What sort of electrical devices generate Harmonics & What Are Harmonics?
Harmonics are waveforms which have a frequency which is a whole number multiple of the base frequency of the grid power supply (50Hz).
The effect of the harmonic waveform is to distort the supplied power to connected electrical loads.
Harmonics distortion is a destructive force in a power distribution system.
It creates safety problems, shortens the life span of transformers and interferes with operation of electronic devices.
Generally, electrical systems nowadays are increasingly flooded with non-linear load variable frequency drives, electronic power supplies etc. These devices in the end products cause harmonic currents to flow into the electrical systems, which in turn leads to heating losses and unwarranted electrical consumption.
Reducing the harmonic distortions to an acceptable level can result in savings of approximately 2 to 2.5% in electrical energy cost and the net savings by way of reduced down-times of equipment, derated electrical switchgears, cables and accessories may amount up to 30%.
Harmonics are also: Any periodic wave can be described mathematically as a series of sinusoids (sine waves) summed together. This is known as the fourier series. The sinusoids are integer multiples of the frequency represented by the periodic cycles.
Each term in the series is referred to as a “harmonic” of the fundamental frequency (50 Hertz). The term having the same frequency as the fundamental is the first harmonic, and is sometime simply referred to as the “fundamental”. The term having twice the fundamental frequency is the second harmonic (100Hz) and so on.
What are the consequences of high harmonic distortion levels?
Just as high blood pressure can create stress and serious problems in the human body, high levels of harmonic distortion can create stress and resultant problems for the utility’s distribution system, the plant’s distribution system, as well as all of the equipment that is serviced by that distribution system. The result may be the plant engineer’s worst fear – the shutting down of important plant equipment ranging from a single machine to an entire line or process.
Equipment shutdown can be caused by a number of events. As an example, the higher voltage peaks that are created by harmonic distortion put extra stress on motor and wire insulation which ultimately can result in insulation breakdown and failure. In addition, harmonics increase RMS current resulting in increased operating temperatures for many pieces of equipment resulting in greatly reduced equipment life.
Harmonic distortion disrupts plants. Of greatest importance is the loss of productivity, throughout and possibly sales. These occur because of process shutdowns due to the unexpected failure of motors, drives, power supplies or just the spurious tripping of breakers. Plant engineers realize how costly downtime can be and pride themselves in maintenance and repair budgets can be severely stretched. For example, every 10oC rise in the operating temperatures of motors or capacitors can cut equipment life by 50%.
Total Harmonic Distortion (THD) is the ratio of Harmonic distortion to the fundamental frequency.
Ideally, Voltage THD should not exceed 5% and current THD should not exceed 20%.
- Variable frequency drives
- DC drives soft starters
- Welders, induction furnaces
- HID lighting, electronic ballasts
- Computers, UPS, copiers, faxes
What are the negative effects of harmonics?
- Additional heat in conductors and other distribution system components.
- Nuisance tripping of circuit breakers or fuses blowing.
- Erroneous operation of control system equipment.
- Electronic communication interference.
- The reverse phase rotation of negative harmonics reduces forward motor torque and increases the current demand.
- Zero sequence harmonics can cause additional heating in the neutral conductor of 3 phases 4- wire system.
- The neutral current problem.
The neutral current problem: This is a typical problem, where these currents may be 173% larger than the phase conductor currents and are caused by the presence of Triplen harmonics (3rd, 6th, 9th….) and are zero sequence. This means that they have the same relationship in each conductor of a three phase circuit.
Unlike balanced frequency currents, which cancel in the neutral, balanced Triplen currents add arithmetically in the neutral. This can create a hazardous situation, especially in wiring systems with undersized neutral conductors. In the US, the national electrical code no longer allows derating of neutral conductors in circuits serving electronic loads.
These neutral currents can cause unwanted MCB (Miniature Circuit Breaker) tripping in the power system; data corruption in computer systems; and unwarranted breakdowns in critical sectors such as hospitals equipment and telecom equipment power systems. The right solution to overcome these problems is to conduct harmonic analysis and audit at these sites, and install third harmonic filters at each of the major loads producing harmonics. Prime Technologies specializes in conducting such audits and specifying, and installing such harmonic filters wherever necessary.
Harmonics and power factor correction in industrial environments, the addition of power factor correction capacitors in systems present with harmonic generating equipment causes the harmonic current to resonate and grow larger, resulting in major breakdowns of equipment.
We believe that our knowledge in solving harmonics related problems is unmatched in the industry, and this gives us a technological advantage when specifying the inclusion of power factor correction systems, as we always conduct an audit to ensure that harmonic distortions are filtered out through the use of automatic harmonic filters and that the power factor correction systems provide the savings promised, and not magnify the bad quality of power present in the system, which so commonly occurs. [/expand]