Hospital power quality optimization case application
Case background: A tertiary hospital suffered from serious harmonic pollution and insufficient reactive power in the power distribution system due to the upgrade of medical equipment. Non-linear loads such as MRI and CT machines generated a large number of 5th and 7th harmonics, resulting in a total harmonic distortion (THD) of up to 15%, far exceeding the 5% upper limit stipulated in the national standard (GB/T 14549-93). This caused false alarms of precision medical equipment, overheating and damage to UPS, neutral line overload, voltage fluctuations of ±10%, and affected the stability of ICU life support equipment. In addition, the power factor was only 0.78, and the power supply bureau fined more than $10,000 per month.
Treatment effect
| Iitem | Before renovation | After renovation | Improvement |
|---|---|---|---|
| Total harmonic distortion (THD) | 15% | 3.8% | ↓ 74.7% |
| Power factor (PF) | 0.78 | 0.98 | ↑ 25.6% |
| Average monthly electricity fine | 10000 | 0 | eliminated |
Solution and equipment selection
Based on the on-site conditions, Strong Power engineers used power quality analyzers to track and measure data and recommended customers to adopt the APF+SVG collaborative governance solution. It is also equipped with an active power filter (APF) and a static VAR generator (SVG) to dynamically filter out 2~50th harmonics and compensate for reactive power to stabilize voltage. The APF is connected in parallel to the distribution cabinets on the radiology and ICU floors for high-harmonic equipment such as MRI and DSA; the SVG is installed on the low-voltage side of the main transformer to compensate for reactive power and improve the power factor.
The role of SVG and APF:
Dynamic harmonic cancellation: By real-time detection of load harmonic current, APF generates reverse compensation current to reduce the 5th harmonic content of MRI equipment from 28A to 3A.
Neutral line overload protection: 3rd harmonic current is reduced by 90%, avoiding the risk of fire caused by cable overheating.
Millisecond response: At the moment of elevator motor starting, SVG outputs 200Kvar capacitive reactive power within 2ms, suppressing voltage fluctuations from 8% to 1.5%.
Energy saving and consumption reduction: After the power factor is improved, the copper loss of the transformer is reduced by 35%, saving about 150,000 yuan in electricity bills annually.
Conclusion
The collaborative management of APF and SVG not only solves the triple problems of harmonics, reactive power and energy efficiency, but also provides a standardized template for the safe operation of medical equipment and energy efficiency improvement.
