Demands:
Realize low voltage or even zero voltage crossing, meet the requirements of continuous production in various industrial fields, avoid the loss caused by equipment shutdown due to grid fluctuations.
NANCAL Electric Solution：
NC HVVF series VFD main control platform hardware adopts three core control system platform based on DSP+FPGA+ARM. The control system and main circuit are specially designed for the situation of domestic power grid. The built-in standard low voltage riding through (LVRT) function module has strong ability to resist voltage fluctuation of power grid.
According to statistics, among the events caused by voltage problems experienced by users using single loop power supply every year, voltage disturbances with deep voltage sag amplitude and duration less than 1s account for 95%.
Typical wave forms are shown below:
Voltage Waveform during Electric Shock
MV drive with LVRT function can deal with voltage sag problem to the greatest extent, as far as possible to protect the equipment from power interference, ensure continuous production, and reduce customer loss.
Application:
Load: Compressor
Nancal Products: 2 sets of 10kV 7100kW air cooling VFD
Model: NC HVVF 10/6.6-7100
Input voltage: 10kV
Output voltage: 6.6kV
Cooling Method: Air cooling
Motor: Asynchronous motor
Rated voltage: 6.6kV
Rated current: 702.5A
Rated speed: 1500rpm
Rated frequency: 50.4Hz
VFD on Site
The LVRT function of the VFD is tested by controlling the short-time power loss of the 35kV busbar switch in the substation under rated working conditions.
The VFD drives the compressor to run, with the output voltage of 6.6kV and the output current of 625A. It controls the substation to open the busbar switch of 35kV, and the power grid will recover after losing power for about 4.6s. The VFD realizes the low-voltage riding through control by means of kinetic energy buffer, and the kinetic energy of the motor and compressor is converted into electric energy and fed back to the energy storage capacitor of the DC link of the power unit. Ensure that the DC bus voltage is normal and the VFD can continue to work. When the grid voltage recovers, the frequency converter returns to normal and the speed returns to the given value. The operation data and waveform are as follows:
LVRT Test Waveform
When the rated speed and the maximum driving power are reached on site, the MV drive can run continuously without stopping after several LVRT tests with different power loss times, and the speed can be quickly increased to the original operating speed after the power supply is restored. Under the condition of full load operation at 1486rpm, the power is restored after 1.6s, and the minimum speed in the crossing process is 1266rpm. It will be restored after power failure for 4.6s, and the minimum speed of the crossing process is 935rpm.
NC HVVF series VFD has mature LVRT function, can realize low voltage or even zero voltage crossing, meet the requirements of continuous production in various industrial fields, and avoid the loss caused by equipment shutdown due to power grid fluctuations.
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