Power factor improvement device

Technology outline:
Electrical equipment such as induction motors, magnetic ballasts and transformers require two types of power to operate, namely active power and reactive power. Active power produces useful work while reactive power is used by inductive devices to generate magnetic fields. Total power is the vector sum of the two powers above. Power factor is the ratio of active power to total power. Good power factor indicates that the current is being effectively converted into useful work. A load with a power factor of 1.0 results in the most efficient loading of the supply. Poor power factor can be result from inductive loads or a distorted current waveform. When an electric load has a power factor of lower than 1, the apparent power delivered to the load is greater than the active power that the load consumes. The remedial methods for poor power factor are described as follows.

Power factor correction is a technique of counteracting the undesirable effects of electric loads that create a power factor that is less than 1. Power factor improvement for inductive load can be achieved by reducing the inductive component of the current. This can be done by the addition of capacitors in parallel with the connected inductive load circuits. The inductive effects of the load can be cancelled out by the current generated by the capacitors. The figures below show two connection examples of power factor improvement by capacitors.

Two arrangements of power factor improvement by capacitors image 1. The text above describes the image.
(a)
Two arrangements of power factor improvement by capacitors image 2. The text above describes the image.
(b)
Two arrangements of power factor improvement by capacitors

Poor power factor due to a distorted current waveform can be mitigated with a harmonic filter. The filter allows current only at the frequency of the voltage (e.g. 50 Hz) to pass through. The filter can eliminates harmonic current, which means that the non-linear loads are forced to become linear loads. After that, the power factor can be corrected using capacitors as required.

How it can save energy
Improving the power factor can enhance current-carrying capacity, increase the portion of useful electrical energy produced from the source, improve voltage to equipment, reduce power loss, and thus improve the efficiency of the power distribution system. Both power companies in Hong Kong require that the total power factor for any circuit should not be less than 0.85.

Applicable Standards

1. Code of Practice of Energy Efficiency of Electrical Installations,, Electrical and Mechanical Services Department, HKSAR
   
2. Supply Rules, March 2001, CLP Power Hong Kong Limited.
   
3. Supply Rules, August 2005, The Hongkong Electric Co., Ltd.

Further sources of information:

1. This web page has hyperlinks which may transfer you to third-party website.EMSD website, HK Energy Efficiency Registration Scheme for Buildings - Code of Practice for Energy Efficiency of Lift & Escalator Installations, 2005 edition
   
2. This web page has hyperlinks which may transfer you to third-party website.EMSD website, HK Energy Efficiency Registration Scheme for Buildings -Guidelines on Energy Efficiency of Electrical Installations

Harmonics filter

Technology outline:
Harmonics are currents produced by non-linear load such as the AC to DC power conversion circuits. They usually occur in multiples of the supply fundamental frequency. For example, on a 50 Hz supply, the 5th harmonic is 250 Hz, 7th harmonic is 350 Hz. Other sources of harmonics in buildings include computer equipment, VSDs, ACVV/VVVF lift drive systems and electronic ballasts etc. The presence of harmonics on the power distribution system will definitely reduce the efficiency of the system. Typical problems associated with harmonics include overheating distribution transformers, overloading neutral conductors, distorted supply voltage waveform and inefficient distribution of electrical power etc. The damages of harmonics can be eliminated by applying passive or active filters at appropriate location.

  1. Passive filters
    Passive filters generally consist of passive elements such as resistance, inductance and capacitance and connected as shunt elements in the power system. Many types of passive filters are available, the most common ones being single-tuned filters and high-pass filters.

     
  2. Active filters
    Power electronic equipment itself can perform much power processing functions, including harmonic cancellation. Harmonic cancellers using power electronics are called Active Power Filters. The principle of active power filter is based on the injection, at the connection point, of the image of harmonic current consumed by the load.

How it can save energy
The elimination of harmonics in power systems can reduce thermal stress due to harmonic currents and reduce phase to neutral voltage drop, thus enhance the power distribution efficiency. From the perspective of system operation, mitigating the harmonic problems in power systems can reduce the chance of abnormal failure of the systems such as false operation of protection equipment.

Applicable Standards

1. Code of Practice of Energy Efficiency of Electrical Installations, Electrical and Mechanical Services Department, HKSAR
   
2. Supply Rules, March 2001, CLP Power Hong Kong Limited
   
3. Supply Rules, August 2005, The Hongkong Electric Co., Ltd.
   
4. IEEE 519-1992: IEEE Recommended practices and requirements for harmonic control in electrical power systems.
   
5. 5. BS EN 61000-3-2: Electromagnetic compatibility (EMC) - Part 3-2: Limits - Limits for harmonic current emissions (equipment input current greater than or equal to 16 A per phase)

Further sources of information:

1. This web page has hyperlinks which may transfer you to third-party website.EMSD website, HK Energy Efficiency Registration Scheme for Buildings - Code of Practice for Energy Efficiency of Lift & Escalator Installations, 2005 edition
   
2. This web page has hyperlinks which may transfer you to third-party website.EMSD website, HK Energy Efficiency Registration Scheme for Buildings -Guidelines on Energy Efficiency of Electrical Installations

Electrochromic glazing

Technology outline:
Electrochromic glazing allows dynamic changes of a window's thermal, solar, and visible transmittances by applying small amounts of electric current to an electrochromic film affixed to the glass. The actions of changing the window's transmittance can be actuated through devices such as rheostats, thermostats, photocells etc.

Another switchable glazing technology, the liquid crystal suspended particle device (SPD), contains molecular particles suspended in a solution between plates of glass. In normal status, the particles move randomly and collide, blocking the direct passage of light. However, when energized, the particles align rapidly and the glazing becomes transparent. This type of switchable glazing can block up to about 90% of light.
Electrochromic glazing technology offers savings through cooling, lighting and peak load reduction.

How it can save energy
By changing the window's thermal, solar and visible transmittances, the cooling load due to the solar heat from the windows can be reduced. At the same time, the daylight utilization can be maximized by proper control of the transmittance of the windows.

Heat pump water heater (HPWH)

Technology outline:
Heat pumps have traditionally been used for space conditioning, but are now being used for water heating. HPWH are an efficient type of electric storage water heater that extracts heat from the environment to heat water.

In a heat pump water heater cycle, heat from the air heat up and boils the refrigerant to become vapour at a low temperature in an evaporator. The temperature and pressure of the refrigerant vapour is then increased by the compressor. The refrigerant vapour with high temperature and pressure leaves the compressor and flows to the heat exchanger in water tank to heat up the water inside. The refrigerant condensed into liquid after releasing heat in the heat exchanger. The liquid refrigerant returns to the evaporator at low pressure and temperature after passing throttling valve to complete the cycle. The figure below illustrates the structure of a typical heat pump water heater.

How it can save energy
In the operation of the heat pump water heater, energy is extracted from the air onto the evaporator. Energy is extracted from the "free source", and only a small amount of electricity is required to operate the compressor. Further, the HPWH removes heat from surrounding air to provide additional benefit of space cooling.

How much energy can be saved
Since the HPWH extracts heat from air, it delivers about twice the heat for the same electricity consumption as a conventional electric resistance water heater [1].

Heat pump water heater. The text above describes the image.
To view project example, please click here.

Reference:
[1] Washington State University Extension Energy Program

   
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