4. Distance I section fast action program logic block diagram
The fault handling program of distance protection mainly consists of three components: manual closing and section I fast tripping part; section I and II delayed action part; tripping and post-acceleration part. The latter was analyzed in the protection fault handling program in Chapter 2 as a program common to all types of protection. Here we only analyze the program logic block diagram of section I, as shown in Figure 3-9.
The program first determines whether the sampled I and U are in error based on the interrupt service program self-test flag bits LHCB and YHCB. The logical judgment of the program starts from the phase selection component to determine the fault type and fault phase, that is, first select the phase and then calculate the fault phase impedance. If it is hand-joined, check whether the calculated impedance value is within the offset rectangle and segment III. In order to prevent the three phases of the manual circuit breaker from closing at different times, the capacitive current in the first closing phase will cause misjudgment of the faulty phase, so the manual closing needs to be delayed and six fault types (Z, Z, Z, Z, Z, Z) need to be calculated. Only in this way can we finally make the correct judgment. If it is not hand-operated, the direction can be determined by adjusting the voltage of the previous week and comparing it with the real-time current. In the forward direction, if the calculated impedance is checked to be within the offset and I segment range, the jump will be selected. The tripping judgment made in this way is very fast. If the impedance value is not in the forward direction or is not within the range of the offset rectangle and segment III when the hand is closed, the oscillation blocking ZDBS section will be entered to further determine whether the system is oscillating. If it is forward but not within the range of stage I, and it is not single-phase grounded, it can switch to phase II and stage III delay.
The program logic judgment part of the action. Figure 3-9 is a simplified block diagram. The actual program logic block diagram of the manual and I section of the type 11 protection is shown in Figure 13. The "small deviation" and "large deviation" setting values in the figure refer to the setting values of R and R values plus the offset characteristics. It is worth noting that before the phase selection sub-process in Figure 13 of the actual protection, the "Drive QDJ" program command is first adjusted to release the protection latch and start the protection device.
5. Single-phase grounding and sequential fault identification program logic block diagram
- Continuous fault identification
The so-called cascading fault means that a single-phase ground fault develops into a phase-to-phase fault, that is, after a single-phase fault is diagnosed in the program, two sound phases fail one after another. The starting element Dl1 uses the phase current difference mutation amount to exceed a certain value to judge single-phase faults. Obviously, the phase current difference mutation amounts of two sound phases can be used to judge successive faults (DI2). The criterion is similar to the starting component, but this alone is not enough. It must also be strictly checked through the calculation of the three impedance components of the original healthy phase before it can be judged as a developmental fault. For example, if the phase selection component determines that a single phase is grounded (such as phase A), but it is not within the range of segment I, and then develops into a fault of sound phase B and phase C, then the three impedances of Z, Z, and Z can be calculated. As long as any one If the impedance is within the range of offset section II and section III, it can be determined that the fault has developed into a phase-to-phase fault. The program logic is shown in Figure 3-10 (a).
(2) Program logic principle of sequential fault distance II and III
In fact, during the delay process of sections II and III, the impedance is continuously recalculated and the delay cycle is carried out, as shown in Figure 3-10(b). During the recalculation and delay time, every time the sampling interrupt service routine is entered, it is necessary to detect whether DI2 is activated. Once activated, the flag DIFLGB = 1 is set, indicating that a sequential fault has occurred. When a sequential fault is detected, it is transferred to calculate whether the three impedances of the two non-fault phases are within the range of II section. If they are within the range of II section, the flag DEVB=l is set, indicating that there is indeed a continuous fault, and the cycle is waited for t delay. When the time is up, enter the three-hop and jump selection procedures; if no successive fault occurs, then calculate whether the original fault phase impedance is within the offset section II. If it is within the range of the II section, return to the loop and wait for the t delay time to expire, and then select the jump. Faulty phase or three jumps. If the fault is within the range of section III, the fault phase impedance is repeatedly calculated during the waiting t delay time until the t delay time expires and then three jumps are made.
If the fault does not develop into a sequential fault and is not within the offset range of segment II and segment III, then the process of checking single-hop or three-hop inputs and non-corresponding inputs will be entered. Because other protections may operate during the delay process of stages II and III, such as high-frequency protection or zero-sequence protection and single or triple jumps, the auxiliary contacts of the circuit breaker or the open contact inputs of these protections are Distance protection. If it is detected that there is already a single-hop or three-hop input and does not correspond to the input, the program will enter the program flow after the single-hop or three-hop. The actual block diagram of the program logic of the distance II and III sections of Type 11 is shown in Figure 14.