Because the supermarket building was built a long time ago, harmonic issues were not taken into consideration in the power system configuration at that time.When designing the distribution system, the diameter of the N-phase cable was smaller than that of the A/B/C three-phase cable.
At present, there are serious N-phase heating and excessive current problems in the distribution circuit on the first floor of the building.
Distribution system diagram and main harmonic loads
There are 4 load outgoing cabinets in the on-site power distribution room, and the power consumption of the supermarket on the first floor is drawn from the 3# and 4# feeder cabinets.
In the on-site power distribution structure, the power supply upstream of the 3# and 4# feeder cabinets is a dual power switch, which is a 4P switch.
The typical harmonic source equipment at this site is LED indicator lights. The initial manifestation of the problem was that the N-phase shell of the dual power switch was hot.
Harmonic Data Testing and Analysis
The incoming line cabinet behind the transformer was selected for testing to gain an overall understanding of the power quality issues on site.
Harmonic Compensation Solution
Because it is necessary to solve the heating problem of N-phase cables and switches in the supermarket on the first floor, and the main harmonic source equipment is in the supermarket on the first floor, a local control solution is selected to specifically control the harmonics of the 3# and 4# feeder cabinets and reduce the N-phase current at the dual power switch position to solve the heating problem of N-phase here.
Solution: Choose our company’s active harmonic filter (AHF) equipment and install it in the distribution room for local treatment.
Compensation Effect
After harmonic compensation by active harmonic filter equipment:
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 significantly from the original 251.4A to 17.2A, so the N-phase cable heating problem was solved;
3. The total harmonic distortion rate of the system dropped from 47.2% to 4.6%, and the harmonic control effect was significant.
