Protection configuration of the hottest rural powe

2022-08-14
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Abstract: This paper puts forward views and improvement suggestions on the protection configuration of various electrical equipment for the problems existing in the rural electrical protection configuration

key words: rural electrical relay protection configuration

1 problems in rural electrical protection configuration

(1) due to the large changes in the system operation mode, it is sometimes difficult to meet the requirements of rapidity, selectivity and sensitivity at the same time by using simple current and voltage type protection

(2) with the implementation of rural power transformation project, ring and double circuit frames are increasing, and the existing protection configuration (non directional components) is difficult to meet the requirements of operation mode

(3) the electromagnetic type, transistor type and integrated circuit type relay protection still in operation are less reliable than microcomputer protection

(4) with the shortening of the line length, the current quick break protection range is correspondingly shortened, so the short line generally has no protection range, affecting the rapidity and sensitivity. Because the phase-to-phase section 1 (current quick break) has no protection range, the overlapping area of the protection range of phase-to-phase section 1 and phase-to-phase section 2 is reduced, so that the protection reliability is reduced

2 35kV line protection configuration problem

(1) ring, double circuit and intermediate line protection are configured according to the phase to phase distance:

① price analysis:

after the microcomputer transformation of the protection device, all kinds of protection are the same in hardware configuration, but different in software settings. In terms of price, compared with distance protection, current (voltage) protection has a slightly higher price, mainly in software, However, with the decline of the cost of computer hardware and the intensification of the competition in the sales market of power products, the price of software is also declining. Therefore, the overall device price shows a downward trend

② technical performance analysis:

1) improve sensitivity. The protection range of phase to phase section is increased from 15% - 20% of the total length of the line (current and voltage protection), with good lubricity to 85% (distance protection), and the protection sensitivity is not affected by the change of operation mode

2) the rapidity range of phase to phase section is improved, and the fault is removed in 0s within 0% - 85% of the total length of the circuit

3) the distance protection of 35kV line is configured as two-phase current transformer, which can reduce the non selective action probability when two points are grounded at different points on the line

4) for double circuit and ring lines, the fault can be removed by the dynamic protection with the function of absorbing sound waves and various small vibrations through the successive speed carbon, and there is no need to configure the double circuit line protection separately

(2) the terminal line is configured according to the conventional current voltage type protection (without directional elements):

because the terminal line does not have the problem of coordination with the primary line protection under the same voltage level, it can be configured according to the conventional current voltage type protection, which can meet the requirements of selectivity and sensitivity

(3) the time limit is configured according to the fixed time limit:

35kv system has large transmission power. If non selective action occurs, there will be more load shedding, which will also have a great impact on the system, so good selectivity must be guaranteed. The characteristic of inverse time limit characteristic is that the protection action time is related to the system short-circuit current level. If the short-circuit current error calculated at the coordination point is large or the system impedance changes, the coordination quality will be affected, and even non selective action will occur. On the other hand, due to the inverse time limit characteristic, the time accuracy of the relay itself is not high. Generally, the protection time level difference is 0.6 ~ 0.7s, while the fixed time limit protection time level is not conducive to long-term storage, and the difference is 0.3s (microcomputer protection). Obviously, the use of fixed time limit is conducive to improving the rapidity and selectivity of protection

3 10kV lines adopt two-stage phase-to-phase current protection

(1) generally, 10kV lines belong to single power radiation frame, and one line carries many branches:

with the rural power transformation, 10kV power is gradually equipped with breakers, reclosers, shunt fuses, which greatly improves its protection level and greatly reduces the burden of 10kV outgoing line protection of substation on the remote backup of this level of power. Therefore, the configuration of two-stage current type interphase protection is sufficient to meet the requirements. The first section is configured with current limited time quick break. Because there are many T-connected lines in 10kV lines, if instantaneous current quick break protection is adopted, the protection setting calculation is difficult to meet the selectivity requirements, and it is proposed to adopt current limited time quick break. The second section is configured with overcurrent of low-voltage lockout. Generally, the load of 10kV line changes greatly. If the overcurrent setting value is set large, the sensitivity is not enough; If the overcurrent setting value is set small, it is easy to misoperate when the system is overloaded. Therefore, it is more reasonable to apply low voltage lockout

(2) the time limit is configured according to the inverse time limit:

10kv distribution adopts a large number of protection elements with inverse time limit characteristics. In order to ensure the integrity of the overall protection cooperation, it is proposed to adopt the inverse time limit configuration

4 main transformer protection configuration (35kV voltage level)

(1) configure gas protection: gas protection is one of the effective measures to ensure the safe operation of oil immersed transformer. The main advantages of gas protection are rapid action, high sensitivity, simple installation and wiring, and can reflect various faults in the oil tank. Because the old gas relay (floating barrel mercury contact relay) is not stable enough in operation and has poor seismic resistance, it is easy to cause malfunction due to the flow of Mercury due to vibration, so it is replaced by the open cup baffle gas relay. Its biggest advantage is good seismic resistance and reliable action

light gas acts on signal and heavy gas acts on tripping

(2) configure pilot differential protection: as we all know, the fatal weakness of current quick break protection is that it can only protect part of the winding of the main transformer, and there is a protection dead zone. With the continuous expansion of rural electric transformers (35kV and above voltage levels), it is obvious that current quick break protection cannot meet the sensitivity requirements. Therefore, differential protection must be configured. Changing from current quick break to differential protection increases the engineering cost from the perspective of engineering cost, but from the perspective of protection capacity, it is very beneficial to the quality and operating life of transformer, especially the wide use of microcomputer protection, which shows great advantages. The following is a comparison between electromagnetic type and microcomputer type differential protection from several aspects, as shown in Table 1

(3) backup protection is configured with low-voltage overcurrent protection: the double winding transformer should be installed on the main power side, and the protection device can be set with one or two time limits according to the main wiring conditions. The shorter time limit is used to reduce the scope of fault influence, and the longer time limit is used to disconnect the circuit breakers on each side of the transformer. The time limit is configured according to the fixed time limit

(4) overload protection: as the protection of symmetrical overload of transformer, it acts on the signal with time limit

Table 1 comparative characteristics of electromagnetic and microcomputer based differential protection electromagnetic microcomputer

versatility different systems Transformers with different capacities must choose different models of relays, which are suitable for all kinds of transformers under various modes

wiring mode wiring requirements flexible fixed wiring

setting calculation complex calculation simple

difficulty of debugging complex debugging simple

sensitivity sometimes the sensitivity is not enough to meet the requirements

reliability components are easy to age and have high reliability

communication ability no other protection configuration

5 Set

(1) the existing configuration of 10kV capacitor protection is relatively perfect, maintaining the status quo

(2) 35kV Power is equipped with fault recording device. The transmission line is equipped with automatic reclosing

(3) 10kV distribution outgoing line is equipped with low-frequency load shedding device. The review of the project feasibility study report is completed and the line selection device for small current grounding is completed

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