What are the effects of the tower lightning cable system on the DC current distribution?

a.The tower-overhead line system is also an important distribution path for DC current into the ground, which will increase the DC current distribution on the transformer windings.

b.The substation near the DC pole is more affected by the overhead line system of the tower, and the DC current of the transformer winding of some substations near the DC pole increases by more than 10% under the condition that the overhead line grounding resistance RL = 1 km and the tower grounding resistance rt = 10. The smaller the RL and RT, the higher the DC current content in the tower overhead line system, and the higher the DC current on the transformer winding.

Conversely, the higher the RL and RT, the smaller the transformer winding DC current is affected by the tower-overhead line system.

c.Since the ground wire is connected to the substation ground network, the ground current and the ground current of the tower are not equal. The current entering the substation ground grid from the lightning line changes the potential of the substation nodes, thereby increasing the DC current distributed within the AC grid.

d.In the same line, the tower grounding current presents non-uniformity, and the tower with the largest current generally appears near the side substation where the current is larger in the direction of entering and exiting the ground, and often the tower current closest to the substation is not the largest, which is caused by the induced potential of the tower near the grounding current distortion of the substation.

e.Generally, the direction of the ground current of the tower near the DC pole is the same as that of the DC pole, and the direction of the tower far away from the DC pole is the opposite.

Motor. diàn jī]

Electric machinery (commonly known as "motor") refers to an electromagnetic device that converts or transmits electrical energy according to the law of electromagnetic induction. In the circuit it is indicated by the letter M (D in the old standard).

Its main function is to generate driving torque, as a power source for electrical appliances or various machinery. Generators are denoted by the letter G in the circuit. Its main role is to utilize electrical energy to convert into mechanical energy.

Answer]: a, b, c

According to the "Electric Power Engineering High-voltage Transmission Line Design Manual" (Second Edition) p "Second, reduce the grounding resistance of the tower" part of the content: to reduce the grounding resistance of the tower, the general use of additional grounding devices (belts, pipes), the use of external grounding devices or continuous elongation of the grounding wire (in the moment of crossing the canyon across the valley chain, its coupling Chana fierce effect, etc.). The continuous elongation grounding wire is to bury 1 2 grounding wires in the ground along the line, and can be connected with the tower grounding device of the next base tower, and it is one of the effective measures to reduce the grounding resistance of the tower.

In addition, chemical drag reducing agents can also be used for special sections to reduce the grounding power defeat and bridge resistance of the tower.

Answer]: B, D

The lightning resistance level and the lightning trip rate are important indicators for the power grid to evaluate the lightning protection performance of the transmission line. Lightning trip rate: refers to the number of trips caused by lightning strikes per year for 100km of the line under the condition of 40 days of thunderstorms, and the unit of defense is "times (100km·40 thunderstorm days)" lightning resistance level:

It refers to the maximum lightning current amplitude of the insulation that does not cause flashover or the minimum lightning buried slip amplitude that can cause the insulation flashover when the lightning strikes the line, and the single liquid transport position is ka

Shunt coefficient. Tower equivalent circuit inductance.

Tower impact ground resistance.

Coupling coefficient between conductor and ground wires.

and the impact flashover voltage of the insulator string u50%.

The function of the current regulator is to limit the maximum current (excessive starting current, overload current) and make the mechanical characteristics of the sag very steep when overloaded (when the maximum allowable current is reached); When starting, the current can be kept at the maximum allowable value to achieve fast start of large constant current; It can effectively suppress the adverse effects of grid voltage fluctuations on current. The role of the speed regulator:

It can effectively eliminate the speed deviation and keep the speed constant; When there is a large deviation in the rotational speed, it can quickly reach the maximum output voltage and deliver it to the current regulator, so that the current rises rapidly and realizes a fast response.

1) In addition to the direct grounding transformer and its connected lines flowing from one substation to another through the neutral direct grounding transformer, the overhead ground wire connecting the transmission lines of the two substations will also be connected to the grounding network of the two substations.

2) A part of the current will flow through the overhead ground wire, which will change the potential difference between the substations, thus affecting the DC current flowing through the transformer windings.

3) The influence of the tower-lightning line system should be considered when analyzing the DC current distribution of the AC power grid. Since the overhead ground wire is also connected to the tower and its grounding body, considering the tower lightning protection wire system will make the existing DC distribution calculation extremely complicated: the lightning protection wire model is similar to the line, but it is connected to the substation ground grid and the tower; The tower model is similar to the substation model, the tower body resistance (the aboveground part of the tower) branch is connected to the lightning cable and the tower grounding body, and the underground part of the tower also needs to be Zevenin equivalent.

If the proportion of line-ground current is small, the effect of line-ground can be ignored when analyzing the DC current between two substations, simplifying the calculation. If the overhead ground wire has a great influence on the DC distribution of AC power grid, its calculation model, DC distribution characteristics, scope and degree of influence need to be studied in depth.

The induced electromotive force generated by the rotation of the rotor of a DC motor in a magnetic field is the main force to resist the applied voltage, and since it is DC, the inductance is only useful at the moment of start-up, and the current does not change after start-up, and the inductance is useless. In addition, the coil resistance of DC motors is extremely small, almost negligible.

Ground resistance transformation - reduce the grounding resistance, improve the lightning resistance level of the tower, and reduce the counterattack accident.

Strengthen the insulation level - install or replace new insulators, and improve the lightning resistance level of the tower by improving the flashover voltage of the insulator string by 50%.

Install negative angle protection needle - reduce the protection angle and improve the ability of the tower to prevent lightning winding.