( Finally ( , ( ( to ( keep ( ( electric field ) constant ) ) ) ( , ( voltage ( ( is ( ( ( reduced ( by ( 30 % ) ) ) , ) ( ( ( reducing energy ) ( by ( ( ( 65 % ) and ) ( power ( -LRB- ( ( ( at 1.4 ) ( x frequency ) ) -RRB- ) ) ) ) ) ) ( by ( 50 % ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (ADVP (RB Finally)) (, ,) (S (VP (TO to) (VP (VB keep) (S (NP (JJ electric) (NN field)) (ADJP (JJ constant)))))) (, ,) (NP (NN voltage)) (VP (VBZ is) (VP (VBN reduced) (PP (IN by) (NP (CD 30) (NN %))) (, ,) (S (VP (VBG reducing) (NP (NN energy)) (PP (IN by) (NP (NP (CD 65) (NN %)) (CC and) (NP (NP (NN power)) (PRN (-LRB- -LRB-) (NP (QP (IN at) (CD 1.4)) (NN x) (NN frequency)) (-RRB- -RRB-))))) (PP (IN by) (NP (CD 50) (NN %))))))) (. .)))
Finally, to keep electric field constant, voltage is reduced by 30%, reducing energy by 65% and power (at 1.4x frequency) by 50%.
(ROOT (S (NP (PRP We)) (VP (VBP use) (ADJP (JJ voltage) (S (VP (TO to) (VP (VB keep) (NP (NP (NN track)) (PP (IN of) (NP (JJ electric) (JJ potential) (NN energy))))))))) (. .)))
We use voltage to keep track of electric potential energy.