Role of har­mon­ics stan­dards in re­duc­ing power qual­ity prob­lems in the grid by Ravichan­dran Pu­rushothaman, Pres­i­dent, Dan­foss In­dia In­dus­tries Pvt Ltd.

Power Watch India - - CONTENTS - The au­thor is Pres­i­dent, Dan­foss In­dia In­dus­tries Pvt Ltd By Ravichan­dran Pu­rushothaman

The term har­mon­ics for decades has been a ter­mi­nol­ogy or a buzz word, mak­ing many peo­ple re­con­sider the ef­fec­tive­ness of their build­ing’s wiring sys­tem. But over the years, it has shaped new mean­ings. The pres­ence of har­mon­ics in elec­tri­cal sys­tems means that the cur­rent and volt­age are dis­torted and de­vi­ate from si­nu­soidal wave­forms. Har­mon­ics have short and long-term ef­fects on grids, grid con­nected elec­tron­ics and power elec­tron­ics equip­ment such as mal­func­tion, fail­ure and losses. These re­duce re­li­a­bil­ity, life­time and ef­fi­ciency of the elec­tric­ity net­works. Har­mon­ics can also cause over­load­ing of con­duc­tors and trans­form­ers and over­heat­ing of util­i­sa­tion equip­ment, such as mo­tors. Har­monic fre­quen­cies in the power grid are a frequent cause of power qual­ity prob­lems, and re­duc­tion of har­mon­ics op­ti­mises pro­duc­tiv­ity, thus, in­creas­ing ef­fi­ciency. Har­mon­ics in power sys­tems re­sult in in­creased heat­ing in the equip­ment and con­duc­tors, mis­fir­ing in vari­able speed drives, and torque pul­sa­tions in mo­tors. Har­mon­ics can also have detri­men­tal ef­fects on trans­form­ers, ca­bles, fuses, cir­cuit break­ers, light­ing, etc. How­ever, tech­nol­ogy de­vel­op­ment has kept pace with de­mands of the power sec­tor in the coun­try. Tech­nol­ogy such as ad­vanced ac­tive fil­ters are now avail­able which can lead to re­duc­tion in grid har­monic pollution and hence clean grids.

How to di­ag­nose and fix har­mon­ics:

One needs to first de­tect and recog­nise har­mon­ics in the sys­tem. Once you’ve recog­nised that har­mon­ics ex­ist in a cir­cuit or elec­tri­cal sys­tem, the next step is to carry out tests to de­ter­mine the mag­ni­tude and type of har­mon­ics. If there are huge har­monic com­po­nents present, one should first learn what the elec­tri­cal sys­tem is car­ry­ing on its lines. To do this, it is a must to use har­monic mea­sure­ment me­ters.

Har­mon­ics anal­y­sers:

A har­mon­ics anal­yser is the most ef­fec­tive in­stru­ment for per­form­ing a de­tailed anal­y­sis of power qual­ity to de­ter­mine the wave shapes of volt­age and cur­rent on re­spec­tive fre­quency spec­trums. A har­mon­ics anal­yser is also use­ful in in­stances where the lack of ob­vi­ous symp­toms pre­vents you from de­ter­min­ing if har­mon­ics are a cause for con­cern. A har­mon­ics anal­yser is used to pro­vide a de­tailed anal­y­sis of the sus­pect source. We need con­vinc­ing graph­ics and quan­ti­ta­tive ev­i­dence along with an au­thor­i­ta­tive ref­er­ence.

Using an os­cil­lo­scope:

Os­cil­lo­scopes have tra­di­tion­ally been used to trou­bleshoot elec­tronic and elec­tri­cal cir­cuits. The dig­i­tal stor­age-style scopes, in ad­di­tion to per­form­ing their tra­di­tional func­tions, have the ca­pa­bil­ity to ac­quire and store sig­nals and per­form math­e­mat­i­cal op­er­a­tions for de­ter­min­ing fre­quency char­ac­ter­is­tics. These units col­lect and store the wave­form data using volt­age and cur­rent probes. This data then is down­loaded into com­put­ers and syn­the­sised to de­ter­mine the wave­form fre­quency char­ac­ter­is­tics.

Re­duc­ing har­mon­ics to curb car­bon foot­print

A poor power grid sys­tem can have sig­nif­i­cant eco­nomic and tech­ni­cal con­se­quences for a fa­cil­ity. If har­mon­ics are not suit­ably ad­dressed, it will cre­ate losses which could be min­i­mal at the be­gin­ning, but will in­crease as the load fac­tors and other vari­ables in­crease. This will cre­ate ef­fi­ciency losses thereby in­creas­ing the over­all load re­quire­ments. By addressing har­mon­ics ef­fec­tively, we can avoid over­load­ing elec­tri­cal sys­tems, re­duc­ing losses and power de­mand, and in­creas­ing the equip­ment life­time. When we look at the cycli­cal na­ture of in­vest­ments, we can see that by in­vest­ing in mit­i­gat­ing har­mon­ics we have avoided many other in­vest­ments which would have added to the cost and foot­print. Thus, by ex­am­in­ing har­monic volt­age and cur­rent data, you can get im­por­tant in­for­ma­tion about the op­er­at­ing char­ac­ter­is­tics of a power sys­tem and work to­wards its mit­i­ga­tion.

Any elec­tri­cal sys­tem’s re­li­a­bil­ity and nor­mal op­er­a­tion of the equip­ment re­lies pro­foundly upon a clean dis­tor­tion-free power sup­ply. It is hoped that har­monic mit­i­ga­tion tech­niques if used wisely, will pro­vide use­ful in­for­ma­tion to help make se­lec­tion of an ap­pro­pri­ate har­monic re­duc­tion method for a given ap­pli­ca­tion an eas­ier task.

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