More and bigger problems due to harmonic pollution
Harmonic pollution: the ‘silent killer’ in electrical installations
To a greater or lesser extent, harmonic voltages, often described as harmonic pollution, are present in almost every electrical installation. The higher the level of harmonic pollution, the greater the potential risk to the installation. In installations with a large number of power electronics (non-linear loads) the risk of problems caused by harmonic pollution is particularly high. Harmonics also provide extra reactive power, or distortion power. As a result of the presence of harmonics, switching equipment (such as frequency drives) may sometimes consume more than 50% of reactive power.
Risks of harmonic pollution:
- Equipment failure
- Unexpected disconnection of security devices
- Generators do not start up when needed
- Spontaneous ignition of cables and distribution boards
- Unnecessary losses of energy and capacity
- Reduced lifespan of equipment
- Unnecessary service and maintenance costs
Causes of harmonic pollution
Harmonic pollution is caused by the harmonic currents of non-linear loads. These non-linear loads are electrical devices that do not demonstrate ‘linear’ behavior; the voltage and current are not synchronous. These devices attempt to convert the pure sinusoidal alternating voltage into a direct current. The resulting alternating current is no longer purely sinusoidal.
Power electronics, or equipment in which power electronics are present, are typical non-linear loads. In industrial and commercial installations, this type of equipment is being used to an increasing extent. As a result, harmonic pollution within these installations is increasing exponentially.
Examples of non-linear loads
- Frequency inverters/variable speed drives (for AC and DC motors)
- Industrial devices (welding equipment, electric arc furnaces, induction ovens, battery dischargers)
- Uninterruptible Power Supplies (UPS)
- IT equipment (servers, computers, printers)
- Lightning with electric loads (TL-lightning, LED lightning)
- Most devices that use semiconductors (transistors and/or diodes, solid state relays)
Consequences of harmonic pollution
The consequences of harmonic pollution in an installation vary from equipment defects to completely burned-out distribution boards. Depending on the degree of harmonic pollution and the sensitivity of connected equipment, negative effects of harmonic pollution may reveal themselves more quickly.
Negative effects of harmonic pollution:
- Elevated cable resistance, resulting in more heat in the cables => risk of fire & ‘skin effect’
- High zero currents that can cause unforeseen problems => failure risks
- Unexpected switch-off of security devices => safety risk
- Additional reactive power (distortive reactive power) in the installation => energy and capacity loss
- Switching equipment – such as frequency converters – may consume more than 50% of reactive power => energy and capacity loss
- Unwanted currents through the cables => errors
- Overload of motors and transformers => increased noise & negative direction of rotational field
- Shortened life span of equipment due to increased operating temperatures => unnecessary costs
What is a harmonic?
A harmonic is a frequency that is a whole multiple of its fundamental frequency. The fundamental of the European voltage grid is 50Hz. With a fundamental of 50Hz, multiples exclusively include frequencies of 100Hz, 150Hz, 200Hz and so on. These ‘multiple’ frequencies are called harmonics. If the fundamental frequency is 50Hz, the 3rd harmonic is 150Hz, the 5th harmonic is 250Hz and the 7th harmonic is 350Hz.
The Total Harmonic Distortion, or THD, of the voltage and the current is expressed from the 2nd harmonic to the 50th harmonic. More specifically, THDu describes the total harmonics in the voltage and THDi describes the total harmonics in the current.
Three groups of harmonics
Harmonics can be divided into three groups, also known as directions of rotation. Assuming a ground frequency of 50Hz, which is clockwise, each of these groups has a different effect.
Still in the neutral (homopolar)
Etc. until 50th
Leads to increased neutral currents that can result in heating and ignition of cables and components.
Left turning field (counterclockwise)
Etc. until 50th
Leads to losses in, for example, motors and transformers as well as heat generation in the electrical infrastructure.
Right turning field (clockwise)
Etc. until 50th
Leads to losses in, for example, motors and transformers and heat generation in the electrical infrastructure.
Each device has its own distinctive harmonics. For example, frequency drives often produce 5th and 7th harmonics and LED lightning often produces 3rd harmonics.
In Power Quality we measure the harmonic pollution up to the 50th harmonic. For this, we use Fluke meters and Power Quality analyzers. Above 50th harmonics, more advanced equipment is required, such as an oscilloscope to take measurements in the EMC spectrum.
Standards regarding maximum harmonic pollution
The maximum harmonic pollution (of the voltage) – in both public and non-public networks – are defined in different standards relating to the quality of electricity.
(NEN) EN50160 (EN50106)
- The standard for the voltage quality for energy suppliers/network operators.
- Describes the maximum harmonic pollution to the 25th
- When prescribing the minimum quality of the voltage, the Net Code refers to NEN-EN50160. This is a Dutch standard, based on the European standard EN50106 and part of the Netcode.
- The EN50160 (EN50106) specifies the requirements for grid quality that the energy supplier supplies in low, medium and high voltage networks. This standard describes the most important characteristics that the grid quality must meet at the ‘point of coupling’ - the transmission point from the network operator to the end user. This standard does not describe the average situation usually experienced by an end user.
- This is a standard for the immunity, susceptibility and emissions of electrical devices and systems, often referred to as the IEC61000 standard.
- Numerous IEC61000 standards have been created specifically to apply to all kinds of electrical installations, ranging from basic household installations to large industrial installations.
- IEC61000 describes several standards for different types of equipment. These include standards for industrial frequency drives as well as standards for measurement equipment designed to reach a specified level of measurement quality.
- While IEC61000 can only be applied in a device-specific manner, it can be used in combination with an analysis of the quality of the applied power to the device, to map certain risks in each individual situation.
- IEC61000 not only describes immunity and maximum emissions in the Power Quality aspects of electrical equipment. One of the other topics described in the IEC61000 is the immunity and emissions of the EMC related aspects.
What can HyTEPS do for you?
HyTEPS has the knowledge, experience and specialized equipment required to measure, analyze and test harmonic pollution within your installation. We provide insight and advise you on possible improvements. In addition, we supply innovative product solutions to achieve these improvements. The Active Harmonic Filter is a frequently used solution in case of harmonic pollution.