Cut costs: Mitigate harmonics for compliance at optimal cost

Cost-effective harmonic mitigation

In the power transmission network, many forms of power distortion are present. Harmonic distortion is the most regulated form of distortion, occurring in the frequency range up to 2 kHz. Harmonics can damage equipment, leading to inefficiency and even failure. To reduce risk and optimize operating costs, it’s worth mitigating power distortion. Learn how to mitigate harmonics cost-effectively by planning ahead .

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Harmonics compliance: Use mitigation only when needed

Excessive total harmonic distortion in the distribution network costs money. You risk damage to critical equipment, reduced productivity and lower efficiency. Danfoss gives you expert advice on how to reduce this risk, at optimal cost. Using new drive technologies, you can save significantly on sizing and dimensioning of the electrical network, whilst mitigating harmonic content.. Therefore, to optimize the overall electrical system, it’s vital to select the drive (VFD) early in the system design phase.

How can you curb costs and still comply with power quality regulations?

1. Mitigate harmonic content only when needed

For transformer load below 40%, and 5% THDv* limit, no mitigation is required.

For non-linear transformer loads of 40% and above, use the most energy efficient technology to achieve < 5% THDv*.

Aim to regulate harmonics only to meet the required standard and according to the installation requirements. Do not over-compensate for harmonic content. Need help in regulating harmonics? You’re welcome to contact us.

*Abbreviations: THDv: total harmonic voltage distortion. THDi: total harmonic current distortion

2. Design to meet regulations

The most popular regulations (for example, IEEE 519) set THDv requirements, but do not specify total harmonic distortion requirements in terms of THDi. Therefore, design to 5% THDv, to meet regulations. Some regulations require THDi ≤ 5% or even THDi ≤ 8% at drive mains terminals. When these THDi levels are specified, designing to meet them can bring unnecessary cost and additional losses, so contact Danfoss to get the best advice.

Perform a simple analysis. Fewer than 10 minutes of calculations can save you thousands of dollars. Evaluate the entire system to find the best solution. Try our free digital tool, MyDrive® Harmonics.

3. Select equipment based on OPEX calculations

In an installation, energy consumption is a major contributor to the operating costs. That is why validation of efficiency, including calculation of energy losses, is an important step when choosing equipment to mitigate harmonics. Efficiency of 6-pulse drives normally differs by only 0.5% between different variable speed drive suppliers. However, efficiency variations of as much as 1-2% are not unusual in mitigation equipment from dierent suppliers. It’s important to do the calculations before you make your choice.

Use harmonic mitigation only when needed

Find the balance between total harmonic distortion (THDi), efficiency, and the cost of purchased equipment. For transformer load below 40%, and 5% THDv limit, typically no mitigation is required. Standard 6-pulse drives with chokes can be enough to deal the harmonics present, in these cases.

Don’t buy what you don’t need. For help in calculating when to mitigate, contact us.

Analyze at full load current where THDv impact is highest

Design the system to withstand the full load worst case requirements from the driven load(s) and other loads.

Use calculation tools to dimension transformers and generators, or test the capacity of items already chosen.

Adjust and iterate the mitigation equipment scenarios to meet a suitable cost and performance outcome.

To find different mitigation scenarios, use MyDrive^® Harmonics.

Target THDv of 5% for best cost / performance balance

THDv of 5% is a good compromise between lowest distortion levels, the cost of the equipment needed to reach that level, the resultant efficiency of the components chosen, and the overall system efficiency.

Driving the distortion lower follows the law of diminishing returns. It’s possible to reduce distortion levels even further, but the gains can cost too much.

To calculate energy efficiency of your application, try MyDrive^® Energy.

What’ s new in variable speed drive technology?

Today, harmonic mitigation in drive systems has improved. Variable speed drive systems optimized for low-harmonic performance can now operate at 3-5% total harmonic distortion (THDi), at unity power factor, with lower common mode impact, and lower supra harmonic impact. Drives can also eliminate the full load current impacts caused by direct-online (DOL) motor starting. All of this means that supply transformers and backup generators can be dimensioned significantly (10-30%) smaller. Cables, fuses and switchgear can also be smaller. These components are expensive and can affect the ability to meet the budget constraints of a project. Careful, early drive (VFD) selection can therefore play a major part in ensuring project success.

Is harmonic distortion costing you money and downtime?

Factors impacting choice of harmonic mitigation methods include: compliance load profile, power factor distribution, electrical grid conditions, physical size of the installation (especially for retrofits), efficiency, and performance of power systems.

Need advice on harmonic mitigation? Contact us today

Harmonic mitigation: When designing a system, plan the drive (VFD) first

Using new drive technologies, you can mitigate harmonics while saving significantly on sizing and dimensioning of the electrical network. Therefore, to optimize the overall electrical system, it is vital to select the drive (VFD) early in the power system design phase. Drives offer much more than just turning your motors.

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Optimize electrical system design

When designing an electrical system, optimizing for harmonic mitigation also means optimizing system design for cost, power quality, and Scope 1, 2, and 3 emissions. Whether for new-build or retrofit, design the electrical system to ensure:

Reduced initial up front capital cost
Minimal long-term operational costs
Minimal practicable impact of harmonics from drives on the supply network and the wider system, including driven loads

Consider the needs for lower greenhouse gas (GHG) emissions in accordance with legislation. The design must also match the ambition of the site (or client) to meet their Scope 1,2, and 3 (GHG) emission targets, and commitments to achieve carbon net zero.