Several wiring methods of metal zinc oxide arrester manufacturers in shunt capacitor installations and their main technical parameters and model selection

Metal Oxide Arrester, the English name is Metal Oxide Arrester, or MOA for short. Gap-free metal oxide lightning arrester refers to a lightning arrester composed of only metal oxide non-linear resistors in series and (or) parallel, no parallel or series discharge gaps. It is used to protect electrical equipment from various overvoltage hazards. Protection equipment. Power system overvoltages are caused by lightning strikes, switching operations or faults, and can be divided into three categories: temporary overvoltages, operating overvoltages, and lightning overvoltages (or atmospheric overvoltages). MOA is a new type of lightning arrester developed in the 1970s, which is mainly composed of zinc oxide varistors. Each varistor has its certain switching voltage (called varistor) from the time it is manufactured. Under normal working voltage (that is, less than the varistor voltage), the varistor has a large value, which is equivalent to an insulating state, but Under the action of impulse voltage (greater than the varistor voltage), the varistor is broken down at a low value, which is equivalent to a short-circuit state. However, the hit state of the varistor can be restored; when the voltage higher than the varistor voltage is removed, it returns to the high resistance state. Therefore, after installing MOA on the power line, when an overvoltage is generated, the high voltage causes the varistor to break down, and the current flows into the ground through the varistor, so that the voltage on the power line is controlled within a safe range, thereby protecting electrical equipment Security. In order for the arrester to reliably protect electrical equipment, the volt-ampere characteristics of the arrester are required to be below the volt-ampere characteristics of the electrical equipment. When the system generates an overvoltage, the voltage across the capacitor rises and the arrester operates to limit the voltage across the capacitor to the arrester. Below the protection level. At present, the main component of the oxide arrester valve is zinc oxide, so it is often called zinc oxide arrester.

There are two types of surge arrester manufacturers currently in use: porcelain sleeve type and composite jacket. The main material of the jacket material of the composite jacket arrester is methyl vinyl silicone rubber.

Compared with the porcelain sleeve arrester, the composite jacket arrester has the following characteristics:

(1) Light weight and small size;

(2) The arrester has good pollution resistance, and the hydrophobicity of the silicone rubber jacket is used to improve the outer insulation performance of the arrester and reduce the maintenance workload of the device;

(3) The explosion-proof performance of the arrester is good. The composite jacket made of epoxy glass filament tube and silicon rubber material is beneficial to release the internal pressure when the arrester fails, and avoids the harm of the arrester explosion to other equipment.

Therefore, nowadays, composite jacket oxide arresters are often used.

Product Type:

Y—Porcelain sleeve type oxide arrester YH—Composite jacket oxide arrester

Structure:

W—no gap C—series gap B—parallel gap

Use place:

S—distribution type Z—power station type B—for shunt capacitor D—for motor T—for electrified railway X—line type

Additional features:

W—Anti-pollution type G—High prototype TH—Used in humid tropics According to the pollution situation in the area where the arrester is installed, the pollution level of the outer insulation of the arrester is selected according to the standard GB/T5582. The pollution level is divided into 4 grades, which stipulates the minimum nominal creepage distance requirements of the outer jacket: 17mm/kV for lightly polluted areas of grade I; 20mm/kV for moderately polluted areas of grade Ⅱ; 25mm/kV for heavy dirty areas of grade Ⅳ; The level of heavy pollution area is 31mm/kV.

Terminology of arrester:

Continuous operating voltage (Uc), allows the effective value of the power frequency voltage to be permanently applied between the terminals of the arrester.

Rated voltage (Ur), the maximum allowable effective value of the power frequency voltage applied between the terminals of the arrester.

Nominal discharge current (In), used to classify the arrester level, with 8/20 waveform of the lightning impulse current peak value.

Residual voltage (Ures), the maximum peak voltage between the terminals when the discharge current passes through the arrester. DC 1mA reference voltage (U1mA), the voltage on the arrester measured by the arrester under 1mA DC reference current. Generally not less than the peak value of the rated voltage of the arrester. The DC 1mA voltage is usually referred to as the turning voltage. When the terminal voltage is less than U1mA, the current through the arrester is very small, dominated by the capacitive component. When the terminal voltage is greater than U1mA, the arrester current increases rapidly, and the resistive component is the dominant component.

Charge rate (η), the percentage of the peak value of the continuous operating voltage to the DC 1mA reference voltage. The high or low charge rate directly affects the aging speed of the arrester, generally less than 80%. The nominal discharge current In of the arrester is an important parameter with a waveform of 8/20μs to classify its class.

There are five levels of 1.5, 2.5, 5, 10, and 20kA. The first three levels correspond to the neutral point, the motor arrester, and the capacitor arrester. The power station arrester is divided into the last three levels.

Protection features:

The protective characteristics of MOA are completely determined by its residual pressure. Generally, the residual voltage is proportional to the rated voltage of the arrester. For a MOA of a certain rated voltage, its residual voltage is a function of the current passing through the arrester.

The protection characteristics consist of the following combinations:

a) Residual voltage under steep wave current impact;

b) Residual voltage under lightning impulse current;

c) Residual voltage under operating impulse current.

The operating surge protection level of the arrester is the maximum residual voltage under the specified operating surge current. The metal zinc oxide arrester in the shunt capacitor device mainly limits the operating overvoltage, and the system bus arrester 8/20μs lightning impulse residual voltage mainly limits the protection characteristics of the atmospheric overvoltage arrester under the operating overvoltage, and stipulates the residual voltage test under the operating impulse current. The apparent wavefront time of the experiment is 30μs but less than 100μs, and the half peak time of the apparent wave tail is about twice the peak discharge current of the apparent wavefront time, because the wavefront time of the operating impulse current is in the range of 30-100μs. The residual pressure value has no obvious effect. The current amplitude is specified for different values according to different voltage levels

(GB11032-2000 8.3.3 Table 14 Parallel compensation capacitor surge arrester operating impulse current peak value is 125A and 500A).

The operating overvoltage of the capacitor bank may be:

(1) Closing overvoltage;

(2) Asynchronous closing overvoltage;

(3) The contact bounces over the voltage when closing;

(4) There is a single-phase grounding fault or single-phase heavy strike crossing voltage without a single-phase grounding fault on the power supply side when opening;

(5) Two-phase heavy blow through voltage when opening;

(6) The voltage across multiple heavy blows caused by one operation of the circuit breaker;

(7) Other overvoltages related to the operation of the capacitor bank.

It can be seen from the test data that the overvoltage during the opening operation is the main one. The opening overvoltage mainly occurs during single-phase heavy breakdown, two-phase heavy breakdown and multiple heavy breakdowns during one operation. The odds are very small.

Selection of main parameters for lightning arrester manufacturers, European-style cable joints, and cold-shrinkable cable terminals:

GB50227-1995 Design Specification for Shunt Capacitor Devices: The operating overvoltage protection and lightning arrester wiring of high-voltage shunt capacitor devices shall meet the following requirements:

1. The group circuit of the high-voltage parallel capacitor device should be equipped with operating overvoltage protection.

2. When the circuit breaker only has a single-phase heavy breakdown, the neutral point arrester connection method can be used, or the relative ground arrester connection method can be adopted.

3. When the probability of a two-phase heavy breakdown of the circuit breaker is extremely low, the two-phase heavy breakdown fault protection may not be set. When it is necessary to limit the overvoltage between the capacitor poles and the power supply side to the ground, the protection method should meet the following regulations:

(1) When the reactance rate is 12% and above, the parallel connection of the arrester and the reactor and the connection of the neutral point arrester can be used

(2) When the reactance rate is not more than 1%, the parallel connection of the arrester and the capacitor and the connection of the neutral point arrester can be used

(3) When the reactance rate is 4.5% to 6%, the wiring method of the arrester should be determined by simulation calculation.

3～66kV is an ungrounded system, and the neutral point of the capacitor bank connected to this system is not grounded. Therefore, if a single-phase heavy breakdown occurs when the capacitor bank is switched off, the power supply side (high voltage end) of the capacitor bank may have an overvoltage that exceeds the insulation level of the equipment to the ground, such as the theoretical maximum when the reactance rate K=0 The value is 5.87 times the phase voltage, and with the increase of the K value, the overvoltage shows an upward trend; the single-phase thumping through voltage generated when there is a single-phase grounding fault on the power supply side is much higher than that of no grounding. Therefore, the single-phase thumping through voltage should be limited. For vacuum circuit breakers that operate more frequently, the possibility of single-phase heavy breakdown should be considered.

     Yichang Hengyuan Technology Co., Ltd. is a professional manufacturer of European-style cable connectors, plug connectors, cable branch boxes, American elbows, high-voltage vacuum circuit breakers, high-voltage load switches, lightning arresters, zinc oxide arresters, tank arresters, overvoltage protectors, Counters, monitors, heat-shrinkable cable accessories, cold-shrinkable cable accessories, T-heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbows Manufacturers of type cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products