1. Project Overview
This supermarket was built many years, and harmonic problems were not considered in the power system configuration at that time. When designing the power distribution system, the diameter of the N-phase cable was smaller than that of the A/B/C three-phase cable.
The building is divided into three floors. The first floor is a large supermarket, and the second and third floors are clothing stores. In the first floor’s power distribution circuit, serious N-phase heating, excessive current problems occurred.
2. Distribution system diagram and main harmonic loads
There are 4 load outlet cabinets in the power distribution room, among which the power consumption of the supermarket on the first floor is led out from the 3# and 4# feeder cabinets.
In the power distribution structure, the power upstream of the 3# and 4# feeder cabinets is a dual power switch, and this switch is a 4P switch.
The typical harmonic source at this site is LED indicator light
The first symptom of the problem discovered at the site was the heating problem of the N-phase shell of the dual power switch.
3. Harmonic data testing and analysis
After selecting the on-site transformer, we conducted a test at the incoming cabinet location to gain an overall understanding of the on-site power quality issues.
4. Harmonic solution
On-site improvement needs include resolving the overheating of the N-phase cables and switches in the first-floor supermarket. As the main harmonic source equipment is located in the first-floor supermarket, targeted measures are chosen to address the harmonic issues in the 3# and 4# feeder cabinets to reduce the N-phase current at the dual power switch positions and resolve the overheating issue in this N-phase location.
Equipment Selection: Active Power Filter (APF)
Equipment model: CoEpo APF/200-0.4-D
Management method: local treatment
Installation capacity: 200A
Installation method: rack type
Installation location: power distribution room
5. Effect
After harmonic improvement by active power filter:
1. The system current waveform has been significantly improved, from the original distorted waveform to a normal sine wave waveform;
2. The N-phase current dropped from the 251.4A to 17.2A. The N-phase current dropped significantly, so N-phase cable heating problem is solved;
3. The total harmonic distortion rate of the system dropped from 47.2% to 4.6%, and the harmonic control effect was significant.
