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36 Cards in this Set
- Front
- Back
Manny tools designed to improve a power supplies quality are not only among the first to suffer from a lack of quality but are some times ______ the problems they are intended to resolve |
Contributors |
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Companies have relied heavily on an increased use of _____? to achieve increase productivity |
Information technology |
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List two characteristics of all IT devices |
Use power and are sensitive to fluctuations in the supply |
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Companies invest in additional backup equipment which adds to the demand on the power supply and are sensitive to _____? in the system |
Fluctuations |
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While IT devices can be made more efficient businesses ever-growing reliance on IT still results in a net ____? in the use of electrical power |
Increase |
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Power quality disturbances may result from circumstances that exists _____? Or _____? a business's control |
Inside or outside |
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What does a significant percentage of the work involved in maintaining a company's power supply involve |
Dealing with power equality phenomenons |
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_____? of all computer problems and ____? of all data loss is associated with PQ phenomena can be traced back to the power line |
1/2 & 1/3 |
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From a business perspective what is considered a significant issues? |
Downtime the company experiences |
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What can the underlying cause of most power quality problems be traced to? |
Simple rules of electrical circuits = generation transmission distribution system |
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Voltage's and currents within a facility are generally not pure ___? |
Sine waves |
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Harmonic currents are induced by loads that draw current in a ____? wave form |
Distorted |
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Voltage's phasers or vectors are separated by ____? degree in a normal 3 phase power distribution system |
120° |
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Putting electric Drive in front of a 3-phase motor to make an adjustable speed drive or a variable frequency drive Alters the phase angle to reflect a ____? |
Nonlinear distorted sine wave |
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Current vectors will ___? Significantly when one phase conductors shorted either to ground or to another conductor |
Shift |
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List the six categories of power quality phenomena |
RMS voltage variation, voltage transient, waveform Distortion, voltage fluctuations, imbalance, power frequency variation |
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RMS voltage variations due to PQ phenomena are also referred to as ____ _____ _____ |
Sags, swells , interruption |
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A ____? Is a decrease from the nominal voltage supply level |
Sag |
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A ____? Is an increase in the voltage level |
Swell |
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List 3 causes of sag originating within a facility |
Load changes, electrical system faults, improper wiring |
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Swells are frequently the result of a sudden ___? From fault protection |
Decrease |
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Interruptions are usually the result of being ___? From the fault protection |
Downstream |
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Voltage transients are usually categorized by the shape of the? |
Waveform |
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____? transients add energy to the voltage waveform, while ____? transient subtract energy from the curb |
Positive/negative |
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The PQ phenomena classification which encompasses harmonics inter-harmonic voltage fluctuations notching and DC off sets is waveform? |
Distortion |
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The main source of harmonic current today are at the phase angle controlled ____? And ___? |
Rectifiers and inverters |
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Three phase, full wave rectifier cause non-linear harmonic currents since the conduction of current takes place only when the transistor generator ___? allow it and not throughout the completed 60 hertz cycle |
Switches |
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When are even numbered harmonics found in electrical systems? |
Unless there is current drawn on only one half of the sine wave |
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Notching can be caused by switching semiconductor creating a brief ____? between two phases |
Short circuit |
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When does imbalance in a three-phase system occur? |
When amplitude or phase angle of the voltage or current wave forms are not equal |
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The use of proper personal protective equipment is intended to ___? or ___? injury |
Prevent or reduce injury |
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What single activity was identified as being performed when an accident occurred? |
Troubleshooting (important to know) |
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According to NFPA 70b, equipment should be D energize for inspections, test, repairs and other services. Such maintenance tasks can be performed when the equipment is energized provided ___? are made to allow maintenance to be performed ___? |
Provisions and safely |
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According to NFPA 70b, switchboards, panel boards, industrial control panels, and motor control centers that are likely to require examination, adjustment, services, or maintenance while energize, should be ____? to warn qualified persons of potential electric arc flash hazards |
Field marked |
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According to NFPA 70b, as a general rule no electrical apparatus should be worked on while it is? |
Energized |
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What are the exceptions to the rule of working on D energized systems? |
Not feasible to turn off ( can't make voltage measurements, or can't turn on the main switch) or creates a greater hazard to work on the equipment by de-energizing |