Faktor daya

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Faktor daya dina sistim daya listrik AC nyaeta rasio (babandingan) antara daya nyata jeung daya nu katempo, nileyna antara 0 tepi ka 1 (kadang-kadang ditulis dina persentase, contona .5 pf = 50% pf). Daya nyata nyaeta kapasitas sirkuit keur ngalakukeun pagawean dina hiji wanci tinangtu. Daya nu katempo nyaeta hasil ngalikeun arus jeung tegangan sirkuit. Alatan energi nu disimpen dina beban sarta malik deui kana sumberna, atawa alatan beban non linier nu ngaruksak wangun gelombang arus nu asalna tina hiji sumber, daya nu katempo bisa leuwih gede tibatan daya nyatana. Beban nu faktor dayana leutik nyababkeun ningkatna karugian dina sistim distribusi daya sarta nyababkeun naekna ongkos energi.

Faktor daya dina sirkuit linier[édit | sunting sumber]

Daya instan (saharita, sesaat) jeung daya rata-rata diitung tina tegangan jeung arus AC kalayan faktor daya hiji (φ=0, cosφ=1)
Daya instan (saharita, sesaat) jeung daya rata-rata diitung tina tegangan jeung arus AC kalayan faktor daya enol (φ=90, cosφ=0)
Daya instan (saharita, sesaat) jeung daya rata-rata diitung tina tegangan jeung arus AC kalayan faktor daya nu katinggaleun (φ=45, cosφ=0.71)

Dina hiji sirkuit AC resistif murni, wangun gelombang tegangan jeung arus baris salengkah (safase), ngarobah polaritasna babarengan dina unggal siklusna. Nalika aya beban reaktif, saperti lamun make kapasitor atawa induktor, nyimpen energi dina beban ngahasilkeun beda wanci antara wangun gelombang arus jeung tegangannana. Energi nu disimpen ieu malik deui kana sumberna sarta henteu tepi kana beban. Hiji sirkuit nu faktor dayana leutik bakal make arus leuwih gede keur mindahkeun sajumlah daya nyata tibatan sirkuit nu faktor dayana gede.

Sirkuit nu ngandung élemén panas résistif murni (lampu filamén, pamanas strip, kompor listrik, jsb.) boga faktor daya 1.0. Sirkuit nu ngandung élemén induktif atawa kapasitif (ballast lampu, motor, jsb.) mindeng boga faktor daya sahandapeun 1.0. Contona, dina sirkuit lampu listrik, ballast faktor daya normal (normal power factor, NPF) ilaharna boga niléy (0.4) - (0.6). Ballast nu faktor dayana leuwih gede tibatan (0.9) dianggap ballast faktor daya luhur (high power factor ballasts, HPF).

Pentingna faktor daya teh alatan kanyataanana yen pausahaan utilitas nyadiakeun daya ka konsumen dina volt-ampere, padahal ngitung tagihannana dina watt. Faktor daya sahandapeun 1.0 nyababkeun perluna ngabangkitkeun leuwih tina volt-ampere minimum nu perlu keur nyadiakeun daya nyata (watt). Hal ieu nambah ongkos keur ngabangkitkeun jeung transmisi. Contona, lamun faktor daya bebanna 0.7, daya katempona bakal 1.4 kalieun daya nyata nu dipake ku beban. Arus line dina sirkuit oge bakal 1.4 kalieun arus nu diperlukeun lamun power faktorna 1.0, sahingga karugian dina sirkuit bakal ngalipet dua (sabab proporsional jeung kuadrat arus). Minangka alternatif, sakabeh komponen sistim siga generator, konduktor, transformator, jeung switchgear bakal nambah ukuran (jeung ongkosna) pikeun mawa arus nu leuwih gede.

Faktor daya nu hade dianggap leuwih gede batan 90 tepi ka 95%. Pausahaan nu nyadiakeun daya biasana nambahkeun ongkos ka nu marake nu faktor dayana sahandapeun wates tinangtu, nu ilaharna 90 tepi ka 95%. Insinyur mindeng katarik ngeunaan faktor daya dina hiji beban minangka salasahiji faktor nu mangaruhan efisiensi transmisi daya.

Definisi jeung itungan[édit | sunting sumber]

Aliran daya AC boga tilu komponen: daya nyata (P), nu diukur dina unit watt (W); daya nu katempo (S), diukur dina unit volt-ampere (VA); jeung daya reaktif (Q), diukur dina unit volt-ampere reaktif (VAr).

Faktor dayana didefinisikeun minangka:

\frac{P}{S}.

Lamun wangun gelombangna sinusoidal sampurna, P, Q jeung S bisa dikedalkeun minangka vektor nu ngawangun hiji segitilu vektor saperti kieu:

S^2\,\! = {P^2\,\!} + {Q^2\,\!}


Lamun \phi\, nyaeta juru fase antara arus jeung tegangan, mangka faktor dayana sarua jeung \left|\cos\phi\right|, sarta:

 P = S \left|\cos\phi\right|

Sabab hjianana tetep, faktor daya sacara definisi mangrupakeun nomer tanpa dimensi antara 0 jeung 1. Lamun faktor dayana 0, energi nu ngalir sagemblengna reaktif, tur energi nu kasimpen dina beban bakal malik kana sumberna dina unggal siklus. Laun faktor dayana 1, sakabeh energi tina sumber dipake ku beban. Faktor daya biasana dinyatakeun minangka "miheulaan" (leading) atawa "pandeurieun" (lagging) pikeun nuduhkeun tanda juru fase, leading nunjukkeun tanda negatif.

Lamun beban resistif murni dihubungkeun kana sumber daya, arus jeung tegangan bakal robah polaritasna babarengan, faktor dayana bakal hiji (1), tur energi listrikna bakal ngalir saarah dina jaringan dina unggal siklusna. Beban induktif kawas trafo jeung motor (sagala rupa beulitan) make daya reaktif nu wangun gelombang arusna katinggaleun ku tegangan. Beban kapasitif kawas bank kapasitor atawa kabel nu dikubur ngabangkitkeun daya reaktif nu fase arusna miheulaan tegangan. Dua tipe beban ieu bakal nyerep energi dina sabagean siklus AC, nu disimpen dina widang magnetik atawa elektrikna divais, sarta ngan bisa mulangkeun energina deui kana sumber dina sesa siklusna.

Contona, keur meunangkeun 1 kW daya nyata lamun faktor dayana hiji, 1 kVA daya katempo kudu dipindahkeun (ditransfer) (1 kW ÷ 1 = 1 kVA). Lamun niley faktor dayana leutik, daya katempo nu kudu ditransfer kudu leuwih gede deui lamun heug hayang meunangkeun daya nyata nu sarua. Keur meunangkeun 1 kW daya nyata lamun faktor dayana 0.2, kudu transfer daya katempo 5 kVA (1 kW ÷ 0.2 = 5 kVA).

Mindeng yen faktor daya hiji sistim bisa di-adjust sangkan ngadeukeutan hiji. Praktek kieu katelah koréksi faktor daya sarta bisa dihontal ku jalan nyaklar nyambung jeung muka bank induktor atawa kapasitor. Contona pangaruh induktif tina beban motor bisa di-offset ku cara ngahubungkeun kapasitor sacara lokal.

Komponen non-sinusoidal[édit | sunting sumber]

Dina sirkuit nu ukur boga arus jeung tegangan sinusoidal, pangaruh faktor daya ukur mucunghul alatan beda fasena antara arus jeung tegangan. Sacara heureut hal ieu katelah "faktor daya nu pidah". Konsep ieu bisa digeneralisasi jadi faktor daya total, distorsi atawa sajati nu daya katempona kaasup sakabeh komponen harmonik. Hal ieu penting dina sistim daya praktis nu ngandung beban non-linier kawas panyaarah, sababaraha wangun lampu listrik, electric arc furnace, alat patri, switched-mode power supplies jeung alat lianna.

Conto penting husus nyaeta komputer pribadi nu ilaharna make switched-mode power supply (SMPS) kalayan daya output rata-rata ti 250 W tepi ka 750 W. Dumasar sajarahna, catu daya nu hargana kacida murah ieu make panyaarah gelombang pinuh basajan nu ngonduksi ukur nalika tegangan saharita utama (mains instantaneous voltage) ngaleuwihan tegangan dina kapasitor input. Hal ieu nyababkeun rasio arus input nu kacida gedena, nu nyababkeun oge faktor daya distorsi nu leutik sarta sacara potensial ngeunaan kaluarna fase jeung netral (potentially serious phase and neutral loading concerns).

Panneau travaux.png Artikel ieu keur dikeureuyeuh, ditarjamahkeun tina basa Inggris.
Bantosanna diantos kanggo narjamahkeun.

Badan pangaturan siga EU geus nyetel wates harmonis minangka hiji cara keur ngahadean faktor daya. Declining component cost has hastened acceptance and implementation of two different methods. Normally, this is done by either adding a series inductor (so-called passive PFC) or the addition of a boost converter that forces a sinusoidal input (so-called active PFC). For example, SMPS with passive PFC can achieve power factor of about 0.7–0.75, SMPS with active PFC, up to 0.99, while SMPS without any power factor correction has a power factor of only about 0.55–0.65.

To comply with current EU standard EN61000-3-2, all switched-mode power supplies with output power more than 75 W must include passive PFC, at least.

A typical multimeter will give incorrect results when attempting to measure the AC current drawn by a non-sinusoidal load and then calculate the power factor. A true RMS multimeter must be used to measure the actual RMS currents and voltages (and therefore apparent power). To measure the real power or reactive power, a wattmeter designed to properly work with non-sinusoidal currents must be used.

Ngukur faktor daya[édit | sunting sumber]

Power factor in a single-phase circuit (or balanced three-phase circuit) can be measured with the wattmeter-ammeter-voltmeter method, where the power in watts is divided by the product of measured voltage and current. The power factor of a balanced polyphase circuit is the same as that of any phase. The power factor of an unbalanced polyphase circuit is not uniquely defined.

A direct reading power factor meter can be made with a moving coil meter of the electrodynamic type, carrying two coils on the moving part of the instrument. The field of the instrument is energized by the circuit current flow. The two moving coils, A and B, are connected in parallel with the circuit load. One coil, A, will be connected through a resistor and the second coil, B, through an inductor, so that the current in coil B is delayed with respect to current in A. At unity power factor, the current in A is in phase with the circuit current, and coil A provides maximum torque,driving the instrument pointer toward the 1.0 mark on the scale. At zero power factor, the current in coil B is in phase with circuit current, and coil B provides torque to drive the pointer towards 0. At intermediate values of power factor, the torques provided by the two coils add and the pointer takes up intermediate positions. [1]

Digital instruments can be made that either directly measure the time lag between voltage and current waveforms and so calculate the power factor, or by measuring both true and apparent power in the circuit and calculating the quotient. The first method is only accurate if voltage and current are sinusoidal; loads such as rectifiers distort the waveforms from the sinusoidal shape.

Mnemonik[édit | sunting sumber]

Murid tehnik daya biasana dititah ngapalkeun dina basa Inggris: "ELI the ICE man" atawa "ELI on ICE" – tegangan E miheulaan arus I dina induktor L, arus miheulaan tegangan dina kapasitor C.

Atawa leuwih pondokna: CIVIL – in a Capacitor the I (current) leads Voltage, Voltage leads I (current) in an inductor L.

Tempo ogé[édit | sunting sumber]

Rujukan[édit | sunting sumber]

  1. Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 0-07020974-X page 3-29 paragraph 80