AC Capacitor Application Guide This guide covers Cornell Dubilier’s AC capacitor types in depth within microseconds. These capacitors boast low losses where and discloses the latest information on performance and appli- very low Dissipation Factor and ESR allow for relatively high current density. cation. CONTENTS PAGE 1 Characterization and Circuit Model 1 Rated Temperature 1 Rated Capacitance 2 Dissipation Factor (DF) 2 Equivalent Series Resistance (ESR) 2 RMS Current 2 Leakage Current 2 Insulation and Grounding 2 Voltage Withstand Test 2 Self-Resonant Frequency 2 Dielectric Absorption 2 Vibration Withstanding Capability 2 Safety Considerations 2 Reliability and Lifetime 2 Failure Modes Rs Ls Figure 1 PARAMETRIC CHARACTERIZATION The table below shows useful capacitor parameters for the series equivalent-circuit model shown schematically in Figure 1. Parameter Unit Symbol Formula Approx. Capacitance farads (F) C Capacitive Reactance ohms (Ω) Xc 1/(2πfC) Z Current amperes (A) I C(dV/dt), Vz/Z Dissipation Factor none DF Rs/Xc, 2πfCRs, tan(δ), cot(θ) Energy Joules (J) E ½CV² 2 Equivalent Series Resistance ohms (Ω) Rs DF/(2πfC) Early Life Failures 2 Frequency hertz (Hz) f Wear-Out 2 Impedance ohms (Ω) Z Operating Life 2 Inductance henries (H) Ls Shelf Life 3 Inductive Reactance ohms (Ω) XL 2πfLs Mounting 3 Loss Angle degrees (°) δ tan-1(DF) Typical Applications 3 Phase Angle degrees (°) θ cot-1(DF) Power watts (W) P - Motor Run 3 - Power Supply 3 - Power Factor Correction 3 TABLES Capacitor Parameter Formula 215 Expected Life vs Applied Voltage and Case Temperature 217 AC CAPACITOR CONSTRUCTION Cornell Dubilier’s AC capacitors are constructed with biaxially oriented metallized polypropylene film wound into a cylindrical roll. End contact is formed by zinc metal spraying all of the layers on each side of the winding which assures low ESR and low inductance. Metallized polypropylene film provides a self healing mechanism in which a dielectric breakdown “clears” away the metallization and isolates that area of the capacitor [Rs²+(Xc–XL)²]½ PF AC Capacitor Construction CAPACITOR SERIES EQUIVALENT CIRCUIT MODEL Xc I²Rs Rs/Z, sin(δ), cos(θ) Xc/Rs, 1/DF, cot(δ), tan(θ) Power Factor none PF Quality Factor none Q Self-Resonant Frequency hertz (Hz) ωo 1/[2π(LC)½ ] Voltage volts (V) V Vc=IXc, Vz=IZ Volt-Amperes V-A VA IVz, I²Z DF 1/PF DEFINITIONS RATED TEMPERATURE The rated temperature is the range in temperature in which the capacitors will perform to their full rated service life objective. Typically AC capacitors will have a rated temperature of –40 to +70 °C for a motor run application and -40 to +90 °C for a power supply type application. 1 RATED CAPACITANCE SELF RESONANT FREQUENCY The rated capacitance is the nominal capacitance and it is specified between 50Hz to 120Hz and a temperature of 25 °C. The rated capacitance is also the capacitance marked on the unit. DISSIPATION FACTOR (DF) Dissipation factor is the measurement of the tangent of the loss angle (tan δ) expressed as a percentage. It is also the ratio of the ESR to the capacitive reactance and is thus related to ESR by this equation: DF = 2πfC(ESR)/10,000 Where DF is a unit-less number expressed in percent, test frequency f is in Hz, capacitance C is in µF and ESR is in Ω. EQUIVALENT SERIES RESISTANCE (ESR) AC The equivalent series resistance (ESR) is a single resistance representing all of the ohmic losses of the capacitor and connected in series with the capacitance. The self-resonant frequency is the frequency at which the capacitive reactance (1/2πfC) equals the inductive reactance (2πfL). At this point, where its impedance approaches zero, the capacitor can be considered to be purely resistive. At frequencies above self resonance, the capacitor is inductive. DIELECTRIC ABSORPTION Is a property of an imperfect dielectric material that allows the capacitor utilizing this material to absorb and accumulate a certain amount of energy even after being completely discharged. These charges will accumulate in the dielectric body and not on the capacitor plates (electrodes). Dielectric absorption can be approximated by the ratio of the voltage before discharge to the self recharged (absorbed) voltage level. VIBRATION WITHSTANDING CAPABILITY AC capacitors are manufactured to withstand a test outlined in the EIA 186-7E STD of (10 to 55Hz per plane) test method III with modification to the duration time which is reduced to 30 minutes from of 120 minutes equating to 5G. RMS CURRENT SAFETY CONSIDERATIONS AC capacitors with ¼” x 0.032” blade style terminals can handle a maximum RMS current of 15 Arms, including harmonics, 60Arms for the enclosed block terminals. The capacitor’s safety pressure interrupter is designed to disconnect the capacitor element as the cover expands upward due to gas pressure build up. Catastrophic failure may result if movement of the cover and or terminals are restricted. Rigid bus bars are not recommended as they may restrict movement of the cover or terminals. Customers are advised to provide at least 0.5” clearance above the cover to allow for its expansion. LEAKAGE CURRENT When energized between their shorted terminals and the capacitor case at a potential of 115 Vac 60 Hz their leakage current shall not exceed the following: Nominal Capacitance Leakage Current 0 - 14 µF 60 µA 14.1 - 20 µF 70 µA 20.1 - 35 µF 100 µA 35.1 - 80 µF 150 µA RELIABILITY AND LIFETIME AC capacitors are rated for a full service life of 60,000 h with an estimated 94% survival rate when operated at full rated voltage, 60 Hz and rated ambient temperature. FAILURE MODES AC capacitors feature an internal mechanical pressure Interrupter that disconnects the capacitor winding from the voltage source in the event of failure. Failure occurs in open circuit mode. INSULATION AND GROUNDING In either event the capacitor will remain in an open circuit mode. AC capacitors are manufactured to minimize electrical leakage from terminal to terminal and terminal to case. Due to the non ideal nature of all insulating materials a maximum allowable leakage current to the case as well as between terminals has been established. EARLY LIFE FAILURES Grounding of the metal case is recommended. VOLTAGE WITHSTAND TESTS AC capacitors are designed and 100% tested to withstand a potential difference equal to 1.75 X rated AC voltage between terminals and 2 X rated AC voltage plus 1,000 volts for one second between terminals and case. 2 Early-life failures are mostly associated with short-circuit failures from imperfections in the dielectric system. Incidences can be reduced with extended aging or burn-in. WEAR-OUT Wear-out failures are mostly open-circuit failures where the integral Pressure Interrupter mechanism has been activated due to material fatigue (wear-out). OPERATING LIFE Onset of wear-out is determined mainly by the capacitor’s rated voltage and temperature and is relative to the actual applied voltage (both at the fundamental frequency and any harmonic content) and ambient temperature. Operating life can be expressed as (Tr - To)/10) 6.2 Lo = Lr x 2 x Vr Where TYPICAL APPLICATIONS Motor Run AC capacitors are utilized to provide the necessary starting torque to split phase motors by introducing a phase shift on a secondary motor winding. Motor-run capacitors also provide the necessary power factor correction during the run stage for a more energy efficient motor operation. Vo Lrated is the rated operating life in h, (60,000 h) Loperation is the expected operating life in h, Trated is the rated operating temperature in °C, Tapplied is the actual temperature applied to the capacitor in ºC, Vrated is the capacitor’s rated voltage in Vrms, Vapplied is the actual voltage applied to the capacitor in Vrms. Power Supply AC capacitors are utilized in power supply circuits where noise suppression, voltage regulation and line current reduction is required. These applications typically expose the capacitor to higher order harmonics. The sum of the fundamental and all harmonic currents must not exceed the capacitor’s maximum current rating. In addition the chart below can be utilized to estimate service life when AC capacitors are to operate at specific conditions outside of the rated specified conditions. Power Factor Correction AC capacitors are also utilized in power factor correction circuits where they supply leading reactive power (KVAR) to correct the lagging current caused by inductive loads. The circuit is said to be running at unity power factor if the capacitive reactance of the applied capacitors exactly matches the inductive reactance of the load. AC PF = KW / KVA SHELF LIFE KW = (HP x 0.746) / % efficiency AC capacitors are expected to perform for their full service life objective after being exposed to a maximum shelf life of 10+ years when stored in a controlled environment. KVA = KW / PF =√ (KW)2 + (KVAR)2 MOUNTING AC capacitors are manufactured in round and oval metal cases which can be fastened and mounted by a variety of methods. These capacitors can be secured to a chassis or mounting plate by means of a mounting bracket (hardware) or by an optional M8 or M12 mounting stud provided at the bottom of the capacitor case. Please note that the capacitor case will be at the voltage potential of the chassis or mounting plate. The capacitor’s safety pressure interrupter is designed to disconnect the capacitor element as the cover expands upward due to gas pressure build up. Catastrophic failure may result if movement 5 6 4 2 4 of the cover and 3or terminals are restricted. 1 bars are Rigid bus not recommended as they may restrict movement of the cover or terminals. Customers are advised to provide at least 0.5” clearance above the cover to allow for its expansion. 7 5 4 8 2 3 6 7 B 4 (single phase) KVA = V I / 577 (three phase) C = (KVAR x 103) / (2 π F (KV)2) KVAR = (2 π F C (KV)2) / 1000 3 1 5 KVA = V I / 1000 3 2 Power Triangle 2 1 1 D D D D B A D SF, HV Series Pressure Interrupter C C C C C PC Series Pressure Interrupter B B B B 3 AC Notice and Disclaimer: All product drawings, descriptions, specifications, statements, information and data (collectively, the “Information”) in this datasheet or other publication are subject to change. The customer is responsible for checking, confirming and verifying the extent to which the Information contained in this datasheet or other publication is applicable to an order at the time the order is placed. All Information given herein is believed to be accurate and reliable, but it is presented without any guarantee, warranty, representation or responsibility of any kind, expressed or implied. Statements of suitability for certain applications are based on the knowledge that the Cornell Dubilier company providing such statements (“Cornell Dubilier”) has of operating conditions that such Cornell Dubilier company regards as typical for such applications, but are not intended to constitute any guarantee, warranty or representation regarding any such matter – and Cornell Dubilier specifically and expressly disclaims any guarantee, warranty or representation concerning the suitability for a specific customer application, use, storage, transportation, or operating environment. The Information is intended for use only by customers who have the requisite experience and capability to determine the correct products for their application. Any technical advice inferred from this Information or otherwise provided by Cornell Dubilier with reference to the use of any Cornell Dubilier products is given gratis (unless otherwise specified by Cornell Dubilier), and Cornell Dubilier assumes no obligation or liability for the advice given or results obtained. Although Cornell Dubilier strives to apply the most stringent quality and safety standards regarding the design and manufacturing of its products, in light of the current state of the art, isolated component failures may still occur. Accordingly, customer applications which require a high degree of reliability or safety should employ suitable designs or other safeguards (such as installation of protective circuitry or redundancies or other appropriate protective measures) in order to ensure that the failure of an electrical component does not result in a risk of personal injury or property damage. Although all product-related warnings, cautions and notes must be observed, the customer should not assume that all safety measures are indicated in such warnings, cautions and notes, or that other safety measures may not be required. 4