Source: Jibao high-voltage technical exchange
The fault recorder is used in the power system, which can automatically and accurately record the changes in various electrical quantities before and after the fault when the system fails, and through the analysis and comparison of these electrical quantities, it plays an important role in analyzing and dealing with accidents, judging whether the protection is correct, and improving the level of safe operation of the power system.
Fault recorder is an important automatic device to improve the safe operation of the power system, when the power system fails or oscillates, it can automatically record the changes of various electrical quantities in the whole fault process.
The role of a faulty recorder
01
Based on the recorded waveforms, it is possible to accurately analyze and judge the exact location, development process, and type of power system, line, and equipment failures, so that they can quickly eliminate faults and formulate preventive measures.
02
Analyze the operation of relay protection and high-voltage circuit breaker, find equipment defects in time, and reveal the problems existing in the power system.
03
Accumulate first-hand materials, strengthen the understanding of the laws of the power system, and continuously improve the operation level of the power system.
How the faulty recorder is started
The start-up mode should be selected to ensure that the faulty recorder can be reliably started in the event of any type of system failure. Generally, it includes analog start-up and switching start-up.
Analog start-up: sudden start of voltage and current, start-up of voltage and current out-of-limit, start-up of negative sequence voltage and current, start-up of zero-sequence voltage and current out-of-limit, start of harmonic voltage, start of frequency out-of-limit, start of reverse power, start of over-excitation, etc.
Switching start-up: tripping exit signal for all protections, and secondary power displacement signal for all switches.
(1) Sudden change in phase current and phase voltage:
By using phase discrimination, the calculated phase current or phase voltage mutation is compared with the fixed value, and the starting value of the mutation amount is satisfied three times in a row, which is confirmed as starting.
(2) Phase current, phase voltage out-of-limit and zero-sequence current and zero-sequence voltage out-of-limit start:
The calculated voltages of each phase, the currents of each phase, the zero-sequence voltage, and the zero-sequence currents (calculated using dedicated channel inputs, rather than the symmetrical component method) are compared with the setting values to determine whether to start.
(3) Frequency out-of-limit and frequency rate of change start:
Hardware frequency measurement is used, and the measured frequency is compared with the frequency limit value to determine whether to start.
(4) Switching start:
Any switching quantity can be set as a starting condition and a variable displacement method can be set through the configuration.
(5) Positive-sequence, negative-sequence and zero-sequence voltage start-up:
In the event of a power system failure, the positive, negative, and zero-sequence voltages can all be regarded as fault components, so these changes can be used to start recording.
Fault recorder analysis requirements
1. It can automatically synthesize double-ended data for fault ranging;
2. It can form a waveform according to the recorded current and voltage, and derive the sequence components and their vector diagrams and impedance change trajectories;
3. It has perfect database management function.
The basic method of analyzing a recording image
1. Roughly judge what failure occurred in the system and the duration of the failure.
2. Take the zero-crossing point of a certain phase voltage or current as the phase reference, and check whether the phase relationship between current and voltage before the fault is correct, whether it is a positive phase sequence, and how many degrees the load angle is.
3. Take the zero-crossing point of the voltage or current of the fault phase as the phase reference to determine the phase relationship of the current and voltage of each phase in the fault state. (Note that when selecting the phase reference, first, the non-periodic component is large, and second, the voltage and current angle is converted from the load angle to the line impedance angle jumps largely, which is easy to cause error analysis)
4. Draw a vector diagram and analyze it.
Simple fault waveform analysis
A phase single-phase grounding fault record analysis points
1. When the current of a certain phase increases, the voltage decreases, and the zero sequence current and zero sequence voltage appear. ——It can be determined that the fault of the system is a single-phase grounding fault.
2. The current increases and the voltage decreases to the same phase. - It can be determined that the current and voltage are not connected wrongly.
3. The phase of the zero-sequence current is in the same direction as the current of the fault phase, and the zero-sequence voltage is reversed from the voltage of the faulty phase.
4. The fault phase voltage is about 80° ahead of the fault phase current (that is, the line impedance angle), and the zero sequence current is about 110° ahead of the zero sequence voltage. - It can be determined that there is no problem with the protection device and the secondary circuit as a whole.
For single-phase faults, the voltage of the fault phase is about 80° ahead of the current of the fault phase, and for multi-phase faults, the voltage between the fault phases is ahead of the current of the fault phase by about 80°.
If a single-phase ground fault does not meet the above conditions, then it needs to be carefully analyzed to find out if there is a problem in the secondary circuit.
Key points of AB two-phase short-circuit fault recording and analysis
1. The two-phase current increases, and the two-phase voltage decreases, and there is no zero sequence current and zero sequence voltage.
2. The current increases and the voltage decreases to the same two phases.
3. The currents of the two fault phases are basically reversed.
4. The voltage between the fault phases is ahead of the fault phase, and the current between the fault phases is about 80°.
If the two-phase short-circuit fault does not meet the above conditions, then it is necessary to carefully analyze and find out whether there is a problem in the secondary circuit.
Key points of AB two-phase grounding fault record analysis
1. The two-phase current increases, the two-phase voltage decreases, and zero sequence current and zero sequence voltage appear.
2. The current increases and the voltage decreases to the same two phases.
3. The phase of the zero-sequence current is located between the two phases of the fault.
4. The voltage between the fault phases is about 80°, and the zero sequence current is about 110° ahead of the zero sequence voltage.
If the two-phase ground fault does not meet the above conditions, then it is necessary to carefully analyze and find out whether there is a problem in the secondary circuit.
Key points of three-phase short-circuit fault recording and analysis
1. The three-phase current increases, and the three-phase voltage decreases, and there is no zero-sequence current and zero-sequence voltage.
2. The voltage of the fault phase is ahead of the current of the fault phase is about 80°, and the voltage between the fault phases is ahead of the current of about 80°.
If the three-phase short-circuit fault does not meet the above conditions, then it is necessary to carefully analyze and find out whether there is a problem in the secondary circuit.