Relay Protection Knowledge Quiz Collection (Part 4)
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A: The function of the wave trap is to prevent the outflow of high-frequency signal currents, because the outflow of high-frequency signals must be connected in series with the earth impedance of the wave trap and the processing bus to form a shunt loop. The bus-to-ground impedance is capacitive reactance in general, but it may also be inductive reactance. Therefore, it is required that the blocking impedance of the wave trap contain a sufficiently large resistance component to ensure that even if the impedance component of the impedance blocker is exactly the same as that of the busbar. Barriers also have a good blocking effect when offset.
62. Why does the submarine current appear after single-phase tripping on both sides of the ultra-high voltage long-distance transmission line? What effect does it have on reclosing?
A: The article describes C-phase ground fault. After the single-phase trip on both sides, the non-fault phases A and B are still in working condition. Since there is a coupling capacitance C between the phases, the A and B phases supply the capacitive current Icl to the fault point k through Cl, and due to the mutual inductance between the phases, the A and B phases with load will be in the fault phase. An induced electromotive force is generated which passes through the fault point and the capacitance C. A loop is formed and an inductive current is supplied to the fault point. These two parts of the current are collectively referred to as the latent current. Due to the influence of the submergence current, the arc at the short circuit can not be extinguished quickly. If a single-phase fast recloser is used, it will be built again. Continuous arc grounding failed the single-phase reclosing. Therefore, the influence of the submergence current must be taken into account during the single-phase reclosing.
63. What is the working principle of high-frequency wave traps?
A: The high-frequency wave trap is a device that prevents the high-frequency signal from diverting into the bus direction. It is a parallel resonant circuit composed of an inductor and a capacitor. It is tuned to the selected carrier frequency, and therefore presents a high impedance to the high-frequency carrier current, prevents the outflow of high-frequency signals, and presents a low impedance to the power frequency current. Does not affect the transmission of power frequency power.
64. What is the role of coupling capacitors in high frequency protection?
A: Coupling capacitors are important connecting devices between high-frequency transceivers and high-voltage transmission lines. Because of its small capacitance, it has a large impedance to the power frequency current, which can prevent the power frequency high voltage from invading the transceiver, and the impedance presented to the high frequency signal is very small, without hindering the transmission of high frequency current. Another function of the coupling capacitor is to form a bandpass filter with the combined filter.
66. Draw the current distribution diagram when the double busbars are damaged in the complete differential protection zone and external fault after the fixed connection is broken, and explain the differential protection action of the busbars. Answer: After the fixed connection of the double busbar is damaged, the fault outside the protection zone is selected. Parts of the components KAl and KA2 flow a part of the short-circuit current, but the start-up element KA has no current, so the bus differential protection does not operate. Its current distribution destroys the current distribution of the busbar 1 in the protected area after the double busbar is fixedly connected. At this time, the short-circuit current flows through the selection elements KAl and KA2. The short-circuit current flowing through the selection element KAl is large, and the breakers QF1 and QF2 of the connection elements on the bus-tie breaker and busbar 1 are cut. The short-circuit current flowing through the selection element KA2 is small, and if it does not act, the short-circuit current is still supplied through the QF4 and the failure is still not eliminated. Therefore, if the double busbars are damaged, the contact points of the selecting elements KAl and KA2 must be shorted so that the busbar differential protection becomes a non-selective action, and all the connecting elements on the busbar 1 and the busbar 2 are cut off.
67. Describe the basic operating principle of the current phase comparison bus protection.
Answer: Regardless of the current differential bus protection or busbar protection comparing bus phase breaker current phase and total differential current phase, the operating current of the starting element must avoid the maximum unbalance current during external short circuit. When the number of connected components on the bus is large and the unbalanced current is large, the sensitivity of the protection device may not meet the requirements. Therefore, there is a current phase comparison type bus protection, and its working principle is as follows. The article describes the bus wiring, when its normal operation or bus external short circuit, the current I1 flows into the bus,
I2 flows out of the busbars. They are equal in size and 180° out of phase. When a short circuit occurs on the busbar, the short-circuit currents I1 and I2 flow to the short-circuit point. If the electromotive force of the power supplies I1 and I2 is in phase, and the short-circuit impedance angles of the I1 and I2 arms are the same, I1 and I2 are in phase. The phase angle difference is 0°. Therefore, it can be judged by the phase comparison element whether there is a failure on the bus. This bus protection only reflects the phase between currents and therefore has a high sensitivity.
68, draw the circuit breaker light monitoring control, signal circuit diagram. And explain its wiring characteristics.
Answer: The circuit breaker light monitoring control and signal circuit diagram are shown in Figure 9-1. The wiring features are as follows. (1) The control switch SA adopts LW2-2 type. The status of the circuit breaker is indicated by red and green lights. The red light means that the circuit breaker is in the closing state and indicates that its trip circuit is in good condition; the green light means that the circuit breaker is in the trip state and indicates that its closing circuit is in good condition. Closing resistance of the closing contactor KM is 249, (using CZ. DC contactor), and the circuit breaker tripping coil resistance is generally 881'1. If both the red and green lights are off, it indicates that there is a problem with the DC control power supply, but no sound signal is emitted at this time.
(2) When the automatic synchronization or standby power automatic input contact lAS is closed, the circuit breaker is closed and the red light HR flashes; when the protection action, the outlet intermediate relay KC contact is closed, the circuit breaker trips, the green light HG flashes, indicating that the circuit is open The actual position of the device does not match the position of the control switch. When the circuit breaker is in the closing position, the control switches SAl-3 and SAl7-19 are closed. In this case, when the protection action or the circuit breaker is accidentally tripped, the auxiliary contactor QF of the circuit breaker is closed, and the accident signal is connected to the WF circuit of the small bus bar. Accident sound signal.
(3) The short pulse of the circuit breaker closing and tripping coil is guaranteed by the auxiliary contact QF of the circuit breaker of the circuit breaker.
(4) When the control switch SA is in the "pre-set" or "pre-split" position, the indicator lamp is turned on via the SA9-10 or SAl4-13 contact with the flash bus (+) WH circuit and the indicator light flashes.
(5) The anti-jump of the circuit breaker is realized by a special anti-kick relay KCF.
(6) The number of cores connecting the main control room to the operating mechanism is five cores.
69. After the completion of the new installation of the relay protection device, what are the major items for acceptance?
A: After the newly installed protection device is completed, the main items of acceptance are as follows:
(1) The actual measurement parameters of electrical equipment and lines are complete and correct.
(2) All the protection device as-built drawings are in line with reality.
(3) The device setting meets the requirements of the setting notice.
(4) The inspection items and results are in compliance with the provisions of the inspection regulations and relevant regulations.
(5) Check the current transformer ratio and volt-ampere characteristics, and the secondary load meets the error requirements.
(6) The equipment in front of and behind the screen should be neat and intact, and the circuit is well insulated. The signs are complete and correct.
(7) The secondary cable is well insulated and the labels are complete and correct.
(8) Perform an acceptance test with the primary load current and the operating voltage to determine the correctness of the transformer polarity, ratio and loop, and determine the correctness of the components and wiring of the protection device such as direction, differential, distance, and high frequency.
70, What are the characteristics of phase difference high frequency protection?
Answer: (1) Half of the high-frequency protection is installed on both sides of the protected circuit, and transmission and comparison of high-frequency signals are used to achieve the purpose of protection. Its protection zone is limited to this line, and its action time limit does not need to cooperate with the protection of adjacent components. Various types of failures occur within the full length of the protected line and can be removed without time limit.
(2) Because the high-frequency protection does not reflect faults outside the protected line, it cannot be used for backup protection of the lower-segment line. Therefore, additional protection is required for the line to be used for backup protection of the line and the next line.
(3) The phase difference high-frequency protection has good selectivity and high sensitivity, and is widely used as the main protection on the high voltage transmission lines of 110-220kV and above.
Relay Protection Knowledge Q&A Compilation by Yangzhou Tuopu Electric Technology Co., Ltd. Department of Biotechnology, Consultation Hotline, Website:
71. In the large grounding current system, why should the DC operation power supply for phase-to-phase horizontal-direction protection be locked by zero-sequence-cross-directional protection?
Answer: The zero-sequence transversal direction protection adopts the zero-sequence current and the zero-sequence voltage compound starting component. When the external phase of the parallel line fails, the zero-sequence current and the voltage relay do not act. When the internal phase fault occurs, the zero-sequence current relay may act, but the zero-sequence voltage relay does not act, and the phase-to-phase current protection is not blocked. When the grounding short circuit occurs inside the parallel line, the zero-sequence current and the voltage relay are all actuated, and the phase-to-phase and cross-direction protection is blocked. This prevents the phase-to-phase differential protection from being affected by the non-fault phase current and may cause malfunction.
72. Under what conditions will the power system operate, there will be zero-sequence current? Try five examples.
Answer: The power system will have a zero-sequence current in three-phase asymmetrical operating conditions. For example:
(1) The three-phase operation parameters of the power transformer are different.
(2) There is a ground fault in the power system.
(3) Two-phase operation during single-phase reclosing.
(4) three-phase reclosing and manual closing when the three-phase circuit breaker in different phases of investment (5) no-load investment in transformer three-phase excitation inrush current is not equal.
73. There are several operating modes for reclosing: What is the performance?
A: The integrated reclosing can be realized by the following four reclosing modes:
(1) Comprehensive reclosing mode, the function is: single-phase fault, single-phase jump, single-phase overlap (check the same period or check no pressure), coincide with permanent fault trip three-phase.
(2) Three-phase reclosing mode, the function is: any type of fault is jumped three-phase, three-phase overlap (check the same period or check no pressure), coincide with a permanent fault jump three phases.
(3) Single-phase mode, the function is: single-phase fault jump single-phase, single-phase overlap, three-phase tripping does not coincide when the phase fault.
(4) Disable mode, the function is: When any fault occurs, it will jump to three phases and not overlap.
74, negative sequence current relay, when its reactance transformer two primary winding or secondary winding and intermediate converter winding corresponding polarity reverse, what will happen? How to prevent?
Answer: Negative sequence current relay reactance Transformer When the primary or secondary windings and the corresponding polarity of the intermediate converter winding are reversed, the negative sequence relay will become a positive sequence relay. After the relay protection is put into operation, no asymmetry fault occurs, but if the load current reaches a certain value, it will malfunction. In order to ensure the correct connection of the negative sequence current relay and prevent the above situation, the following measures must be taken:
(1) Pass the three-phase power supply to check the setting of the negative sequence current relay.
(2) When testing with a single-phase power supply, the relative polarity should be measured in accordance with the principle of the negative-sequence filter, so that it meets the requirements, and the load current must be used for inspection. After confirming that the wiring is correct, it is put into operation.
75. Why does a DC two-point grounding sometimes cause a circuit breaker to trip accidentally, sometimes it causes the circuit breaker to refuse to jump, sometimes it causes the fuse to blow?
Answer: (1) Two-point grounding may cause circuit breakers to trip by mistake: As the description of the article shows, when DC grounding occurs at two points A and B, the current relays 1KA and 2KA contacts are shorted, and KC is started, KC touches. Tap closed and trip. A, C Short-circuit the KC contact and trip when grounded at two points. At points A and D, D, F and the like can all cause the circuit breaker to trip by mistake.
(2) Two points of grounding may cause the circuit breaker to refuse to move:
As shown in Figure 9-7, grounding occurs at two points B and E or two points C or E, and the circuit breaker may cause refusal.
(3) Two-point grounding causes the fuse to blow:
As shown in Figure 9-7, the ground point occurs at two points A and E, causing the fuse to blow.
When the grounding point occurs at points B, E, and C and E, the circuit breaker will not only refuse to jump, but also cause the fuse to blow, and at the same time it may burn out the relay contacts.
76. Why is the sensitive angle of negative sequence power direction relay -105°±10°?
Answer: The negative sequence power direction relay is used in the relay protection device to judge the negative sequence power direction when the two phases are short circuited. When a two-phase metallic short circuit (such as BC two-phase short circuit) occurs in the power grid, if the non-fault phase A phase is the reference, the boundary condition of the fault point is Uk0=0, UkA1=UkA2=IkA1, IkA1=IkA2 and its phasor Picture shows. When the impedance angle of ZIΣ is 75°, that is, IkA1 is 75° behind UkA2, and IkA2=−IkA1, that is, UkA2 leads IkA2. Therefore, in order to make the negative sequence power relay sensitive and correct to determine the direction of the negative sequence power, the maximum sensitivity angle is set to -105°±10°.
77. Why do large-capacity generators use negative-sequence inverse-time overcurrent protection?
A: The asymmetry of the load or system causes a negative-sequence current to flow through the stator windings of the generator and a negative-sequence rotating magnetic field is established in the air gap of the generator, causing the rotor to induce twice the frequency of the current, causing the rotor to heat up. Because of the direct cooling type (water internal cooling and hydrogen internal cooling), a large generator requires a smaller volume increase than a larger capacity. At the same time, the thermal capacity margin of a large unit is generally lower than that of a large generator due to economic and technical reasons. Small units are small. Therefore, the negative sequence additional heating of the rotor should pay attention to, the general trend is that the greater the capacity of the single machine, the smaller the value of A, the lower the ability of the rotor to withstand the negative sequence current, so we must particularly emphasize the negative sequence protection of large generators. The duration of the allowable negative sequence current of the generator is A=I2t. The larger the I2 is, the shorter the allowable time is, and the smaller the I2 is, the longer the allowable time is. Because of the inverse time characteristics of the generator to I2, negative sequence reverse time overcurrent protection should be used on large units.
78. Why should the generator be equipped with negative sequence current protection?
Answer: When an asymmetric short-circuit or three-phase asymmetrical operation occurs in the power system, there is a negative sequence current in the stator winding of the generator. This current generates a reverse rotating magnetic field in the air gap of the generator, which is twice the synchronous speed with respect to the rotor. As a result, a frequency-doubling current occurs in the rotor component. This current causes local burns in certain parts of the rotor where the current density is high. In severe cases, the guard ring may be loosened by heat, causing significant damage to the generator. Another 100Hz alternating electromagnetic torque will act on the large rotor shaft and the stator frame, causing a frequency of 100Hz vibration.
In order to prevent the occurrence of the above-mentioned hazardous generator problems, negative sequence current protection must be set.
79. Try to analyze the role of generator differential protection and horizontal differential protection and the scope of protection? Can they replace each other?
Answer: Diffusion protection is the most effective method of protection against internal short-circuit fault protection of the generator and is the main protection against short-circuits between generator stator windings.
The horizontal differential protection is to protect the stator winding of the generator from a phase-to-turn short circuit and the inter-turn short circuit protection between the two parallel branches of the same phase. For generators with a star connection and two parallel lead-out lines per phase, they must be installed. Set the horizontal difference protection. When the phase windings near the stator windings or near the neutral point are short-circuited, the current in the two neutral point connections is small, and the horizontal differential protection may not operate and the dead zone may reach 15% to 20%. Therefore, it cannot replace the longitudinal differential. protection.
80. Draw the circuit breaker audio monitoring control and signal loop diagram. And explain its wiring characteristics.
Answer: The circuit breaker audio monitoring control, signal loop diagram, the article explained. The wiring features are as follows. (1) The control switch SA uses LW2-YZ type with the signal inside the handle. The normal closing position of the circuit breaker is indicated by the SA handle in the closing position, its contact SA20-17 and the KCC contact turn-on signal light to achieve; trip position indication is the handle in the trip position, its contact SAl4— 15 and KCT contact signal lights to achieve. The indicator light flashes when the position of the circuit breaker does not correspond to the position of the SA handle. If the handle is in the closing position, the indicator light flashes, indicating that the circuit breaker has tripped; if the handle is in the tripping position, the indicator light flashes, indicating that the circuit breaker is automatically closed.
(2) When the fuses FU1 and FU2 of the control circuit are blown, the coils of the relays KCC and KCT are simultaneously de-energized, the normally closed contacts thereof are closed, the small bus WCO of the disconnection signal is connected, and an acoustic signal is issued. At this point from the lights out, you can find the fault control circuit. The audible signal device should be time-delayed, because when the closing or tripping pulse is issued, the corresponding KCC or KCT is short-circuited and the voltage is lost. At this time, the acoustic signal may also act.
(3) KCT and KCC relays can be used as a monitor for the next operation loop. If the circuit breaker is in the closing position, the KCC starts and its normally closed contact is opened; at the same time, the KCT is powered off and its normally closed contact is closed. When the closing circuit is disconnected, the KCC is powered off and the KCC normally closed contact is turned on, thereby emitting an acoustic signal. Trip circuit monitoring is similar to this. Find out the faulty control circuit by extinguishing the indicator light.
(4) In the process of manual closing or tripping (that is, SA is in the "pre-coordination" or "pre-split" position), the indicator lamp can also emit flashes through SAl3-14 or SAl8-17.
(5) When this connection is normal, it can be operated in a dark screen, and it can make the signal light bright to facilitate checking the integrity of the circuit. In the figure, (+) WS is a small bus that can control dark or light operation.
(6) Contact between the main control room and the circuit breaker operating mechanism The cable core has three cores. (Finish)
Source: Yangzhou Tuopu Electric Technology Co., Ltd. Website http:// 