In power grids with voltage levels of 220kV and above, circuit breakers with phase-by-phase operation are commonly used. Due to equipment quality and operational reasons, abnormal states such as inconsistent operation of the three-phase circuit breakers may occur during operation. Different understandings exist regarding how to eliminate this abnormal state, and different systems have different practices. The following section, based on the actual operation of the system and protection, elaborates on the necessity of installing incomplete phase protection for circuit breakers, analyzes common current incomplete phase protection schemes, and discusses some issues related to incomplete phase protection for 32-phase circuit breaker wiring. 1. Necessity of Installing Incomplete Phase Protection During power system operation, due to various reasons, one or two phases of the three-phase circuit breaker may disconnect, resulting in incomplete phase operation. If the system adopts single-phase or combined-phase reclosing, the system must also be in an incomplete phase operation state during the waiting period for reclosing. However, the time of incomplete phase operation should be limited because: a. System requirements. When the system is in an incomplete phase operation state, the negative sequence and zero sequence components appearing in the system can cause certain hazards to electrical equipment. b. Protection requirements. The presence of negative-sequence and zero-sequence components can cause some protection systems to be in an activated state. For example, in the commonly used 11-series microprocessor-based line protection, when the system changes from full-phase to non-full-phase operation, if the protection's sudden change element activates, after determining there is no fault, the protection program switches to the oscillation blocking module. If the zero-sequence component value of the line is greater than the zero-sequence auxiliary starting element setting, the program will be in an oscillation blocking state. If this exceeds 12 seconds, the protection will report a current transformer (CT) disconnection, leaving only a few protection functions active, severely impacting the reliability of the protection. Negative-sequence and zero-sequence components in the system can also cause some protections (such as zero-sequence current protection) to trip, mistakenly disconnecting normally operating lines. For systems using single-phase or combined-phase reclosing methods, non-full-phase operation caused by fault tripping will quickly switch to full-phase operation if reclosing is successful; if reclosing occurs at the fault, the circuit breaker trips all three phases, and the system also switches to full-phase operation. The equipment and protection systems in the system must consider this non-full-phase state of waiting for reclosing. For example, some protection sections can adopt measures such as increasing the setting value and increasing the delay to avoid the reclosing cycle. The situation is more complex for incomplete phase states caused by equipment quality, circuit problems, etc. For example, if a circuit breaker trips one phase, the reclosing should be activated to reclose the circuit breaker because the circuit breaker position is not corresponding. However, if the circuit breaker is faulty, the tripped phase cannot be reclosed, and the circuit breaker will operate in an incomplete phase. For this type of incomplete phase state, the main equipment protection is not often able to eliminate it. Taking the 11 series microprocessor-based line protection as an example, if incomplete phase operation is caused by protection selective tripping or failure to reclose after circuit breaker tripping, from the perspective of protection function, only the insensitive zero-sequence section or sensitive zero-sequence section protection may be effective. However, these are also constrained by the setting value and directional elements, meaning that the line protection itself may be powerless in this situation. Therefore, considering all the above factors, incomplete phase protection that can reflect the incomplete phase operation state of the circuit breaker should be installed to trip the circuit breaker that is already in an abnormal state. Regarding the protection that reflects the inconsistency of the three-phase positions of the circuit breaker in some circuit breaker mechanism boxes, local areas can use it according to their actual situation. 2. Analysis of Common Schemes for Incomplete Phase Protection The implementation of incomplete phase protection generally requires a circuit that reflects the inconsistency of the three-phase positions of the circuit breaker. This can be achieved by using a combination of circuit breaker auxiliary contacts, or by using a combination of contacts of trip position and close position relays (this contact combination is generally provided by the operating box). Hereinafter, these are referred to as three-phase inconsistency contacts. Currently, the common schemes for dedicated incomplete phase protection are as follows: 2.1 Direct Start Time Relay of Three-Phase Inconsistency Contact As shown in Figure 1, when there are no current contacts, this scheme is similar to the incomplete phase protection configured in the circuit breaker mechanism box, which is relatively simple and can still play the due protective role. Figure 1 Simplified Diagram of Typical Circuit for Incomplete Phase Protection The North China Network clearly requires in its countermeasure implementation details that "incomplete phase protection should directly use the circuit breaker auxiliary contacts as the criterion, and cancel the current discrimination circuit." However, due to the unreliability of the circuit breaker auxiliary contacts and the influence of the operating environment of the introduced cables, several instances of maloperation of the incomplete phase protection have occurred during operation. For example, on February 1, 1997, the cable from the control box to the circuit breaker of phase A of the 2212 circuit breaker HWJ at the Xiaoying substation in North China broke, ultimately leading to maloperation of the incomplete phase protection. Based on operational experience, we believe that the safety of this scheme is questionable. 2.2 The three-phase inconsistent contact is connected in series with the zero-sequence current relay contact to start the time relay, as shown in Figure 1. Compared with the scheme in Section 2.1, this scheme adds a zero-sequence current blocking criterion, which greatly improves safety. Since the zero-sequence current is relatively easy to obtain, this scheme has been widely used in the system. The main problem is the setting of the zero-sequence current. At present, the Hebei power grid is generally set to avoid the unbalanced current under normal load (the primary value is about 100A), but obviously, when the line load is small, the incomplete phase protection may fail to operate. For example, on January 21, 1999, the 242 circuit breaker on the Lizhang line at Lixian Station in Hebei Province experienced insulation breakdown in phase A of the manually tripped relay, resulting in incomplete phase operation of the line. The incomplete phase protection failed to operate, and the on-duty personnel manually disconnected phases B and C. The reason for the incomplete phase protection's failure to operate was that the line load was relatively small, and the zero-sequence current during incomplete phase operation did not reach the set value (primary value is 120A). Another problem with this scheme is that it cannot be used for radial lines where the neutral point of the terminal transformer is not grounded. This is because when a radial line operates in incomplete phase, only the negative sequence component appears in the system, and no zero-sequence current flows through the line; therefore, the incomplete phase protection of this scheme will naturally fail to operate. For example, on August 13, 1998, the 263 circuit breaker of the Sunren line at Suncun Station in Hebei Province failed to reclose during a line fault reclosing due to a problem with the reclosing contacts, resulting in incomplete phase operation. However, the incomplete phase protection failed to operate because, under the system operating conditions at the time, the Sunren line was operating with only Rendong Station connected to it, and the neutral point on the 220kV side of the main transformer at Rendong Station was not grounded. When the 263 circuit breaker was incomplete phase, there was no zero-sequence current on the line. Currently, in microprocessor-based protection devices, the CSI101121 uses this scheme, which is a microprocessor-based product of traditional incomplete phase protection. The three-phase inconsistency contact is the switch input, which is judged by internal zero-sequence current and then outputs after a delay. 2.3 The scheme of starting the time relay after connecting the three-phase inconsistency contact in series with the negative sequence current relay contact is similar to the scheme in Section 2.2, except that the current judgment uses the negative sequence component. It is generally used when the negative sequence current is easily obtained, such as in generator-transformer integrated protection systems. Negative sequence current can also be set to avoid unbalanced current during normal operation, and may fail to operate when the load is small. Its advantage over the scheme in Section 2.2 is that it can be used for radial lines where the neutral point of the terminal transformer is not grounded. Currently, the WFBZ-01 microprocessor-based protection device uses this scheme. 2.4 Combining Three-Phase Position Contacts with No-Current Criteria to Start Time Relays With the development of microprocessor-based protection devices, the current criteria for incomplete phase protection, and even its structure, have become increasingly diversified. We will only analyze the structure of incomplete phase protection in the widely used LFP-921 device. As shown in Figure 2, the contacts of the three-phase trip position relay are used as the switch input. When any phase TWJ operates and there is no current, it confirms that the circuit breaker of that phase is in the open position. When any phase circuit breaker is in the open position but not all three phases are in the open position, if the control switch is closed, it is confirmed that the three phases are inconsistent, and tripping occurs after a delay. Figure 2 shows the logic block diagram of the LFP-921 incomplete phase protection. The advantage of this scheme is its wide applicability, applicable to various situations. The disadvantage remains as mentioned earlier: under low load, the incomplete phase protection may fail to operate. However, the no-current threshold can be set lower, resulting in higher sensitivity than schemes with zero-sequence and negative-sequence current blocking. Currently, the no-current threshold of the LFP-921 device is fixed at 0.06In. Comparing the above schemes, the scheme using only three-phase inconsistent contacts is simple but has poor safety. The scheme with current blocking improves safety but reduces reliability. When using the scheme with current blocking, if the load is low, the incomplete phase protection will inevitably fail to operate. However, considering that the negative-sequence and zero-sequence components the system experiences are very small at this time, it has little impact on the operation of the system and protection. Furthermore, in this situation, there are corresponding light signals to indicate to the operating personnel, allowing for manual handling. Therefore, incomplete phase protection with current blocking is preferable. The current blocking setting should consider the system and protection's tolerance capacity and be as low as possible. 3. Non-full-phase protection for 32-circuit breaker wiring For substations with 32-circuit breaker wiring, non-full-phase protection can be configured based on either the circuit breaker or the line (transformer). When configured based on the circuit breaker, if the scheme described in Section 2.1 is adopted, each circuit breaker can be set independently. However, as mentioned earlier, this scheme has safety issues. If current blocking is added, regardless of whether it's zero-sequence or negative-sequence, there are two cases: 1) The current uses the line current, i.e., the sum of the currents. The three-phase inconsistencies of each circuit breaker's contacts are connected in series with the zero-sequence (negative-sequence) current relay contacts of the line. The intermediate circuit breaker uses the parallel connection of two line current relay contacts as the current criterion. In this case, if only one circuit breaker experiences non-full-phase activity, while the other circuit breaker does not simultaneously experience non-full-phase activity, or if the two circuit breakers disconnect different phases, then the normal operation of each circuit breaker is still maintained. Zero-sequence and negative-sequence currents can be set according to the aforementioned method. The main problem with this scheme is that the panel wiring is more complex, and the division of installation units is not very clear. 2) The current uses the circuit breaker current. The main problem with this scheme is the setting of zero-sequence and negative-sequence currents. During normal operation, the load distribution between the two circuit breakers may be uneven, resulting in large zero-sequence and negative-sequence currents. In this case, the zero-sequence and negative-sequence current blocking scheme is undesirable. A more feasible scheme currently is the one mentioned in Section 2.4, such as the LFP-921 non-full-phase protection using a current-free criterion. When configured according to the line (transformer), the three-phase inconsistency contact is the connection of the two circuit breakers connected in series, and the current blocking naturally uses the line (transformer) current. For example, the non-full-phase protection of the generator-transformer unit at the Xibaipo Power Plant in Hebei Province is configured in the generator-transformer unit integrated protection cabinet, and the current blocking uses the negative-sequence current of the generator-transformer unit, introduced into the three-phase inconsistency contact of the two circuit breakers connected in series. This configuration is similar to the case of using line current blocking when configured according to the circuit breaker. Comparing the two configuration methods above, each has its advantages and disadvantages. Considering that circuit breakers must be deactivated before handling non-full-phase operation, and also considering the simplicity and clarity of secondary wiring, non-full-phase protection should ideally be configured as circuit breakers, with the presence or absence of circuit breaker current used as the criterion for current blocking. 4. Conclusion Non-full-phase operation of power systems presents many complex problems. During non-full-phase operation, many protection systems require technical measures to ensure correct operation. Non-full-phase protection is merely an auxiliary protection configured to limit the duration of non-full-phase operation. Based on the above analysis, non-full-phase protection should be installed and current blocking should be considered. For 32-wire connections, non-full-phase protection should preferably be configured as circuit breakers, using a no-current criterion. While non-full-phase protection is not the main protection of a power system, its role in operation cannot be ignored. In the North China power grid alone, non-full-phase protection operated 5 times in the second half of 1998, 2 of which were incorrect operations. With the development of relay protection technology and the widespread use of microprocessor-based devices, the configuration and use of non-full-phase protection will inevitably develop further. It is hoped that relay protection professionals will pay sufficient attention to incomplete phase protection, strive to improve its reliability, and make due contributions to the safe and stable operation of the system.