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Geng dong yong, a researcher at jincheng coal group power company, wrote in the 12th issue of electrical technology in 2015 that there was a frequent burning of the electric voltage sensor at shincheng coal group power substation 35kv, which designed a electro-voltage sensor protection technique and effectively avoided the burning of voltage sensors。
The country's power distribution system in 3-35 kv is mainly based on the non-effective grounding of neutral points, whose power supply is much more reliable than that of an efficient land distribution system of neutral points. From the experience of years of operation and the development of voltage distribution systems in recent years, the non-effective grounding of the neutral point also poses problems for the mesopressure distribution system: when a single-stage failure occurs in a non-effective ground-to-ground system, the neutral point is usually in the form of arc-light-to-ground, when the non-fast-phase line-to-ground voltage can rise to a maximum of 3. 5 times the phase-to-phase voltage, and the system's excess voltage often causes insulation-to-ground flashes in the weak insulation of the system。
Electromagnetic voltage sensors (pt) have non-linear electromagnetic properties. Pt cores saturated, electrons decreased sharply, and complex magnets were easily and system parameters triggered by external factors such as lightning overture, operational voltage, ground failure recovery and pt's own various periods of lockingResonanceHigh frequency (hf), high frequency (fw), low frequency (lhf) perforated voltage. At the same time, the saturation of pt steel cores produces large magnetic surges and low-frequency oscillation currents that flow through pt when ground failure resumes may lead to pt melting and even to pt burning in serious cases。
1 questions raised
Issues such as the burning of pt and the melting of high-pressure filaments in the old 35kv system of the jincheng coal group group have not been effectively addressed for many years. In particular, the 35-kv substation of the pt, which operates on the 35-kv system, has been burned several times after more than a decade of transport, while high-pressure smelting devices have been frequently melted, seriously threatening the safe operation of the equipment and the electricity grid. The pt burned down and melters melted throughout the years, as shown in table 1。
Table 1 statistics on the burning and melting of pt in calendar year 1
The most recent incident occurred at 2306 hours on 7 september 2013, when on board the queen's 35kv power station operating on duty, the queen's 35kv substations discovered that the back-station alarm was “23:06:40 35kv ii main voltage uab exceeding the upper limit, 23:07:15 35kvii main voltage uab above the upper limit, 23:07:3035kvii main voltage uab exceeding the lower limit, 23:07:31 king ii returning to the 0 msecond homeline breakout at 354 relative time, 23:07:41 2 # main retrotment reserve at 0 msecond。
Examination of the chart of the voltage bar showed that: 35kvii a phase voltage was 15. 2kv, b and c phase voltage was normal (21. 6kv) and a preliminary determination was made that the a phase had failed, and then went to the 35kv room to check that there was smoke and aerobics in the room and, when the fan was ventilated, to examine 35kvii phase pt, a phase insurance and a phase pt body burst and that internal insulation material had been released. Damage at site pt, as shown in figure 1。
Figure 1 pt site damage
2 reason analysis and conservation methodology studies
The results of the simulation and dynamic simulation show that: common pt malfunctions are mainly due to the failure phase voltage being raised from ground to phase following the elimination of single-stage failures and the normal phase being reduced from wire to phase voltage. Along with this process of trajectories, the amount stored in relative electricity caps of the grid needs to be redistributed. Since the central point is not effective in the grounding system, only the pt neutrals are located, the charges are bound to form a circuit through the pt circuit and the neutrals。
In this oscillation circuit, which consists of relative electro-performance and pt-t around-the-clock magnetic resistance, the vibration frequency of the circuit is very high. Combined with the saturation properties of pt cores, high values can be achieved through pt shock surges. Figure 2
Figure 2pt shock surge test wave shape
The blue line is a current through pt with a peak of 4. 2 ampere and a shock frequency of 5 hz. The rated current of the pt-protector smelt is generally 0. 5a. So there's a good chance that pt's smelts will be burned or pt's own damage will be caused. To limit the flow of the shock to protect the pt, consideration could be given to a stringing of non-linear electrical resistance at the pt neutral point and short-linking it with a contact when the grid is functioning to prevent an impact on the accuracy of the pt's measurements。
The contact point was broken only after the single-stage failure of the grid, which was quickly short-cut after normal operation. As shown in figure 3, a test waveform that effectively inhibits shock surges with protective devices at the pt neutral point:
Figure 3 pt neutral point with protective devices to effectively contain test wave shapes of shock surges
3. Protection design
Pt high-speed combination protection: a combination of non-linear electrical resistance and contact-connected side protections and a combination of protections to prevent the triangulation of the pt from exporting false past voltage signals quickly and effectively prevents various pt failures. And it can prevent micro-systems from receiving false voltage signals. Pt high-speed combination protection units are shown in figure 4 below:
Figure 4 pt high-speed combination protection diagram
A side protection device (ptb): use of carbon silicon non-linear resistance and vacuum switches at the neutral point of the pt and chained to the ground. Silicon carbide resistance (sic) by-pass k during normal operation of the system is equivalent to a neutral pt site, completely inhibiting the voltage of the measurement opening of the system and not affecting the measurement and protection of the system。
When the voltage intersensor undergoes an iron-magnetic resonance, the neutral point produces an asymmetrical three-phase voltage, produces zero-order voltage at both ends of the open triangle, and the intersensor high-pressure group flows through the zero-order current. The control system issued orders for k to disconnect and input the sic, effectively inhibit the system's resonance and, following the restoration of the site failure, for k's delayed closure and effective containment of the flow and low frequency of the system。
Secondary protective devices: high-speed full-frequency secondary desorptioners use micro-machine technology for grid decoupling, using computer rapid and accurate data processing capabilities to achieve a fourier analysis with the correct frequency of selection. Through the collection of pt-3 and open triangulation voltage, various frequency components can be rapidly analysed and processed for grid resonance。
The control of controllable silicon conduits and shutdowns by microcomputers enables pt secondary circuits to form effective zero-order current flow channels. This zero-order current is a demagnetic effect on the magnetic flow created by the zero-order current in the high-pressure circuit group. The second zero sequence of currents close to the second pt circuit short circuit, with a very good magnetic effect. However, the control period is short, with three to five cycles. As shown in figure 5 below: channel 2 is a switch signal and channel 1 is a zero-order voltage signal。
Figure 5
The main line is capable of holding the voltage absorber: when the parent line is dropped, the main line is in a state of protection without the voltage. There is often a tendency to trigger multiple energy overcharges, endangering the normal operation of pts. There is therefore a need to install large-capable voltage absorbers on the side of the main line。
(b) pressure intersensors: the selection of full-saturated insulation intersensors with high-quality, twice the saturation point; and cabinet structure: the selection of standard switch cabinets, the installation of quarantine knives and the protection of breakers。
The main connection to the pt cabinet once designed is shown in figure 6 below:
Figure 6 pt cabinet first-time wiring
4 on-site applications
On 6 april 2015, at 1152 hours, the fence operated on the 35kv station on the 35kv system in the old zone, and the insulation of the c-phase cable head of the high-voltage inflow cable, 35kv system in the old zone, caused the site to be hit, causing the c-phase c interface of the 35kv system in the old zone to occur, while the cable fire over a long period of time resulted in a short arc (b, c-phase short road)。
The pt protection plant at the 35kv substation of the crown station was collected in wave shape at 11:52:15. 928 as shown in figure 7. As can be seen from the figure, when c phase voltage is reduced, the a phase and b phase voltage rises and changes occur, and the zero sequence voltage rises significantly by 30 u0. A single waveform can indicate the c interface。
Figure 7 pt protection fail-safe waveform
11:52 the unit ua = 83. 72 v, ub = 80. 34 v, uc = 31. 05 v, 3u 0 = 150. 17 v, f = 12. 10, reported low frequency coordination, as shown in table 2。
Table 2 low-frequency harmonization exports
11:52:18. 959 devices collected ua = 85. 21 v, ub = 112. 83 v, uc = 22. 15 v, 3u 0 = 98. 58 v, arc-lighted, c-ray-lighted exports as shown in table 3. At the same time, the queen's 35-kv changes 35-kvii, the pt smart switch, corrects the action and removes electrical resistance。
Table 3c corresponding light exports
In the light of the above, the retrofitting of the pt cabinet of the 35kv power station in the queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's queen's zone, due to the correct application of the intellectual switch in the 6 april 2015 accident, there. On the day of the local accident, the operator carried out a thorough examination of the pt and found no apparent anomalies。
The tester tested pt on 15 april 2015, and the test results were complete pt. As a result, the voltage intersensor protection technique has effectively addressed the burning of the voltage intersensor to ensure the safe operation of the system。
5 conclusion
A pt circuit at the mid-point of 35kv without a pt-magnetic resonance in the grid often causes insulation of the equipment, discharge of the external insulation and an increase in accidents due to delays in its handling; the arc-ray of the grid leads to frequent burning of the pt; a single pt circuit on the main line will become the sole metal link to the grid, either on a stand-alone or when it disappears; the pt-to-geary has an electrical transition process through a pt round-up, at which time the test detects an industrial semi-wave surge of up to a maximum of anbé, at which time there is likely to be a pt high-pressure fuse (0. 5a)。
The current approach to the above-mentioned problem, which involves the introduction of a neutral pt to add a filter, has had a better effect on containing the pt surge, but has had little effect on the complex pt resonance caused by changes in system parameters。
This paper uses smart switches to be used in conjunction with a silencer through the study and design of voltage intersensor protection, when the system is running properly, when the system is closed, when the one is short-circuited, when the neutral point of the intersensor is directly connected, when the system is subject to abnormal conditions such as arc-light, when the smart switch is turned on, and when the one is neutral, the problem of pt smelting or pt damage is addressed in a fundamental way when the single-stage system failure has been eliminated, when the three-phase power balances have been restored, and when the system-to-ground flow is caused by a pt-neutral point. It can effectively solve the problem of pt burningElectricity systemOperational maintenance management to ensure the safe, stable and reliable operation of the electricity grid is positive。
