Presentation on theme: "2. Terms and definitions1 # Terms and Definitions # Voltage Sags and Interruptions."— Presentation transcript:
2. Terms and definitions1 # Terms and Definitions # Voltage Sags and Interruptions
2. Terms and definitions2 Definitions Sag (or dip) is a decrease to a low voltage (between 0.1 and 0.9 per unit rms) at power frequency for durations of 0.5 cycle to 1 minute Swell is an increase to a high voltage (between 1.1 and 1.8 per unit rms) at power frequency for durations of 0.5 cycle to 1 minute
2. Terms and definitions3 Definitions Transient refers to an event of duration < 0.5 cycle Instantaneous: duration 0.5 cycle to 30 cycles Momentary: duration 30 cycles to 3 sec Temporary: duration 3 sec to 1 min. Sustained or long-duration: duration > 1 min.
2. Terms and definitions4 Impulsive transient due to lightning
2. Terms and definitions5 Shunt capacitors may be installed in substations or on poles or in enclosures
2. Terms and definitions13 Waveform distortion DC offset Harmonics Interharmonics Notching- It is a periodic voltage disturbance caused by the normal operation of power electronic devices when current is commuted from one phase to another. Noise- It is defined as unwanted electrical signals with broadband spectral content lower than 200 kHz superimposed upon the power system voltage or current in phase conductors, or found on neutral conductors or signal lines.
2. Terms and definitions15 Harmonics + interharmonics
2. Terms and definitions16 Three-phase rectifier driving DC motor As V B rises above V A, current is commuted from A to B. While diode B is turning on, diode A is turning off. A is shorted to B (for a short time while both diodes conduct), producing notching.
2. Terms and definitions17 Waveform distortion due to notching
2. Terms and definitions18 Voltage fluctuation # Voltage magnitude does not normally exceed the ranges of 0.9 pu to 1.1 pu. Series of random or continuous voltage fluctuations –Flicker is undesirable results (such as lamps flickering) from continuous rapid variations in voltage –Called voltage flicker (to refer to the voltage fluctuation) –Often measured by short term flicker sensation Pst (IEC standard)
2. Terms and definitions19 ITI (Information Technology Industry) curve Replaces CBEMA (Computer Business Equipment Manufacturers Association) curve # A set of curves representing the withstand capabilities of computers in terms of the magnitude and duration of the voltage disturbance. Susceptibility of 120-volt computer equipment to voltage sags and swells
2. Terms and definitions20 ITI curve Voltage tolerable Voltage swell intolerable Voltage sag intolerable Duration in cycles Voltage in percent
2. Terms and definitions21 ITI curve Voltage tolerable Voltage swell intolerable Voltage sag intolerable Voltage in percent Duration in sec
Industrial Power System 115 kV 13.8 kV TRANSMISSIONINDUSTRIAL DISTRIBUTION Sensitive Load Sensitive load’s own circuit Other distribution circuits
Utility Power Distribution System 115 kV 12.47 kV TRANSMISSION INDUSTRIAL DISTRIBUTION with sensitive loads Customer’s circuit owned by utility Other distribution circuits Utility Distribution System