Harmonics are troublesome but cannot be avoided. However it is as a result of automation, modern electronics, with direct consequences.

The objective being to locate, mitigate and optimize productivity. Harmonics are indeed a strange bedfellow that must be managed and first step towards the solution is to know where to find them.

GUIDELINES

A harmonic survey will give you a good idea, if you have the problem and where it is located.

 Here are a few TIPS to follow;

1. Load inventory.

Make a walking tour of the facility and take a look at the types of equipment in use. If you have a lot of personal computers and printers, adjustable speed motors, solid-state heater controls, and certain types of fluorescent lightning, there’s a good chance that harmonics are present.

2. Transformer heat checks.

Locate the transformers feeding those non-linear loads and check for excessive heating. Also make sure the cooling vents are unobstructed.

3. Transformer secondary current.

Use a  true-rms power quality analyzer to check transformer currents.

• Verify that the voltage ratings for the clamp meter are adequate for the transformer being tested.
• Measure and record the transformer secondary currents in each phase and in the neutral (if used)
• Compare the kVA delivered to the load against the nameplate rating, (if harmonic currents are present, the transformer can overheat even if the kVA delivered is less than the nameplate rating.)
• Use the k-factor measurement from a three-phase analyzer to determine de-rating or transformer replacement.
• Measure the frequency of the neutral current. 180Hz would be a typical reading for a neutral current consisting of mostly third harmonic.
  
  
  

D. Sub-panel neutral current check

Check the sub-panels that feed harmonic loads. Measure the current in each branch neutral and compare the measured value to the rated capacity for the wire size used. Check the neutral bus bar and feeder connections for heating or discoloration. A non-contact infrared thermometer,  is useful for detecting excessive overheating on bus bars and connections.

E. Receptacle neutral-to-ground voltage check.

 Neutral overloading in receptacle branch circuits can sometimes be detected by measuring the neutral-to-ground voltage at the receptable.

• Measure the voltage when the loads are on. Two volts or less is about normal. Higher voltages can indicate trouble depending on the length of the run, quality of connections, etc.
•  Measure the frequency. A frequency of 180 Hz would suggest a strong presence of harmonics, while 60Hz would suggest that the phases are out of balance. Pay special attention to under carpet wiring and modular office panels with integrated wiring that uses a neutral shared by three-phase conductors.
• Because the typical loads in these two areas are computer and office machines, they are often trouble spots for overloaded neutrals.

In other to mitigate harmonics and save your facility from its consequences, you need a good survey.

At FullSpectrum Energy Solutions, we help locate, mitigate harmonics & other Power Quality concerns without wasting your time. Ensuring you have seamless Operations, Enhanced Productivity & Ultimately increased Profits.

Enquires

Victor Oyedu, FNSE, FNIEEE, CPQ.
Power Quality and Energy Management Specialist.
Publisher at Afrienergyonline.com & 
CEO, FullSpectrum Energy Solutions Limited, Nigeria.