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Power Capacitors - Power Quality / Power Factor Correction

Power Factor Correction - Commercial Benefits - Power Quality - Active Filters - Surge Suppression - Capacitor Sizing


Under normal operating conditions, certain electrical loads draw not only active power from the supply (kilowatts kW), but also reactive power (reactive kVA, kVAr). This reactive power has no useful function but is necessary for the equipment to operate correctly. Loads such as induction motors, welding equipment, arc furnaces and fluorescent lighting would fall into this category.

Power Factor Correction - Definition

The Power Factor of a load is defined as the ratio of active power to total demand, that is to say kW divided by kVA. In layman’s terms, Power Factor is the percentage of the burden on the supply which is actually doing real, useful work. Power Factor Correction (PFC) is the application of properly designed, manufactured and installed equipment which will compensate for the ‘useless’ yet essential part of the demand on the supply, leaving only ‘useful’ power to be drawn from the mains. The nearer Power Factor is to unity, the less reactive power is drawn from the supply, the lower the demand, and the greater the overall efficiency.

Commercial Benefits

Financial penalties imposed by the supply companies can be avoided by maintaining a Power Factor better than 0.95 lagging under all load conditions. Power Capacitors Ltd will typically select a target Power Factor of between 0.96 and 0.98 lagging, depending on the specific requirements of each installation. By maintaining an improved Power Factor:

- Excess Reactive Power charges are avoided.

Half-hourly metered consumers are charged for ‘excess reactive power’, which is defined as occurring when the power factor is lower than 0.95 lagging. These charges vary between tens of pounds to thousands of pounds per month depending on the loading. Installation and proper maintenance of a well-designed PFC system can remove the charges completely.

- The Overall Demand on the supply is reduced.

A chargeable item on all half-hourly metered supplies is ‘Authorised Capacity’. By improving the power factor, less supply is required to do the same amount of work. This may permit a reduction in the authorised supply capacity required, with an associated reduction in charges from the supply company.

- System Losses are reduced.

Losses in distribution networks increase exponentially with the load. Doubling the load quadruples the losses. By reducing the demand on the supply network, the losses in all network components are reduced. Depending on the installation, this reduction may be between 0.5% and 3% of the total kWh consumption. These additional hidden savings can amount to many thousands of pounds over the course of a year.

Technical Benefits

By improving and maintaining the Power Factor at an optimum level:

- Power Quality is improved.

The ‘voltage drop’ evident on an increasing load is greatly reduced by maintaining an optimum level of Power Factor. The improvement in this aspect of Power Quality has numerous benefits, not least that any load connected to the network will be presented with a clean and consistent supply voltage. Reliability and performance are improved when compared to less well-regulated supplies.

- The Demand on the supply is reduced.

 A significant reduction in the demand for any given loading can release additional supply capacity. This can then be used to connect additional loads to the existing distribution network. Otherwise, supply reinforcement is the only option, often costing many tens of thousands of pounds.

- Network Reliability is increased.

The reduction in demand as a result of improvement in Power Factor affects all components of the upstream distribution network. The resulting reduction in losses means that transformers, cables and switchgear all operate at lower temperatures. This reduction in stress on the distribution system increases both the reliability and useful life of these components, resulting in a more reliable and longer lasting network.

- Harmonic Distortion is reduced.

When a properly-specified ‘Detuned’ Power Factor Correction system is installed on a network subject to significant levels of Harmonic Distortion, the levels of distortion are reduced. The amount of reduction varies according to the particular characteristics of each system. This reduction in distortion increases the reliability and lifetime of any item of equipment and is a significant improvement in Power Quality.

Environmental Benefits

The increasing focus on environmental issues is supported by maintaining an optimum level of Power Factor:

- Carbon Dioxide emissions are reduced.

 The reduction in demand, losses and loading, which is achieved by properly improving the Power Factor, is accompanied by a reduction in Carbon Dioxide emissions. The exact reduction will vary according to each particular installation but studies have shown that reductions in the region of 150kg of CO2 per kVAr of PFC equipment are readily achievable.

- Building Regulations compliance.

Part ‘L’ of the Building Regulations 2010 details reductions in the effective carbon dioxide emissions of a building, which can be applied if a properly designed and implemented Power Factor Correction scheme is installed and monitored. The optimum Power Factor Correction system can attract a reduction of 5% in the total CO2 emissions for the building.

Reactive Power Penalty Charges

The Reactive Power charge is the means by which consumers with a poor power factor pay more for their electricity than consumers with a good power factor. A common charging method is in force across all UK Electricity Supply Companies and applies to ALL half-hourly metered consumers. By installing power factor correction equipment and ensuring that the average power factor is better than 0.95 lagging under ALL load conditions, no “excess” reactive power is consumed. Smaller capacitor stages ensure that these charges are avoided under almost all load conditions. This means that ALL excess Reactive Power charges can be avoided.

Contact our team of sales engineers to discuss existing or imminent Reactive Power charges and how to avoid them.

Total Power Quality

Power Factor Correction is now an integral part of a co-ordinated Power Quality strategy, which should also include Harmonic Distortion and Surge Suppression. Power Capacitors Ltd has the products and experience to identify, manufacture and supply the right solution for each application.

Active Filters

In addition to the extensive range of PFC equipment, Power Capacitors Ltd can offer Active Filter solutions for 3 and 4 wire systems. Filter systems start at 50A and are available up to of 400A in standard designs.

Surge Suppression

Correctly integrating Surge Protection Devices (SPD) into electricity distribution systems is now a key part of any co-ordinated power quality strategy. The three types of SPD are broadly intended for application nearest the supply (type 1), along the distribution system (type 2), and close to the sensitive devices (type 3). The optimum solution would involve a lengthy and costly survey, with the use of all three types of SPD at various key points in the distribution system. Power Capacitors Ltd is able to offer this service to its clients, but much more popular is the ‘one-size fits all’ approach, which is more easily understood and is far simpler to integrate into an existing distribution system.

Maintenance & Service

Most Power Factor Correction equipment works invisibly in the background, but as capacitors deteriorate, it easily goes unnoticed until long after the higher bills arrive. Responsible companies acknowledge the cost-effectiveness of avoiding unnecessary downtime and maintenance. Power Capacitors has a team of skilled and experienced engineers available throughout the UK providing regular servicing and maintenance to ALL makes of power factor correction equipment, regardless of manufacturer. This ensures that the rated output is maintained, maximising the financial and technical benefits.

Technical Support

Whether you need a quick telephone consultation or a full set of surveys and specifications, we are always willing to make ourselves available to customers, old and new. As undisputed experts in the field of power quality, we relish the challenge and are always comfortable in sharing our wealth of expertise with you. Contact us to arrange one of our recognised CPD sessions on Power Factor Correction and Power Quality.

Capacitor Sizing

To obtain capacitor sizes (in kVAr) for a given power factor, multiply the kW load by the number shown at the axis between the existing and the required power factors.

Click the PDF image to view the technical information in full

Power Factor Correction

Request Power Capacitors Info

Power Capacitors Limited
30 Redfern Road
B11 2BH

Email Power Capacitors

Tel: 0121 708 4511
Fax: 0121 765 4054
Sales: Tim Brown
Technical: Matt Robbins

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