3 Important Factors Affecting the Electrical Power Quality

Electrical power quality plays an important role in supplying electricity effectively to consumers. As power becomes a more essential and valuable resource for the entire world, it is important to maintain its quality at all levels of usage for the reliable working of the equipment.

Due to the usage of nonlinear loads and power electronic equipment in power system transmission, distribution and utilization sectors leads to distortion in voltage and current waveforms. We are already aware of the total harmonic distortion by phase control and integral control of AC power.

Now a day’s power distribution companies are showing competitive nature to improve power quality by increasing concern over it to get the profitability and customer satisfaction.

What is Electrical Power Quality?

If the power supplied to devices or equipment is deficient, it results in poor performance. Good power quality makes the equipment function properly without affecting performance or life expectancy.

IEEE standard defines electrical power quality as “the concept of powering and grounding sensitive electronic equipment in a manner suitable for the equipment with precise wiring system and other connected equipment”. It is the deviation of voltage and currents from the ideal or actual waveforms.

In the figure, power supplied at mains is pure sine waves of current and voltages. While power reaches the load it no longer maintains its shape due to nonlinear switching devices.

As observed, the shape it deviated from the ideal former one. This deviation causes severe problems in electrical equipment like light flickering, malfunction of various devices, low motor speedrunning, etc.

By using power quality analyzers we can estimate or analyze the distorted waveform.

Power Quality Issues

The quality of the power is decided by the end-users. If the power equipment works satisfactorily for given supply then power is at good quality. If it doesn’t function well or fails to work, then power quality is bad. Reasons for bad power quality or power quality issues are discussed below.

1.Power frequency disturbances

a.Voltage sags and swells

Voltage sag or dip is the decrease of voltage levels from nominal values at power frequency. It lasts from about half of a cycle to several seconds. Low voltages are due to several factors like electrical motors, arc furnaces, utility problems, flickering, etc.

Motors like different types of induction motors during starting take a very large current, which results in a drastic voltage drop.

Also, arc furnaces initially take large amperes to produce high temperatures. Utilities drop the voltages by some of the factors like lightning, contact of trees, birds, and animals to power supply lines, switching operations, insulation failures, etc.

Voltage swells occur due to the transfer of loads from one source to another, sudden rejection and application loads. Flickering is a low-frequency problem that occurs mainly at starting or low voltage conditions.

Flickering is due to low voltages or frequency that can be observed by the human eye.

Voltage sags and swells result in a malfunction of equipment, loss of efficiency of motors, insulation failures, fluctuation of light illumination, tripping of relays and contractors, etc.

Power frequency disturbances are not easily cured if they arise at source level because it deals with high powers. However, these can be reduced if occurred internally due to loads by separating off end loads from the sensitive loads.

b. Electrical Transients

Transients are sub-cycle disturbances that last for less than one cycle of AC waveforms. Due to limited frequency response or sampling rate, detection and measurement of transients are very difficult.

These are also sometimes called as spikes, surges, power pulses, etc. These occur due to atmospheric disturbances like lighting and solar flares, fault current interruptions, switching the loads, switching capacitor banks, switching power lines, etc.

Some of the devices are designed with transients in mind but most of the devices can handle few transients depends on the severity of the transient and life of the equipment. These transients are limited by surge protection suppressors, filters and other transient suppressors as shown in the figure.

c. Harmonics

The harmonic nature of voltage and currents is the deviation from the original or pure sine waves. Harmonic frequencies are integral multiples of the fundamental frequency and are very common in electric power systems.

Order of harmonics differentiates these as even (2, 4, 6, 8, 10) and odd types (3, 5, 7, 9, 11). Major nonlinear loads produce odd harmonics and even harmonics are produced due to uneven operations of the electrical devices like transformer magnetizing currents contains even harmonic components.

The frequency of these harmonics depends on the order of harmonics as 2nd harmonic frequency is 2 times the fundamental frequency.  These are generated due to nonlinear loads, arc furnaces, electric motors, UPS systems, different battery types, welding equipment, etc.

The fundamental waveform is superimposed by odd harmonics, which results in the distorted waveforms. These harmonics have serious effects on various electrical equipment such as overheating of cables and equipment, interference with communication lines, errors while indicating electrical parameters, the probability to produce resonant conditions, etc.

These can be easily measured by harmonic analyzers and reduced by using various harmonic filters like active and passive types.

2. Power Factor

The power factor is another main factor that affects the electrical power quality. Low power factor causes several problems like overheating motors and poor lightening. It also leads to the users being penalized to meet electric demands. The power factor is the ratio of active power to apparent power and determines the amount of electrical power utilization.

Suppose if the power factor is 0.8, it tells that 80 percent of the power is utilized and the remaining energy is wasted as losses. The low power factor is due to induction motors, apparent power elements in the electrical power system network, etc.

The low power factor is improved by using power factors correction devices such as capacitor filter banks, synchronous condensers, and other compensation equipment.

Power factor improvement, with the use of capacitors, results in a reduction of electric bills. Here apparent power drawn from the supply is reduced by capacitors which offer leading power in nature.

3. Grounding

Good power quality includes safety to the appliances as well as to operators. Grounding provides system protection as well as equipment protection. Earth serves as constant reference potential with another potential that is going to be measured.

If the equipment body is not properly grounded it results in a severe shock to individuals. System ground protects various equipment against fault conditions and other abnormal conditions occurring at electrical power systems.

Signal reference ground is entirely different from normal grounding since it does not provide any protection to equipment or individuals. But it is necessary for the proper working of electronic components or devices to provide low impedance path or reference.

We hope, by now you are having a clear understanding of electrical power quality and its causes. We thank you for spending your valuable time reading this article. Please write your opinions and suggestions about this article in the comment section below.

Photo Credits:
Voltage sags swells by compliance-club
Electrical Transients by hersheyenergy
Harmonics by hersheyenergy
Power factor improvement by capacitor by lesl
Equipment and system groundings by 2.bp