1. Ensure the reliability of power supply Adopting two-phase incomplete star can ensure that when single-phase grounding occurs in the small grounding power grid, only Remove one line, and the other line can run with faults. Ensure the reliability of power supply. The neutral point ungrounded small current grounding system is also the neutral point ungrounded system.
2. In the small current grounding system, the installation of 2 current transformers (stipulated in phases A and C) can meet the requirements of protection and measurement devices, and there is no need to install current transformers in each phase of the three phase.
3. When the small current grounding system is grounded at two points. Small current grounding system allowsXu single phase-to-phase operation for one to two hours. When two points of different lines are grounded, the three-phase complete star-shaped wiring 100% removes two lines, and the power outage range is large; two-phase incomplete star-shaped wiring has a two-thirds of the chance to remove one line, and the power outage range is small and the reliability is high.
4. Two-phase incomplete star-shaped wiring form. ( Post-transmission) x0dx0a is the most used in actual work. It saves a current transformer and uses the synthetic currents of phases A and C to form a reverse phase B-phase current.
5. The two-line transformers are installed in different phases (for example, the 1st line B phase is not installed, and the 2nd line C phase is not installed). In a total of 6 kinds of two-point grounding short circuits (A1BA1CB1AB1CC1AC1B2), when only the two-line transformer phase two-point grounding short circuit (B1C2), the two The line does not work.So it is 1/6.
The analysis is as follows: high-current grounding and small-current grounding are both grounded by neutral points in the power system, and they are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.
When a single-phase grounding fault occurs in a neutral point direct grounding system (including a system grounded by a small impedance), the grounding short-circuit current is very large, so this system is called a high-current grounding system. It adopts a system that is not grounded at the neutral point or grounded by an arc coil.
The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system.The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.
For the grounding of primary equipment, there are mainly direct grounding, resistance grounding, and extinguishing arc coil grounding. In a system above 220kV, the neutral point of the main transformer is directly grounded, which is called a high-current grounding system. In the 110 and 66kv systems, the neutral point arc coil of the main transformer is more grounded, which is called the small current grounding system.
Small current grounding system refers to a system that uses neutral point non-grounding or grounding through arc coils.
In a system with direct grounding at a neutral point, when a single-phase grounding fault occurs, the grounding short-circuit current is large. This system is called a high-current grounding system. Generally, the system of 110kv and above adopts a high-current grounding system.
Small current grounding system includes: neutral point non-grounding system, neutral point through arc coil grounding system, neutral point through large resistance grounding system. ( Neutral point ineffective grounding system), the grounding current is relatively small when a failure occurs.
The characteristic of a small grounding current is that when a one-phase grounding fault occurs, the grounding current is limited to a smaller value, and the steady-state voltage of the non-fault phase may reach the line voltage. The large grounding current system is also known as the effective grounding system. Including neutral point direct grounding and low-impedance grounding systems.
In China, the classification criteria: the system of X0/X14 to 5 belongs to the small grounding current system (the system of X0/X13 in the United States and Western Europe belongs to the small grounding current system), of which: X0 is the zero-sequence reactor of the system, and X1 is the positive sequence reactor of the system. Note: X0 is the zero-sequence reactor of the system, and X1 is the positive sequence reactor of the system.
Large grounding current system - a three-phase system that is directly grounded at the grounding power system. When a single-phase grounding failure occurs, the grounding short-circuit current is very large, so it is called a large grounding current system. Generally, 110kV and above systems or 380/220V three-phase four-wire systems.
The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system. The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.
When a single-phase grounding fault occurs in a neutral point direct grounding system (including a system grounded by a small impedance), the grounding short-circuit current is very large, so this system is called a high-current grounding system. It adopts a system that is not grounded at the neutral point or grounded by an arc coil.
High-current grounding and small-current grounding are both grounded by neutral points in the power system, which are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.
In a system where the neutral point is directly grounded, when a single-phase grounding fault occurs, the grounding short-circuit current is very large. This system is called a high-current grounding system. Generally, the system of 110kv and above adopts a high-current grounding system.
1. The characteristic of a small grounding current is that when a one-phase grounding fault occurs, the grounding current is limited to a smaller value, and the steady-state voltage of the non-fault phase may reach the line voltage. The large grounding current system is also known as the effective grounding system. Including neutral point direct grounding and low-impedance grounding systems.
2. In the neutral point ungrounded system, when the insulation of any phase is destroyed and grounded, the line voltage between the phases remains unchanged and can continue to operate with faults, while the ground voltage and the ground capacitance current of each point change, and the point of the neutral point is far from the earth potential.
3. The neutral point is not grounded, and the earth and the system are not electrically connected.
4. When one-phase grounding occurs in the small current grounding system, the grounding relative voltage is zero, and the relative ground voltage of the other two is increased by three times. The magnitude of the grounding current at the contact point is equal to the sum of the grounding capacitance current of all lines.
5. When a one-phase metallic grounding occurs in a small-current grounding system, the ground relative voltage is zero, and the non-ground relative ground voltage rises to line voltage.
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1. Ensure the reliability of power supply Adopting two-phase incomplete star can ensure that when single-phase grounding occurs in the small grounding power grid, only Remove one line, and the other line can run with faults. Ensure the reliability of power supply. The neutral point ungrounded small current grounding system is also the neutral point ungrounded system.
2. In the small current grounding system, the installation of 2 current transformers (stipulated in phases A and C) can meet the requirements of protection and measurement devices, and there is no need to install current transformers in each phase of the three phase.
3. When the small current grounding system is grounded at two points. Small current grounding system allowsXu single phase-to-phase operation for one to two hours. When two points of different lines are grounded, the three-phase complete star-shaped wiring 100% removes two lines, and the power outage range is large; two-phase incomplete star-shaped wiring has a two-thirds of the chance to remove one line, and the power outage range is small and the reliability is high.
4. Two-phase incomplete star-shaped wiring form. ( Post-transmission) x0dx0a is the most used in actual work. It saves a current transformer and uses the synthetic currents of phases A and C to form a reverse phase B-phase current.
5. The two-line transformers are installed in different phases (for example, the 1st line B phase is not installed, and the 2nd line C phase is not installed). In a total of 6 kinds of two-point grounding short circuits (A1BA1CB1AB1CC1AC1B2), when only the two-line transformer phase two-point grounding short circuit (B1C2), the two The line does not work.So it is 1/6.
The analysis is as follows: high-current grounding and small-current grounding are both grounded by neutral points in the power system, and they are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.
When a single-phase grounding fault occurs in a neutral point direct grounding system (including a system grounded by a small impedance), the grounding short-circuit current is very large, so this system is called a high-current grounding system. It adopts a system that is not grounded at the neutral point or grounded by an arc coil.
The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system.The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.
For the grounding of primary equipment, there are mainly direct grounding, resistance grounding, and extinguishing arc coil grounding. In a system above 220kV, the neutral point of the main transformer is directly grounded, which is called a high-current grounding system. In the 110 and 66kv systems, the neutral point arc coil of the main transformer is more grounded, which is called the small current grounding system.
Small current grounding system refers to a system that uses neutral point non-grounding or grounding through arc coils.
In a system with direct grounding at a neutral point, when a single-phase grounding fault occurs, the grounding short-circuit current is large. This system is called a high-current grounding system. Generally, the system of 110kv and above adopts a high-current grounding system.
Small current grounding system includes: neutral point non-grounding system, neutral point through arc coil grounding system, neutral point through large resistance grounding system. ( Neutral point ineffective grounding system), the grounding current is relatively small when a failure occurs.
The characteristic of a small grounding current is that when a one-phase grounding fault occurs, the grounding current is limited to a smaller value, and the steady-state voltage of the non-fault phase may reach the line voltage. The large grounding current system is also known as the effective grounding system. Including neutral point direct grounding and low-impedance grounding systems.
In China, the classification criteria: the system of X0/X14 to 5 belongs to the small grounding current system (the system of X0/X13 in the United States and Western Europe belongs to the small grounding current system), of which: X0 is the zero-sequence reactor of the system, and X1 is the positive sequence reactor of the system. Note: X0 is the zero-sequence reactor of the system, and X1 is the positive sequence reactor of the system.
Large grounding current system - a three-phase system that is directly grounded at the grounding power system. When a single-phase grounding failure occurs, the grounding short-circuit current is very large, so it is called a large grounding current system. Generally, 110kV and above systems or 380/220V three-phase four-wire systems.
The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system. The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.
When a single-phase grounding fault occurs in a neutral point direct grounding system (including a system grounded by a small impedance), the grounding short-circuit current is very large, so this system is called a high-current grounding system. It adopts a system that is not grounded at the neutral point or grounded by an arc coil.
High-current grounding and small-current grounding are both grounded by neutral points in the power system, which are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.
In a system where the neutral point is directly grounded, when a single-phase grounding fault occurs, the grounding short-circuit current is very large. This system is called a high-current grounding system. Generally, the system of 110kv and above adopts a high-current grounding system.
1. The characteristic of a small grounding current is that when a one-phase grounding fault occurs, the grounding current is limited to a smaller value, and the steady-state voltage of the non-fault phase may reach the line voltage. The large grounding current system is also known as the effective grounding system. Including neutral point direct grounding and low-impedance grounding systems.
2. In the neutral point ungrounded system, when the insulation of any phase is destroyed and grounded, the line voltage between the phases remains unchanged and can continue to operate with faults, while the ground voltage and the ground capacitance current of each point change, and the point of the neutral point is far from the earth potential.
3. The neutral point is not grounded, and the earth and the system are not electrically connected.
4. When one-phase grounding occurs in the small current grounding system, the grounding relative voltage is zero, and the relative ground voltage of the other two is increased by three times. The magnitude of the grounding current at the contact point is equal to the sum of the grounding capacitance current of all lines.
5. When a one-phase metallic grounding occurs in a small-current grounding system, the ground relative voltage is zero, and the non-ground relative ground voltage rises to line voltage.
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