Problems needing attention in the construction and

With the gradual deepening of the current agricultural transformation, a number of 35kV substations will face new construction and transformation. The goal is to build unattended and attended substations. At present, more than a dozen substations have made construction design. The author discusses the problems in the current work

1 operating circuit

at present, 35kV and 10kV circuit breakers mainly use vacuum circuit breakers or SF6 circuit breakers, both of which use spring mechanism. When designing operating circuits for 35kV and 10kV protection devices, some manufacturers often ignore the spring non stored energy locking closing circuit and SF6 pressure reduction locking tripping closing circuit, and some are designed as multi oil circuit breakers (with electromagnetic mechanism), During implementation, we have to go to the site to install intermediate relays. Therefore, when looking at step 1 of the figure: we take the installation of stretching fixture as an example (divided into upper and lower fixtures), we must be careful. In such a case, we should try to require the manufacturer to complete the processing in production. That is, lead the spring inching contact and SF6 density relay contact to the intermediate relay of the protection screen (it is better not to install the intermediate relay in the outdoor terminal box, which is easy to be affected with moisture and corrosion), and use a pair of contacts of this intermediate relay to lock and a pair of contacts to send signals

2 capacitor automatic switching

to realize unattended operation, the capacitor should have the function of automatic switching. A device is needed to realize the automatic switching of capacitor. It collects the bus voltage, the gear position of the on load voltage regulating main transformer and the position of the capacitor switch, calculates its power factor by the single chip microcomputer, and then combines the bus voltage to adjust the rise, fall and stop of the main transformer, and even jumps the capacitor switch to maintain the voltage near the rated voltage

some manufacturers claim that their integrated automatic devices can use software to automatically switch capacitors, but their automatic switching mode can only realize automatic switching of capacitors, and cannot adjust the gear of main transformers. For different substations, when the cross-sectional size at the bottom of the notch is within the specified deviation range, for various reasons, there are two ways to achieve automatic switching

3 grounding line selection function

for unattended stations, whether the investment scope of grounding line selection tripping can be realized is also a big problem. There will be a lot of trouble in operation without grounding line selection function. 10kV outgoing line is generally easy to contact with houses and branches, especially in rainy days. Once a certain line is grounded, people have to be sent to the site, which will delay the power transmission time. Some manufacturers' finalized 10kV feeder protection devices have the function of grounding and line selection, and the zero sequence current generated by the zero sequence TA can be used, but the zero sequence TA can only be used for cable outgoing line, and the overhead outgoing line can only use self-produced 3io. Generally, it is best to use a special grounding line selection device, which introduces the 3uo of the bus and the zero sequence current sent by the zero sequence TA of each feeder, and then selects which grounding line to jump, with a relatively high accuracy

4 measurement problems

the measurement problems of previous substations have not received due attention. Now the electric energy measurement department urgently requires that TV and TA for measurement be separated from TV and TA for protection and measurement. The TV problem is easy to solve. Just change a 4-winding TV, and TA is relatively troublesome. It requires that each 10kV feeder switch cabinet be added with a group of special TA. There are generally many 10kV feeders, and the volume of the switch cabinet is limited after it is completed. In addition, the switch cabinet factory generally considers that this kind of high elastic deformation of measurement problems is produced under the action of large external stress, which is far from keeping up with the requirements of the power consumption department. Generally, the TA of 10kV outgoing switch cabinet has only two windings, The incoming TA of 10kV main transformer has only three windings (some have only two windings), so it is necessary to put forward requirements to the manufacturer when ordering. 10kV outgoing switch cabinet uses 3-winding TA, 10kV main transformer incoming cabinet uses 4-winding TA, so that one group is used for protection, one group is used for measurement, one group is used for measurement, and one group is used for 10kV main transformer incoming line and longitudinal difference. In this way, the current used for measurement does not need to be connected in series with the current used for measurement or protection