Power quality refers to the stability of electric power supply. CLP provides stable and noise-free electric power to our customers, yet such stability is prone to a number of factors:

Causes of Power Quality Issues

The causes of power quality issues can be broadly classified into two categories:

Intrinsic factors

Power disturbances caused by customers' own systems/equipment, for example,

  • Switching of large power equipment, e.g. large motors
  • Improper wiring and grounding
  • Overloaded circuits or harmonic interference, etc

External factors

Certain power quality issues are not caused by customers' own systems/equipment, for example,

  • Lightning
  • Damage from third party
  • Adverse weather conditions
  • Vegetation, animals, etc

Reasons for the Public Attention to Power Quality Issues

Power quality issues are largely due to the compatibility of electronic equipment with the supply system. Hong Kong’s power supply is more stable and reliable today, compared to a decade ago. However, certain power quality issues still attract caution among customers, given the widespread use of high tech equipment which is highly sensitive to voltage fluctuations.

Major Power Quality Issues

There are two major categories of power quality issues:

Voltage Dips

  • According to internationally-adopted definition (under European standard EN 50160), a voltage dip occurs when the power voltage drops to a level below 90% of standard voltage
  • Most voltage dips last for less than 0.1 second before the standard voltage of the power supply is restored
  • During a voltage dip, the power supply is not interrupted

Please click here for more information about Voltage Dip.

Harmonic Inference

Electronic equipment and switching devices being widely used (such as computers, fluorescent lamps, variable speed drives, DC motors and switch-type power sources) often create harmonics in an electric power system. This results in distortion of electric current and voltage waveforms, as well as:

  • Overheating of cables, transformers, and motors
  • Unstable operations of circuit breakers and relays
  • Extra power consumption

Power Quality Related Products

How to Resolve Power Quality Issues?

Each power quality issue needs to be resolved individually. Typical solutions include installation of relevant protective devices (e.g. uninterruptible power supplies, surge suppressors, and isolating transformers), reinstallation or modification of equipment. Below are a few types of frequently used equipment for resolving power quality issues:

Uninterruptible Power Supply (UPS)

UPS is a comprehensive protective device which provides an alternative power source for the connected equipment while mitigating power interruptions or fluctuations. Among all types of UPS, the true on-line UPS systems are the most effective solutions to date.

Harmonic Filter

Harmonic filters not only effectively suppress harmonics, but also help cut power demand by increasing the power factor. There are two types of harmonic filters, namely the passive filters and the active filters.

Filter Type

Auxiliary Power


Passive Filter

Not Required

Suitable for equipment that generates constant harmonics

Active Filter


Suitable for equipment with dynamic harmonic distortions

Value-added Customer Services

CLP offers a range of power quality services to our business customers as detailed below.

Power Quality Investigation

By testing your equipment and identifying sensitive components onsite, we can recommend cost effective solutions that will improve the performance of your equipment when a voltage dip occurs. Also, by monitoring your electrical supply points, we can help identify possible types and sources of power quality problems.

Power Quality Enquiry

We can also provide a wide range of practical information to address any power quality concerns you may have.


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