Fault Analysis of Transmission Equipment Based on Condition Monitoring

Abstract

This paper proposes a method for evaluating the operating status and reliability of power transmission equipment in power systems. First, by analyzing the aging factors, common faults, and major faulty components of the main transmission equipment, the main condition monitoring parameters of each transmission equipment are determined. Then, the key parameters such as the environment, machinery, and electricity of the transmission equipment are monitored to obtain the operating status data of the transmission equipment, and fault limits and alarm limits are set to determine the operating status of the transmission equipment. Finally, a health index for monitoring parameters and a comprehensive health index for transmission equipment are proposed. This method has a wider scope of application and a more specific analysis process than previous methods, which is conducive to analyzing the working status of power transmission equipment and improving the reliability and safety of normal operation of the power system. Introduction The operating status of power equipment is closely related to the safety and reliability of the power system. Failure of power equipment will cause local or large-scale power outages and result the entire power system in an unsafe operating state. Therefore, it is necessary to adopt reasonable maintenance strategies for power equipment, timely discover and solve problems in the operation of power equipment, and ensure that the system can supply power safely and reliably. The accuracy and reliability of the judgment method of fault diagnosis will directly affect the normal operation and maintenance of power transmission equipment, and even affect the safety and reliable operation of the entire power system. With the application of a large number of sensing technologies and intelligent terminal equipment, a fault diagnosis method for power transmission equipment based on condition monitoring is one of the effective means to improve the efficiency of equipment condition maintenance and improve the ability of fault discrimination. This paper proposes a method for measuring fault conditions of power transmission equipment based on condition monitoring data. This method determines the status of the power transmission equipment by analyzing the common fault types of the power transmission equipment. Based on the study of the environmental, electrical, and mechanical condition monitoring parameters of the transmission equipment, the corresponding relationship between the monitoring parameters and the fault is established. This paper is organized as follows. The second II analyzes the transmission equipment, and analyzes the main aging factors and fault types of the transmission equipment. The section III introduces the process of condition monitoring of transmission equipment and the transmission equipment condition monitoring technology and the main monitoring parameters of transmission equipment. The section IV takes the SF6 circuit breaker as an example to establish a state assessment model and a health index. Section V analyzes the example and finally gives the conclusion. Analysis of Transmission Equipment Reliability Analysis of Transmission Equipment In the operation of power transmission equipment, aging is mainly caused by aging of insulation equipment [1-4] . The main influencing factors are [4,5] : high temperature, voltage, mechanical wear, dust and other environmental factors. High temperature factors: Temperature rise of insulation materials leads to deterioration and aging of insulation materials Voltage factor: When the applied electric field reaches the initial discharge voltage of the air gap, a partial discharge will occur, which will damage the insulation. Mechanical wear factors: Vibration caused by mechanical action can cause damage and wear to welding points and operating mechanisms in equipment structures. Analysis of Fault Types of Transmission Equipment Transformer fault: transformer internal faults, external short circuit faults causing transformer winding damage, open windings, damping discharge of transformer main insulation, etc. High voltage circuit breaker fault: Opening and closing fault, malfunction and refusal fault, insulation fault, current-carrying fault, leakage fault. Isolation switch fault: Corrosion of switches, contact overheating, and fault of porcelain pillars. Capacitor and reactor fault: Fault caused by missing insulation medium, over-voltage fault and over-current fault, discharge fault, capacitor three-phase current imbalance. Transmission line fault: Short circuit to ground, disconnection fault, overheating of the line. Monitoring Method of Power Transmission Equipment Figure 1 shows the flow chart of power transmission equipment monitoring. The condition monitoring process of power transmission equipment is: (1) The first step is to analyze the monitored transmission equipment, and analyze the major fault types of the equipment, the major components of the fault and the main parameters involved in the fault, and determine the monitoring parameters of the equipment. (2) The second step is to monitor and collect the main fault parameters of the equipment and process the parameters. (3)The third step uses the threshold method to set the parameter's fault limit and alarm limit, and compare the collected parameters with the limits, and make a preliminary judgment of the operating status of the equipment. (4) The fourth step is to calculate the health index of the equipment, and determine the operating trend of the equipment and the necessary maintenance measures. Equipment Monitoring signals Status recognition Parameter limit (Threshold method) Maintenance measures Equipment analysis Signal Acquisition (sensor) Signal processing Comparision Figure 1. Power transmission equipment status monitoring flow chart. Signals such as temperature, pressure, current, voltage, vibration, and energy will inevitably be generated during the operation of power transmission equipment. According to different status monitoring requirements, different signals can be selected to indicate the status of power transmission equipment. The system monitors several key parameters of the transmission equipment operation, finds potential failures, and judges the operation status of the transmission equipment. These parameters may be related to the environment in which the transmission equipment is located, mechanical wear, gas density, and electrical quantities during operation. In the power transmission equipment monitoring technology, some sensors are used, such as pressure sensors, fiber optic sensors, etc., in combination with microprocessors to perform monitoring tasks. Table 1 lists several transmission equipment and signals that need to be monitored. Once a parameter exceeds the limit, the monitoring system will generate an alarm. Table 1. Monitoring parameters of transmission equipment. Equipment Monitoring Parameters Capacitive insulation equipment Dielectric loss tangent, capacitance and current Lightning arrester Resistive current in total current Cable Dielectric loss tangent, capacitance and current Transformer Dissolved gas content High voltage circuit breaker Temperature, air pressure, opening and closing coil current, mechanical vibration, contact response time and speed State Monitoring Model of Transmission Equipment Condition Monitoring Modeling Method The paper supposes the vector m X (m=1, 2...) reflects a monitored parameter over time (m is the number of monitored inputs). If a value reaches the fault limit in any equipment operation, it is called the fault limit m F . Alarm limits are set with upper and lower limits max m A and min m A . The vector m D is the difference between the fault limit and the alarm limit [7] : max max max = , 1,2,..., m m m D F A m k   (1) min min min = , 1,2,..., m m m D A F m k   (2) In order to determine whether the equipment operates safely and reliably, the parameter threshold map of the monitored equipment is designed as shown in Figure. 2. If the main parameter value of the monitored equipment does not exceed the alarm limit and is located in area 1, the equipment is safe and reliable. If the monitored parameter value exceeds the alarm limit and does not exceed the fault limit, the device is located in area 2, indicating that the monitored device may be in an alarm state. If the monitored parameter value exceeds the fault limit and is located in area 3, it means that the monitored equipment is in a fault state and is not safe and reliable. max 1 X min 1 X max 2 X min 2 X max 1 A min 1 A max 2 A min 2 A Area 1 Area 2 Area 3 Figure 2. Threshold map of monitored transmission equipment parameters. m X V is the value where m X exceeds the upper and lower alarm limits. When the vector m X exceeds the fault limit, the corresponding m X V is considered a fault. max max max , . m X m m m m V X A if X A    (3) min min max , . m X m m m m V A X if X A    (4) min max 0, . m X m m m V if A X A    (5) when m X exceeds the alarm limit but does not exceed the fault limit, the vector m X V lies within the threshold range. When m X is within the required alarm limit, its value is zero. Condition Assessment Model Four SF6 circuit breakers CB # 1, CB # 2, CB # 3, CB # 4 are selected as examples. The selected circuit breakers are divided into reactor breaker, bus bar breaker, transformer breaker and line breaker according to the installation position and function. The main fault components of these circuit breakers and the parameters that need to be monitored are analyzed. The characteristics of the selected circuit breaker are shown in Table 2. Table 3 shows the main monitoring parameters and their upper and lower limits for fault and alarm limits. Table 2. Selected Circuit Breaker Feature. Circuit breaker type Major faulty parts Main monitoring parameters CB#1 Reactor breaker Contacts,Trip latch mech, Auxiliary contacts Temperature, O