Zero loss deep current limiter (zlb)
As we all know, when the short-circuit fault occurs in the power system, the short-circuit current is generally more than ten times of the rated current, which causes great harm to the transformer, generator, circuit breaker, transmission line and other electrical equipment. At present, the breaking capacity of the more economical and practical vacuum circuit breaker is less than 40ka, and the breaking time needs tens of milliseconds. With the development and growth of various types of power consumption enterprises, the power load has risen greatly, and the capacity of main transformer has also increased accordingly. The power grid system of each enterprise is faced with the problems of short-circuit current approaching and reaching the maximum service limit of load vacuum circuit breaker, insufficient breaking capacity of vacuum circuit breaker at load side, and insufficient design of transformer anti short-circuit current impact capacity, which seriously threaten the safe operation of enterprises that 's ok.

Faced with more and more serious problem of short-circuit current exceeding the standard, many enterprises use high impedance transformer to limit the short-circuit current of the system. However, increasing the impedance of the transformer does not solve the problem of current limiting depth ultimately, and the reduction of electric power is very small, which also brings active and reactive power loss and increase of investment cost.

The application of common series current limiting reactor has not fundamentally solved the problem of current limiting depth (reactance rate is about 10%). At the same time, it brings some disadvantages, such as active and reactive power loss, bus voltage drop, magnetic field leakage and so on. When the system is short circuited, due to the insufficient current limiting depth, it can not effectively protect the main electrical equipment such as generator, transformer and so on The winding is damaged due to deformation, and catastrophic accident occurs.
At present, the explosion type high-speed breaking device with large capacity and parallel operation of reactor in the market can solve the problems of active and reactive power loss, voltage drop and magnetic leakage field leakage of reactor, but when the primary components act after short-circuit fault occurs, the problem of current limiting depth is not solved when the reactor is put into operation. This type of device needs to be replaced with new spare parts before it can be put into operation again. The operation cost of the enterprise not only increases, but also increases the installation space of the cabinet and the bus connection between the reactor devices, and sets the hidden trouble points artificially.

Therefore, it is very important not only for the safe and reliable operation of power system, but also for reducing the equipment cost of electrical equipment manufacturers.
High quality current limiting reactor must have:
When there is no short-circuit fault in the system, the impedance of the reactor is minimum zero loss;
When the short-circuit fault occurs in the system, the impedance of the reactor is very large --- deep current limiting;
After the short circuit fault of the system is removed, it will return to the original working state immediately.
Zero loss deep current limiting device (zlb) is a new type of short-circuit current limiting protection device developed by our company in order to meet the needs of short-circuit protection in power system. It can quickly put into deep current limiting reactor at the initial stage of short-circuit current, that is to limit the short-circuit current to a reliable range, so as to achieve the purpose of protecting power generation and distribution equipment and power supply lines.

Fig. 1 (single phase equivalent circuit diagram in case of short circuit, zero loss depth current limiting device in dotted line box)

Key words definition: current limiting ratio and current limiting depth
The system voltage is: U
The original impedance of the system is: x1,
The impedance of the deep current limiter is x (see Figure 1)
The total impedance of the system is x2 x2 = X1 + X after being connected in series with the depth current limiter
The expected short-circuit current of the device is I1 = u / x1,
The expected short-circuit current value of the series in depth current limiter is I2 = u / x2,
Current limiting ratio: K1 = I2 / I1 = X1 / X2, that is, X1 / (x1 + x)
Current limiting depth: k = 1-k1 = x / (x1 + x)
For example, the original impedance of the system is 12%, and that of the deep current limiting device is 36%,
Current limiting ratio: K1 = I2 / I1 = 8 / (24 + 8) = 0.25
Current limiting depth: k = 1-k1 = 0.75
In other words, the device can reduce the expected short-circuit current to 25% of the original value, and the current limiting depth is 75%.
For example, if the current limiting depth (k) is 50%, then the current limiting ratio (K1) is 50%, x = x1, and the short-circuit current of the system is reduced to half of the original value.
The deep current limiting can greatly reduce the short-circuit current impact of the transformer, and the transformer is well protected. At the same time, the breaking capacity of load side vacuum circuit breaker is also greatly reduced.
Working principle of zlb zero loss deep current limiting device
The device monitors the system current through Rogowski coil. When the short-circuit current is greater than the set amplitude, the high-speed DCP can quickly and accurately predict the accurate time of zero crossing point of three-phase current through special algorithm, and send out signals before each phase current cross zero.
When the current of the high-speed switch is close to zero crossing point, the three-phase is opened and disconnected accurately, and the short-circuit current commutation enters into the deep current limiting reactor, which limits the short-circuit current and greatly reduces the short-circuit current amplitude.
The measurement and control unit sends the action indication signal to the background.
The device can limit the short-circuit current to less than 50% of the original amplitude within 7-15 MS, which greatly reduces the short-circuit impact of the system, protects the electrical equipment such as transformers and generators in the system, and improves the service life of the load vacuum circuit breaker at the short-circuit point, so as to ensure the safe operation of the system.
After the short-circuit fault is removed, the measurement and control unit automatically detects the rise of bus voltage, immediately sends the closing command to the high-speed switch, and the deep current limiting reactor exits, and the system can resume normal operation.
Characteristics of zlb zero loss deep current limiting device:
It's fast
The device can cut off the short-circuit current within 7-15 ms of the system short-circuit, and the deep current limiting reactor can reduce the short-circuit current to less than 50%.
The breaking time of short-circuit protection device consists of four parts: sampling, calculating and command issuing time of monitoring unit; inherent opening time of special circuit breaker; arcing time; time of short-circuit current changing into deep current limiting reactor.

In general, the sampling time of microprocessor-based protection is 20 ms per cycle; it takes 30 ms for fast FFT calculation and command sending; the inherent opening time of common circuit breaker is more than 50 ms; the arcing time after breaking is about 10 ms, and the current can pass through zero arc extinguishing. Therefore, it takes about 100 ms to cut off the short-circuit current. Long time short-circuit current has high requirements for dynamic and thermal stability of transformers, buses, switches and generators.
High speed eddy current drive switch is used in the device, which can realize opening within 5ms and closing within 10ms. At the same time, the measurement and control unit uses high-precision, high-speed digital to analog converter to continuously detect the system current. When the current is greater than the set value, through high-speed DSP technology and special algorithm, it can quickly calculate the short-circuit current and the accurate time of current zero crossing, and send out the action signal before the zero crossing, and drive the switch to cut off the circuit before the zero crossing, so as to ensure the shortest arcing time In 7-15 MS, the short-circuit current is transferred into the deep current limiting reactor.
Strong breaking capacity
The imported switch in the device is three-phase independent action, and the reasonable control of the contact's rigid opening time ensures that each phase action is critical zero crossing breaking, so as to minimize the arcing time. The breaking margin of the interrupter is greatly increased, and the short-circuit breaking capacity can easily reach 80kA.
The current limiting effect of current limiting reactor is good
There is no current passing through the deep current limiting reactor in the device due to normal operation. Therefore, there is no loss, no voltage drop and no leakage magnetic field. Only when the short-circuit occurs, the reactance value can limit the short-circuit current to less than 50% of the expected short-circuit current value according to the needs of the system, so that the short-circuit current will be greatly reduced in the process of short-circuit, the transformer will be free from the huge short-circuit current impact, and the breaking capacity of the circuit breaker in the system will also be reduced accordingly.

Long service life
The switch in this device uses high-speed eddy current drive mechanism, which reduces 80% of the moving parts of spring operating mechanism used by ordinary circuit breaker, and uses simple linear motion without complicated transmission mechanism, so the wear is very small, and the mechanical life and reliability are greatly improved. At the same time, the device is zero crossing breaking, the arcing amount during arcing is less than 10% of ordinary circuit breaker, the breaking capacity is greatly improved, the contact burning is small, and the contact electrical life increases in series. When there is no short circuit in the deep current limiting reactor, it is in zero loss, no heating, no voltage drop and long service life.
High performance and reliability
The core components of the device are all made in foreign countries, which can operate reliably even under strong electromagnetic interference environment. At the same time, the electronic controller has a real-time self-test function to ensure its reliable operation all the time, and all function information can be monitored by sending background alarm.
The movement dispersion is small
Because the closing time is greatly shortened and the high-speed eddy current drive mechanism is equipped, the closing dispersion can be controlled within 0.1 Ms.
No rebound when closing
According to the site conditions, anti-collision device can be installed to ensure no rebound when closing.

Application scope of zlb zero loss depth current limiting device
The device is the best energy-saving and the most economical and effective current limiting scheme
The device can replace high impedance transformer, common series current limiting reactor and explosive type high-speed breaking device. In the design of new power supply system and enterprise system transformation, the deep current limiting reactor of this device can be used to increase the system impedance, further reduce the breaking current of the circuit breaker at the load side and reduce the cost.

Greatly reduce the investment of system expansion or networking operation
In case of short-term occurrence, the device quickly puts into operation the bus coupling deep current limiting reactor to increase the internal reactance of the system. After the fault point is removed, the deep current limiting reactor will exit, which will not affect the normal operation of the whole system. The use value of the transformer will be improved by networking operation.

It can improve the quality of power supply for the important load which does not allow instantaneous interruption of power supply and must be forced to start automatically
When the line is short circuited, the reactor is put into operation quickly, and the residual voltage on the deep current limiting reactor can fully meet the requirement of maintaining the important load continuously without being affected.

The short circuit of generator outlet or high voltage side can be protected quickly and effectively
The device has large breaking capacity and deep short-circuit current limitation. It is an ideal protection device for generator outlet and auxiliary branch, so that the generator and transformer can be protected quickly and effectively.

Technical parameters of zlb zero loss deep current limiting device
Equipment name: 6-10-35kv zero loss deep current limiting device (zlb)
System rated voltage: 6-10-35kv
System rated current: 1000a-1600a-2000a-3000a-4000a-5000a
Lightning impulse withstand voltage (peak value): 75kv-180kv
Short time (1min) power frequency withstand voltage: 42kv-90kv
Rated frequency: 50 Hz
Rated short time withstand current: 100ka-200ka
Rated peak withstand current: 100ka-200ka
Rated short-time breaking current: 40ka-80ka
Contact resistance < 100 μ Ω
Closing time: 10ms
Opening time < 5ms
Closing asynchrony < 2ms
Rated reactance rate% 20% ~ 50% ~ 80%
Rated inductance (MH)
Dimension (mm) ds h 6-10KV: 35kV:
Height of lower porcelain base
Unit base pitch diameter (dcmm)