KUALITAS DAYA KUALITAS DAYA (POWER QUALITY) ASNIL ELEKTRO FT - UNP
Definition of power Quality terms Th t The term power quality is applied to a wide variety of lit i li d t id i t f electromagnetic phenomena on the power system. The increasing application of electronic equipment and increasing application of electronic equipment and distributed generation has heightened the interest in power quality in recent years, and this has been accompanied by q y y p y the development of a special terminology to describe the phenomena.
Principal Phenomena Causing Electromagnetic Disturbances as Classified by the IEC
Categories and Characteristics of Power System Electromagnetic Phenomena y g
Transients A transient is an undesirable momentary deviation of the supply voltage or load current. Broadly speaking, transients can be classified into two categories, impulsive and oscillatory. g , p y An impulsive transient is an abrupt change in the steady state voltage and/or current, that occurs outside the t t lt d/ t th t t id th power frequency range and is unidirectional in polarity. A i An impulsive transient is a sudden, non–power l i i i dd frequency steady-state condition of voltage, current, or both that in polarity (primarily either positive or or both that in polarity (primarily either positive or negative).
Figure Lightning stroke current impulsive transient. Figure Waveform showing an impulsive transient event
An oscillatory transient is a sudden, non–power requency change in the steady-state condition of voltage requency change in the steady state condition of voltage, current, or both, that includes both positive and negative polarity values. p y Figure Oscillatory transient current caused by back-to-back capacitor switching.
Short-Duration Voltage Variations This category encompasses the IEC category of voltage dips and short interruptions Each type of variation can be dips and short interruptions. Each type of variation can be designated as instantaneous, momentary, or temporary, depending on its duration depending on its duration Short-duration voltage variations are caused by fault conditions, the energization of large loads which require high starting currents, or intermittent loose connections in power wiring. Depending on the fault location and the i i D di th f lt l ti d th system conditions, the fault can cause either temporary voltage drops ( sags) voltage rises (swells) or a complete voltage drops ( sags), voltage rises (swells), or a complete loss of voltage ( interruptions).
Interruption A An interruption occurs when the supply voltage or load current h h l l l d decreases to less than 0.1 pu for a period of time not exceeding 1 min. Interruptions can be the result of power system faults, equipment failures, and control malfunctions. The interruptions are measured f il d t l lf ti Th i t ti d by their duration since the voltage magnitude is always less than 10 percent of nominal. The duration of an interruption due to a fault on the utility system is determined by the operating time of utility protective devices.
Sags (dips) A sag is a decrease to between 0.1 and 0.9 pu in rms voltage or current at the power frequency for urations from 0.5 cycle to 1 min. The power quality community has used the term sag for many years to describe a short-duration voltage decrease. Although the term has not been formally defined, it has been increasingly accepted and not been formally defined, it has been increasingly accepted and used by utilities, manufacturers, and end users. The IEC definition for this phenomenon is dip.
Swells A swell is defined as an increase to between 1.1 and 1.8 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min cycle to 1 min As with sags swells are usually associated with system fault As with sags, swells are usually associated with system fault conditions, but they are not as common as voltage sags. One way that a swell can occur is from the temporary voltage rise on the unfaulted phases during an SLG fault. Swells can also be caused by switching off a large load or energizing a large capacitor bank.
Figure Three-phase rms voltages for a momentary interruption due to a fault and subsequent recloser operation. i Figure Instantaneous g voltage swell caused by an SLG fault.
Figure Voltage sag caused by an SLG fault. ( a) RMS waveform for voltage sag event. ( b) Voltage sag waveform.
Figure Temporary voltage sag caused by motor starting.
Long-Duration Voltage Variations Long-duration variations can be either overvoltages or ndervoltages. Overvoltages and undervoltages generally are not the result of system faults, but are caused by load variations on the system and system switching operations. Overvoltage An overvoltage is an increase in the rms ac voltage greater than percent at the power frequency for a duration longer than 1 min. Overvoltages are usually the result of load switching (e.g., switching off a large load or energizing a capacitor bank).
Undervoltage An undervoltage is a decrease in the rms ac voltage to less than 90 percent at the power frequency for a duration longer than 1 min. Undervoltages are the result of switching events that are the opposite of the events that cause overvoltages. A load switching on or a capacitor bank switching off can cause an undervoltage until p g g voltage regulation equipment on the system can bring the voltage back to within tolerances. Overloaded circuits can result in undervoltages also undervoltages also. Sustained interruptions When the supply voltage has been zero for a period of time in excess of 1 min, the long-duration voltage variation is considered a sustained interruption Voltage interruptions longer than 1 min are sustained interruption. Voltage interruptions longer than 1 min are often permanent and require human intervention to repair the system for restoration.
Voltage Imbalance Voltage imbalance (also called voltage unbalance) is sometimes defined as the maximum deviation from the average of the three- phase voltages or currents, divided by the average of the three-phase h lt t di id d b th f th th h voltages or currents, expressed in percent. Unbalance describes a situation in which either the voltages of a Unbalance describes a situation, in which either the voltages of a three-phase voltage source are not identical in magnitude, or the phase differences between them are not 120 electrical degrees, or b th both . The simplest method of expressing voltage unbalance is to measure the voltage deviation Δ u at each of the three phases, and compare it the voltage deviation Δ u at each of the three phases, and compare it to the average phase voltage Ua: where: Cvu - the voltage unbalance coefficient
Figure Voltage unbalance trend for a residential feeder. Fi V lt b l t d f id ti l f d
The primary source of voltage unbalances of less than 2 percent is single-phase loads on a three-phase circuit. Voltage unbalance can g p p g also be the result of blown fuses in one phase of a three-phase capacitor bank. Severe voltage unbalance (greater than 5 percent) can result from single-phasing conditions can result from single-phasing conditions. Waveform Distortion Waveform Distortion Waveform distortion is defined as a steady-state deviation from an ideal sine wave of power frequency principally characterized by the ideal sine wave of power frequency principally characterized by the spectral content of the deviation. There are five primary types of waveform distortion: p y yp DC offset Notching Harmonics Noise Interharmonics
DC offset. The presence of a dc voltage or current in an ac power system is termed dc offset. This can occur as the result of a geomagnetic disturbance or asymmetry of electronic power t f l t i ti di t b converters. Incandescent light bulb life extenders, for example may consist of diodes that reduce the rms voltage example, may consist of diodes that reduce the rms voltage supplied to the light bulb by half-wave rectification. Direct current in ac networks can have a detrimental effect by biasing transformer cores so they saturate in normal operation. This causes additional heating and loss of transformer life. Direct current may also cause the f lif Di l h electrolytic erosion of grounding electrodes and other connectors connectors.
Harmonics. Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at which the supply system is designed to operate (termed the fundamental frequency; usually 50 i d i d t t (t d th f ll 50 d l f or 60 Hz). Gambar Gelombang fundamental Gambar Gelombang fundamental Gambar Gelombang fundamental dan Gambar Gelombang fundamental dan dan harmonik ke-3 berbeda fasa 180 0 harmonik ke-3 berbeda fasa 0 0
Figure (a) Power flow at the fundamental frequency; (b) harmonic power flow Batas distorsi tegangan menurut standar IEEE 519-1992 Batas distorsi tegangan menurut standar IEEE 519-1992 Bus voltage at PCC Individual voltage Total voltage distortion distortion (%) d s o o (%) THD (%) (%) 69 kV and below 3.0 5.0 69.001 kV through 161 kV 1.5 2.5 161.001 kV and above 1.0 1.5
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