Research On A New Test Method Of Loop Resistance Of Circuit Breakers

Circuit breaker is the most important control and protection equipment in power system,which ensures the stability of power system operation and the reliability of power supply.The loop resistance of the circuit breaker is an important technology index to reflect the performance and operation status of the circuit breaker,and its value directly reflects the contact reliability of the contacts.Through the loop resistance test,the wear degree of contact system as well as the contact condition of the contacts can be estimated,and then the electrical life of the contacts is predicted. The research of loop resistance intelligent test belongs to the field of the power switch equipment monitoring and fault diagnosis technology.The loop resistance of circuit breaker is generally micro-ohm resistor.The loop resistance tester commonly is measured through the use of large constant current source,in which there are some defects,such as test time is long,temperature rise of the contacts will influence the test results,moreover the size and weight of this kind of equipment is large.A new loop resistance test method is presented,which uses short-term large current discharging characteristics of the super capacitor,and a new type of loop resistance test device for circuit breaker is designed.The test system is powered by lithium batteries,and super capacitor is used as the current generator to generate the current of more than100A,the test time is200ms,which can effectively reduce the influence of temperature rise on the test results.The core of the device is designed by the DSP minimum system,to achieve the charging and discharging control of the super capacitor,the voltage and current signals are processed by conditioning and amplifier circuit before sampled,limiting average filtering method is used to filter the sample values,at last the loop resistance value is calculated according to Ohm’s law.In order to acquire the test results conveninently,test data is displayed via LCD,the test values and time information are stored in SD card through the chip—PB375A read&write solution,at the same time,which is convenient for further Weibull statistical analysis of the test data. The12kV vacuum circuit breaker was tested with four terminal wiring method,and the results showed that the test equipment can work reliably.Using the FL-2(75mV/300A)shunt as a standard resistor,the testing precision of the device can reach1%,meanwhile the sources of test error are analyzed,the improved methods are also proposed.The device could be used for quick and accurate testing of the resistance within the scope of1-2000μΩ.A new type of circuit breaker loop resistance test device is designed,which has high test precision,can satisfy the requirements of the electrical testing standard.The device is small,light,convenient to carry,and has a certain application prospect and practical value.