Current status of low voltage and the reasons for its formation

Current situation and reasons of low voltage

The current low voltage is mainly troubled by rural users who use public transformers. Small-scale industrial users who do not have dedicated transformers will also suffer from transformer capacity.

The amount of electricity or the long transmission line has low voltage problems.

Rural power grids are characterized by scattered users, large power supply radius (the national grid standard is 500 meters), few distribution points, small public transformer capacity, long lines and long lines.

Insufficient diameter, large line loss. These are basically shapes

The main reason for the low end voltage of rural lines.

In recent years, with the rapid economic development, household equipment and farmland irrigation equipment have surged, the load has grown rapidly, and the contradiction between power supply and electricity consumption has increased day by day. Although the country

The domestic standard allows low voltage (220V/380V) voltage allowable deviation value of +7%~-10%, but some rural areas still cannot meet this requirement during peak electricity consumption.

At the same time, the voltage deviation (too high or too low) causes frequent occurrence of line wire burnout.

The hazards of low voltage operation

Hazards of low voltage operation

Burn out the motor. When the voltage drops more than 10%, the current of the motor will be too large, and the temperature of the coil will be too high. In severe cases, the motor will not be able to drag the machinery (such as fans,

Water pump, etc.) stop running or fail to start, or even burn out the motor.

The lights dimmed. When the voltage is reduced by 5%, the illuminance of ordinary electric lamps is reduced by 18%; when the voltage is reduced by 10%, the illuminance is reduced by about 35%, and the service life is halved.

Increase the line loss. When a certain amount of power is delivered, the voltage decreases, the current increases, and the line loss increases accordingly. Take the power system with a maximum load of 1 million kw as an example,

The annual line loss electricity increases by about 50 million kW.h.

The capacity of power transmission and transformation equipment is reduced. For example, when the voltage is reduced to 80% of the rated value, the active load transmitted by the transformer and the line is only 64% of the rated capacity.

When the voltage is increased to the rated value and basically no reactive power is sent, the full rated capacity of the power transmission and transformation equipment can be used to send active loads.

The generator's active power output is reduced. When the grid voltage is too low and the generator voltage is forced to decrease by 10% to 16%, the active and reactive power output of the generator will be reduced by about 19%

-28%. If the generator has a large reactive load, the active load capacity will be further reduced.

Caused voltage collapse and large-scale blackout accidents. Electricity may occur when the voltage of the grid hub substation and the power receiving area drops to about 70% of the rated voltage.

Voltage collapse accident, that is, a slight increase in the load of the transmission line, and a drop in the voltage in the receiving area, which further causes the line load to increase. This forms a vicious circle, resulting in

Large-scale blackouts.