1.Introduction to parallel capacitor status evaluation
1.1 Parallel capacitor status evaluation background
Before 2008, the AC and DC filters and shunt capacitors of DC converter stations had been inspected once a year in the traditional way (of course, the same is true for other equipment in DC converter stations). We usually call this centralized maintenance method of DC converter stations the annual comprehensive overhaul of converter stations. The annual comprehensive overhaul of AC and DC filters and shunt capacitors has always been carried out in accordance with DL/T 596-1996 “Procedure for Preventive Tests of Power Equipment”. Because there are no special test items for filters and shunt capacitors in DC converter stations in this procedure, the test personnel working on site are actually just referring to it. With the increasing number of DC systems and the international requirements for indicators such as the availability of DC systems, this annual comprehensive overhaul based on equipment preventive tests has become increasingly unable to meet the urgent needs of society and enterprises for improving efficiency. The annual power outage maintenance test items are numerous and the cycle is long. Because of the total power outage, the power outage time is long, and the equipment test rate is too high, the DC equipment availability and other indicators cannot be compared with the international advanced level, which leads to high equipment operation and maintenance costs. Sometimes there will be some negative effects during the maintenance process (such as: some equipment that was originally in good operation, due to various reasons during the maintenance test, the equipment is not as good as before the maintenance after the maintenance). By introducing the method of parallel capacitor status evaluation and combining the concept of condition maintenance, the maintenance strategy can be optimized more effectively to avoid the shortcomings of traditional overhaul methods.
Therefore, in view of the above situation, the concept of equipment condition maintenance is proposed. The condition maintenance of equipment is based on safety, reliability, environment, and cost. Through equipment status evaluation, risk assessment, and maintenance decision-making, it is a strategy to achieve safe and reliable operation and reasonable maintenance cost. Before the equipment status maintenance, the equipment needs to be evaluated. Specifically, the parallel capacitor status evaluation of the filter and shunt capacitor equipment is the basis and basis for the implementation of status maintenance. This chapter focuses on the relevant standards and requirements for the evaluation of AC and DC filters.
1.2 Terms related to status evaluation and the composition of status quantities
As the relevant standards for equipment status evaluation and maintenance have only been gradually issued and put into production in China in recent years, the following introduces the commonly used terms for status quantity evaluation:
(1) Status quantity: various types of information that directly or indirectly represent the status of the equipment, such as data, sound, image, phenomenon, etc., which are divided into general status quantities and important status quantities.
(2) General status quantity: status quantity that has a relatively small impact on the performance and safe operation of the equipment
(3) Important status quantity: status quantity that has a greater impact on the performance and safe operation of the equipment.
(4) Normal state: all status quantities are within a stable and good range, and the equipment can operate normally.
(5) Attention state: the trend of a single (or multiple) status quantity changes in the direction of approaching the standard limit, but does not exceed the standard limit, or some general status quantities exceed the standard value. The equipment can continue to operate, but the monitoring during operation should be strengthened.
(6) Abnormal state: a single important status quantity changes greatly and has approached or slightly exceeded the standard limit
The operation should be monitored and power outages and maintenance should be arranged in a timely manner.
(7) Severe status: A single important status quantity seriously exceeds the standard limit and a power outage for maintenance needs to be arranged as soon as possible.
(8) Equipment status score (referred to as status score): A method of expressing the status of equipment in percentage. 100 points represent the best equipment status, and 0 points represent equipment that needs to be repaired as soon as possible. The status score for other situations is between 0 and 100 points.
(9) Positive degradation: The degradation of the status quantity is manifested as an increase in the value of the status quantity, such as dielectric loss factor, etc.
(10) Negative degradation: The degradation of the status quantity is manifested as a decrease in the value of the status quantity, such as insulation resistance, etc.
(11) Deviation degradation: The degradation of the status quantity is manifested as the inconsistency between the status quantity and the initial value, such as the DC resistance of the transformer winding, etc.
(12) Basic score: For new equipment that has passed the handover test and is ready for commissioning, or equipment that has passed the acceptance test after maintenance and can be put into operation again, its status is scored once as the basis for subsequent scoring. This score is called the basic score.
2.Composition, weight and degree of degradation of state quantity
The parallel capacitor status evaluation of filters and reflects the internal conditions, surface phenomena, common problems, equipment parameters and other elements (or factors) of the equipment through state quantities. These elements together form the evaluation parameters of the entire equipment. The quality of the parameters determines the quality of the equipment evaluation.
2.1 Specific composition of state quantity
(1) Original data. The original data of filter and shunt capacitor equipment mainly include: nameplate, type test report, order technical agreement, equipment supervision report, factory test report, transportation and installation record, handover acceptance report, installation and operation manual, etc.
(2) Operation data. The operation data of filter and shunt capacitor equipment mainly include: daily inspection records of equipment, records of equipment defects and abnormalities, infrared temperature measurement records, etc.
(3) Test data. The test data of filter and shunt capacitor equipment mainly include case reports, online monitoring information, special test reports, and relevant countermeasures.
(4) Other data. Other information of filter and shunt capacitor equipment mainly includes: the operation, defects and failure of the same type (class) equipment; changes in the equipment operating environment, changes in the system operation mode; other factors that affect the safe and stable operation of the equipment, etc.
2.2 Weight of equipment state quantity
Depending on the degree of influence of the state quantity on the safe operation of AC and DC filters and shunt capacitors, it is divided into four levels from light to heavy, and the corresponding weights are weight 1, weight 2, weight 3, weight 4, and the coefficients are 1, 2, 3, and 4. Weight 1 and weight 2 correspond to general state quantities, and weight 3 and weight 4 correspond to important state quantities
2.3 Deterioration degree of state quantity
Depending on the degree of degradation of the state quantity, it is divided into four levels from light to heavy, namely, industrial,, and level. The corresponding basic deduction values are 2, 4, 8, and 10 points.
2.4 Deduction value of the state quantity of AC and DC filters and shunt capacitors
The deduction value of the parallel capacitor status evaluation is determined by the degree of degradation of the state quantity and the weight. The deduction value of the state quantity is equal to the basic deduction value of the state quantity multiplied by the weight coefficient. No points will be deducted when the status is normal. The relationship between the status weight, degradation degree and deduction value is shown in Table 1.
Table 1 The relationship between the status weight, degradation degree and deduction value
