Power supply reliability refers to the ability of the power supply system to continuously supply power. It is an important indicator for evaluating the power quality of the power supply system. It reflects the degree to which the power industry meets the power demand of the national economy. It has become one of the standards for measuring the degree of economic development of a country.
The reliability of power supply can be measured by the following series of indicators: reliability rate of power supply, average power outage time of users, average number of power outages of users, and equivalent hours of system power outages; the reliability rate of power supply in general urban areas in my country has reached 3 nines (99.9%) Above, the average annual power outage time of users is ≤ 8.76 hours; the central area of important cities has reached more than 4 9 (ie 99.99%), and the average annual power outage time of users is ≤ 53 minutes.
When the power system equipment fails, it measures the degree of ability to minimize the power supply obstacles of users powered by the faulty equipment and maintain the stable operation of the power system itself (including the operation of the operating personnel).
1. Main factors affecting power supply reliability
The main factors affecting the power supply reliability of the medium-voltage distribution network are: line failure rate, fault repair time, operation outage rate, operation outage time, user density and distribution, etc.
1.1 Line failure rate and failure repair time
Line faults may be caused by insulation damage, lightning damage, natural deterioration or other reasons. For overhead bare conductors:
1.1.1 Insulation damage refers to faults caused by falling objects from high altitude, insufficient safe distance between trees and lines, etc., and is related to the geographical environment along the line; it is generally believed that the insulation damage rate is proportional to the length of the line.
1.1.2 The failure caused by lightning is related to the installation of the arrester; the failure rate of lightning is generally inversely proportional to the installation rate of the arrester, and proportional to the failure rate of the arrester itself.
1.1.3 Faults caused by natural aging are related to line equipment and materials; for the same type of equipment and materials, the natural aging rate is proportional to the length of the line.
1.1.4 Other reasons mainly refer to failures caused by external force damage and human error.
1.1.5 The fault recovery time is related to the operation management level, network structure, and distribution network automation level. Because the point of failure can be identified correctly and quickly, the time of power outage can be greatly shortened. For the distribution network with the same network structure, operation management level and automatic degree, the average fault repair time is taken.
1.2 Operation downtime rate and downtime
Operational outage refers to the outage of distribution lines caused by testing, maintenance and construction; construction outage is related to the development of the line power supply area. The rate of line construction outage in developing areas is high, and the development is close to saturated areas. Line construction outage low rate.
The operation downtime is related to the complexity of the operation and the level of construction technology, and generally the average value can be taken.
1.3 User Density and Distribution
User density refers to the number of users connected to the line per unit length. Due to different user loads, the user density of each circuit is generally different. When estimating the influence of wiring mode on power supply reliability, the average density can be taken.
According to the current statistical indicators of power supply reliability, for the same connection mode, different user distribution conditions may have different power supply quality service indicators.
According to the analysis of user distribution mode, most of the users are distributed in the front section of the line, and faults in the middle and back sections of the line can be isolated by section circuit breakers, so that the front section of the line can resume operation, so there is the best evaluation result; most of the users are in the middle section of the line The pattern is next, and the distribution pattern where users are concentrated at the end of the line is the worst.
2. Power supply reliability evaluation of basic wiring mode
2.1 Evaluation of basic wiring methods
According to the above-mentioned main factors affecting the reliability of power supply, according to the distribution line reliability index and parameters set in Table 1, the circuit breaker is set to be manually operated, and there is a fault isolation operation time of the contact line (including fault location and restoration of power supply to the intact line section) ) is 1h, the operation isolation operation time is included in the operation outage time, and the basic wiring method with a total length of 12km (each section of the line is 2km long) is evaluated. The evaluation method adopts the failure mode effect analysis method.
2.2 Influence of main factors on reliability
2.2.1 Failure rate and failure repair time:
Reducing the line failure rate is the most beneficial for the full-connection branch network. If the failure rate is reduced to 0.05 times/km·year, the average annual power outage time of users can be reduced from 3.4h/household to 2.7h/household, which is reduced by 20.6%. At the lowest, the average annual power outage time of users can be reduced from 15.6h/household to 13.8h/household, which is only reduced by 11.5%. Reducing failure repair time has the same conclusion.
2.2.2 Operation outage rate and operation outage time:
Due to the reason for users to increase capacity and report installation, there is little room for reducing the outage rate of power grids with better operation management. Shorten the operation outage time, if it is shortened from 4h to 2h, the annual average power outage time of branch network users can be reduced from 15.6h/household to 9.6h/household, a reduction of 38.5%; and the annual average power outage time of full-connection tree branch network users It can be reduced from 3.4h/household to 2.4h/household, a reduction of 29.4%.