When it comes to mitigating harmonics to comply with Australian Standards for harmonic distortion, the two main technologies that are commonly applied are Passive Harmonic Filters (PHF) and Active Harmonic Filters (AHF).
With such effective options at our disposal, the common question asked is “Which one do I use?”
How would you answer that question?
Actually, as with most things in life there isn’t one definitive answer….it depends on a number of factors. Whether to use Passive Harmonic Filters or Active Harmonic Filters is largely a question of how to win the project and balancing a combination of commercial vs engineering considerations.
How many VSD’s and where are they located?
If you are providing harmonic mitigation for one VSD, a PHF would be the logical solution due to the lower cost. However as soon as you are working with more than one VSD, an AHF becomes more cost effective.
Maintenance
Being a passive device, a Passive Harmonic Filter on each drive can be a less intrusive method of compensation as it does not require any ongoing maintenance.
Performance
A Passive Harmonic Filter (PHF) is designed specifically to mitigate the harmonics for VSD’s. Although most PHF’s achieve 6-8%, the MTE Matrix AP can reduce the THDi to 5% from 30%-100% of load and will also assist with the power factor. This is a great result but if you require even greater performance, you need to consider an Active Harmonic Filter (AHF).
An AHF can produce a result better that 5% THDi across the load range and it can also improve the power factor and balance the load on all three phases if required. An AHF mitigates all types of harmonics from VSD’s, lighting, switch mode power supplies, thyristor switching to data centres and it will do it at any location within the plant.
Is it a new ‘greenfield’ site or an existing site?
Another consideration is the choice of compensating at the switchboard or at the individual source of harmonics. This group compensation vs centralised compensation decision depends on the nature of the site or project.
If you are considering a greenfield opportunity, the harmonic mitigation strategy can be implemented at the design stage. If you are operating with an existing site, the solution provided must adapt to the parameters & limitations of the existing system.
Perhaps the most significant decision – Sizing
The types of loads in a system need to be considered so that the optimum cost vs performance outcome can be achieved. Often there are many possible combinations of AHF & PHF solutions that can be employed for an application and the important consideration is choosing the combination that achieves the desired performance at the most economical cost.
If there are many and varied loads, an AHF would be the preferred method. However, if there is a significant single load in a system such as a chiller for example, then the correct solution could be a PHF on the chiller and an AHF on the main switchboard or an AHF on the chiller and AHF on the main switchboard. In both cases, sizing is important……as size dictates the cost. In other applications, a cumulative VSD load spread across many different floors of a commercial building can be catered for by an AHF at each floor’s switchboard or motor control centre.
Drawing on many years of experience with such calculations, Fuseco’s Power Quality engineers can assist you to achieve the optimum cost vs performance outcome for your project. We welcome you to contact Fuseco to organise a consultation to discuss your requirements.
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In simple terms, harmonics are extra frequencies that when present in an electrical circuit, distort the AC sine wave. A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. For example, if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f... etc.
Harmonic frequencies are equally spaced by the width of the fundamental frequency and can be found by repeatedly adding that frequency. In the case of the Australian electricity supply, the fundamental frequency is 50Hz. The frequencies of the harmonics are 100Hz, 150Hz, 200Hz, 250Hz, 300Hz, 350Hz and so on.
For electrical systems to function in their intended manner without significant loss of performance or life, they require a supply of electricity that is of good quality. Good quality electrical power has the following characteristics:
- It must have a continuity of service (not be interrupted).
- It must have a very low Harmonic content.
- It must have a very low variation in the voltage magnitude.
- It must have very low transient voltages and currents.
The term 'clean power' is used to describe electricity that is considered to be of good quality (see above) with particular reference to a very low harmonic content. Therefore, the term 'dirty power' is used to describe electricity that is considered to be of low quality (opposite to the above) with particular reference to a very high harmonic content.
In Australia, our electricity is supplied in alternating current at a frequency of 50Hz. In alternating current (AC) the movement of electric charge periodically reverses direction. In direct current (DC), the flow of electric charge is only in one direction. 50Hz means that the AC has a frequency of 50 cycles per second. This is also known as the 'fundamental' frequency. AC is the form in which electricity is delivered to businesses and residences. Most electrical devices (such as motors) need clean electricity to function properly. This means that the electrical supply needs to be a clear sinusoidal wave.
If you occasionally experience some unexplained occurrences such as flickering lights, alarms going off, or MCB's, MCCB's, RCD's and Earth Leakage devices tripping for no apparent reason, you are most likely experiencing harmonics in your electrical environment. Other signs are cables running hot, hot switchboards or overheating motors. If you are replacing your motor's bearings & insulation often, that's a strong indication of the presence of harmonics.
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Harmonics are very harmful within an electrical system and can have serious consequences. For example, the presence of harmonics reduces the life of equipment. It is possible that the investment that you made in your motors & drives will not be realised if they are damaged and need replacing before their expected life span. This can be very expensive. Harmonics cause things to run hot, which cause stress on the cables and equipment.
In the long term, this degrades an electrical system. The presence of harmonics will also mean that although you will get billed for the power that you are supplied, a large percentage of that power may be unusable. Harmonic mitigation is taking action to minimise the presence of harmonics in your electrical system and can achieve great cost savings.
Variable Speed Drives (also known as Variable Frequency Drives) are prolific creators of harmonics in electrical systems and as a result, most of the harmonic mitigation effort focuses on the input side and output side of a VFD.
Depending on the specific situation, there are a variety of products that are used to mitigate harmonics. Fuseco's Power Quality Consultants can assist by conducting a site analysis or simply providing advice based on the details of the particular electrical system. Here is a brief summary of the product groups:
Line (input) side of the VSD
Device Features:
- Line Reactors Simple & cost-effective method to reduce harmonics. Available in 3% & 5% versions.
- Passive Harmonic Filters Significantly reduces harmonics from the VSD back out to the system and also improves true power factor.
- Meets the IEEE519 Standard.
- Active Harmonic Filters Active filters inject a 180 degree inverse current to nullify the harmonic content going back out to the system. They mitigate harmonics, compensate for voltage dips & can handle multiple VSD's relative to the reactive power required. Meets the IEEE519 Standard.
Load (output) side of the VSD
Device Features:
- Load Reactors Simple & cost-effective method to reduce harmonics. Available in 3% & 5% versions.
- dV/dT Filters dV/dT filters have been designed to limit peak voltage and increase voltage rise time. In addition to mitigating harmonics, the dV/dT filter also clips voltage spikes.
- Sinewave Filters The ultimate load side harmonic mitigation product. Filters all harmonics, including reflective currents, eddy currents, common mode currents. Can be used for long cable runs (many kms). Stops the heating of cables. Great for the longevity of motors.
Knowledge Centre
It’s been a pleasure working with Fuseco on this project. Initially, we thought that the power quality issues on this job were insurmountable. Fuseco conducted a power quality site audit and consulted with us to find a suitable solution that would work reliably in this challenging environment. The reactors and harmonic filters specified & supplied by Fuseco have been the perfect solution.
Peter Carney
ELECTRICAL ENGINEER AT SIEMENS
Just wanted to say thank you again to the Fuseco team. When presented with an electrical harmonics problem of this nature, I wasn’t sure how to approach it. You guys explained it in logical, scientific terms and expertly demonstrated the capability of your technology. It is now one month post-installation and I can say that the Active Filter is working well and the harmonics levels on this site are now negligible.
John Ulverstone
ELECTRICAL ENGINEERING AT BHP
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