UNDERSTANDING POWER QUALITY AND ITS IMPORTANCE

According to Institute of Electrical and Electronic Engineers (IEEE) standard IEEE 1100, power quality is defined as “the concept of powering and grounding sensitive electronic equipment in a manner suitable for the equipment”.

WHY POWER QUALITY MATTERS

Power quality and supply reliability are extremely important. Our world is increasingly dependent on electronic equipment and controls, and high sensitivity devices and processes are heavily dependent on a clearly defined power quality. Some facilities operate 7 days a week, 24 hours a day, so incur a high cost of downtime.

Secondly, the modern power grid is continuously changing. Urbanization, living standards and advancement in technology have increased the demand for energy. This rising demand is growing the complexities of power grids by increasing requirement for greater reliability, efficiency, security and environmental and energy sustainability concerns.

Many of the electric transmission grids in service around the world were designed and built more than a half century ago. Many are unreliable, have high transmission losses, poor power quality, prone to brownouts and blackouts, supply inadequate electricity, and discourage integration of distributed energy sources.

In order to ensure stable processes and adequate power supply despite the struggling power grids and increasing number of devices which generate grid distortions, steps must be taken to improve the power quality.

Maintaining Power Quality to the level that is required by the application enables safe operation and reduces costly downtime for organisations. It helps eliminate or reduce problems such as power failure, equipment malfunction, overheating, flickering light, energy waste, etc.

POWER QUALITY STANDARDS

Poor power quality affects generators, distributors, and end-users of electric power. There are several standards and guidelines to aid in understanding poor power quality from the end-user's point-of-view. End-users such as commercial and industrial facilities use these standards as power quality metrics.

These metrics are used to assess the impact of their own equipment on the serving distribution grid. They are also used to assess the susceptibility of the end-user's own process, instrumentation and control equipment to both internally and externally generated poor power quality events.

Some important standards include:

EN 50161: Characteristics of the voltage (PQ) in public electricity supply networks.

IEEE 519: Recommended Practices and Requirements for Harmonics Control in Electrical Power Systems.

IEC/EN 61000-2-4: Electromagnetic compatibility (EMC): Ambient conditions; compatibility level for low frequency, conducted interferences in industrial plants.

IEC/EN 61000-4-30: Testing and measurement techniques – Power quality measurement methods.

TYPES OF POWER QUALITY PHENOMENON

Harmonics

Harmonics are extra frequencies (multiples of fundamental frequency) that when present in an electrical circuit, distort the AC sine wave. Harmonics are caused by non-linear electrical loads; loads with rapidly changing energy consumption. They result in inefficient operation; excess heat (skin effect); decreased efficiency and lifespan of equipment. Harmonics can cause overheating in neutral conductors, and circuit breakers can trip.

Measuring harmonics can help to identify the source of harmonics in the electrical system, and Increase operational safety and efficiency.

Sags & Swells

Voltage Sag is a decrease in rms voltage less than 0.9 pu for a duration less than 1 min. Voltage Swell is an increase in rms voltage greater than 1.1 pu for a duration less than 1 minute.

This phenomenon is caused by heavy energy loads turning on or off (inside) or network faults (outside), and can result in damage to machines and equipment; loss of use. Even short interruptions can be catastrophic for sensitive applications.

Measuring can help users avoid damage and costly downtime.

Transients

Transients are high frequency energy packets which superimpose on fundamental frequency wave and severely affect the high impedance circuit.

Transients are caused by switching operation (arcing), lightning strike or malfunction. They can cause fast change in voltage, current or load; insulation breakdown; breaker trips and damage to equipment.

Measuring can help avoid costly downtime and damage to equipment.

Unbalance

Unbalance refers to deviation in voltage or current waveform from perfect sinusoidal, in terms of magnitude or phase shift is called unbalance in a system. It is caused by asymmetry of loads like single phase loads, phase-to-phase loads or unbalanced three phase loads (e.g. welding equipment).

Unbalance causes reduced efficiency; excess heat and overheating; device failure and damage to equipment; reduced lifespan of equipment.

Measuring can help users increase lifespan, avoid overheating and reduce unwanted downtime.

Flicker

When voltage variations cause light density changes in lamps, it can result in visual perceptions referred to as flicker. It is caused by load variations (furnaces, welding machines, generators, VFDs, large motors); wind generators, and can result in visible fluctuations in brightness of a lamp, and even possible health problems.

Measuring helps to find out what equipment within the electrical distribution is causing Flicker, so as to minimise its impact.

Residual Current Monitoring (RCM)

RCM plays an important role in high availability supply systems such as Data Centres and Hospitals. Rapid & direct identification of faults and insulation problems helps to avoid fire risks and increases system availability.

RCM provides extra safety in areas in which no RCDs can be used due to operational reasons.

Preventive maintenance leads to higher productivity &uptime.

POWER QUALITY MONITORING (PQM)

Power Quality Monitoring (PQM) is the process of gathering, analyzing and interpreting raw measurement data into useful information. PQM is often done to improve system-wide power quality performance and includes:

•Power Quality metering, monitoring and onsite measurements

•Temporary and Permanent power quality monitoring to facilitate problem solutions

•Documenting and trending system performance to increase system reliability

Benefits of Power Quality Monitoring (DIN EN 50160)

The ability to review stored, continuously recorded waveforms helps in the diagnosis of problems before an unwanted event recurs. Power quality analysis can also be used for pre-function testing to look closely at systems and their responses and to simulate transients and other events.

Power quality analytics could pinpoint what the root cause was e.g. an electrical spike, or a floating ground. Thus, PQM offers many benefits. These include:

•Secure, high-availability power supply

•Assured quality of the electrical energy through continuous monitoring and analysis

•Avoidance of overload situations

•Avoidance of production stoppages

•Maximisation of operating time

•Ensuring product quality and stable processes

•Production-related quality assurance by monitoring the local power quality

•Optimisation of maintenance costs

JANITZA AND POWER QUALITY MONITORING

For efficient power quality monitoring, power measurement and analysing, Messung presents Janitza's UMG 512 PRO - a fixed Class A