Analysis and solution for the influence of DC bias of a merging unit on bus protection
DOI:DOI: 10.19783/j.cnki.pspc.201522
Key Words:merging unit  A/D sampling  ADC chip  sampling circuit disconnection  DC bias  bus protection
Author NameAffiliation
YAO Zhiqing1,2 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
CHEN Guanghua3 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
WANG Pengfei4 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
ZHU Jihong5 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
ZHANG Youjun4 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
HE Chun4 1. School of Electrical and Mechanical Engineering, Xuchang University, Xuchang 461000, China
2. Henan Key Laboratory of Relay Protection and Automation, Xuchang 461000, China
3. Zhuhai Ketop Testing Technology Co., Ltd., Zhuhai 519000, China
4. Xuchang Ketop Testing Research Institute Co., Ltd., Xuchang 461000, China
5. Nanjing Hz-ieds Electric Co., Ltd., Nanjing 210000, China 
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Abstract:In recent years, accidents in protection action caused by the output DC bias signal of a merging unit have been occurring frequently in smart substations. To solve this problem, we need to improve the stability and security of the sampling value output of the merging unit. The reason for DC bias of a merging unit when the sampling circuit is broken is analyzed by introducing the working principle of a merging unit and the design principle of an ADC chip. Based on the sampling value differential principle of a bus protection device, the influence of DC bias output of the merging unit on bus protection is analyzed from the action behavior. By reforming the peripheral circuit of the ADC chip, a solution to reduce the DC bias of the merging unit is proposed. The test system is built to verify the output value of the sampling value and bus protection action. It proves the effectiveness of the DC bias solution for the merging unit. This work is supported by the National Natural Science Foundation of China (No. U1804252).
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