What is low voltage ride through?

Question 1: What is low voltage ride through? Can you say it briefly? The so-called low voltage crossing the ocean refers to the ability of wind turbines.

With the increase of the installed capacity of wind turbines, when the power grid fails and the voltage drops, wind turbines that do not have low voltage ride-through capability or have insufficient low voltage ride-through capability will quit the power grid for self-protection. If a large number of wind turbines leave the grid, the grid voltage will continue to drop and the power supply grid will be paralyzed.

Wind turbines with low voltage ride-through capability are different. When the voltage drops, they will increase the transmission of reactive power to the grid and try their best to maintain the grid voltage. When the grid voltage is restored, the normal active output is restored.

Question 2: What is a low-pressure ride-through system? Low voltage ride-through (LVRT) means that when the grid voltage of wind turbines drops, wind turbines can keep connected to the grid, and even provide some reactive power to the grid to support the grid recovery until the grid returns to normal, thus "crossing" this low voltage time (region).

The main equipment of the low-voltage crossing system is installed indoors, and the core components include reactor combination, circuit breaker combination, control system and measurement system. The reactor is designed and produced by Siemens or Schneider, an internationally renowned brand. The circuit breaker combination adopts the products of internationally renowned brands Siemens, Schneider or ABB.

1) reactor: The current-limiting reactor is considered as a whole according to the capacity of the connected power grid and the wind turbine to be tested, and can adapt to various power grid conditions and wind turbines. The current limiting reactor adopts adjustable resistance design to ensure that the impact on the power grid during testing is within the allowable range. The resistance of short-circuit reactor can be adjusted, and the short-circuit reactor and current-limiting reactor can be adjusted in coordination to realize different degrees of voltage drop.

2) Connecting copper bar: The connecting copper bar is divided into conductive copper bar and grounding copper bar, and the conductive copper bar is used to connect reactance to realize various combinations.

3) Lightning arrester: the lightning arrester is connected between each phase of the reactor and between each phase and the ground; The lightning arrester is installed between the joints of the reactor, which plays a good role in protecting the reactor.

4) Power supply system, HVAC and lighting equipment.

5) Reactor temperature monitor: During the test, excessive short-circuit current may flow in the reactor, causing the reactor to heat up. Install a reactor temperature monitor as required to monitor the reactor temperature at any time. By setting the reactor temperature protection limit, the reactor and the whole test system can be cut off from the power grid when the temperature is too high.

6) Emergency alarm system: When the temperature of the reactor is too high, the emergency alarm system will start and enter the corresponding control program.

7) Circuit breaker combination: The circuit breaker combination consists of SF6 gas-insulated combined electrical appliance and SF6 gas-insulated indoor circuit breaker. SF6 gas insulated switchgear is small in size, all live parts are sealed with gas, and there is no live body. Each circuit breaker is equipped with a three-position switch, which is safe and reliable, simple to operate and convenient to install. The combination of switch cabinet and indoor circuit breaker can jointly realize the functions required by the test equipment.

8) Local control system: The local control system is used to control the opening and closing of all circuit breakers, disconnectors and grounding circuit breakers, and automatically complete all test items.

9) Measurement and data processing system: the system starts to measure and record all test information in the test process according to the trigger instruction, and completes relevant calculations; The system can display and export the measurement results in real time, and export them to open format data for analysis and calculation. The test system also includes a remote monitoring system, which remotely controls all test items and processes test data and results during the test.

Beijing Qunling Energy provides you with technical specifications for low-voltage ride-through system.

Question 3: What is low voltage ride through? When the grid fault or disturbance causes the grid voltage of the wind farm to drop, the wind turbines can be continuously connected to the grid within the voltage drop range.

Question 4: What is a low-voltage ride-through device? When the grid fault or disturbance causes the grid voltage of the wind farm to drop, the wind turbines can be continuously connected to the grid within the voltage drop range.

Question 5: The introduction of Low Voltage Through Capability refers to the ability of the wind turbine to keep running without leaving the power grid when the terminal voltage of the machine drops to a certain value, and even provide part of reactive power for the system to help the system restore voltage. Wind turbines with low voltage ride-through capability can avoid protection action time and resume normal operation after fault elimination. This can greatly reduce the frequency of repeated grid connection of fans under fault conditions and reduce the impact on the power grid.

Question 6: Information about low voltage ride-through. According to the new rules of power grid, when the grid voltage drops, the wind turbine can operate without leaving the grid like traditional thermal power and hydropower generators, and provide certain reactive power to the grid to support the grid recovery until the grid voltage is restored, so as to "ride through" this low-voltage period (region), which is called low-voltage ride-through (LVRT). Technical principle of low voltage ride-through of doubly-fed wind turbine: When the external system has a short circuit fault, the stator current of doubly-fed motor increases, the stator voltage and magnetic flux suddenly drop, and a large current is induced on the rotor side. The rotor-side converter is directly connected in series with the rotor circuit. In order to protect the converter from loss, the doubly-fed wind turbine is equipped with a rotor short-circuit device on the rotor side. When the rotor-side current exceeds the set value for a certain time, the rotor short-circuit breaker operates, the rotor-side converter stops running, and the grid-side converter and the stator side are still connected to the grid. Generally, each phase of the rotor is connected in series with a turn-off thyristor and a resistor and in parallel with the rotor-side converter. The resistance value of the resistor should not be too large to prevent the rotor-side converter from overvoltage, but it should not be too small, otherwise it is difficult to limit the current, and the specific value should be determined according to the specific situation. After the fault of the external system is cleared, the thyristor of the rotor short-circuit breaker is turned off and the rotor-side converter is put into operation again. When the stator voltage and flux decrease, the output power and electromagnetic torque of doubly-fed machine decrease. If the mechanical power of the fan is constant at this time, the reduction of electromagnetic torque will inevitably lead to the acceleration of the rotor. Therefore, when the low voltage caused by the external system failure persists, the output power and electromagnetic torque of the wind turbine will decrease, so it is necessary to adjust the pitch angle of the fan to reduce the wind energy and mechanical torque captured by the fan, so as to realize the LVRT function of the wind turbine when the external system fails. Denmark, Germany, the United States and other countries with leading wind power generation technology have successively given low voltage ride-through standards for wind power generation systems. The picture shows the American power grid LVRT standard. As can be seen from the curve in the figure, the area above the curve is the part where the wind farm needs to keep connected with the power system, and only the area below the curve is allowed to leave the power grid. When the grid voltage drops to 15% of the rated voltage, the wind farm must have the low voltage ride-through ability to maintain grid-connected operation for 625ms; When the grid-connected voltage of the wind farm can be restored to 90% of the rated voltage within 3 seconds after the drop fault occurs, the wind farm must keep the grid-connected operation. Only when the power system has the fault shown in the area below the curve is it allowed to leave the power grid. In addition, dynamic voltage sag compensator should be embedded in the control system to compensate the voltage immediately when sag occurs to prevent the control system from jumping first. ABB claims to use active CROWBAR to realize low voltage ride-through function.

Question 7: What is the low voltage ride-through experiment? First of all, we should understand what low-voltage ride-through is: for provincial (regional) power grids with installed wind power capacity accounting for more than 5% of the total capacity of other power sources, wind farms operating in the power grid area should have low-voltage ride-through capability. The energy storage device shall meet the following requirements:

? When the grid voltage drops to 20% of the rated voltage, the energy storage device in the wind farm has the ability to keep running continuously for 625 ms.

? When the grid voltage of the wind farm can be restored to 90% of the rated voltage within 2s after the drop, the energy storage device in the wind farm can operate continuously.

You can refer to some instructions from some manufacturers of low-voltage ride-through test and detection equipment. In grid-connected mode, it can be verified by simulating instantaneous voltage drop through step-down device.

Question 8: What does zero voltage ride through mean? At present, the country has introduced new norms; With regard to the requirements of grid-connected inverter zero-voltage ride-through technology, this requirement requires not only grid-connected photovoltaic, but also grid-connected wind power zero-voltage ride-through technology.

"Low voltage ride-through and zero voltage ride-through are the core technologies of photovoltaic and wind power equipment, and they are the key indicators to determine whether they can be safely connected to the grid." GL Lloyd's Register of Classification in Germany is specifically aimed at the technical requirements of this zero-voltage ride-through test, but at present, there are less than three domestic enterprises that have passed the zero-voltage test. "Shenzhen Jushui Royal began to study this technology in 2008, and Xie has rich experience in this field.

Question 9: Is there a low voltage ride-through in schneider inverter? Explanation of low voltage of frequency converter.

The frequency converter is actually used in motor dragging occasions, which can accurately control the speed of the motor. Simultaneous control

As we all know, the motor will produce the starting current when it is started at power frequency.

seven

reach

eight

Multiplied by the rated current of the motor. This current value will greatly increase the electrical stress of the motor winding and produce

Heat, thus shortening the life of the motor. Inverter can also generate electricity when low voltage passes through.

When the current is low, the following formula shows that the inverter crosses at low voltage.

Generated current value:

P/U=I

P

Motor power,

U

Inverter input voltage,

I

Inverter output current

From below

three

In this case, calculate the current values of different input voltage values:

1

, the inverter input voltage drops to

90%

time

22kW/342V=64.3A

2

, the inverter input voltage drops to

80%

time

22kW/304V=72.4A

three

, the inverter input voltage drops to

60%

time

22kW/228V=96.5A

four

, the inverter input voltage drops to

40%

time

22kW/ 152V= 145A

five

, the inverter input voltage drops to

20%

time

22kW/76V=290A

According to the above formula, the output current of the inverter will increase with the decrease of the input voltage.

In addition And normal

22kW

The output current of the frequency converter is

57A

. General inverter undervoltage protection

The value is set to

85%

There are some frequency converters such as schneider inverter.

65%

Left and right

Under-voltage protection value, across the low voltage will lead to internal inverter.

When the current is large, the circuit breaker at the front end of the inverter will trip with the increase of current. So in

In the case of low voltage ride-through, the normal operation of the inverter will not be affected.

Product requirements are very strict.

The output waveform of the frequency converter is

Pulse width modulation (short for pulse-width modulating)

Waveform, different from normal sine wave.

Pulse width modulation (short for pulse-width modulating)

be

English

pulse

width

Modulation (

Pulse width lamp

)

Abbreviation, changing pulse according to certain rules.

Adjust the pulse width of the pulse sequence to adjust the output and waveform.

Pulse Amplitude Modulation (short for pulse amplitude modulation)

It's English

pulse

amplitude

Modulation (

pulseamplitude modulation

)

Abbreviations change according to certain rules.

A modulation method in which the pulse amplitude of a pulse sequence is used to adjust the output amplitude and waveform.

The main circuit of frequency converter can be roughly divided into two categories.

：

Voltage type is DC conversion of voltage source.

For AC inverter, the filtering of DC loop is capacitance.

;

The current mode is to change the DC of the current source.

Replace it with an AC frequency converter, and its DC loop filters the stone inductance.

The frequency of the inverter drops.

(

low speed

)

time

,

If the same power is output

,

The current increases.

,

But in

Under the condition of constant torque

,

The current is almost constant.

The frequency converter is used for operation. As the motor starts up at an accelerated speed, the frequency and voltage increase accordingly.

Current is limited to

150%

Below rated current

(

According to different models, it is

125%-200%)

.

When the power frequency power supply is used for direct starting, the starting current is

6-7

Therefore, the times will produce machinery and electricity.

On influence. Using frequency converter to drive can start smoothly.

(

The start time is longer.

)

. starting current

rated current

1.2- 1.5

Second, the starting torque is

70%- 120%

Rated torque; For those

The frequency converter has the function of automatic torque enhancement, and the starting torque is

100%

Above, you can start from full load.

Move it.

Voltage when frequency drops.

V

Is also reduced proportionately,

V

and

F

The proportional relationship is to consider electricity.

Machine characteristics and predetermined, usually in the memory device of the controller.

(read only memory)

There are several special functions in.

Gender can be selected by switch or dial.

When the frequency decreases, the voltage decreases proportionally, so the AC impedance becomes smaller and straighter.

Constant current resistance

,

The torque generated at low speed tends to decrease. Therefore, at low frequencies,

given time

V/F，

So that the output voltage is higher.

,

So as to obtain a certain starting torque.

,

This kind of compensation

This is called enhanced startup. It can be achieved by various methods.

,

There are automatic methods and choices.

V/F

model

Type or adjust the potentiometer, etc.

exist

6Hz

Power can still be output below, but according to the temperature rise and starting torque of the motor.

Articles ... >>

Question 10: Why should wind turbines have low voltage ride-through capability? 5. Because the grid voltage is unstable (especially in China), when the grid voltage of wind turbines drops, wind turbines can remain connected to the grid, and even provide some reactive power to the grid to support the grid recovery until the grid returns to normal, thus "crossing" this low-voltage time (region). This can ensure uninterrupted power supply, protect the power grid and protect the fans.