Chencun Hydropower Station is currently the largest hydropower station in Anhui Province with 5 installed capacity and a total capacity of 184MW. In March 1999, when combined with Chencun No. 1 computer monitoring and AGC engineering construction, No. 1 generator and No. 1 main transformer electromagnetic type Protection and replacement for LFP~900 type microcomputer protection This paper summarizes our experience in field design, construction, commissioning and operation in generator and transformer microcomputer protection applications. 1 Generator and transformer microcomputer protection site design and commissioning 1 On-site system condition 5kV The electric brake is the normal shutdown braking mode No. 1 main transformer: auto-coupling, OSSPSt 120000/220 - secondary main wiring as shown, generator differential protection with 2TA, 7TA, main transformer differential protection with 1.2 microcomputer Protection device introduction No. 1 generator protection screen is configured as 3-layer chassis LFR981 device with high sensitive cross section of unit, stator ground loss, over voltage, composite voltage overcurrent reverse power protection and symmetric overload negative sequence overload signal, TV Broken wire discrimination, three-phase operation circuit. LFP 982 device has longitudinal (proportional differential, differential quick-break) rotor one-two two-point grounding negative sequence over-current phase-to-phase voltage loss, non-electricity protection and TA disconnection discrimination CM~90 is the microcomputer protection communication management machine No. 1 main transformer The protection screen is configured as a 4-layer chassis. The LFR972A device has main variable differential protection, including second harmonic braking ratio differential and differential quick disconnect. The LFR 973E unit has a main transformer 110kV, 220kV side backup protection (each set of devices), including composite voltage direction overcurrent protection, directional zero sequence overcurrent protection, overload signal and start main converter cooler. The LFR 973F device has a main transformer single transmission 10. 5kV low-voltage side single-phase ground signal and a main transformer common coil overload signal. LFR973D device has main variable light and heavy gas protection, cooler power failure, SF6 switch low pressure alarm and other non-electrical (heavy) protection and three-phase operation circuit 1.3 Field design and debugging problems analysis a generator protection plus original electromagnetic type The excitation disappearance protection in protection, that is, the generator de-excitation switch FMK exciter de-excitation switch LMK electric brake is stopped. The LK switch of the main excitation circuit is disconnected. The normally closed auxiliary contact of the three is connected in parallel and the HWJ of the outlet switch is normally open. The contact is composed in series. When any switch is turned on, the LFP~982 non-electricity protection is activated. The trip pulse is 200msFMK. The voltage type tripping coil of the DM4 type de-excitation switch is used to ensure the reliable operation of the original generator grounding protection device. On the No. 1 main transformer protection screen, there is no stator grounding protection function during the startup of the generator. Considering the actual situation of the primary equipment on the site, the stator grounding protection is configured this time, but when the generator is out of service, the main transformer is shipped 10.5kV. There is no single-phase grounding monitoring on the low-voltage side, so the single-phase grounding protection of the main transformer 10. 5kV side is set.
Phase voltage, and the generator outlet TV used V/V wiring, which can only measure the line voltage. Therefore, the original TV is replaced with a three-phase five-column TV. The secondary B phase is grounded, and the neutral point plus the breakdown fuse is used. The original auto-coupling zero-sequence differential protection configuration that satisfies the main change of the generator synchronous device is canceled, and the sensitivity of the microcomputer differential protection LFR972A when the single-phase ground fault occurs inside the main transformer can be satisfied (the original electromagnetic type BCfr4 is not satisfied) The main transformer differential protection has a total of 4 sides TA (12TA, 15TA, 17TA, 19TA), and the secondary parallel connection of the plant high pressure side 17TA and the main transformer low side 15TA is introduced into the LFR972A as a set of TA, and the protection current phasor is performed. A short-circuit test method with reasonable correct polarity was established during the test.
The 972A differential protection starts to print the main transformer excitation inrush current waveform, and the protection reliably avoids the impact closing excitation current.
The rotor grounding protection adopts the switching sampling method to display the rotor-to-ground insulation resistance in real time when the unit is running. It can be seen that after the unit is overhauled, the rotor-to-ground insulation resistance is increasing and tending to stabilize as the unit running time is extended. (No. 1 machine reaches more than 5001 gongs) However, the hydro-motor unit with frequent start-stop can not monitor the rotor insulation stator of the generator when the unit is shut down. (The fundamental zero-sequence voltage in the grounding protection can protect the generator 85%~95 % of the stator windings are single-phase grounded, and the third harmonic zero-sequence voltage can protect the single-phase grounding of the stator windings near the neutral point of the generator. Since the neutral point of the No. 1 generator is not equipped with TV, the 100% grounding protection function of the stator cannot be fully realized. In the actual analog single-phase grounding protection action LFR973E on the machine side, the correct direction of the power direction with direction protection is determined by the self-produced 3U0,3/. The direction of protection is clearly used to display the phase sequence and phase difference of the current and voltage in real time. The size of the differential protection three-phase differential current provides a technical guarantee for grasping the peripheral circuit of the microcomputer protection and the correct operation. 2 Generator and transformer microcomputer protection Check that the auxiliary contact conversion of the No. 1 switch is not synchronized. The No. 1 switch has just tripped, because the HWJ normally open contact (the No. 1 switch normally open the auxiliary contact is slow) and the normally closed auxiliary contact of the de-excitation switch LMK (LMK has been disconnected when the machine is stopped), the non-power protection 0s exit trip is improved in series. The measure is to analyze the misoperation of the non-electrical protection 2 generator ratio differential protection zone. On October 3, 2000, when the No. 1 switch was connected to the grid, the non-synchronous closing caused by the switch mechanism problem caused the generator ratio. The oscillogram of the LFP982 device in the differential protection zone is seen when the switch A phase and B are closed at the same time, and the C phase delay is closed for 5 ms. The A phase and C phase surge current of the generator contain a large aperiodic period. The component, the non-periodic component and the periodic component of the three-phase current all decrease the difference current /da of the A phase and the C phase with time, /dc is the discontinuous wave, and the /da occurrence time is 70 ms after the closing, the maximum difference current /da It is 3.8A, large = 0.3), and the differential protection action exits after the switch is closed for 95ms. Further analysis of the terminal A phase current / AT non-periodic component from negative to positive at 62ms, neutral phase A phase current / an non-periodic component from positive to negative at 105 ms, due to the DC component in the two sides of the current is different (even On the contrary, the AC transfer error is generated, and the differential current check result is that the models of the TAs on both sides of the generator are different (the secondary load is basically the same), 2 TALMCDI10, 5000A/5A, and D. 7TA LMZD-10, 5000A/5A, Class D Under the action of generator non-synchronous closing impulse current, the current transfer error greatly exceeds the steady-state current error of the differential protection setting due to the inconsistent characteristics of the TA on both sides (10) %) and the non-periodic component coefficient (2.0), the result of the large difference flow, resulting in the ratio differential protection misoperation.
Delay time into fear (ie.) 6 tripping service 1EleCtrniC oil on the generator micro-protection Pan. In the protection; algorithm how to solve the secondary current waveform without distortion, mainly the non-periodic component of the current The dynamic protection has adverse effects. The measures taken at the site are to replace the model of the TA on both sides of the generator with the same model, that is, the volt-ampere characteristics are the same. Because the differential protection of the microcomputer is much smaller than the electromagnetic protection, the action is sensitive, so the difference is small. The secondary circuit load and TA characteristics of the dynamic protection TA are strictly required. At the same time, the influence of the non-periodic component of the short-circuit current needs to be further explored. 10,5000A/5A, D. The generator differential protection side TA is The same model, through the TA volt-ampere characteristic test, selects the same phase of the TA volt-ampere characteristic curve on both sides to reduce the difference current protection program caused by the inconsistent TA characteristics and saturation, and also upgrades to the anti-TA saturation program12. To avoid misoperation after adopting high-sensitivity settings, it is still necessary to accumulate operational experience (refer to the power industry standard "Guidelines for the calculation of relay protection for large generator transformers" (DL/T68 know 1999)) 23 main transformer backup protection action analysis of the tree fault high-resistance grounding and the failure of the development of the permanent failure, LFP 941A microcomputer line protection trip overlap after the rejection, the oscillography shows the fault zero-sequence current When the time is small, the LFR941A protects the zero-sequence current from starting for a long time, and the protection exit is blocked (the original protection program is designed to lock the protection exit when the zero-sequence current is started for a long time (greater than 10s), and the program version is upgraded). Development, the fault current is suddenly large, because the 485-line microcomputer protection outlet has been blocked, causing the direction zero-sequence current I-stage protection action of the LFP973E on the 110kV side of the main transformer No.1, which plays a role of backup protection, thus strengthening the backup of the main transformer. Protection is essential for the safe operation of the site. 24 Understanding the correct level of operation of the protection of the microcomputer components. From the operation of the microcomputer protection of our station, we can see the line LFI!
The correct operation rate of the 900 type microcomputer protection is as high as 100%, and the generator and transformer microcomputer protection can operate correctly in the case of faults in the area, and the incorrect action occurs in the out-of-zone fault. First, the protection principle is in the quick action and Reliability needs to be improved, such as generator differential protection (the original BCR2 is used by the fast-saturated converter for non-periodic components). If the criterion for adding non-periodic components will cause the differential protection to delay in the region. Export, which is not conducive to rapid removal of faults; second, there are hidden dangers in the outer loop, the old equipment loop and special performance meet the operational requirements of electromagnetic protection, but can not meet the operational requirements of the microcomputer protection, these must be added in the future technical transformation work At the same time, it is necessary to strengthen the analysis of the action of microcomputer protection. The analysis of the impact of the electric brake shutdown on the protection of the microcomputer 1 The characteristics of the electric brake shutdown a. The electric brake shutdown technology is adopted in the normal shutdown of the hydroelectric generator of the peaking hydropower plant. The optimal speed value of the electric brake input is 60% Ne, that is, 30 Hz, and the constant braking excitation current is added to the stator winding in the stator winding for about 3 minutes. There is always braking current (take generator / e), its current amplitude is basically constant, the frequency decreases with the speed drop, the unit brake stops at zero speed, the current is attenuated by /e to 0 c. Electric brake short circuit point It is determined by the installation position of the electric switch FDK at the site, in the generator or transformer differential protection zone. Therefore, the protection affected by the electric brake is: 1 generator or main transformer differential protection, 2 generator negative sequence current protection under the action of generator electric brake low frequency current, microcomputer protection due to sampling frequency and frequency factor involved in the algorithm Other reasons can not be fully normal operation, in addition, the protection setting current is small, easy to cause misoperation 3.2 Analysis of the impact of the electric brake shutdown on the microcomputer protection 3.21 The microcomputer micro-machine protection is reduced under the electric brake shutdown condition, both Not reaching /.2= 3.235A, that is, the three-phase current sampling value at 30 Hz is low and asymmetrical, and then the QD signal is started. When the FDK is in the differential protection zone of the generator, the LFP~982 liquid crystal display: the differential current/d has a maximum value of 1.6A at the moment of electric brake input, and the QD signal is generated, which decreases as the unit speed decreases, and the unit stops. /d is reduced to 0 differential protection / coffee is set to Q65A, after the introduction of electric brake shutdown lock will not malfunction LFR981, LFR982 BJ light is on, but the exit TJ is not moving, the generator protection fault signal is issued.
Due to the decrease of the current frequency, the sampling value of /a, /b, /c does not satisfy the sum of the instantaneous values ​​of the three is 0, so that the microcomputer calculates the sampling result and the negative sequence current/2 value/2 appears at the moment of the electric brake input. The value is 0.85A, which decreases with the decrease of the unit speed. When the unit stops, /2 drops to 0. /2. The duration is longer, about 1min. The generator negative sequence overcurrent protection setting value is 1.6A. To prevent accidents, the low-frequency short-circuit current and main transformer of the generator under electric braking conditions are affected by the influence of the outlet plate 3.22 on the main transformer differential protection and improvement measures 15TA before the electric brake is put into operation. The medium-voltage side load current magnitude and phase relationship are not fixed. According to the calculation and actual simulation test, the differential current generated by the main transformer differential protection may cause misoperation to prevent accidents caused by protection misoperation, from the electric brake screen and the local LCU. The screen introduces the double-locked contact to the main transformer protection screen. Each time the No. 1 machine stops, it must reliably block the No. 1 main transformer differential protection, so that the No. 1 main transformer has no main protection operation within a few minutes of the No. 1 electromechanical brake shutdown. This is a security implied way of running the main device of my station. To this end, the field equipment is used once for the first three-winding transformers. Because the main transformer is still running when the unit is electrically braked, in order not to affect the main transformer differential protection operation, the FDK wiring should be selected as much as possible, and the main transformer differential protection No. 1 The 5kV side 15TA is shifted to the 1st switch room through-wall busbar bushing (7TA, 15TA after shifting), so that the FDK is outside the range of No. 1 main transformer differential protection, so that when the No. 1 electromechanical brake is stopped Does not affect the safe operation of the No. 1 main transformer. At the same time, the electric brake shutdown lock No. 1 main transformer differential protection is changed to the lock No. 1 generator differential protection. LFR982 has the function of electric brake blocking generator differential protection in hardware and program design. When the line is changed, the blocking contact is re-moved by ST24A intermediate relay and then connected to AC1 and AC7 terminals of LFR982 to improve the anti-interference ability of the device. The work has completed the evaluation of 900 generator and transformer microcomputer protection in December 2000. LFR900 protects the manufacturing quality, the device debugging and setting parameters are easy to operate, and the real-time information component protection outlet of the liquid crystal display can be measured and protected. The software trip is adopted. The principle and criterion of flexible microcomputer protection applied in the field after the matrix is ​​better than the electromagnetic type protection and the action is sensitive. Especially in the case of the out-of-zone fault, this point complies with the relevant regulations of the microcomputer protection for the external circuit including anti-interference measures.
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