Power Quality

Question 1

Harmonics do not benefit a power system they what?

Answer 1

Have no useful purpose

Question 2

Excessive heat caused by harmonics do what for a transformer

Answer 2

Reduce the life of the transformer
10° above the insulation rating will cause 50% reduction in life

Question 3

A K factor transformer is an index of the transformers ability to carry harmonic currents while operating in the temperature limits.

Answer 3

The higher the K rating the more non linear loads it can handle

Question 4

Standard transformers aree designed for what load?

Answer 4

Linear loads only

Question 5

The neutral conductor in a k rated transformer is?

Answer 5

Double the size of a standard transformer

Question 6

Harmonics are sinusoidal waveforms with frequencies that are integral multiples or the?

Answer 6

Fundamental frequency

Question 7

While viewing the fundamental 60Hz display and the 5th harmonic 300Hz display the fundamental frequency completes?

Answer 7

1 complete cycle for 60Hz and the 5th harmonic completes 3 cycles within the same duration

Question 8

Harmonics originate in:

Answer 8

The switch mode of power supplies
Examples:
Electronic ballasts
VFDs
And oven and furnace controls

Question 9

The K rating on a transformer reflects?

Answer 9

The ability of the transformer to operate properly with certain types of loads

Question 10

Some problems caused by harmonics are?

Answer 10

Blown fuses
Burn out motors
Tripped breakers
Overheated neutrals
Overheated transformers
Excessive heat

Question 11

The detrimental (harm) effects on transformers caused by harmonics are? (5 of them)

Answer 11

Increased temperature
Increased neutral current flow
Increased core losses
Increased sound levels
Decreased efficiency

Question 12

Triple harmonics

Answer 12

Add up of the neutral conductor because they are in phase and cannot cancel each other out

Question 13

K rated transformers do not eliminate harmonics, they help?

Answer 13

Deal with the added heat caused by electronic equipment

Question 14

Power quality problems that have multiples of the fundamental frequency of 60Hz are known as

Answer 14

Harmonics

Question 15

Power quality problems that cause incorrect signals to be sent to the input modules or equipment to behave erratically are referred to as what?

Answer 15

Noise

Question 16

Power quality problems that refuse insulation life damage equipment and have fast bulb burnouts is known as

Answer 16

Over voltage or Swell

Question 17

Power quality problems caused by abrupt increases in source impedance or loose connections are typically know as

Answer 17

Voltage Sags (Sags)

Question 18

Standard transformers are not designed for what kind of loads?

Answer 18

Both linear and non linear loads. Used only for linear loads

Question 19

The sine wave of a lineal load is

Answer 19

A true sine wave

Question 20

Some of the methods used to deal with harmonics are?

Answer 20

Instal k rated transformers
Harmonic filters
And oversize the neutral conductor

Question 21

Kinds of problems harmonics cause?

Answer 21

Neutrals to over heat
Motor burnout
Transformer burnout
Distort the voltage sinewave

Question 22

When referring to an induction motor a negative sequence harmonic will?

Answer 22

Rotate in the opposite direction of the fundamental frequency

Question 23

When referring to an induction motor, a positive sequence harmonic

Answer 23

Rotates in the same direction as the fundamental frequency

Question 24

A metal oxide varistor is used to help

Answer 24

Protect against transients, swells and other high voltage conditions

Question 25

The seven categories of power quality disturbances are?

Answer 25

Voltage sag Voltage swell Interruptions Transients Wave distortion Voltage fluctuation And Frequency variation

Question 26

The seven power quality PROBLEMS are

Answer 26

Nuisance tripping Flicker Motor burnout Equipment control problems High temoerstures in server rooms Computer crash and False alarm trips

Question 27

Some possible SOLUTIONS if it’s been determined that harmonics exist are?

Answer 27

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

Question 28

Voltage spikes are usually caused by

Answer 28

High winds and animal contact

Question 29

If the voltage sinewave is too high is known as

Answer 29

Voltage swell

Question 30

If the voltage sinewave is too low is know as?

Answer 30

Voltage Sag

Question 31

Excessive currents in the neutral conductors with non linear loads is caused by?

Answer 31

Triple harmonics

Question 32

The sinewave of a non lineal load is?

Answer 32

Not a true sine wave

Question 33

A VFD is a source of?

Answer 33

5th and 7th harmonics

Question 34

What is a line reactor?

Answer 34

Is a current limiting decicd installed before the VFD. Used to filter the waveform and reduce electrical noise and transients.

Question 35

What are load reactors?

Answer 35

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

Question 36

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?

Answer 36

Increase reliability Increase performance and Increase the efficiency of VFDs

Question 37

What are two advantages of line reactors?

Answer 37

Reduce electrical noise and reduce electrical transients

Question 38

What are two advantages of load reactors?

Answer 38

They slow the rate of rise of the short circuit current and Absorbs the overloads create by the motor