Description, Causes and Results:

The most widely recognized kinds of Power Quality issues are exhibited beneath alongside their small description, causes and outcomes: 

1. Voltage drop:

Description: A decrement in the level of normal voltage between 10% and 90% of the estimated rms voltage for durations of 0.5 cycle to 1 minute, at the power frequency.

Causes: The causes are due to the fault on the transmission line or distribution network (most likely on parallel feeders). Also, due to the fault in the consumer’s installation and due to the onnection of larger loads and running of large motors.

Result: The equipments of information technology do not work properly, mainly the control systems that are based on microcontrollers such as (PCs, PLCs, ASDs, etc) that may lead in the stopping of process. Also, the contactors and electromechanical relays also stop working. Also, disconnection and efficiency loss occurs in electrical rotating machines.

2. Short interruptions:

Description: The total interruption of electric supply for delay from few milli-second to one or two milli-second.

Causes: This mainly causes due to the opening and automaticaly re-closure of devices of protection. The main misfortunes are insulation failure, insulator flashover and lighting.

Result: It will trip the protection devices, losses of important information and not functioning of data processing devices. The sensitive equipment will stop, such as PCs, PLCs, etc, if they have not ability to deal with that type of situation.

3. Long interruptions:

Description: The total interruption for duration greater than 1 to 2 seconds, of electrical supply. 

Causes: Working devices failure in the network of power system, storms and different objects striking to the supply lines or poles, fire, human error, or failure of protection devices, etc.

Result: All equipments will stop and do not work properly.

4. Voltage spikes:

Description: The very much fast riples in the value of voltage for the time from some microseconds to few milliseconds. These riples reaches to thousands of volts, even when voltage is low.

Causes: Switching of different lines or correction of capacitor's power factor and disconnection of large and heavy loads.

Result: It will destroy components (mainly electronic components) and also the insulation material you are using, errors or data loss comes in data processing , interference of electromagnetic.

5. Voltage swelling:

Description: Instantly increase in the voltage at the power frequency, at the outer side of the normal tolerances, with the delay of more than one rotation and less than a few seconds.

Causes: Due to start or stop of heavy loads, poorly dimensioned sources of power, poorly regulated transformers (mainly during at peak-off hours).

Result: It will loss data and flicker of lights and screens, malfunctioning of sensitive devices, if the value of voltages are too high.

6. Harmonic losses:

Description: The voltage or current waveforms in the shape of non-sinusoidal waves. This type of waveforms corresponds to the sum of different sinusoidal-waves with different shapes and magnitudes and phase, which have the frequencies that are the multiples of different power-system frequencies.

Causes: The electric machines which are working above the knee of the magnetization curve (magnetic saturation), welding machines, DC brush motors and  rectifiers.

Modern sources: All the non-linear heavy loads, such as equipments of electronics including ASDs, switching mode power supplies, data execution components, highly efficient lighting.

Result: It will increase the probability in the occurrence of the resonance, neutral overloading in the three-phase systems, increased rate of heating of all cables and devices, losses in efficiency of electric machines, errors in measuring when the use of average reading equipments and tripping of thermal protections.

7. Voltage fluctuation:

Description: The oscillation of voltage rate, at which the amplitude is modulated by using signal with frequency ranges between 0 to 30 Hz.

Causes: Thermal furnaces, instant starting/stoping of electrical motors (for instant using of elevators) and oscillating loads, etc.

Result: The very perceptible result is the light's flickering and screening, giving the impression  of visual perception.

8. Noise:

Description: The superimposing of large frequency signals on the type of the power-system frequency waveform.

Causes: The electromagnetic interferences provoked by using Hertzian waves such as microwave signals, radiation due to welding machines, electronic equipment, arc furnaces, etc. 

Result: It causes the variation on sensitive electronic devices, mostly not destructive. It may cause the data losses and data processing malfunctions.

9. Voltage Unbalancing:

Description: A variation in the voltage of the three-phase systems in which the magnitudes of the three voltages between them are not equal.

Causes: It causes the incorrect distribution of all the single-phase angle difference or loads by the three phases of the system.

Result: The unbalanced systems imply the existence of a negative sequence that is harmful to all three- phase loads.