Harmonics, a key Power Quality (PQ) phenomenon has made a common occurrence in today’s electrical power system leading to inefficiencies, safety hazard and higher operating costs. It existed in the power system since decades, however due to less non-linear loads before 1990s, its effect on power systems were negligible. In today’s scenario of electrical and electronics equipment, the non-linear loads are increasing and approaching 75-90% of the loading on our nation’s electricity grid. High levels of harmonic lead to problems for the utility’s distribution system and any other equipment serviced by that system. Its effect can range from spurious operation of equipment to a shutdown of important equipment, such as unwarranted tripping of lines. Some of the adverse effects of harmonics are: conductor overheating, heating of capacitors, fuses, increased transformer losses, malfunctioning of generators, faulty utility meters causing inflated bills, interference in communication devices etc.

Passive Filters are applied extensively by design engineers to mitigate harmonics due to their low cost, simple design and high reliability.

Given the existing condition of utility power systems, harmonic mitigation and improvement of power quality are very essential. There are various harmonic mitigation methods available like Harmonic Mitigating Transformer, Active Harmonic Filters, etc. but Passive Filters are applied extensively by design engineers due to their low cost, simple design and high reliability. Passive filters are the ideal solutions for reducing harmonics in medium and high-voltage networks. However, the traditional approach of installing filters mainly on initial capital costs results in higher costs in O&M over life time of equipment.

This blog draws attention towards leveraging passive filters to mitigate harmonic distortion with the minimum of cost using Life Cycle Cost (LCC) approach.

PASSIVE FILTERS TYPES, KEY APPLICATIONS AND TYPICAL SELECTION CRITERIA

Passive filters is one of the simple, well understood and conventional technology solution for mitigating harmonic distortion. Its classification is done on the type of harmonic generation source component present in the system and passive components resistor, capacitor and inductor. They are broadly classified as series, shunt and hybrid filter. Depending on the design of filters, passive filter can be single tuned filter or high pass filter. Single tuned passive filters are probably the most common type of filters which are used in industry for the harmonic mitigation. The objective of using passive filter is that on the tuned frequency, filter offers low impedance through which harmonic current will tend to divert in the system. Another advantage of using passive filter is that it provides the reactive power compensation in the system to improve the power quality.

Some of the typical applications of passive filters are:

• Utility Installations requiring reactive power compensation
• Installations where voltage distortion must be reduced to avoid disturbing sensitive loads
• Installations where current distortion must be reduced to avoid overloads
• Industrial installations with a set of non-linear loads representing more than 500 kVA (variable speed drives, UPS, rectifiers, etc.)

Most passive filters need are custom designed depending on specific system impedance, system short circuit level, the load current harmonics, the background voltage distortion, as well as interactions with other loads and sources in close vicinity. Filter design without considering above points can result in poor performance due to interactions, and overall system performance may also be poorer than it was prior to filter installation in some cases. Hence, designing an appropriate passive filter is more of an art based on engineering science and background data input to designers is not so onerous for utility engineers.

Further, the utility engineers predominantly consider only initial purchase and installation cost of a system thereby resulting in high costs over the life time of equipment. Since most of the utilities are facing financial challenges, it is in the fundamental interest of a utility or design engineers to evaluate life cycle cost before installing passive filters. Often in large power distribution system the choice of passive harmonic filter may prove to be the best option from life cycle cost angle. Hence, there is a strong need of selecting and installing equipment in a step-by-step approach including problem definition, sources of harmonics, load characteristics and evaluation of life cycle costs. Life cycle assessment helps utilities to maintain the cost factor to revamp profitability of its operation.

Life cycle assessment approach helps utilities to maintain the cost factor to revamp profitability of its operation.

• To identify risks to process operation and efficiency
• Enumerate these risks in terms of downtime and
• Determine how to avoid these risks and subsequent losses early in the design of the system

The various cost components of LCC include initial cost, installation and commissioning costs, energy costs, operation costs, maintenance & repair costs, down time costs, environmental costs, and decommissioning & disposal costs. The following pie-chart depicts, in general, the percentage breakup of these costs for equipment.

It can be seen that the initial capital costs represent a fraction (i.e. ~ 9%) of the total life cycle costs for process equipment. Operating costs, maintenance and cost of downtime contribute more (i.e. ~58%) heavily to the total cost. Hence, it is imperative that long term equipment costs need to be fully considered in capital cost assessment. LCC analysis helps utilities and industries minimize overall cost and maximize energy efficiency for many types of systems.

Capital Cost forms approx. 9% of the total life cycle costs for process equipment. Remaining 91% forms other costs like downtime, O&M, energy costs, installation, decommissioning, etc.

A typical LCC process includes steps as shown in above figure. Brief explanation of each is as follows:

• Process Requirements – Determining the present and future capacity for the product, lifetime of the process, defining product quality based on customer requirements, its flexibility, etc.
• Define equipment – This has many variations in basic design and design operations. This is one of the important step in LCC analysis and utility engineers should discuss their requirement with equipment manufacturers/suppliers on: performance, design options, foundation and support requirements, mean-time between failures, spare parts, etc. to have exact equipment as per defined configurations.
• Installation – An important consideration during the layout and installation of equipment is the accessibility to allow preventive maintenance and future repair.
• Operation & Maintenance – O&M are two areas that are critical to avoiding downtime and both are affected by equipment selection, design and operating procedures. Key aspects to consider are: operating within limits/capacities, training of personnel, parts availability in case of unexpected failures, etc.
• Decommission – The concept of decommissioning is not something most engineers tend to consider as they are designing a plant, but some plants will have finite lives of just a few years. Some costs of decommissioning include dismantling and selling of key equipment, and others.