what are the problems caused by harmonics?

Answer 1

The problems caused by harmonics are now much more relevant and can cause considrable damage not only to distr5ibution systems but also to the equipment connected to them. This is why an Electrician will need to control harmonics in their every-day job, as I explain in the three examples.

1. Third harmonic currents oftencaused by high frequency lighting and P.C’s, summate with any existing imbalance in the neutral conductors and create a current that often has not been allowed for by the designer. This value can be determined with the use of a true rms clamp meter. Usualy this value would be given little if any consideration when carrying out periodic inspections, however the truth is you may be certifying an installation as being electrically sound when the neutral conductor is in danger of overheating or the equipment connected to it is being compromised by these very elements. If the customer cannot rely on us to unveil such detrimental influences then who can they call upon.

2. Another example is where an Electrician’s own testing equipment was affected by harmonics.

One of my Field Technicians commented that his test meter was providing unstable test results in certain circumstances, usually on higher impedance lighting circuits. After an investigation into the possible causes of this phenomenon we confirmed our suspicions.

The meter was sent back to the manufacturer with an accompanying report outlining the specific issues. The meter was tested in the laboratory on a known source of 0.51 ohms and the results were repeatedly accurate. We subsequently suggested that they test the meter on a circuit with earth loop impedance of approximately 2ohms in order to replicate the example that we had given. This was done and once again the results were satisfactory.

It transpires that these meters are tested on LINS units (Line Impedance Network Stabilisers), in simple terms, a clean supply. The networks that we are testing are often subject to harmonic distortion emanating from various switch mode power supplies connected to the system. Although these meters do have a degree of harmonic filtration integrated, these currents would appear to be the reason for the inconsistent readings that we had been recording.

For clarity, it would appear that all meters currently on the market are subject to the same issues until technology can provide suitable means of filtration, perhaps in a modulating capacity.

Further investigation by technical team unveiled a quote made by one of the instrument manufacturers within a technical manual. “…In addition, where harmonic elements are present, the stability of certain test results on the installation may be decreased due to the incorrect triggering of electronic circuitry at voltage zero-crossing.”

3. Our final example is based purely on harmonic voltage distortion and is surprisingly common on sites that have a high number of variable speed motor drives.

I have, in recent months had a number of calls from various electrical contractors who have been struggling to acquire measured earth fault loop impedance values on such sites. The test equipment used in these instances had a high voltage limit value preset into the test instrument for both self protection and for the purpose of indicating voltages outside of the permitted levels stipulated in the ESQCR regulations 2002. On further investigation it has transpired that these increased voltages are in fact site-generated and are caused by these pulsed drive units that distort the AC sign wave and in a way further described in this document, increase the voltage at the source.

In some cases the Consultants or Engineers involved, having been informed of this dilemma, have simply put the responsibility of providing suitable results onto the Contractor. Subsequently, in some cases, results have been submitted based on simply adding the Ze value to the (R1+R2) value. Our advice in these cases is that the Contractor should check in the specification document to see if the responsibility for mitigating distorted, increased voltages is in fact in his scope of works at all. It is hardly surprising that this is seldom the case.

In my experience, it would usually be the responsibility of the Designer to highlight equipment likely to create such problems at the design stage and subsequently include mitigation equipment into the specification.

Answer 2

a good worse subject occurs on airliners. great numbers of in flight leisure gadgets and VCRs use rectifier kind means aspects. this would generate lots harmonic distortion that the airplane alternator cuts out, inflicting an entire on board electric powered failure. the respond is to apply categories of means aspects interior the leisure gadget, that don't generate lots harmonic distortion.

Answer 3

noise, intereference, unwanted vibration, distrortion or degradation of fundamental freq of interest

Example
Stereo amps have a measure called total harmonic distortion, the higher this is the poorer the sound quality and freq response in region of harmonics,
stress, fatigue etc