control/operation cum monitoring including unmanning
* Visual monitoring systems
* Maintenance planned & Situational decisions
* Energy auditing & Frequency & Voltage
* Losses w.r.t revenue
* Implementation of smart grids will force utilities to renovate their existing stations so as to match with latest trends like;
* Renovation with latest trend and efficient equipment & Installation of GIS stations
* Using Numerical relays for SCADA implementation
* Load restriction cum feeder selection for load management.
* Regular Training to working personals for awareness & up gradation
* Awareness in regard to system complexity
* Using proper gadgets as required (Tools & Plants).
* Working unscheduled or unplanned. inviting multinational firms and powerful nations to initiate production domestically. This stimulates the demand for dependable electrical power.
The Digital India theme emphasizes smart grid tech implementation to counter growing competencies and security systems amid the existing terrorism threat to the country and the world. This implies electric power control (transmission cum distribution) in a computer-controlled program. Smart Grid or SCACA monitors and controls round the clock with the following features.
ADHERING TO OPERATING GUIDELINES FOR RELIABILTY
* Regular Training to working personals for awareness & up gradation
* Awareness in regard to system complexity
* Using proper gadgets as required (Tools & Plants).
* Working unscheduled or unplanned.
CONCLUSION
* Smart City Schemes to be approved along with deployment of VAR Compensators to avoid fluctuation and disturbances etc. Etc.
* Compensators need to be installed at sub transmission level.
* SMART GRID/CITY strongly require such controllers for smooth functioning
* Installations of automatic voltage controllers by deploying sensors on transformers ie ETOS While approving schemes system requirement need to be reviewed from all angles.
(The author is Gen. Mgr. (Retd.), Powergrid Corporation of India Ltd )
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