Smart power grids are intelligent grids based on integrated, high-speed two-way communication networks, through advanced sensing and measurement technologies, advanced equipment technology, advanced control methods, and advanced The application of decision support system technology to achieve the goal of reliable, safe, economical, efficient, environmentally friendly and safe use of the power grid.
The basic feature of China's smart grid is to realize informationization, automation and interaction in technology. The most basic work is the establishment of various parameter collection systems for power system operation, such as on-line monitoring of load energy, online monitoring of transformer operation, and online monitoring of SF6 gas in GIS room. However, the current online monitoring work has just started, and much work is urgently needed.
0.4KV ring network power supply is one of the most basic and extensive power supply network architectures in power systems, and its importance is self-evident. The quality of the 0.4KV ring network power supply directly affects the service quality of the power supply industry. However, it should be noted that due to various uses, the basic system often suffers from the phenomenon of phase sequence reversal, phase misconnection, poor wiring or leakage of fuses due to various reasons during operation. Class defects occur frequently, but often due to various circumstances such as the dispersion of the environment and the lack of professionalism of the users, the time of discovery is delayed, which affects the quality of power supply and delays the normal use of electricity. It has a negative impact on both the power system and the user.
The PT secondary metering voltage loop involves the billing problem of the meter. Due to the use of a cable with a too small diameter, the metering voltage drops, which directly affects the billing. What's more, the phase sequence of the metering circuit is reversed, and the abnormal situation is not enough. This will cause the speed of the meter to slow down or even not turn, resulting in a large reduction in the revenue of the power supply company.
In the power system and some large consumers of electricity, there is no good automatic detection method for the above two situations, mainly to send special personnel to conduct inspections, which is inefficient and costly. Of course, for the metering system involving the electricity collection fee, for some important users, a load power meter is installed in the system for monitoring. However, due to the high cost, it cannot be widely promoted.
In view of the above situation, in the current power system and the future smart grid, it is hoped that a voltage phase sequence distributed online monitoring method can be applied to the 0.4KV ring network power supply and metering system, the cost is not high, no monitoring blind zone, when the voltage in the system The loop wiring abnormality can be found in real time, and the abnormal signal can be instantaneously sent to the relevant automatic monitoring system. The monitoring system quickly judges and gives a processing instruction, and notifies the relevant team and personnel to process the processing task and the abnormal occurrence point. The rapid processing of such anomalies has important practical significance for improving the power supply quality and service quality of the power system.
1. Distributed voltage wiring abnormal online monitoring technology realization principle and characteristicsThe distributed voltage wiring abnormal online monitoring technology is not only a technical means, but also a management means. By establishing a distributed problem, the chronic disease that causes the abnormality of the voltage wiring has long been plagued by the power system management department.
Of course, for 0.4KV ring network power supply loop and PT secondary metering loop, it is not difficult to establish distributed online monitoring. Because there are many devices involved, phase sequence anomalies or phase loss may occur as long as there is a wiring connection. In the case, if too many online phase sequences are used to monitor components online, the cost is not small. Even for a 35KV substation system, the application of online phase sequence anomaly detection components is estimated to be tens or even hundreds. That is to say, if there is a real-time monitoring effect, a large number of online phase sequence monitoring components must be used. Then, the development cost of phase sequence monitoring components is a very important indicator. After careful analysis, it is not difficult to find that in order to make the online phase sequence monitoring technology widely used, the developed monitoring components must meet the following standards: 1. Low cost, 2 easy installation (can be installed without power failure), 3, free Maintenance, 4, does not affect the monitored circuit, 5, the alarm signal can be collected, can be transmitted far.
Monitoring the voltage loop wiring is abnormal, there is a ready-made mature technology, and the negative sequence filter principle is applied to achieve the corresponding purpose. The principle is also very simple to implement. In order to make the developed components suitable for both the requirements of the 400V ring network power supply system and the voltage connection abnormality of the PT secondary metering circuit, the negative sequence filter circuit is added in addition to the appropriate parameters. An adaptive circuit. Moreover, due to the asymmetry of the load in the 400V ring network power supply, the power supply imbalance often causes the negative sequence filter to malfunction, resulting in false alarms. In order to avoid this phenomenon, a floating threshold should be added to avoid the effects of three-phase unbalanced voltage. In the implementation of the principle, we can use the vector diagram for detailed analysis.
Figure 1 Three-phase negative sequence voltage filter
According to the above vector diagram, the voltage amplitude between mn when various types of voltage wiring abnormalities occur is analyzed, and the following conclusions can be drawn:
The online phase sequence monitoring component developed is capable of detecting both the voltage loop abnormality of the 380V ring network power supply system and the online detection work of the PT secondary metering voltage loop (phase-to-phase voltage is 100V). These two cases are further analyzed.
According to the working principle of the negative sequence filter, from the above formula, it can be concluded that under the standard voltage input, the relevant output voltage Umn value can be calculated, see Table 1.
It can be found from the table that the Umn output voltage is the largest when the 380V voltage loop is reversed, and the Umn output voltage is the smallest when the B phase is missing in the PT secondary metering voltage loop.
The online phase sequence monitoring component developed must be able to provide alarms for the above 9 cases and can withstand high voltages up to 700V. This is mainly to consider the system abnormality such as lightning transient overvoltage and operating overvoltage, and the phase sequence monitoring component should not be damaged. After the system is normal, the phase sequence monitoring component can resume normal operation.
The design of the online phase sequence monitoring component should be able to avoid the Umn output caused by the three-phase voltage imbalance. According to the empirical value, the unbalanced voltage output of the 400V ring network system is estimated to be around 15~20V. Consider the margin again, multiply the reliability coefficient K, which is generally 1.5 times. That is to say, the online phase sequence monitoring component should be able to escape the unbalanced output voltage below 30V during operation. Considering the three-phase unbalance caused by the severe asymmetry of the load, the online phase sequence monitoring component needs to adopt a floating threshold to ensure that the transmission is not mistaken.
Considering the importance of the ring network power supply circuit and the metering circuit, the online phase sequence monitoring component, such as its own component abnormality, should not affect the main circuit, and must have relevant protection measures. There are two situations that affect the main circuit: 1. Due to the failure of the online phase sequence monitoring component, the main circuit is short-circuited to ground; 2. Due to the online phase sequence monitoring component, the internal chip is selected, and a larger power chip is selected. The magnitude of the measured voltage results in less metering and a loss in energy billing.
Therefore, the online phase sequence monitoring component must eliminate the occurrence of the above two situations.
2. Distributed online phase sequence monitoring component circuit composition and practical application
Figure 2 Functional block diagram of online phase sequence monitoring components
Among the online phase sequence monitoring component circuit components, the most critical are the power input (sampling) loop and the alarm output loop. Due to the local alarm, it can not meet the requirements of centralized collection, classification and timely transmission and processing of data in the automatic monitoring system. Therefore, the dry contact output is also provided to meet the needs of various automatic monitoring systems.
The installation technology of the online phase sequence monitoring component is also important to consider. The general relay installation requires either screw fixing or special channel fixing, which is very inconvenient. If the online phase sequence monitoring component is also equipped with the above-mentioned mounting structure, it is not feasible to install in an electrical cabinet screen with extremely high safety requirements. It is necessary to solve this problem by adopting a new structure and installation process. Due to the online phase sequence monitoring component, the electronic circuit is simple, and the chip placement technology can be made very small and light, so it is possible to use a bonding technology to bond the online phase sequence monitoring component to the iron plate to be monitored. On the upper, relay case or the meter's case, the installation is very convenient, and no maintenance, if you do not need to pull directly, there is no safety problem. This also ensures that the online phase sequence monitoring component can be used with great care.
The online phase sequence monitoring component can be widely applied to 0.4KV power supply branch and PT secondary measurement branch road, so that abnormal voltage wiring defects can be effectively monitored, and its practical significance is far more significant than substation DC monitoring. After all, the 0.4KV AC circuit is more widely visible, and this technology also provides a more efficient and convenient means for our users to handle related voltage wiring anomalies in their jurisdiction.
Similarly, for system substation or some large users (with relatively complicated 0.4KV ring network wiring), if the phase anomaly signal that the phase sequence is monitored can be directly managed by the cable or communication mode into the background monitoring system, then The response time of the abnormal voltage will be greatly accelerated, and the efficiency of dealing with the defective personnel will be significantly improved, which will effectively shorten the various power outage times caused by voltage anomalies.
3. SummaryDistributed voltage anomaly online detection technology is not only a technical innovation, but also an innovation of management concept, which makes us reliable for the abnormal voltage wiring of 0.4KV ring network power supply system and PT secondary metering circuit. Effective means of timely discovery and timely processing have a significant role in optimizing grid management and improving service quality.
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