Basic Terminology Of Power Quality


Basic Terminology Of Power Quality Part-1

Basic Terminology Of Power Quality Part 1

1. Recovery Time

The time necessary for the output voltage or current to come back to the specified value after the step load or line changes.

2. Ride Through

It is the ability of the power source to deliver usable power for limited time duration during power loss is called ride through.

3. Sag

A sudden reduction in voltage from normal to 10 - 90% of normal and lasting for half cycle to few seconds.

4. Surge

A surge, or transient is an overvoltage on the waveform that can damage the equipment.
It is a sub cycle overvoltage with duration of less than a half-cycle of the normal voltage waveform.

5. Swell

It is the RMS increase in AC voltage for several cycles after which voltage comes back to normal.

    6. Transient

    Transients are sub-cycle disturbances that last for less than one cycle of.

    These are also sometimes called as spikes, surges, power pulses, etc. This is caused due to lighting, welding equipment, starting and shutting down of equipments. This can be controlled by using the surge arrestors, UPS, isolation transformer.

    7. Oscillatory Transient

    A sudden change in the voltage or the current which may have positive or negative polarity is called oscillatory transient

    8. Overvoltage

    It is the calculated voltage having the value higher than the desired voltage.

    9. DC Offset

    The occurrence of DC voltage or the current in an AC power is called as DC offset.

    10. Common Mode Voltage

    If the noise voltage remains constant from the current carrying conductor to ground is called common mode voltage.

      11. Dropout

      Loss of instrument operation due noise or interruption.

      12. Dropout Voltage

      The loss of voltage when device fails to operate.

      13. Ground Window

      The common area where all grounding conductors enter.

      14. Harmonic Number

      It is the ratio of harmonic frequency to fundamental frequency.

      15. Islanding

      It is a condition in which distributed generation is cut off from a load.

      16. Long Duration Variation

      The deviation in the RMS value from the nominal voltage which lasts for more than 1 min.

      Basic Terminology Of Power Quality Part 2

      1. Harmonics

      Harmonies are sinusoidal voltage/current having frequencies that are integer multiple of fundamental frequency. Harmonics in the system can

      • Make relays maloperate
      • Increase loss in capacitances, noises
      • Telephonic cross talks
      • Can cause increase in resonance.

      2. Inter Harmonics

      The voltage or the current that is not the multiples of power frequencies are called  inter harmonics.

      It is caused mainly due to non linear loads which cause overheating of the equipment. By using harmonic filters this can be eliminated.

      3. Harmonic Distortion

      Presence of higher harmonics makes waveform distorted and causes fundamental waveform distorted.

      Harmonic Distortion
      Waveform Of Harmonic Distortion

      4. Immunity (Or Disturbance)

      The capability of the device to execute without any system degradation in the presence of electromagnetic disturbance is called as immunity.

      5. Impulse

      A pulse that starts and ends within short duration of time within the rise and fall characteristics and mathematically regarded as the infinite.

      6. Isolation

      It is the separation of one system from the other system from the undesired influences.

      7. Noise

      The unnecessary electrical signals that produce unwanted disturbances in the circuits are called as noise.

      Waveform Of Noise
      Waveform Of Noise

      8. Nominal Voltage

      A nominal value assigned to the system for the purpose of proper functioning is called nominal voltage.


      Large current that is drawn when the machine is initially turned ON.

      10. Interruption

      An Interruption is defined as decrease in the supply voltage or load current less than the seconds or in other words it the loss of the voltage of the current or voltage for a complete time period.

      Waveform Of Interruption
      Waveform Of Interruption

      11. Linear Loads

      In steady state operation, if voltage and current are same as sinusoidal waveform then called linear loads. Linear loads do not have harmonics in them.

      12. Non-Linear Loads

      Here current and voltage waveforms are not proportional to each other. They require large inrush current.

      13. Notch

      The disturbances that is produced in that normal waveform which is lasting less than a half cycle is called as the notch.

      14. Power Disturbance

      It is the divergence from the fundamental value of the input AC characteristics.

      15. Periodic

      The voltage or the current is periodic if it exhibits the condition x(t) = x(t + T), where T is the period of the function.

      16. Power Factor

      It is the ratio of real power to the apparent power, which is product of current and voltages.

      Basic Terminology Of Power Quality Part 3

      Basic Terminology Of Power Quality Part 3

      1. Bonding

      Bonding is the link of two or more conductive objects which are interconnected to one another by means of a conductor. 

      Bonding is done primarily for two reasons:

      1. To provide minimal of negligible voltage difference between the bonded parts.
      2. To ensure that, faults incurred can be safely moved to ground or other grids.

      2. Grounding

      Grounding, also referred to as "earthing", is a type of bonding where one or more conductive objects are connected to the ground by means of a conductor. In Fig. , equipment 1 and equipment 2 are connected by means of a thin wire and they are then connected to the ground.


      3. Capacitance

      The property of the circuit characterised by a two parallel plates which are separated by a dielectric medium and expressed in farad (F).

      In other words, it is the means by which the energy can couple from one electric circuit to the other.

      4. Coupling

      The process by which electrical energy from one circuit is transferred to other circuit that are not connected electrically is called as coupling.

      5. Crest Factor

      It is the ratio of the peak value to the RMS value of the voltage/current.
      Crest Factor
      Crest Factor Waveform

      6. Distortion

      Waveform with Distortion
      Waveform with Distortion

      It is the variation of a periodic waveform from its ideal waveform.

      Distortion created in the waveform may cause waveform deformation as well as phase shift.


      7. Distortion Factor

      It is the relation between the RMS value of the harmonic content of a periodic waveform to the RMS value of the periodic wave and usually expressed as a percent.

      8. Form Factor

      It is the ratio of RMS value to the peak value of the periodic waveform.

      It represents the deviation of the system waveform.

      9. Flicker

      It the visible change due to rapid fluctuations in the voltage of the power supply.

      Flicker is due to a modulating low frequency disturbing voltage.

      The frequency range visible to the human eye is about 1-30 Hz.

      10. Frequency

      Number of complete cycle in the periodic waveform and measured in hertz (Hz).

      11. Ground Electrode

      It is the body of the conductor that has contact with the earth for providing grounding to the network.

      12. Ground Grid

      The conductors that are arranged in such a way to make specific pattern and are buried
      below 2.5A from the ground.

      13. Ground Loop

      They are usually formed when two or more connection is provided between two
      conductors. To prevent ground loop the following things need to be done.

      All the ground point should go through one common ground point

      To isolate the source from ground

      14. Ground Ring

      The loop surrounding the structure or which is in straight contact with ground is called the ground ring.

      The depth of the ground ring should be more than 2.5ft below the surface of the earth.

      15. Grounding

      A conductor, by which the electrical circuit or the equipment is connected to the earth or to some conducting body. Grounding is primarily done for two reasons:

      Grounding the metal conductor protects any person coming in direct contact, if fault occurs.

      It also allows the faulty current, to the earth or ground plane.

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