With the development of power systems,a large number of shunt capacitors are used to improve power quality in the distribution network.The shunt capacitor banks are operated much frequently,as a result,the capacitor b...With the development of power systems,a large number of shunt capacitors are used to improve power quality in the distribution network.The shunt capacitor banks are operated much frequently,as a result,the capacitor banks will bear large numbers of over-voltage inevitably.If the over-voltage exceeds certain amplitude,the capacitor will be damaged.This paper aims at the capacitor banks in the 35 kV side of Shanghai Xu-xing 500 kV substation,and applies ATP-EMTP to simulate the over-voltages generated by operating the switches under different angles of the source.Finally,according to the results of simulation and theoretical analysis,a best choice(i.e.angles of the source) to switch on capacitor banks is proposed.In this case the over-voltage on the capacitor will be limited to lowest.展开更多
A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, t...A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, to the IGCT’s over-voltage sensitivity problem, a new technique of reducing the over-voltage is introduced, which releases the elect romantics energy of faulty line by a capacitive current branch to reduce the amplitude of over-voltage. Secondly, the principle of over-voltage suppression with current release branch is analyzed, and the overall control scheme of solid- state breaker is put forward. Finally, the simulation results also demonstrate its obvious effectiveness in over-voltage suppression after adding a current release branch into the SSB.展开更多
In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Current...In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.展开更多
In Tanzania, tobacco is an important cash crop benefiting most farmers and stakeholders. However, the crop is characterized by a low yield per unit area. Several factors are responsible for the low yield and quality o...In Tanzania, tobacco is an important cash crop benefiting most farmers and stakeholders. However, the crop is characterized by a low yield per unit area. Several factors are responsible for the low yield and quality of tobacco, among which are damages caused by the insects and other pests. Major insect pests of tobacco are cutworms (Agrotis spp), budworms (Heliothis virescens (F.)), (Lepidoptera Noctuidae) and aphids (Myzus persicae, Aphis tabaci) (Homoptera: Aphididae). These pests adversely affect crop growth, yield and leaf quality. In order to reduce insect attack in tobacco, applying pesticides is a critical management practices. In Tanzania, various pesticides have been approved for use in controlling the pests. Currently, farmers are using Bamethrine 2.5 EC to control the pests. The Pesticide named Protector 700 WG with an active ingredient imidacloprid 700 g/kg is a new product introduced in Tanzania during the 2021/22 crop season. Research trials were conducted in three research sites, namely Ulowa-Kahama, Tumbi-Tabora and Mtanila-Chunya, on Protector 700 WG efficacy in different rates, 15 g, 20 g, and 25 g each dissolved in 20 litres of water. The Protector 700 Wg was compared with the standard pesticide (Bamethrin 2.5 EC). Absolute control was also inclusive where the plot had no application of pesticides. The results showed that Protector 700 WG at all rates outweigh the commonly used pesticide. The difference in the number of pests between Protector 700 WG and Bamethrin 2.5 EC was significantly at P < 0.005 also, in dry and green weights, the yield was significantly different at P < 0.005. However, when yield and number of insects were compared among the rates of protector, there was no significant difference. From these results, farmers are advised applying Protector 700 WG at the rate of 0.15 kg/ha by dissolving it in 200 litres of water.展开更多
A novel type of leakage current protector chip,implemented in the mixed-signal 0.6μm CMOS process,is presented. This chip has the advantages of low power dissipation （10mW）, accurate protection control based on dig...A novel type of leakage current protector chip,implemented in the mixed-signal 0.6μm CMOS process,is presented. This chip has the advantages of low power dissipation （10mW）, accurate protection control based on digital response delay time and integration of multi-functions such as leakage current/over-voltage/over-load detection and protection,auto switch-on and so forth. Additionally, the chip is programmable to suit different three-level protection applications with a high anti-interference ability.展开更多
基金supported of the Fundamental Research Founds for the Central Universities
文摘With the development of power systems,a large number of shunt capacitors are used to improve power quality in the distribution network.The shunt capacitor banks are operated much frequently,as a result,the capacitor banks will bear large numbers of over-voltage inevitably.If the over-voltage exceeds certain amplitude,the capacitor will be damaged.This paper aims at the capacitor banks in the 35 kV side of Shanghai Xu-xing 500 kV substation,and applies ATP-EMTP to simulate the over-voltages generated by operating the switches under different angles of the source.Finally,according to the results of simulation and theoretical analysis,a best choice(i.e.angles of the source) to switch on capacitor banks is proposed.In this case the over-voltage on the capacitor will be limited to lowest.
文摘A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, to the IGCT’s over-voltage sensitivity problem, a new technique of reducing the over-voltage is introduced, which releases the elect romantics energy of faulty line by a capacitive current branch to reduce the amplitude of over-voltage. Secondly, the principle of over-voltage suppression with current release branch is analyzed, and the overall control scheme of solid- state breaker is put forward. Finally, the simulation results also demonstrate its obvious effectiveness in over-voltage suppression after adding a current release branch into the SSB.
文摘In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.
文摘In Tanzania, tobacco is an important cash crop benefiting most farmers and stakeholders. However, the crop is characterized by a low yield per unit area. Several factors are responsible for the low yield and quality of tobacco, among which are damages caused by the insects and other pests. Major insect pests of tobacco are cutworms (Agrotis spp), budworms (Heliothis virescens (F.)), (Lepidoptera Noctuidae) and aphids (Myzus persicae, Aphis tabaci) (Homoptera: Aphididae). These pests adversely affect crop growth, yield and leaf quality. In order to reduce insect attack in tobacco, applying pesticides is a critical management practices. In Tanzania, various pesticides have been approved for use in controlling the pests. Currently, farmers are using Bamethrine 2.5 EC to control the pests. The Pesticide named Protector 700 WG with an active ingredient imidacloprid 700 g/kg is a new product introduced in Tanzania during the 2021/22 crop season. Research trials were conducted in three research sites, namely Ulowa-Kahama, Tumbi-Tabora and Mtanila-Chunya, on Protector 700 WG efficacy in different rates, 15 g, 20 g, and 25 g each dissolved in 20 litres of water. The Protector 700 Wg was compared with the standard pesticide (Bamethrin 2.5 EC). Absolute control was also inclusive where the plot had no application of pesticides. The results showed that Protector 700 WG at all rates outweigh the commonly used pesticide. The difference in the number of pests between Protector 700 WG and Bamethrin 2.5 EC was significantly at P < 0.005 also, in dry and green weights, the yield was significantly different at P < 0.005. However, when yield and number of insects were compared among the rates of protector, there was no significant difference. From these results, farmers are advised applying Protector 700 WG at the rate of 0.15 kg/ha by dissolving it in 200 litres of water.
文摘A novel type of leakage current protector chip,implemented in the mixed-signal 0.6μm CMOS process,is presented. This chip has the advantages of low power dissipation （10mW）, accurate protection control based on digital response delay time and integration of multi-functions such as leakage current/over-voltage/over-load detection and protection,auto switch-on and so forth. Additionally, the chip is programmable to suit different three-level protection applications with a high anti-interference ability.
