For greater energy efficiency, Hong Kong’s government administration relies on dynamic power factor correction (PFC) from EPCOS.
The typical electrical loads in office buildings are elevators, electronic office equipment and lighting. Because of the nonlinear character of these loads they create a significant amount of reactive power, which exerts extreme stress on the power supply. In subtropical regions such as Hong Kong this situation is amplified by air-conditioning systems needed to cool large office complexes. Because of their constant high power requirements their operation, however, can cause voltage sags and even blackouts.
In order to improve the quality of power, the Murray Building – an administration building for the Hong Kong government – implemented PFC systems right from the start. The conventional PFC technology, however, soon reached its limits. Therefore, the facilities management team at the Murray Building recently decided to modernize its power supply installations with dynamic PFC.
Need for dynamic PFC
While conventional PFC systems are standard in deployments with steady load conditions, they are not well-suited for applications with rapidly fluctuating loads which require real-time reaction. Such electrical loads do not operate continuously, but rather in irregular intervals. These include industrial deployments such as wind turbines, cranes, welding and pressing equipment and elevators and air-conditioning systems – as in the case of Murray Building. In state-of-the-art dynamic PFC systems, standard capacitor contactors are replaced with electronic thyristor switches that are able to switch within a few milliseconds. The electronic switches operate silently and are non-wearing, and they conserve the capacitors.
| | TABLE 1: MEASUREMENTS OF EXISTING PFC SOLUTION WITHOUT DYNAMIC PFC |
| Existing PFC solution | | Transformer station | TS 1 | TS 2 | | THD-V (total harmonic voltage distortion) | 2.2 % | 2.2 % | | THD-A (total harmonic current distortion) | 12 % | 14 % | | Actual power factor (average value during measurement period) | 0.85 | 0.83 | | Actual apparent current (average value during measurement period) | 1350 A | 1400 A |
The measured reactive current of PFC stages was 34 A for stages 1 and 2 (25 kvar each) and 68 A for stages 3, 4, 5 and 6 (50 kvar each). The rated voltage was 380 V. The PFC controller settings were: | 1 s and 640 ms for TS 1 and TS 2, respectively | | 0.98 | | 0.005 |
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To stabilize the power supply at the Murray Building, Babel International, a Hong Kong-based power electronics specialist and one of EPCOS’ partners for Power Quality Solutions, was asked to conduct measurements of the existing PFC system. The existing system consisted of two automatic PFC systems of 210 kvar each and one conventional fixed PFC system with reactors. Attached to each transformer was a large air-conditioning system with a conventional induction motor that created a linear load with no significant harmonics. The building’s elevators were also operated with conventional induction motors. In addition, the power system featured a large number of single-phase loads, with switch-mode power supplies and other electronics. These extras created nonlinear loads by making harmonic contributions of the third and fifth order.
In order to analyze the building’s power supply, a series of measurements and harmonic analysis were carried out during main office hours (Table 1).
| | FIGURE: IMPROVEMENT OF POWER FACTOR WITH DYNAMIC PFC |
 | | Thanks to dynamic PFC, the power factor (cos φ) is in the range of > 0.9 |
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Tailor-made design
Together with the facilities management team at the Murray Building, the targets were defined for two dynamic PFC systems as an upgrade to the installed conventional PFC systems. The main objectives were to stabilize the power supply and significantly improve the power factor, thus reducing the consumption of reactive power. Moreover, harmonic voltage and current distortion were to be reduced.
On this basis, a tailor-made PFC solution was designed and installed at the Murray Building. It consisted of two PFC systems of 250 kvar each with a detuning factor of 7 percent at 189 Hz. The systems feature key PFC components from EPCOS:
- PhaseCap PFC capacitors
- Thyristor modules
- BR6000 power factor controllers
- Harmonic filter reactors
Significant improvements in power quality
The initial targets for the Murray Building project have been fully achieved for both installed transformers. A harmonic analysis of the new dynamic PFC system showed that the power factor was improved from 0.85 to 0.95 at transformer station 1 and from 0.83 to 0.92 at transformer station 2.
TABLE 2: MEASUREMENT AFTER DEPLOYMENT OF DYNAMIC PFC
| Measured values | Improvement |
| Transformer station | TS 1 | TS 2 | TS 1 | TS 2 |
| THD-V (total harmonic voltage distortion) | 1.5 % | 1.6 % | 32 % | 28 % |
| THD-A (total harmonic current distortion) | 7 % | 10 % | 42 % | 29 % |
| Actual power factor (average value during measurement period) | 0.95 | 0.92 | 11 % | 10.8 % |
| Actual apparent current (average value during measurement period) | 1100 A | 1150 A | 23 % | 22 % |
Outlook
The two new dynamic PFC systems were designed modularly. This allows the systems to be expanded easily to up to 250 kvar. This can become necessary, for example, when further electrical loads are installed or the air-conditioning systems require more power.
| | KEY COMPONENTS FOR DYNAMIC PFC |
 | | PhaseCap® The PhaseCap series of PFC capacitors deliver constant capacitance over more than 100,000 hours of reliable operation. The series covers capacitors with a reactive power up to 60 kvar for rated voltages up to 525 V AC. |  | | Thyristor modules EPCOS offers thyristor modules for rated power from 10 to 200 kvar for rated voltages up to 690 V AC. The switching times of the modules are in the region of only 5 ms. The thyristor switches enable the PFC capacitors to be switched without wear, ensuring a longer life. |  | | PFC controllers The BR6000 series of PFC controllers offers the automatic control of PFC systems. The BR6000 controllers display the most important parameters such as reactive power, switching status, switching operations, operating time of PFC capacitors etc. |
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Author: Dr. Peter Goldstrass, Product Marketing Manager PFC
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