Instantaneous Calibration Current Error Analysis And Control System

With the continuous development of electric power system, as well as the increasingelectricity demand, the consumption of low-voltage circuit breaker increased gradually.Low-voltage circuit breaker does not also has the function of closed and breaking, but alsoelectric leakage protection, short circuit protection, overload protection. Based on theprotected capability of short circuit protection （which is also known as instantaneousprotection）, when circuit has short troubles, breaker cuts off the electric circuitinstantaneously and protect both electric-equipment and electrified wire netting. Allproducts of circuit breaker instantaneous characteristics need to pass the strict test beforecircuit breaker products leave the factory. The limited detection technology, results in theinaccuracy of circuit breaker instantaneous validation. However both circuit breaker"malfunction" and “rejection” still exit in Practical application which leads to hugedamage for electric power system and potential threats of electrical safety. Therefore, it isof the great importance for research of circuit breaker instantaneous calibration accuracy.In view of existing situation which circuit breaker instantaneous calibration accuracy isnot high, the paper analyses the test standard and test method of circuit breakerinstantaneous at home and abroad. By comparing the differences between standards,analyze the advantages and disadvantages of them. Meanwhile, according to the design ofinstantaneous calibration equipment, this paper first analyze s the reason for inaccuracy ofinstantaneous calibration, then classify the reasons into different types.In order to minimize the check current error, this paper proposed check current errordecomposition method. The testing system is a MISO system. The check current errordecomposition accomplished the control system of decoupling for testing system and wellprepared the control and regulation of testing system. The theoretic and practicaldemonstration proves the accuracy and practicability of this method.The evaluation mechanism of test current is proposed to ensure the accuracyrequirement for test current which requires to limit the test current error at the same time.Only when test current accuracy meets the requirement, the test current could be used ascheck current in circuit breaker products. If the errors happen in test current， both inputsof the testing system need to be adjusted. According to the characteristics of the system, this paper raises the idea of generalized closed-loop control system. Through feedbackmethod, each error which occurred in the check current is used as the rationale for nextcontrol and regulation of testing system. Based on comparing the two control resultsbetween PID and Fuzzy-PID, Fuzzy control method has more advantages.For signal processing technology part, FFT to calculate signal in phase is used ascurrent technology. This paper analyzes the variation on signal frequency, amplitude, andphase by adopting FFT method, to calculate the errors in signal phase. To enhance theaccuracy of calculation signal phase (which is also known as the ability of calculation ofinstantaneous phase), this paper raised Hilbert alternative approach to measure signal phase.By the supporting of simulation and practical system verification, the method shows greatrobustness and accuracy in signal frequency and amplitude change.Meanwhile, based on test current error decomposition and evaluation method, thispaper accomplished the evaluation and error analysis during every test current; improvedthe accuracy of test current, and ensure the quality of instantaneous calibration currents.Applying the proposed Fuzzy-PID control method into testing system, does not onlystrengthen the stability, accuracy and rapidity of testing system adjusting calibrationcurrents, but also reinforce the ability of to calculation instantaneous phase, by adoptingHilbert alternative approach to measure signal phase. Furthermore, when signal frequencychanges, this method contains great Robustness. After being designed and improved,instantaneous calibration system has passed the testing system. The results show that themethod mentioned above has the advantages of high accuracy and quick adjustment. Also,it testified the validity and practicability of the theory proposed in this paper.