Various case studies on operation and control schemes for grid sub-station contd

Er. P.K.Pattanaik, is presently working with OPTCL as General Manager, EHT (O&M) Circle Bhubaneswar - Odisha and associated with the Protection and Control schemes of Electrical systems. Having 29 years of technical experience on various HT and EHT voltage level in the field of transmission sector. Specialization on the development technoeconomical design of protection control schemes for system development and planning. At present involved with various on-going projects on GIS, SAS and updated Remote SCADA control stations of OPTCL. Published 105 technical papers in National and International arena and is a regular contributor to the National journals like Electrical Mirror, Electrical India, CBIP journal and IEEMA journal and author of many technical books. Also Awarded in various arena on National level. He is also the coordinator of a Nationwide Power Engineers’ Technical Group named “SPARK- Ignited to share” consisting of Senior Electrical Engineers from different parts of the country. ele.pkpattanaik@optcl.co.in

VARIOUS CASE STUDIES VARIOUS CASE STUDIES ON OPERATION AND CONTROL ON OPERATION AND CONTROL SCHEMES FOR GRID SUB-STATION SCHEMES FOR GRID SUB-STATION Contd…. Contd….

1. Introduction: For the last few months, the response of the readers to the case studies on various incidents is overwhelming. Hence this month we are again choosing the write up on similar kind of studies for developing the synchronization of practical observation to the theoretical concepts. The analysis of each incident being supported by actual observations had been described during the situation to add awareness amongst the operation, testing and commissioning engineers to know the cause of problems and be helpful for easy rectification of the problems. This can also help to develop economic schemes for the smooth running of the operation and control system in the Grid Sub-Station. 2.1. Abnormal Outage of System: At one of the 220/132 Kv system, one circuit from DC (Double Circuit) transmission line was planned for maintenance shutdown. But while removal of the CVT fuses, it was observed with total outage of the healthy line. Observations: 1. All operations like disconnection of isolators, circuit breaker and closure of earth switches were done correctly from both end as per the SOP. 2. The other parallel line from the 220Kv DC tower was allowed to continue with the supply for maintaining the connectivity between stations. 3. Now the next process was there to remove CVT fuses from the Dead circuit to avoid inadvertent back feed from secondary 110 Volt to 220 KV system. 4. Both the CVT secondary box of both circuit were installed at the

central place and labeled as 220CVTAJB and 220CVTBJB. 5. The operator by mistake removed the fuses of LIVE circuit from 220CVTBJB rather from the dead circuit 220CVTAJB. 6. This mistake resulted due to followings a. Both the CVTJB were at central place rather at field yard with almost similar labelling differed by one letter of A or B b. These JBs were not provided with LOCK and KEY arrangement c. No physical isolator available for primary side dis-connection of CVT d. Lack of remembrance by the operator while attending the job for removal of CVT fuses. 7. Because of CVT fuse removal from the healthy circuit, the LIVE feeder tripped causing delink of interconnection and system LOAD throw of approximately 220MWatt and subsequent disturbance. Action Taken: 1. The system was revived putting the removed fuses in the JB, allowing the load flow between stations. 2. This time Lock and KEY arrangements were done and JBs were labelled as circuit no and Bay No. 3. Caution note was issued as instruction in the SOP to avoid confusion. 4. The existing relays were replaced by new relays and logic was also changed for the system to provide fuse failure scheme rather issuing of trip command. Technical Analysis: 1. The OLD relays were set with the simple logic of TRIPPING of the system in case of Voltage reduction/ failure with current in the circuit. 2. This is being considered for voltage outage of all three phases. 3. In this case while removal of one fuse, it was observed with VT fuse fail, but due to communication link miss between the operator at switch yard and operator at control room, the switch yard operator removed all the fuses in the row. 4. So due to old logic of no voltage on all the phases and current in the system caused tripping of the healthy circuit. 5. In the replaced new numerical relay, the logic was changed in corporation the threshold limit and ZERO sequence allowable current in the system for tracing as fuse failure situation instead issuing of tripping of the system. 6. The matter was even tested and simulated correctly.

7. Finally, the system was taken in the scheme. 2.2. Case of DC and AC mixing on the DC battery System: At one of the 132/33Kv Grid Sub-Station, abnormal tripping resulted with a breaker in the system due to automatic closure of the Lockout contact from the master trip relay. Observations: 1. The master trip relay was equipped with the Normally OPEN (NO) contact that had extremely small gap between the contact of approximately 0.02 to 0.025 inch. 2. This contact was automatically getting closed and issuing the tripping command of the breaker. 3. But during the next moment after resetting the Master relay, the breaker was getting charged. But issuing the tripping command once again without any sequence of time interval. 4. Even in few of the incident, the breaker was getting tripped at the very moment of the breaker closure. 5. This automatic closure of the contact was very peculiar in nature and reason could not be established. 6. However, physical search was conducted regarding the supply availability to one of the terminal of the said NO contact. 7. The peculiarity was found with mixing of AC voltage to the terminal along with DC supply. Action Taken and Technical Analysis: 1. The AC supply as available was due to loss of insulation of the flexible cable used for lighting system and inadvertent touch of the Phase terminal to one of the NO terminal as mentioned. 2. This inadvertent touch was resulting rise of the momentary voltage rise on this point and arching on the small gap allowing the continuity of supply to the tripping coil and was causing tripping of the breaker. 3. The PEAK VOLTAGE of the AC supply mixed with RMS voltage of the DC supply was the culprit of the tripping action. 4. So, the defective flexible AC wire was replaced by a good one and routing was changed to avoid the inadvertent touch and mixing up with DC supply. 5. Even this peculiar supply mixing behavior was resulting some other chattering of auxiliary contacts in the system. 6. After modification of the circuit, the issues were resolved. 2.3. ZERO Megger value of CT: At one of 132/33 KV 63MVA Transformer, it was found with oil leakage from the Tan-delta point. Then the oil level was checked and found with low level. On filling the oil, the IR value was measured from Primary point to Ground, but found with ZERO-ohm resistance.

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udy sT Case

Observations: 1. The Oil leakage on CT was found at the Tan-Delta point. 2. As suspected that this had been resulted during Tan-Delta measurement by the testing wing and loosened during that point. 3. So, the tightness was attended for arresting of the oil leakage. 4. At the same time, oil level was also checked and found with less than that of the limit. So, required level was filled and tested with the Primary to Earth megger value. 5. The result was found with ZERO value. 6. ZERO resistance of the running CT was suspected with the process of taking Insulation resistance measurement. 7. So, the grid personnel were inquired about the measurement process. 8. The actual mistake point was revealed on inquiring that the grid personnel had taken the measurement, keeping Transformer winding in the system, without removing of the NEUTRAL EARTH. 9. On knowing the mistake, the NEUTRAL EARTH of transformer was removed and IR value taken thereafter. 10. This time the actual megger value came above the allowable limit. 11. The Transformer was charged along with this CT and stood OK. Technical Action: 1. On first instance and hurriedly without thinking about the TRANSFORMER NEUTRAL EARTH link in the system, the grid operator took the insulation resistance measurement by the available motorized 5KV IR tester. ( Refer Fig No 2.3.1).

2. Because of TRANSFORMER NEUTRAL EARTH link in the system, the IR measurement came ZERO. NOTE: This Study seems to be very silly, but sometimes operator forget to remove the Earthing Point during IR measurement. Not only from transformer, sometimes Grid operators do the mistake of removal of EARTH LINK from the PT system. Recommendations: This is recommended to review the system if IR measurement is attempted for combined connected equipment system in case of obtaining ZERO resistance value, before declaring the final result. 2.4. Gradual Damage of LINE conductor: It was observed with Damage of conductor strands during annual maintenance check of the transmission line conductor. Observations: 1. This conductor was of AAAC Zebra and connected in the 220 KV line between TWO tension Tower location. 2. During Jumper tightening work, the workmen reported about the damage of few strands as like shown in the fig 2.4.1. 3. The conductor was connected with gripping hardware, and damage was found just near to connecting point as like shown in fig 2.4.2. 4. Proper VD (Vibration Damper) was also connected outside this damage part.

Damaged strands Fig 2.4.1 Damaged portion of the strands Fig 2.4.2

Action Taken 1. The Conductor span was replaced with new hardware connection with proper gripping. 2. This time the gripping was provided with no slacken looseness of the strands. Technical Analysis: 1. The gripping/clamping of the BASE hardware for holding the main conductor should be done with proper care. 2. The conductor strands should be bound tightly avoiding any slacken among them. 3. If these strands to remain in slacken way, then subsequent deposition of water and dust particle upon the above

part of conductor, corona effect results with ionization of the water particles, subsequent heating with gradual damage may result. 4. This effect shall be more and quicker as observed in AAAC conductor than ACSR conductor. Recommendations: Proper Gripping with NO SLACKEN STRANDs to be done for Transmission Line Conductor 2.5. Failure of Jumper Cone and Snapping of Jumpers: For one 132KV DC (Double Circuit) Transmission System, it was observed with failure of jumper cone at a particular Tower. 1. This DC transmission system (A Particular Tension Tower Location) was positioned with another Tension Tower on one side of the extension and suspension Tower on the other. 2. The next tension tower towards the suspension tower side was at after TWO number of suspension points. (As marked in the position sketch Fig 2.5.1) 3. This particular Tower where issue had been resulted, was having 47 deg angle point towards suspension side and lesser angle towards Tension tower side. 4. The failure of the jumper cones was resulting towards higher angle side (Towards Suspension Side). All the Jumper cones were found with breakage. 5. But no such failure towards the lesser angle side (Towards Tension Tower Side). 6. Each time of failure, temporary PG clamps used to provide on the conductor to allow immediate resumption of power flow in the circuit. 7. The spot was inspected by the experts and found with following observations.

Fig 2.5.1132 KV System, jumper cone damage Towards 47 deg angle side a. The nearest Tension Tower is at around 80 Mtrs away to one side. b. The suspension Tower was at 275 mtrs away on the other side and next Tension Tower was at approximately 650 mtrs away from the discussion tower with TWO Suspension Tower in between. c. There was only one VD (Vibration Damper) at the said Tower towards both side. d. No pilot insulator string was also available for the required support. e. The Tower was positioned at the bank of the river with open sky surrounded by no any physical obstruction and in costal wind zone. 8. The detail was analyzed and found with following solution. a. The jumper towards suspension side was replaced with replaced with T clamp instead of PG clamp. b. Pilot insulator string was provided to avoid any swing. c. Instead one VD, two numbers of VD were used in the system. d. Then onwards it was observed with no failure. Technical Analysis: 1. As analysed from the site position that the area was near the costal zone and bank of the river, wind effect is the main cause affecting tension on the conductor. 2. Maximum time, the wind flow was to develop vibration on the conductor and to allow the transformation of tension from the line conductor to jumper at the point of interconnection. 3. The jumper because of NO PILOT STRING was also swinging not in the same pace to that of conductor due to only one VD on the conductor. 4. So jumper cone being the inter-connection point was to manage this mechanical jerk always with TWO BOLTS in the point. 5. This TWO BOLT jumper cone was not that strong to proper transfer the vibration of the conductor to the jumper cone and then to jumper for onward transmission. 6. So in due course, there developed with hair crack on the jumper cone and subsequent damage failure. 7. This had been resulted to all the conductors and connected jumper cone towards larger tension point side of approximately 650 mtrs away. 8. Moreover, this long span and larger angle point with no PILOT Insulator was also the other reason towards such failure. Recommendations: So, the use of VD (Vibration Damper) should significantly be used in the transmission line system. EM

mr. HonEy rAzA

SaleS heaD solIs IndIA

founded in 2005, ginlong technologies is one of the world's largest and most experienced PV string inverter manufacturers. the cost-effective solutions that ginlong offers for residential, commercial, and large-scale users offer great value at all levels of the solar supply chain. ginlong optimizes its Solis inverters for each regional market, servicing and supporting its customers with its team of local experts.

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All the inverters from Solis are tested under extreme test conditions like temperature test like heat run or extreme cold conditions. Solis Inverters are designed to endure these climatic extremities. We have experience of working in most toughest terrains or the world. Parallelly we are regularly sharing our knowledge sharing segment where installers and end users can get to know the best practices for handling such equipment. Q. Do you detect any significant distinctions between the Indian and other large markets when it comes to inverters? What do you consider to be your most significant market challenge?

India has done very well last year in 2021 if you compare with US or Australia. Europe, Brazil and China Domestic market is still doing well which has support us in overall better revenues. We expect there would be a slight slowdown in Q1, 2022 due to the expect BCD on modules announcement but despite this I am bullish on the total installation to be done this year. Certainly, it would take some time to overcome this taxation change. Overall around increase of 30% capacity as compare to last year, would be figure which would be decent one. Q. Can you tell us about Ginlong Solis' response to the COVID19 pandemic, the following lockdown, and any financial consequences?

During the reporting period, COVID-19 brought some inevitable pressure and challenges to Ginlong Solis. However, the company's capacity rapidly recovered increased to seize more domestic and foreign market share through the positive response of the company." Ginlong Solis pointed in the announcement that due to the recent rapid recovery of overseas market demand, the shareholders of listed companies will increase significantly during the reporting period. As a leading manufacturer of string inverters, Ginlong Solis has achieved steady growth in recent years. In Q3 of last year the company reported its strongest ever quarter. Yiming Wang, the president of Ginlong Solis, said that the company has launched some new products since Q3 of 2019. At the same time, the company promoted sales in traditional and emerging markets with marketing channels and marketing teams. Solis expansion into overseas markets continues to increase with the growth of Ginlong Solis's overseas offices, the company's product improvements, new technology response and competitive prices. As a result, Ginlong Solis boosted its global market share. In Q3 of 2020, since there is no time limit for pre-installation of residential systems, the average monthly installation numbers continue to grow. Sales of commercial inverters are growing rapidly as component and system costs continue to come down. "We expect several markets may exceed 1GW each year, and there will be a gradual improvement over time as installations accumulate and years of use grow. Q. What are your plans in India over the next two years? Is there anything new you're intending to release in the first half of 2022?

We are aggressive about the India market and so is the response. We are very strong in residential and C&I with the total installation, that's why we are the No 1 Solar Inverter Company of India, and achieved almost 80% growth as compared to last years overall. Projects with our utility product of 255k picking up very fast with total installation around 300MW by FY 2021. Next two years we are planning to achieve 80% to 90% growth. This year we are also in process to launch many more products in storage and Utility segments. Utility product shall be of higher capacity than our present product with more advanced features. EM

www.solisinverters.com

Q. Please tell us about DIRAK's performance in India during these turbulent times. From an overall business perspective, we did well despite the challenges. Market demand was good in the segments where we serve. We have long term supply contracts with many customers which we had to honor. However, managing supply chain disruptions and material cost increase was a challenge. Also, managing the business continuity during the pandemic was difficult. We had to lean on technology and adopt new safety processes while maintaining the productivity. Q. What are the market's challenges, particularly in terms of cost, technical advancement, and getting raw materials? Our main challenge was the cost of raw material. Cost of raw materials in our business increased considerably last year. This was applicable for metals, plastic and rubber. Also, the freight costs went up. Q. What are the new innovations introduced by DIRAK in past 6 months? Innovation is our strength and we continue to bring in innovative new solutions to the market. Products that were launched recently were mainly for the railway market where better vibration resistance and IP rating is a requirement. Also we developed new gasket products meeting higher fire safety standards. Q. What are the different products available for Indian market? DIRAK manufactures mechanical and mechatronic hardware for the enclosure industry. Specialized in latching, locking, hinging, and gaskets, we have an extensive range of products in different material grade. Also, for specific applications that require different safety standards. Our products go into various industries like Energy, Machine Construction, Railways, Transportation, IT and into any kind of Sheet-Metal Fabrication. Our products are manufactured under our global specifications and our entire product range is available for the Indian market.

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