HK Electric Investments is the first fixed single investment trust listed in Hong Kong with a focus on the power industry. Our principal operating subsidiary, The Hongkong Electric Company, Limited (HK Electric), commenced operations in 1890 and is one of the longest-established utility companies in the world.
Over our long history, we have consistently supported Hong Kong's economic journey by offering safe, reliable and affordable electricity while minimising the impact of our operations on the environment as we strive to deliver sustainable growth in long-term value to our investors.
HK Electric Investments believes that open and on-going communication with our stakeholders is central to our operation and development. We engage different stakeholders through a variety of channels and stakeholder suggestions and feedback are highly valued in our decision making process as we strive for continuous improvements.
Underpinned by its core value of "Pursuit of Excellence", HK Electric is committed to delivering excellent services and supply reliability to our customers. We have been providing a world-class supply reliability of over 99.999% since 1997 and all our service standards are achieved or even surpassed every year.
To satisfy the aspirations from the community, and in support of Government’s energy and environmental policy objectives, HK Electric has launched a suite of "Smart Power Services".
HK Electric is one of the longest-established power companies in the world. The Company has a world-class record of providing a highly reliable electricity supply to Hong Kong and Lamma islands at a reasonable and affordable price.
HK Electric Investments is committed to meeting the long-term energy needs and supporting the sustainable development of the community we serve. To do this, we focus not only on powering Hong Kong with a world-class electricity supply, but also on the way we deliver it and the impacts it has on the environment.
HK Electric aspires to be an employer of choice. We have policies and systems in place to attract talents and through continuous training and development, nurture them for a fulfilling career. We offer competitive remuneration, an ideal workplace and comprehensive wellness programmes for our employees while maintaining regular and open dialogues with them.
HK Electric is committed to providing adequate and reliable supply of electricity to support the business growth in Hong Kong. With proliferation of sensitive equipment and electronic products, there is a growing concern among customers about the power quality of electricity supply.
What is Power Quality? Power quality is about the compatibility between the power supply source (voltage, current and frequency) and the equipment served. In case of electrical disturbances, the equipment might not be able to operate normally if the equipment has not been specified to cater for such supply conditions.
The following information may help you understand more about power quality and how to safeguard the power supply for your important services.
Typical Power Quality Problems
Generally, supply interruptions, voltage dips and harmonics are the most common power quality problems. Let us first have a closer look at these power quality problems and their definitions based on the European Standard EN 50160.
Supply interruption is defined as a condition that the voltage at the supply-terminals is less than 1% of the declared voltage.
A voltage dip is defined as a sudden reduction of the voltage to a value between 90% and 1% of the declared voltage with a voltage recovery after a short period of time. The duration of a voltage dip may last between 10ms to 1 minute. For HK Electric, the duration of voltage dips is usually less than 1 second.
Harmonic voltage is defined as a sinusoidal voltage having a frequency equal to an integer multiple of the fundamental frequency (i.e. 50Hz) of the supply voltage. Harmonics of the supply voltage are mainly produced by customers' non-linear loads connected to the supply system and harmonic currents flowing through the system impedance give rise to harmonic voltages.
Common Causes of Power Quality Problems
HEC provides a very reliable power supply to our customers with a pledged reliability of over 99.998%. However, as public electricity supply systems, they are liable to external influences. Therefore, despite the fact that we have made every endeavor to ensure reliability of electricity supply and good power quality, power quality problems may still occasionally occur due to various causes.
Besides, loading conditions, defects or faults of the equipment / installations of any one customer may also affect other customers who share the same customer communal electrical installations and / or supply source. In other words, power quality problems may also originate from the customer side.
Let us have a closer look at the common causes of power quality problems.
The most common cause of power interruption is due to damage or fault of underground cable often arising from disturbance by third parties' excavation works. Customers who depend on the supply through the faulty or damaged cable would experience supply interruption until backup supply is connected or the cable is repaired.
When the normal 11kV supply cable is faulty or damaged, our System Control Engineer will remotely isolate the faulty or damaged cable and switch-in the backup cable through the System Computer to restore supply. Thus the duration of supply interruption is usually very short and only a few minutes is needed to restore supply. However, in exceptional circumstances like simultaneous cable faults or transformer or switchgear fault, supply interruption of longer duration may occur.
For low voltage (LV) network faults, supply can only be restored after the fault has been repaired or the backup supply has been connected by the emergency crew. Thus, it will take longer time for the supply to restore. "The Average Time for Supply Restoration After Interruption of Supply" is shown in our "Customer Service Standards".
Other than cable faults and damage incidents, power interruptions may also be due to equipment failures in suppliers' system as well as in customers' installation.
When there are faults on a supply cable or equipment, voltage dip will occur in the part of the power supply system affected by the fault until the protective devices are initiated to clear the fault. Thus, apart from supply interruption to those customers who are supplied directly by the faulty cable or equipment, other customers may also experience voltage dip. In case of an 11kV fault, the voltage dip is localized in the affected geographical area but in case of a transmission fault, the voltage dip will be territory-wide and affect more customers.
Since our supply network is interconnected with CLP Power, which is interconnected with Mainland China, customers on Hong Kong Island might experience momentary voltage dips as a result of faults in the transmission power systems outside Hong Kong Island.
Harmonics are solely generated from non-linear devices at customer side.
Customers' electrical installations are usually connected in a radial network. A fault occurring in any part of customers' electrical installations will trigger the protective device to isolate the faulty part. Supply interruption will then occur to downstream feeders. Common faults in the customers' electrical installations that cause supply interruptions include:
Voltage dips may be caused by customers' electrical installation, such as:
Harmonics are generated by any load which draws current that is not proportional to the voltage applied. In other words, harmonics are generated by non-linear loads that draw non-sinusoidal current. Harmonic currents flowing through the impedances of the electrical system give rise to harmonic voltages. Thus, harmonic currents and harmonic voltages both vary with time. Such non-linear loads include but are not limited to the following:
Mitigation Measures against Power Quality Problems
Power quality problems may originate from either the supply or customer side, efforts from both parties are essential to achieve a high level of power quality.
HK Electric's Input in Power Quality
HK Electric is committed to supplying quality & reliable power supply to our customers. As we have observed, most of the supply interruptions and voltage dips are caused by third parties' excavation works. Thus prevention of cable damage is crucial in the improvement of power quality. The following paragraphs outline some of the actions we have taken to prevent cable damage as well as the services that we provide to ensure power quality:
Liaison with Road Works Contractors
In order to prevent cable damage incidents, HK Electric has arranged seminars to educate the contractors and to provide them with cable map records before they start their excavation works. There are also regular meetings held between our engineers and major contractors about cable damage prevention.
The "Electricity Supply Lines (Protection) Regulation" has been enacted by the Government to govern all works in vicinity of electricity supply lines to ensure that all reasonable measures are taken to prevent cable damages causing supply interruption.
Power Quality Centre
To enable the customers to understand more about the phenomenon of power quality and ways to safeguard the power supplies for their important services in real life situations, a Power Quality Centre had been erected on M / F., Electric Centre. Adopting an interactive approach to promote the power quality concept, the Power Quality Centre is equipped with a voltage dip generator and different mock-up installations to demonstrate the causes and effects of voltage dip and the mitigation measures against voltage dip and supply interruption for various apparatus. Technical advisory services and relevant leaflets on power quality are also available. A guided tour to the Power Quality Centre can be arranged on request. Customers are welcome to call our engineer at telephone No. 2887 3455 for further information.
For those calling and sending fax outside Hong Kong, please dial the area code "852".
HK Electric's Services on Power Quality
Relevant technical information on power quality matters is available to the customer upon request. HK Electric may also arrange site measurements on the supply sources to identify possible types and sources of power quality problems.
What Customers Can Do to Safeguard Power Supplies for Their Important Services
HK Electric has been constantly reviewing and upgrading the reliability of the supply of our system. However, an effective immunity to power quality problems can only be achieved with the joint effort from our customers. Additional information on this topic is available in our "Guide to Connection of Supply" and the leaflet "How to Safeguard Power Supplies for Important Services".
The following suggestions illustrate some effective means that customers can implement for minimizing the impact of power quality problems:
Against Supply Interruptions
Static Type UPS System
Static type UPS system consists of a rectifier / battery charger, a battery, an inverter and a system controller. During normal operation, the rectifier / battery charger converts the input AC power to DC which supplies the inverter and maintains the battery in a fully charged condition. The inverter converts DC to regulated clean AC power for use by the critical load. The power conversion process isolates the critical load from any disturbances present in the power network and, if the power source fails, the inverter draws its power from the storage battery. When power returns to normal, the rectifier resumes its recharging role automatically.
Rotary Type UPS System
Rotary type UPS system is composed of a static type UPS and a Motor / Generator set. During normal operation, power flows from the main supply to the static type UPS, which in turn powers the Motor / Generator set. The Generator converts the mechanical power back to clean AC power and feeds the critical load. In addition to a clean and non-stop power supply that can be provided by a static UPS system, a rotary type UPS system offers also absolute electrical isolation between the supply input and output to critical load provided by the Motor/Generator set.
For services that can tolerate a short delay in power resumption after power failure, a standby generator or alternative supply with automatic change-over device can be a possible solution. For services where a continuous electricity supply is required, a UPS system together with ABS is preferred and should be installed to prevent and minimize any damage, loss or inconvenience caused directly or indirectly by voltage fluctuation, interruption or failure of supply.
If customer installations receive supply from two or more HK Electric transformers or 11kV supplies, customers are strongly recommended to install bus section switch(es) so that a backfeed source is available through the other transformer or 11kV supply in the event of loss of supply from one of the sources.
Discrimination of Protective Devices
Any improper settings of protective devices will result in unnecessary interruption of supply. In the event of a fault, protective devices should be discriminated, so that only the minimum necessary portion of the electrical installations would be isolated. Therefore, customers are recommended to regularly check and review the protection settings in their installations.
Inspection and Maintenance of Customer Installations
Regular inspection and preventive maintenance of customer installations should be carried out to improve the reliability of their electrical installations. Inspection and maintenance for installations that supply important services should be more frequent. More information can be obtained in our leaflet "Guide to the Maintenance of Communal Electrical Installations In Multi-Tenant Building".
Against Voltage Dips
Power Conditioning Devices
Can provide complete security of supply for important services but it is more expensive.
Can maintain the output voltage at a range within 2% of the normal value even when the mains supply voltage varies up to 20%. The device would also prevent voltage spikes and other transient voltages from entering into the circuits of the important services. However, voltage stabilizer does not compensate for a complete interruption of main electricity supply.
Can prevent voltage transients and voltage spikes from entering into the circuits of important services. Similar to voltage stabilizers, it cannot provide complete compensation in some cases.
More information can be obtained in our leaflet "How to Safeguard Power Supplies for Important Services".
Handling Large Motors of Air-Conditioning Systems
Handling High Pressure Discharge Lamps (HPDL)
HPDL is sensitive to voltage dips and cannot be re-ignited in a short time even when the supply has returned to the normal voltage. This may cause interruption to important events and safety problem. Here are several suggestions to relieve this problem:
Specifying Non-linear Loads
It is always more economical to eliminate problems in the design stage rather than to carry out remedial actions afterwards. Customers should specify to the equipment suppliers that the equipment of non-linear load must comply with their relevant international standards for the harmonics performance. Although it may involve higher initial cost, it is a worthwhile investment since the cost of any subsequent remedial work will be more expensive, not to mention the possible inconvenience arising from harmonic interferences caused to business.
Isolation of Harmonics Source
Customers should relocate essential and sensitive equipment to "clean" circuits and separate them from non-linear load as far as possible.
There are passive and active harmonic filters. Passive harmonic filter is capable of minimizing the several pre-determined orders of harmonics only on specified load conditions. Active harmonic filter is more sophisticated and can minimize more orders of harmonics under varying harmonic load conditions.
The materials in these web pages are for general guidance only. In case of doubt, you should seek advice from an expert or a professional engineer. We shall not be liable for any loss and damage suffered by any persons howsoever arising from or in reliance upon the whole or part of the content of these materials.