What is a PQ problem?

What is a power quality problem, one may wonder?

There are many definitions to this out there but my personal favourite will be
“Any power problem manifested in voltage, current, or frequency deviations that result in failure or misoperation of customer equipment”.

The keywords here are “Customer Equipment”. If it does not affect the operation of the equipment, it is not a problem (yet).
For instance, almost every load that we have today is a non-linear load, contributing harmonic current and hence distorting the supply voltages.

At the beginning, it will probably not be a an issue, but over time if not keep in check and with more non-linear loads added, the supply voltages will be distorted further and eventually equipment may start to fail/misoperate.
The problem is made worse if design considerations were not made to ‘cater’ for this harmonic loads (eg undersized neutral cables) and no control was made to what type of equipment (whether it meets relevant product emission standards or not, etc) can be connected to the network. In this situation, a combination of equipment control and benchmarking of power quality indices is needed (more on this in my future posts).

Other than harmonic distortion, other power quality problems include voltage transients, frequency variations, flicker, leakage currents, in-rush currents and voltage dip/swell (just to name a few).

Here in Singapore. the utility company, SP PowerGrid, states in their FAQ that the most important power quality concern in Singapore is voltage dips. This is because a dip will have significant economic impacts on the sizeable semiconductor industries primarily located in Marsiling / Woodlands and Pasir Ris / Tampines area. These semiconductor plants have equipment which are sensitive to these milliseconds variation of the supply voltage. A dip may result in their equipment to trip, halting productions which eventually lead to a host of other costly problems.

My experiences showed that while many of such equipment in the “Facilities” side (Eg variable speed drives to the pumps) are quite well-protected (SEMI F47-rated at least), many equipment in the “Tools” side are not. And one has to take into consideration too that the SEMI F47 has its own limitations as well (more on this in my future posts).

This is not to say that other power quality problems do not exist in Singapore. Things like excessive harmonic distortion for instance are “localized” problems, usually more apparent in the Customer’s end (low voltage side). It is only seen in the Grid’s high voltage side (6.6kV and above) if the problem has escalated considerably.

Having worked for the utility, I do know that there are pockets of the transmission / distribution network that have breached the limits set aside for things like harmonic distortion and flicker. No equipment were known to be affected (yet) and at times, it can also be a complex problem for the utility company to pinpoint the chief cause of the problem, as the grid network is very vast. I believed this is a challenge for many other utility companies worldwide.

Linking back to my favourite definition of a power quality problem, it is a misconception that a PQ problem can only be solved by putting expensive PQ meters / monitoring instrument. A PQ meter is just one of the many tools to aid the PQ investigator. Other tools include earth loop measurement device, earth tester, Infrared Thermal Scan, etc. It is also another misconception that once a PQ monitor is installed, it definitely can pinpoint/solve the problem.

Remember the inputs to the PQ meter is just voltage & current. It is not some “magical”  troubleshooting instrumentation. The selection of what PQ meter to use, its settings, the placement of such meters and more importantly the experience of the PQ investigator matters.

p/s: I will share my experiences on the use of various PQ meters in future posts.


About the author

Muhammad Najmi Bin Bohari is a Singapore-registered professional engineer (and an ASEAN Chartered PE) whose passion lies in the area of power quality. He graduated from Nanyang Technological University with a Master of Science Degree in Power Engineering and a Bachelor’s Degree in Electrical and Electronic Engineering.

Najmi is formerly from Quality Power Management Pte Ltd, where he led its Power Quality & Engineering Analysis Unit in conducting works like power system & power quality studies, assessment on buildings’ earthing & lightning protection system and investigations on possible causes of equipment failures or nuisance tripping issues.

Prior to that, Najmi served in SP PowerGrid’s Power Quality & Transient Management section, where he specialized in power quality investigation & analysis, voltage dip sensitivity testing and working with Customers on compliance to power quality requirements. He was also a regular speaker in SP PowerGrid’s biennial public seminar, the “Power Systems Reliability & Quality Workshop”.

In recent years, Najmi has continued to conduct numerous presentations / training in the area of power quality, both locally and regionally. His most recent presentation in the region was at the 18th Annual PQSynergyInternational Conference and Exhibition 2018 in Bangkok Thailand, where he shared his experiences in Singapore’s PQ scene over the last ten years.

Currently he runs an engineering & consulting company, Potentia Dynamics Pte Ltd. In his free time, he writes on this blog to share his views and experiences in this fascinating world of power quality.

For queries, kindly contact him.

Recent works – selected

  • Third Party Consultancy Study on Power Distribution System Condition Study of a Light Rapid Transit System (Review of Load Flow and Power Quality aspects) – Singapore
  • Analysis of Power Quality Data (Assessment of the quality of supply for the connection of Medical Diagnostic Equipment) – Cambodia, Philippines, Singapore
  • Power Quality Assessment (LV and up to 230kV) for the Connection of Distributed Generation / Grid-Tied Solar / Energy Storage Systems – various projects, Singapore
  • Harmonics Analysis & Study at a specialty chemical plant – Singapore
  • Power Systems Study (Protection Discrimination Review) at a hard-disk manufacturing plant – Singapore
  • Arc-Flash Study at a Test & Manufacturing Facility – Singapore
  • Protection Coordination Study (HT/LT) for a High-rise Telecommunications Building – Singapore

Recent Presentations / Short Courses

  • Harmonics – An Overview
  • Power Quality Training (2-day course for GE Healthcare)
  • Unitest Instruments Seminar on “Know Your Power Quality” – Keynote speaker
  • SS601: COP for Maintenance of Grid-Tied Solar PV Power Supply System (Aspects on Local PQ requirements)
  • Power Quality In Building Services – Case Studies and Examples from Singapore
  • Unitest Instruments Workshop – Power Quality
  • Unitest Instruments Workshop – Electrical Safety
  • Singapore Institute of Technology’s Power Quality and Reliability class – Guest Lecturer

Updated: 08-04-2021

Welcome to powerquality.sg

Welcome to powerquality.sg

Power quality isn’t a new word or term. It has been around for ages. However if one is to search around, there isn’t much information available with regards to this topic here in Singapore.
It is very much still a niche area in the local electrical engineering scene.

Hence, the birth of this blog/site. It is the author’s intention to fill this gap of information here in this website and at the same time a platform to share the author’s views & experiences gained in the subject.

The author is currently the principal consultant for Potentia Dynamics Pte Ltd, an engineering & consulting company.

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