Services We Provide
Harmonic Analysis is the process of measuring and studying the characteristics of any power system to identify, predict and mitigate issues associated with high levels of harmonics.
It involves installing specialist power quality analysers for a minimum of a week and a maximum sample interval of 10 minutes, to monitor the load and collect vital information on the day-to-day running of an industrial or commercial system.
In addition to harmonic analysis, the advanced analysis equipment we deploy also records other important power quality indicators.
The information collected is studied and presented in a technical report detailing findings that include but are not limited to:
The total harmonic distortion (THD) levels.
The individual harmonic levels and whether they exceed IEC design limits.
Concerns about the general power quality levels.
Details of any short-term issues identified as a by-product of the analysis (transients, voltage dips, Swells, power factor correction, etc.)
Most importantly, we provide the necessary recommendations for improvements.
Harmonic Analysis can also be conducted as part of an annual power quality health check to ensure that the electrical supply remains in optimal condition for production processes, residents, or clients to avoid interruption and downtime.
What are Harmonics?
AC systems are generally not perfect sine waves with a frequency of 50Hz due to the proliferation of non-linear devices in IT, UPS, Rectifiers, Drives, Capacitors, and process control equipment.
Figure 1 shows the three-phase voltage and current waveforms captured on the incoming LV supply of a major shopping centre. It is quite apparent that the current waveform is far from the standard sine wave expected due to noticeable distortions.
A waveform such as that shown in Figure 1 is quite typical for large commercial/industrial sites and it is the presence of harmonics that results in such distortion.
AC systems are generally not perfect sine waves with a frequency of 50Hz due to the proliferation of non-linear devices in IT, UPS, Rectifiers, Drives, Capacitors, and process control equipment.
Figure 1 shows the three-phase voltage and current waveforms captured on the incoming LV supply of a major shopping centre. It is quite apparent that the current waveform is far from the standard sine wave expected due to noticeable distortions.
A waveform such as that shown in Figure 1 is quite typical for large commercial/industrial sites and it is the presence of harmonics that results in such distortion.
Harmonics are frequencies that are superimposed upon the 50Hz signal that are an integer multiple of 50Hz; i.e. the 3rd harmonic is 150Hz, the 5th harmonic is 250Hz and so on.
These harmonics are not just a mathematical representation of a distorted waveform, they are real, and their effects are predictable and measurable. Figure 2 shows a breakdown of the load current harmonics, which shows that the 5th and 7th harmonics are predominant, which is very typical for this type of load.
These harmonic currents are produced by the load and flow back to the supply, passing through the impedance of the cables, transformer etc. as they do so. As these harmonic currents flow through the system, they produce harmonic voltage drops which in turn distort the supply voltage. The voltage waveform in Figure 1 exhibits such distortion and the voltage harmonic distortion profile shown in Figure 3 shows a harmonic profile very similar to that of the current. This clearly illustrates the load current passing through the system impedance and deforming the voltage.
Harmonics are produced by loads that draw a current that is not directly proportional to the voltage, often referred to as non-linear load. The type of loads that draw such current are generally loads that incorporate some form of rectification and include the following: –
- UPSs
- Inverter drives
- IT equipment (the power supplies therein)
- DC drives
The impact of harmonics can be felt in many ways including:
- Poor power factor, absorption of capacitors, harmonic magnification due to harmonic resonance.
- Overheating of ac motors, and even mechanical damage due to pulsating torques on motor shafts.
- Interference induced into comms/IT cables if not correctly segregated from power cables carrying distorted current, resulting in noise on telephony systems and possible data issues.
- Premature failure of light fittings.
- Premature failure of dc power supplies.
Harmonic Limits for power systems are set out in the 61000 series of IEC standards. They specify harmonic current injection limits (61000-3-4). Generally, however, it is a better idea to try and comply with the requirements specified in the NESIS-R 2015 Standards to ensure adherence to a blend of local and international standards suitable for the Nigeria environment which equipment will operate in.
What we do
In the last two decades, we have developed expertise in the area of harmonics, offering a comprehensive harmonic diagnostic, assessment, and solution package. In addition, iPEC can assist with a full assessment which captures the harmonic content of the system or pre-existing load, gathering data on the extra load and modelling of the harmonic levels resulting from the connection of the new load. Harmonic analysis can be carried out post load installation to ensure the accuracy of the assessment and to verify compliance with NESIS-R Standards. More often than not, our experience has shown that for most of the African markets, harmonic filtration is always necessary. Herein, we specify and implement active harmonic filtration schemes to minimise load current harmonics. Following the installation, we will also carry out post-installation analysis of the harmonic content of the resultant system to verify the efficacy of the harmonic filters proposed.
If a harmonic resonance is diagnosed, it’s likely to be a result of interaction between system harmonics and the capacitors within a ‘standard’ or ‘plain’ power factor correction unit. In this case, IPEC can design and install a detuned power factor correction system that will eliminate any harmonic base level magnification or even reduce base harmonic levels. We also have dynamic UPS systems based on the MTU Kinetic Powerpack.