Power Quality,Any power problem manifested in voltage, current or frequency deviation that results in failure or misoperation of customer equipment. IEEE (Working Group on Distribution Voltage Quality) : 電力系統擾動的相對程度；以電力公司為立場，所定義之電力品質可以簡述為電力系統對污染源(用戶)之接受度。 CEA (Canada Electric Association) : 在某一電力條件情況下， 電力設備性能的滿意程度；以用戶為立場，所定義之電力品質可以簡述為用戶對電力公司供電品質之滿意度。,換句話說，電力品質必須得到電力公司與用戶雙方皆能接受或滿意，至於滿意與否之界定就必須由電力品質相關因素之管制標準來規範。,電力品質分類,不良電力品質範例,諧波(harmonic),電壓閃爍(flicker),電壓驟降(sag),Sec.,不良電力品質範例,三相不平衡與突入電壓(three-phase unbalance),突入電壓與電流(inrush current),頻率波動,In IEC 61000-2-5:1995, the IEC classifies electromagnetic phenomena into several groups as shown in Table 1. The IEC standard addresses the conducted electrical parameters shown in Table 1. The terms high frequency and low frequency are not defined in terms of a specific frequency range, but instead are intended to indicate the relative difference in principal frequency content of the phenomena listed in these categories.,IEEE Std 1159-2009,Transient,An event that is undesirable but momentary in nature Part of the change in a variable that disappears during transition from one steady state operation condition to another Surge It can be classified into two categories: Impulsive,oscillatory,Impulsive transient,1.An impulsive transient is a sudden, non-power frequency change in the steady state condition of voltage, current or both, that is unidirectional in polarity 2.They are characterized by rise and decay times. 3.lightning 4.They are generally not conducted far from the occurred source 5. It can be divided into three parts,Rise from zero to its peak value of 2000 V in 1.2 , then decay to half its peak value in 50,台 灣 落 雷 日 數 與 頻 率 實 測 圖,Oscillatory transient,1.An oscillatory transient is a sudden, non-power frequency change in the steady state condition of voltage, current or both, that includes both positive and negative polarity values 2.They are characterized by spectral content, duration and magnitude . 3. It can be divided into high, medium and low frequency three parts HF(500kHz, 5us, 0-4pu):the result of a local system responses to an impulsive transient MF(5-500kHz, 20us, 0-8pu):fig.2-2,cable switching or impulsive transient,LF(5kHz):occurred at utility sub-transmission and distribution systems, capacitor bank energization: result is oscillatory voltage transient with frequency 300-900Hz. Peak magnitude can reach 2.0pu(typically 1.3-1.5), duration 0.5-3 cycles,Long-duration variations encompass root-mean-square(rms) deviations at power frequencies for longer than 1 min Over-voltage: rms voltage greater than 1.1pu, duration longer than 1min switching off a large load, energizing a capacitor bank, weak system, inadequate voltage control(TX OLTC, Gen AVR) Under-voltage: rms voltage less than 0.9pu, duration longer than 1min Sustained Interruption: rms voltage drop to zero, duration longer than 1min(outage:it is the same as interruption for utility. For user,any interruption of power that shuts down a process. This could be as little as one-half of a cycle.),Long-Duration Voltage Variations,Short-Duration Voltage Variations,Short-duration voltage variations are caused by fault conditions, the energization of large loads which require high starting current, or intermittent loose connects in power wiring.,Interruption:Interruption can be the result of power system faults, equipment failure, and control malfunctions. The duration of an interruption due to a fault is determined by the operating time of the protective devices,Sag(Dip):Sag are usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors a 20 percent sag will be considered an event during which the rms voltage decreased by 20 percent to 0.8pu,Voltage sag caused by the starting of large motor stating,Swell: Unfaulted phases during a SLG fault, switching off a large load, or energizing a large capacitor bank. Swell are characterized by their rms magnitude and duration Ungrounded system: unfaulted phases will be 1.73pu during a SLG Grounded system:there will be little or no voltage rise on unfaulted phases Faults at different points along four-wire, multigrounded feeders will have varying of voltage swell as shown in the figure,Voltage Imbalance,Imbalance (sometimes called unbalance) in a three-phase system is defined as the ratio of the magnitude of the negative sequence component to the magnitude of the positive sequence component, expressed as a percentage. This definition can be applied for either voltage or current. Typically, the voltage imbalance of a three-phase service is less than 3%. The current imbalance can be considerably higher, especially when single-phase loads are present.,Measuring instruments often use a definition of voltage imbalance based on ANSI C84.1-2006, which defines imbalance as the ratio of the maximum deviation of a voltage from the average voltage to the average voltag