The Problem | The Cause | The Magnitude | Historical Options | The Stakeholders | The Solution

THE HARMONIC PROBLEM

IS THERE REALLY A PROBLEM ?

Yes, there is a problem. In fact, there are so many difficult problems that hundreds, if not thousands, of theses, papers, articles and case studies have been published on this subject. To define and limit harmonic problems, IEEE has published a standard entitled - ‘Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems’ (ANSI/IEEE Std 519-1992).
 
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All electronic loads generate positive and negative sequence harmonic currents. Single-phase electronic loads, connected phase to neutral in a three-phase, four-wire distribution system, also generate zero sequence harmonic currents.

Three-phase motor drives and single-phase lighting loads often account for a significant portion of the system's 480V loads. Single-phase electronic office and data processing equipment typically accounts for more than 95% of a 120/208V power panel's loads. At these levels, 100% Total Harmonic Distortion of Current is common.

SYSTEM PERFORMANCE ISSUES

The injection of harmonic currents into an electrical distribution system, which is based on a non-mitigating 'conventional design', will normally produce the following unacceptable outcomes:

• High Total Harmonic Distortion of Current [THDI]

• High Neutral Currents

• High Harmonic Current Injection into the utility's Point of Common Coupling (ref. IEEE Std 519-1992)

• Increased Voltage Drop in feeder circuits, bus duct risers and branch circuits

POWER QUALITY ISSUES

In an Ohm’s Law relationship with the system’s harmonic impedances, the harmonic currents generate harmonic voltages. These voltages normally produce the following unacceptable Power Quality problems:

• High Total Harmonic Distortion of Voltage [THDV] at the loads (ref. IEEE Std 519-1992)

• High Common Mode Noise [CMN] at the loads (ref. ITIC, formerly CBEMA)

• Large Common Mode Noise Differentials [DCMN] at the office and data processing equipment, which are connected into a communications 'network' (ref. EPRI)

COST ISSUES

A detailed analysis of a 'conventional design' will normally uncover many of the following undesirable financial issues:

• High Capital Cost

• High 'Penalty' Losses, particularly in distribution transformers, 120/208V feeder and branch circuits

• Low Power Factor

• Additional Ventilating and Air Conditioning Costs

• High Power Costs

• Loss of Productivity, Quality and Revenue

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In the early 1980s, the proliferation of personal computers and conversion to electronic lighting ballasts produced harmonic problems in commercial office buildings. Maintenance electricians and designers soon discovered that single-phase electronic loads caused distribution transformers to overheat and 'shared' neutral conductors to become overloaded.

Today, more than 95% of all 120/208V power panel loads, in modern office and data center environments, are electronic. Electronic motor drives are now routinely applied to ventilation fans and elevators at the 480V level.
 
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WHAT WERE THE OPTIONS ?

To improve system performance and provide the best possible environment for the loads, a designer's options have been limited to oversizing distribution transformers and 'shared' neutral conductors. As an alternative, branch circuits have been configured with a separate neutral conductor for each phase conductor. In either case, branch circuits have been underutilized and limited in their length as a means of reducing voltage distortion and neutral-ground voltage (common mode noise) at the loads.

As an alternative to oversizing conventional distribution transformers, many designers have specified K-Rated transformers. Unfortunately, their higher harmonic impedances cause an increase in voltage distortion.
 
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WHO ARE THE STAKEHOLDERS ?

The implementation of these options did not resolve all of the system performance issues or any of the Power Quality and cost issues. Without the means to reduce harmonic currents, the facility's stakeholders were subject to the following potential problems:

THE DESIGNER

• Exceeds IEEE Recommendations & Requirements
• Exceeds CBEMA / EPRI Recommendations
• Power System and Loads are Incompatible
• Exceed Budgetary Goals
• Loss of Client Confidence

THE FACILITY OWNER

• High Capital Costs
• Increased Fire & Safety Risks
• Premature Apparatus Failures
• Significant Tenant Dissatisfaction

THE TENANT

• Higher Power Cost
• Premature Office Equipment Failures
• Data Corruption or Loss
• Computer and System Lock-Ups
• Loss of Productivity
• Reduced Quality Assurance
• Loss of Customer Confidence
• Loss of Revenue.

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IS THERE A SOLUTION ?

Yes, there is a solution. Harmonic current reduction will solve all of these problems. The PQI Solution™, an engineered system solution, includes a Statement of Design Objectives, a comprehensive System Study, a detailed Mitigation Proposal, and a system Performance Guarantee.
 
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