Quality Alchemist (品質煉金術師): Power Quality Workshop

2011年10月19日星期三

Power Quality Workshop

Power Quality Workshop was organized by Hong Kong Science and Technology Parks (HKSTP) on 19 October 2011. HKSTP had coordinated with CLP to conduct this workshop to share the technical solutions for unexpected power quality issues.

The first speaker was Olivera and she introduced CLP reliability comparison with international urban area. CLP had a very good result from 2006 to 2008.

She briefed the supply voltage and frequency in CLP Power. For single phase, it was 220 volts. For three phase, there were (i) 220/380 volts (3 phase 4 wire); (ii) 11,000 volts; and (iii) 132,000 volts. The declared limits of supply under normal conditions were: (i) Voltage: 220/380 volts supply (+/- 6%) and (ii) Frequency: 50 Hz (+/- 2%). Then she introduced the power quality which related to Voltage Dip and Harmonic Distortion.

Voltage Dips defined "Decrease between 0.1 and 0.9 pu in rms voltage or current at the power frequency for duration from 0.5 cycle to 1 min." Its impact was on dropouts of sensitive customer equipment. Voltage Dips could not be totally avoided because of many external causes such as lighting, vegetation, animal, etc.

Harmonics Distortion was come from nonlinear loads. It caused poor energy efficiency, equipment failure and fire hazard. It could be mitigated by supplying different loads with different transformer configurations, installing with active filters and purchasing equipment with low harmonics emission.

However, the most cost-effective solution is planning ahead under project planning stage. Olivera explained CLP's PQ strategy which used a triangle among CLP, customers and equipment suppliers.

IEC 61000-4-34 & -11, SEMI F47 and ITIC Curves were introduced. The purple line is SEMI F47 in which (50%, 0.2s) means voltage drop 50% within 0.2s for equipment test condition.

The 3 level compatibility was used for planning ahead.

The second speaker named Nick. He shared some case studies to us.

He introduced that CLP power network covered Kowloon, New Territories and Lanlau Island. Red line was 400kV overhead line and blue line was 132kV overhead line.

The he mentioned different types of Overhead Lines (OHL) in Hong Kong.

One of case studies was Central Chiller under voltage dip issue. The local control was lockout and it needed manual reset to re-start the chiller.

The solution was installed a UPS to maintain the operation of local control and the chiller would be restart automatically.

He added that there were two UPS types. One was switched-type UPS and the other was true on-line UPS. A switched-type UPS was used which had a slow response under marginal conditions. However, true on-line UPS was used which could secure the power supply to computer equipment.

Finally, Nick shared some commonly PQ problems such as Air-conditioners, Lifts & Escalators, UPS, etc.