Power Quality Flashcards
Harmonics do not benefit a power system they what?
Have no useful purpose
Excessive heat caused by harmonics do what for a transformer
Reduce the life of the transformer
10° above the insulation rating will cause 50% reduction in life
A K factor transformer is an index of the transformers ability to carry harmonic currents while operating in the temperature limits.
The higher the K rating the more non linear loads it can handle
Standard transformers aree designed for what load?
Linear loads only
The neutral conductor in a k rated transformer is?
Double the size of a standard transformer
Harmonics are sinusoidal waveforms with frequencies that are integral multiples or the?
Fundamental frequency
While viewing the fundamental 60Hz display and the 5th harmonic 300Hz display the fundamental frequency completes?
1 complete cycle for 60Hz and the 5th harmonic completes 3 cycles within the same duration
Harmonics originate in:
The switch mode of power supplies
Examples:
Electronic ballasts
VFDs
And oven and furnace controls
The K rating on a transformer reflects?
The ability of the transformer to operate properly with certain types of loads
Some problems caused by harmonics are?
Blown fuses
Burn out motors
Tripped breakers
Overheated neutrals
Overheated transformers
Excessive heat
The detrimental (harm) effects on transformers caused by harmonics are? (5 of them)
Increased temperature
Increased neutral current flow
Increased core losses
Increased sound levels
Decreased efficiency
Triple harmonics
Add up of the neutral conductor because they are in phase and cannot cancel each other out
K rated transformers do not eliminate harmonics, they help?
Deal with the added heat caused by electronic equipment
Power quality problems that have multiples of the fundamental frequency of 60Hz are known as
Harmonics
Power quality problems that cause incorrect signals to be sent to the input modules or equipment to behave erratically are referred to as what?
Noise
Power quality problems that refuse insulation life damage equipment and have fast bulb burnouts is known as
Over voltage or Swell
Power quality problems caused by abrupt increases in source impedance or loose connections are typically know as
Voltage Sags (Sags)
Standard transformers are not designed for what kind of loads?
Both linear and non linear loads. Used only for linear loads
The sine wave of a lineal load is
A true sine wave
Some of the methods used to deal with harmonics are?
Instal k rated transformers
Harmonic filters
And oversize the neutral conductor
Kinds of problems harmonics cause?
Neutrals to over heat
Motor burnout
Transformer burnout
Distort the voltage sinewave
When referring to an induction motor a negative sequence harmonic will?
Rotate in the opposite direction of the fundamental frequency
When referring to an induction motor, a positive sequence harmonic
Rotates in the same direction as the fundamental frequency
A metal oxide varistor is used to help
Protect against transients, swells and other high voltage conditions
The seven categories of power quality disturbances are?
Voltage sag
Voltage swell
Interruptions
Transients
Wave distortion
Voltage fluctuation
And
Frequency variation
The seven power quality PROBLEMS are
Nuisance tripping
Flicker
Motor burnout
Equipment control problems
High temoerstures in server rooms
Computer crash and
False alarm trips
Some possible SOLUTIONS if it’s been determined that harmonics exist are?
Upsize the common neutral conductor
Pull extra neutrals
A harmonic filter at the load
Reduce or balance the load on the transformer
Or
Use a K rated transformer
Voltage spikes are usually caused by
High winds and animal contact
If the voltage sinewave is too high is known as
Voltage swell
If the voltage sinewave is too low is know as?
Voltage Sag
Excessive currents in the neutral conductors with non linear loads is caused by?
Triple harmonics
The sinewave of a non lineal load is?
Not a true sine wave
A VFD is a source of?
5th and 7th harmonics
What is a line reactor?
Is a current limiting decicd installed before the VFD. Used to filter the waveform and reduce electrical noise and transients.
What are load reactors?
They are installed between the VFD and the motor. They are typically used when the motor is farther then 100 feet and also acts as a current limiting device
The reactor absorbs current surgers/overloads created by the motor load that might cause nuisance tripping of the drive. Why are line and load reactors used?
Increase reliability
Increase performance and
Increase the efficiency of VFDs
What are two advantages of line reactors?
Reduce electrical noise and reduce electrical transients
What are two advantages of load reactors?
They slow the rate of rise of the short circuit current and
Absorbs the overloads create by the motor
