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20 Cards in this Set
- Front
- Back
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Power Quality |
Broad term which describes the measure of electrical power performance |
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Linear load |
Any load in which current increases proportionally as the voltage increases. |
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Non linear load |
Any load in which the instantaneous load current is not proportional to the instantaneous voltage |
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Poor power Quality can result in |
Lost productivity Lost and corrupt data Damaged equipment Premature/early failure of equipment |
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Most common symptoms of poor power quality are |
Voltage changes Harmonics Noise |
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Power interruptions (Momentary, temporary, sustained) |
Momentary: (0.5 cycles to 3 seconds) decrease of voltage to 0 on one or more power lines. Temporary: 3 seconds to one minute Sustained: more than 1 minute |
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What normally causes voltage fluctuations |
Overloaded transformers Imbalanced transformer loading High impedance caused by long circuit runs Undersized conductors Poor electrical connections Loose connections |
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Transients |
A temporary unwanted voltage in an electrical circuit |
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Types of transients |
Oscillatory (low level) Impulse (high level) |
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Harmonic |
A frequency that is an integer multiple of a fundamental |
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What happens to the fundamental waveform when harmonics are present |
It becomes distorted |
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What are the three phases sequences associated with harmonics |
Positive Negative Zero |
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Which sequence produces a negative torque on three phase motors and which order causes the most problems |
Negative sequence 5th order |
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What is the main effect of zero sequence harmonics and why does it occur |
Overheated neutral Triplen currents adding in the neutral |
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Types of noise |
Transverse mode: not including the ground Common mode: includes the ground |
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Harmonics cause the production of additional heat in what two ways |
Eddy currents Skin effect |
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Three phase harmonic fingers primary function is to reduce what harmonic content |
5th and 7th order harmonics |
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What are two disadvantages to using a low pass filter |
The specific transient has to be attenuated/tuned Poor tuning can lead to additional problems |
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What type of filter injects equal and opposite harmonic voltages and currents to cancel harmonics |
Active filter |
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Two types of line filter |
Emi Rfi |
