Alf Hartzenburg explains why ensuring that industrial plants are supplied with good-quality electricity is imperative

Many companies are increasingly applying automation to increase material and productivity efficiency, and companies that fail to do so risk losing market share and competitiveness, besides suffering margin erosion and, ultimately, failure of the business.

Process automation is dependent on clean power. For electrical systems to function in the intended manner, they require good-quality electricity, which

must have continuity of service,

very low harmonic distortion,

very low variation in the voltage magnitude and

very low transient voltages and currents.

The term ‘clean power’ is used to describe electricity that is considered to be of good quality, with a very low harmonic content, and the term ‘dirty power’ is used to describe electricity that is considered to be of low quality, with a very high harmonic content.

Power quality problems can cause equipment and processing malfunctions or shut down a process or the entire plant. The consequences can range from excessive energy consumption to a complete work stoppage.

Mission-critical systems exist throughout an industrial plant, and power-quality problems can bring any plant to a grinding halt when the plant can least afford the stoppage. The main causes of power-quality problems are voltage levels, voltage unbalance, a low power factor and harmonic distortion. Most of these problems occur inside the plant and are generally caused by:

• installation – improper grounding and routing or undersized distribution networks;

• operations – equipment operated outside its design parameters;

• mitigation – a low power factor or inadequate shielding or power cables; and

• maintenance – degraded cable insulation and poor earth connections.

Voltage Levels

When operating at less than 95% of design voltage, motors typically lose two to four points of efficiency. Running a motor above its design voltage also reduces the power factor and efficiency. Voltage sags or dips of 10% to 30% below nominal voltage levels for 3- to 30-cycle durations account for the majority of power system disturbances, and are thus the major cause of industry process disruptions.

Voltage Unbalance

An unbalanced system increases distribution system losses and reduces motor efficiency.

Power Factor

A low power factor – caused by induction motors being operated at less than full load – reduces the efficiency of the electrical distribution system, both within and outside a facility.

Harmonic Distortion

In simple terms, harmonics are extra frequencies that, when present in an electrical circuit, distort the ac sine wave. Harmonics are very harmful to an electrical system. The presence of harmonics reduces the operating life of equipment and generates heat, which stresses cables and equipment. It is possible that the return on an investment in motors and drives will not be realised if the motors and drives are damaged and need replacing before the expected end of their operating life.

The following are common sources of harmonic distortion in industrial plants: variable-frequency drives, which are prolific creators of harmonics in electrical systems, and radio frequency interference, which can wreak havoc with electronics, computers, instrumentation and telephones.

Power quality problems can also originate beyond the fence line and, in today’s world, we constantly live with the threat of unplanned power outages and a poor power quality. The impact of a poor power quality is evident in plant downtime, equipment malfunction and inflated electricity bills.

Tips on Reducing Electricity Bills

One should start by recording existing consumption patterns and developing an electricity consumption baseline. Improving electricity consumption (kilowatt hours), the power factor and demand (kilovolt amperes) can be achieved by improving the electrical distribution network in any or all of the following ways:

reducing high neutral currents, improving the voltage balance between phases and eliminating harmonic distortion, especially heavily loaded transformers serving linear loads;

replacing old motors and drives; and

filtering harmonic distortion.

Power factor penalties can be avoided by applying power factor correction capacitor banks once the sine wave distortion has been corrected. Peak demand charges can be reduced by managing peak loads. The impact of poor-quality power on peak loads is especially costly.

Important steps required to improve power quality include:

• examining electrical circuit designs, especially with respect to the ability to meet process and energy system demands;

• complying with existing standards, such as NRS048 and IEC 61000-4-30;

• examining power protection to ensure that it is correctly sized to protect against lightning and current surges;

• developing baselines for all loads and monitoring performance to detect anomalies early;

• interrogating power quality mitigation measures, such as power factor correction sizing and performance;

• reviewing maintenance practices by conducting thermal surveys of critical points and conducting root-cause analyses of failures; and

• continual measurement and monitoring to identify and anticipate voltage distortions and transients before damage is caused.

Perfectly installed equipment in well- designed plant layouts degrade over time and can cause power quality problems over the equipment’s life span. While companies are seldom reluctant to spend money to analyse and test raw materials, components and finished products, many do not grasp the importance of monitoring and analysing the quality of their electrical distribution system.

The South African Industrial Energy Efficiency Project, through its work in industry, has identified the effects of poor power quality and the opportunities for correcting it at both industrial and commercial sites and took the initiative to develop both end-user and expert vocational training courses in power quality with PQS.

Hartzenburg is senior project manager in the Western Cape for the National Cleaner Production Centre South Africa's Industrial Energy Efficiency Project.