“We Need Stable and Flexible Grids!”

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India has made tremen­dous strides in elec­tri­fi­ca­tion in recent years. At the turn of the mil­len­ni­um, around 700 mil­lion peo­ple still had no access to elec­tric­i­ty. This changed thanks to a mas­sive state-run con­struc­tion pro­gram. How­ev­er, pow­er fail­ures are still a dai­ly occur­rence, in some areas elec­tric­i­ty is avail­able for just a few hours each day, and the pop­u­la­tion is grow­ing so quick­ly that grid expan­sion is falling behind demand. In short, the ener­gy hunger of this coun­try of 1.3 bil­lion has still not been sat­is­fied. The IEA assumes that the elec­tric­i­ty needs of the sub­con­ti­nent will triple by 2040.

Cur­rent­ly, India is the third-largest pro­duc­er of elec­tric­i­ty in the world, after Chi­na and the US. Coal is still the num­ber 1 ener­gy source there, with a share of more than 50 per­cent. But things are chang­ing in the ener­gy mix. At the Paris Cli­mate Change Con­fer­ence in 2015, Prime Min­is­ter Naren­dra Modi announced the inten­tion to increase the installed con­tri­bu­tion of renew-able ener­gies to 175 gigawatts by 2022. How­ev­er, this also requires grids to con­nect the cen­ters of gen­er­a­tion and con­sump­tion.

A major­i­ty of renew­able ener­gy comes from solar and wind — from indi­vid­ual pan­els on a house roof to large, mul­ti- hectare solar and off-shore wind parks. In this sun-soaked coun­try, solar pow­er can now be pro­duced much more cheap ly than con­ven­tion­al or nuclear pow­er. How ever, what is good for the envi­ron­ment does not always work with the exist ing grids.

That is why, in a study with the Indi­an Insti­tute of Tech­nol­o­gy Madras (IITM), Rein­hausen is inves­ti­gat ing how the grids can be pre­pared for the upcom ing tasks giv­en the assump­tion that all of today’s plans will soon be made obso­lete by the growth of tomor­row. We asked Ajay Nilakan­tan, tap-chang­er busi­ness devel­op­er at Rein­hausen, and Pro­fes­sor Dr. K. Shan­ti Swarup, Depart­ment of Elec­tri­cal Engi­neer­ing from IITM about the most impor­tant find­ings.

What challenges is India’s power grid currently facing?

PROF. DR. K. SHANTI SWARUP: The Indi­an pow­er grid must become ever more reli­able and resilient, on the one hand, while also respond­ing flex­i­bly to con­stant­ly chang­ing require­ments. We cur­rent­ly have to ensure sta­bil­i­ty for the volt­age in the trans­mis­sion grid. At the same time, bidi­rec­tion­al load flows are caused by gen­er­a­tion with dis­trib­uted renew able ener­gies.

“The Indi­an grid must become more reli­able and respond flex­i­bly to con­stant­ly chang­ing require­ments.”Prof. Dr. K. Shan­ti Swarup of the Indi­an Insti­tute of Tech­nol­o­gy Madras (IITM)

What’s more, the trans­mis­sion com­pa­nies have less direct influ­ence on the gen­er­a­tion units—in regard to both access points and types of oper­a­tion. There­fore, the grid requires solu­tions that enable coor­di­nat­ed oper­a­tion, flex­i­ble and dynam­ic con­trol, opti­mal usage of the pow­er pro­duced, min­i­mal loss­es and low foot­print.

How do these problems manifest?

PROF. SWARUP: That is a very com­plex sit­u­a­tion. Every method for cre­at­ing flex­i­bil­i­ty in grid oper­a­tion increas­es the demand for reac­tive pow­er. Reac­tive pow­er can be pro­vid­ed not only in an inter­state trans­mis­sion grid, but also in a region­al high-volt­age grid or even a pri­ma­ry dis­tri­b­u­tion grid.

Then we also have to deal with dynam­ic volt­age fluc­tu­a­tions due to the increased volatil­i­ty in ener­gy gen era­tion. This also increas­es the risk of over­load­ing cer­tain lines, which in turn leads to them dis­con­nect­ing and there­fore to unwant­ed pow­er out­ages. And with regard to solar farms, the installed pow­er may be high, but there is some­times not enough line capac­i­ty to trans­mit it.

Are there solutions for this?

AJAY NILAKANTAN: We have three approach­es here, in prin­ci­ple: The first is coor­di­nat­ed switch­ing of OLTCs in trans­form­ers; the sec­ond is dynam­ic reac­tive-pow­er compensation—regulated shunt reac­tors are an eco­nom­i­cal solu­tion for this—and the third is the tar­get­ed use of phase-shift­ing trans­form­ers (PST), which active­ly con­trol the pow­er flow between grids or grid seg­ments. In the study, we exam­ined how these three approach­es work.

How did you proceed in the study?

PROF. SWARUP: We con­cen­trat­ed on the effects on the volt­age pro­file of inte­grat­ing renew­able ener­gies, and on load-flow reg­u­la­tion in select­ed grid sec­tions over a peri­od of five to sev­en years. For this pur­pose, we ana­lyzed the trans­mis­sion grid in a five-state area and used spe­cial soft­ware to car­ry out mod­el cal­cu­la­tions and sim­u­la­tions for var­i­ous oper­at­ing con­di­tions. In oth­er words, we sim­u­lat­ed how the five grids behaved over time with lit­tle or no renew­able sources, and how they man­aged with a very high pro­por­tion of them.

What are the most important findings?

NILAKANTAN: Inter­est­ing­ly, we found that just the opti­mized use of exist­ing equip­ment in com­bi­na­tion with phase-shift­ing trans­form­ers or dynam­ic shunt reac­tors (vari­able shunt reactor—VSR) can help cre­ate flex­i­bil­i­ty in the grids and increase reserves in the exist­ing grid. Even bet­ter coor­di­na­tion of the rel­e­vant trans­form­ers in pri­ma­ry sub­sta­tions alone leads to low­er grid loss­es. This is an impor­tant finding—because grid expan­sion should also remain eco­nom­i­cal.

So, would phase-shifter transformers be crucial in creating flexibility in Indian grids?

PROF. SWARUP: Yes. We are look­ing to Europe, in par­tic­u­lar, where phase-shift­ing trans­form­ers have a long tra­di­tion in the inter­con­nect­ed grid sys­tem (ENTSO‑E). In India, we can learn how the pow­er flow can be con­trolled effec­tive­ly between con­trol zones and dif­fer­ent volt­age lev­els. How­ev­er, thus far, we have only one phase-shift­ing trans­former in all of India, in the Koth­agu­dem ther­mal pow­er plant in the state of Telan­gana. It coor­di­nates the exist­ing 220-kilo­volt lines there. With 40,000 prob­lem-free switch­ing oper­a­tions in four years, the expe­ri­ences so far have been very promis­ing.

“India can try to do things dif­fer­ent­ly than Europe.”Ajay Nilakan­tan, Man­ag­er Busi­ness Devel­op­ment at MR

NILAKANTAN: But India can also try to do things dif­fer­ent­ly than Europe. There, for reg­u­la­to­ry rea­sons, phase shifters are usu­al­ly locat­ed on nation­al bor­ders. From the view of net­work topol­o­gy, that is not always the best place. India has the advan­tage of being able to posi­tion phase shifters exact­ly where they will opti­mize the load f low between large renew­able-ener­gy gen­er­at­ing units and load cen­ters.

What should operators be aware of if they want to use phase-shifter transformers?

NILAKANTAN: Phase-shift­ing trans­form­ers must always be adapt­ed to the indi­vid­ual grid con­di­tions. The phys­i­cal require­ments for the equip­ment are a result of these con­di­tions. In addi­tion to typ­i­cal vari­ables like nom­i­nal volt­age, phase angle and short-cir­cuit capac­i­ty, the oper­at­ing schemes as well as logis­ti­cal aspects such as trans­port also play an impor­tant role.

The design of the nec­es­sary tap chang­ers is an impor­tant as-pect in ensur­ing func­tion­al­i­ty in grid oper­a­tion. The tap chang­er influ­ences the design of the active part of the trans­former, and vice ver­sa. In this kind of elec­tric util­i­ty, close com­mu­ni­ca­tion between the grid oper­a­tor, trans­former man­u­fac­tur­er and tap-chang­er man­u­fac­tur­er is indis­pens­able.

What can grid operators learn from this study?

PROF. SWARUP: For devel­op­ing coun­tries with large growth, it offers insights into how the par­ties respon­si­ble for the set­up, expan­sion and oper­a­tion of grids can opti­mize costs through­out the life cycle of equip­ment through intel­li­gent plan­ning. For indus­tri­al­ized nations with a lot of aging infra­struc­ture, the study also pro­vides insight into asset man­age­ment and enhanc­ing the life of the trans­former beyond its present capac­i­ty through tar­get­ed invest­ment in new equip­ment.

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YOUR CONTACT PERSON

Do you have more ques­tions?
Then please con­tact Ajay Nilakan­tan:
A.Nilakantan@reinhausen.com