What factors are related to the voltage of the grid system, and what methods can be used to reduce i

Are you mistaken, 500 thousand volts voltage is ultra-high voltage, at present, only the Three Gorges and Gezhouba power plants after many times of pressure increase and then become direct current transmission voltage, can be sent thousands of kilometers away, I think you must be mistaken.

The level of overvoltage inside the system not only depends on the system parameters and their coordination, but also on the grid structure, system capacity, neutral grounding mode, circuit breaker performance, the number of bus outgoing circuits, and the operation mode and operation mode of the power grid. The main antihypertensive measures:

1. Change the reactive power for voltage regulation, such as generators, condensers, shunt capacitors, shunt reactors, static compensators, etc.;

2. Change the distribution of active power and reactive power for voltage regulation, such as changing transformer taps or voltage regulating transformers for voltage regulation;

3. Change the network parameters for voltage regulation, such as series capacitors, and change the number of transformers running in parallel for voltage regulation.

Learn the upstairs experience.

Because the power loss on the transmission line is proportional to the square of the current (Joule's law q=i 2rt), it is necessary to use a large power transformer to increase the voltage to reduce the current and reduce the heat generation of the conductor in order to effectively reduce the loss of power on the transmission line.

On the premise of delivering maximum power, the transmission current is reduced as much as possible! p=iu i=u/r

The current is smaller, and the line resistance loss is also low! The cost of wire rod is also lower! The difficulty of erection is also reduced! That's why high-voltage power transmission comes in!

In order to reduce wastage.

Power = Current * Resistance.

Current = Voltage Resistance.

In the process of power transmission, the resistance is constant, then the higher the voltage, the smaller the current, and the less power loss.

When transmitting electricity, the resistance and power are basically fixed, the higher the transmission voltage, the smaller the current, and the lower the loss of electric energy, in short, it is to reduce the loss of power.

The measures to suppress the overvoltage of the power system are: (1) Improve the synchronicity of the switching action: Since many resonant overvoltages are caused by non-full-phase operating conditions, improving the synchronicity of the switching action and preventing non-full-phase operation can effectively prevent the occurrence of resonant overvoltage.

2) Install small reactance at the neutral point of the parallel high-voltage reactor: this measure can be used to block the power frequency voltage transmission and series resonance during non-full-phase operation.

3) Destroy the conditions for the generator to generate self-excitation and prevent the parameter resonance overvoltage.

4) Strictly implement the scheduling procedures: in the operation mode and the operation of the reverse gate.

In the process, the circuit breaker break capacitor is prevented from forming a series resonant loop with the no-load bus and bus PT to prevent the flutter from damaging the equipment due to resonant overvoltage.

5) Avoid operating overvoltage: when switching to the empty bus, strengthen the bus voltage monitoring, when ferromagnetic resonance occurs, the circuit breaker with broken capacitor should be closed immediately, the loop capacitance should be removed, and the resonance should be terminated to prevent the development of hidden dangers and accidents.

6) Neutral grounding point: increase the busbar to ground capacitance or reduce the voltage transformer in the system.

The number of grounding stations at the neutral point increases the ground inductive reactance of the busbar, thereby reducing the natural frequency of the natural vibration.

Eggplant skin avoids the ferromagnetic resonance overvoltage of the bus due to the east of the system.

7) Relay protection.

In view of the occurrence of specific accidents, such as single-phase grounding in the bus of the substation, the bus differential protection action, after the bus tie switch trips, if the main transformer switch acts before the line switch, it will not cause resonance.

1. Voltage regulation by changing the voltage at the generator end. Among the various voltage regulation measures, the most direct and economical means is the use of generator voltage regulation, because this is a voltage regulation method that does not require additional investment, so it should be prioritized.

The voltage of the generator adjustment terminal is achieved by adjusting the excitation to change the reactive power output, and the modern generator can be kept running at the rated power in the range of 95% 105% of the rated voltage, that is, the voltage can be adjusted in the range of 10% when the generator maintains the same output.

2. Adjust the voltage by adjusting the transformer ratio. The high-voltage winding of the double-winding transformer and the high-voltage winding of the three-winding transformer generally have several taps to choose from, and the transformer transformer ratio changes by selecting different taps, so as to achieve the purpose of voltage regulation.

3. Voltage regulation through compensation equipment. When the reactive power in the system is insufficient, it is necessary to consider the use of various compensation equipment for voltage regulation. These compensation devices can be divided into two categories, namely series compensation and parallel compensation.

4. Increase the radius of the wire appropriately. Some of the old city networks are due to the small radius of the conductor and the large resistance, which leads to the voltage loss of the power grid and the destruction of the ruler. Therefore, increasing the radius of the conductor is an important part of the transformation of the urban network.

A certain margin needs to be considered for the conductor of the newly erected line, especially for the medium and low voltage lines, which are prone to overload and overload because of their small bearing capacity.

5. Combined pressure regulation. As the name suggests, it is a combination of several pressure regulation measures. Since different pressure regulation measures have their own advantages and disadvantages, various pressure regulation measures should be comprehensively adopted to learn from each other's strengths and weaknesses in order to achieve the best pressure regulation effect.

The main measures are as follows:

1. Increase or decrease reactive power for voltage regulation, such as generators, condensers, shunt capacitors, and shunt reactors;

2. Change the distribution of active power and reactive power for voltage regulation, such as voltage regulating transformer and changing transformer tap voltage regulation;

3. Change the network parameters for voltage regulation, such as series capacitors, switching and stopping transformers running in parallel, and switching and stopping no-load or light-load high-voltage lines for voltage regulation.

Under special circumstances, the voltage is sometimes adjusted by adjusting the electrical load or curtailing.

The effects of reduced or increased grid voltages.

1. For power users.

All kinds of electrical equipment are designed and manufactured according to the rated voltage, and these equipment can achieve the best results when operating at the rated voltage, and the voltage deviates too much from the rated value, which will have a negative impact on the user.

Lighting lamps, for example, are voltage-dependent in terms of luminous efficiency, luminous flux and lifetime. When the voltage increases, the luminous flux of incandescent and fluorescent lamps will increase, but the service life will be shortened; On the contrary, when the voltage decreases, the luminous flux decreases, and the lamp does not emit enough light, which affects people's eyesight and work efficiency. The electromagnetic torque of the asynchronous motor is proportional to the square of its terminal voltage, when the voltage is reduced by 10%, the motor speed decreases, and the torque is reduced by about 19%.

If the mechanical load dragged by the motor remains unchanged, when the voltage decreases, the speed of the motor decreases, the slip increases, the stator current also increases, the heat increases, the winding temperature increases, the insulation aging is accelerated, and the service life is shortened; When the terminal voltage is too low, the motor may stall or even fail to start under heavy load. The output of electric heating equipment such as electric furnaces is roughly proportional to the square of the voltage, and the decrease in voltage will prolong the smelting time of the electric furnace and reduce productivity.

2. For the power grid.

The voltage drop will increase the power loss of the power grid. When the voltage is too low, it may also endanger the stability of the power grid operation and cause a voltage collapse accident. And the voltage is too high to affect the insulation of the equipment.

Therefore, ensuring that the voltage at the user is close to the rated value is one of the basic tasks of power grid operation adjustment.

Power system overvoltage is mainly divided into the following types: atmospheric overvoltage, power frequency overvoltage, operating overvoltage, and resonant overvoltage.

The causes and characteristics are:

Atmospheric overvoltage: caused by direct lightning, characterized by short duration and strong impact, which is directly related to the intensity of lightning activity and has nothing to do with the voltage level of the equipment. Therefore, the insulation level of systems below 220kV is often determined by the protection against atmospheric overvoltage.

Power frequency overvoltage: caused by the capacitive effect of long lines and the sudden change of the operation mode of the power grid, characterized by a long duration, the overvoltage multiple is not high, and the danger of equipment insulation is generally not great, but it plays an important role in determining the insulation level of ultra-high voltage and long-distance transmission.

Operating overvoltage: caused by the operation of the switch in the power grid, it is characterized by randomness, but the overvoltage multiple is high in the most unfavorable case. Therefore, the insulation level of ultra-high voltage systems of 30 kV and above is often determined by the protection against operating overvoltages.

Resonant overvoltage: caused by the resonance circuit composed of the system capacitance and inductance loop, characterized by high overvoltage multiplier and long duration.