Hy­brid power fac­tor cor­rec­tion

DEMM Engineering & Manufacturing - - FOOD AND BEVERAGE - BY: S T E PH E N B E R O S , A PPL I C AT I O N E NG I N E E R – E N G I N E E R I N G A N D T E C H N I C A L S U P P O R T, S C H N E I D E R E L E C T R I C

The def­i­ni­tion of power fac­tor is the ra­tio of true power to ap­par­ent power and it is rep­re­sented as the co­sine of the phase an­gle be­tween voltage and cur­rent in an al­ter­nat­ing cur­rent cir­cuit. Trans­lated into eco­nomic terms, power fac­tor can be loosely de­fined as the ra­tio of use­ful power to the power that is drawn from the sup­ply and rep­re­sents the elec­tri­cal ef­fi­ciency of an in­stal­la­tion.

For many decades, power fac­tor cor­rec­tion was achieved by the ad­di­tion of ap­pro­pri­ate ca­pac­i­tance to the load. In the lat­ter half of the twen­ti­eth cen­tury, con­nec­tion of ca­pac­i­tors to mo­tor ter­mi­nals was a com­mon ap­proach and in terms of ef­fi­ciency worked well. Au­to­matic power fac­tor cor­rec­tion con­trollers were used to op­er­ate ca­pac­i­tor banks at main switch­boards to main­tain over­all site power fac­tor to tar­get.

To­day, ca­pac­i­tor based power fac­tor cor­rec­tion sys­tems are still avail­able and in most ap­pli­ca­tions are a per­fectly suit­able type of sys­tem. They are fit­ted with de­tuned re­ac­tors to counter the ef­fects of har­monic dis­tor­tion and as­so­ci­ated heat dis­si­pa­tion. These re­ac­tors also pre­vent any pos­si­bil­ity of elec­tri­cal res­o­nance oc­cur­ring in the ca­pac­i­tor cir­cuit. Ca­pac­i­tor switch­ing con­tac­tors are fit­ted with in­ser­tion re­sis­tors to re­duce in­rush cur­rent to ac­cept­able lev­els. A ca­pac­i­tor based power fac­tor cor­rec­tion sys­tem can be con­fig­ured to have step sizes that align to the load pro­file to per­form ap­pro­pri­ate com­pen­sa­tion. Elec­tric­ity sup­plier’s mea­sure power fac­tor av­er­aged over half hour in­ter­vals and charge ac­cord­ingly. When a load is rel­a­tively steady, there is no need for in­stan­ta­neous power fac­tor cor­rec­tion nor any ad­van­tage to be gained by in­vest­ing in such tech­nol­ogy.

Ac­tive power fac­tor cor­rec­tion sys­tems utilise power elec­tron­ics and dig­i­tal con­trol to achieve ac­tive re­ac­tive cur­rent com­pen­sa­tion for spe­cific and high per­for­mance so­lu­tions. The Sch­nei­der Elec­tric Ac­cu­sine PFV+ ac­tive power fac­tor cor­rec­tion unit utilises closed loop con­trol to cor­rect power fac­tor with a ¼ cy­cle (5mS) re­sponse. This is suit­able for un­steady fast chang­ing loads such as cranes, welders, saws and de­bark­ing ma­chines. How­ever, sites con­tain­ing loads such as these gen­er­ally have a stead­ier base load. Con­sid­er­ing ac­tive power fac­tor cor­rec­tion pro­duces a sig­nif­i­cant amount of heat, the ques­tion is whether the whole site needs ac­tive power fac­tor cor­rec­tion when only part of the site needs it.

A hy­brid power fac­tor cor­rec­tion sys­tem is com­prised from both ca­pac­i­tor based and ac­tive power fac­tor cor­rec­tion. Ac­tive power fac­tor cor­rec­tion is used to cope with the un­steady fast chang­ing por­tion of to­tal load while ca­pac­i­tor banks sup­port cor­rec­tion by cor­rect­ing the stead­ier base load. This sys­tem of­fers the high level per­for­mance of an ac­tive sys­tem com­bined with the cost ef­fec­tive­ness of­fered by ca­pac­i­tor bank cor­rec­tion.

Oji Fi­bre So­lu­tions ap­proached Sch­nei­der Elec­tric in April 2016 with view to a rec­om­men­da­tion of a suit­able power fac­tor cor­rec­tion sys­tem for its cor­ru­gated card­board pack­ag­ing fa­cil­ity in Levin. Ini­tially, a tra­di­tional sys­tem was con­sid­ered. How­ever, a study of load pro­files showed that when load is un­sta­ble, there would be up to twenty-six con­tac­tor switch­ing events per hour which is not ideal.

Two options of hy­brid so­lu­tions were mod­elled against the mea­sured load and the­o­ret­i­cally, both were ca­pa­ble of achiev­ing re­quire­ments. The more cost ef­fec­tive op­tion was built by Gael Switch­boards in Welling­ton and then in­stalled at the site to­wards the end of 2016.

PER­FOR­MANCE GRAPHS

Power Fac­tor has dis­tinctly im­proved and is con­sis­tently above the de­sign tar­get of 0.96 lag­ging. A fur­ther con­sid­er­a­tion around power fac­tor cor­rec­tion sys­tems is heat dis­si­pa­tion. Ac­tive power fac­tor cor­rec­tion units dis­si­pate con­sid­er­ably more heat per kVAr than their ca­pac­i­tor- based

coun­ter­parts. The hy­brid so­lu­tion in­stalled at Oji will dis­si­pate 4.8 – 5kW of heat at full ca­pac­ity whereas a totally ac­tive power fac­tor cor­rec­tion unit of the same ca­pac­ity would dis­si­pate up to 11.25kW of heat. The hy­brid so­lu­tion of­fers the per­for­mance of an ac­tive so­lu­tion but at a re­duced cost and greatly re­duced heat dis­si­pa­tion.

Neil McLean of Oji Fi­bre So­lu­tions and Stephen Beros from Sch­nei­der Elec­tric with the Hy­brid Power Fac­tor Cor­rec­tion Unit.

Oji Fi­bre So­lu­tions (Oji FS) are now run­ning their Cor­ru­ga­tor Plant more ef­fi­ciently and are sav­ing en­ergy as a re­sult of in­stalling the hy­brid power fac­tor cor­rec­tion sys­tem. A new main switch­board, also built by Gael Switch­boards from Sch­nei­der Elec­tric com­po­nents, has been in­stalled in the Cor­ru­ga­tor build­ing to en­sure the safe and re­li­able distri­bu­tion of power through­out the plant.

Oji FS pack­ag­ing fa­cil­i­ties pro­duce a range of pa­per-based prod­ucts for the hor­ti­cul­ture, dairy, meat, bev­er­age, seafood, re­seller and in­dus­trial sec­tors in New Zealand and Aus­tralia. They are com­mit­ted to de­vel­op­ing in­no­va­tive, en­vi­ron­men­tally sus­tain­able prod­ucts and work­ing col­lab­o­ra­tively to de­velop so­lu­tions that en­hance the com­pet­i­tive­ness of their cus­tomers. Sch­nei­der Elec­tric de­vel­ops con­nected technologies and so­lu­tions to man­age en­ergy and process in ways that are safe, re­li­able, ef­fi­cient and sus­tain­able. Both com­pa­nies have sim­i­lar out­looks.

NEIL MCLEAN OF OJI FI­BRE SO­LU­TIONS AND STEPHEN BEROS FROM SCH­NEI­DER ELEC­TRIC.

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