1. Manual tripping and closing can be performed, and automatic tripping and closing can be realized through relay protection and automatic devices, and the pulse current of tripping and closing can be automatically cut off after the tripping and closing actions are completed (because the tripping and closing coils are designed to be energized for a short time).
2. It can reflect the opening and closing position of the circuit breaker.
3. The integrity of the closed circuit can be monitored during the next operation.
4. It has an anti-jump circuit to prevent the circuit breaker from repeated actions for many times.
5. There are perfect tripping and closing locking circuits.
Second, the typical control loop.
0 1, basic tripping and closing circuit
The above picture is a simplified schematic diagram of tripping and closing, in which +KM and -KM represent positive and negative power supplies, DL is the auxiliary contact of the circuit breaker, and HQ and TQ are the closing and tripping coils respectively.
Note: Manual closing/remote closing/reclosing action contact is not the same closing outlet contact, and manual opening/remote opening/protection opening contact is not the same tripping outlet contact, which is simplified here for easy understanding.
Assume that the circuit breaker is in the closed state, and the auxiliary contact D 1 of the circuit breaker is closed. When the protection device issues a trip command, the trip outlet contact is closed, and the positive power supply → trip outlet contact →DL→TQ→ negative power supply forms a loop, which energizes the trip coil TQ and trips the circuit breaker. After the circuit breaker completes the tripping action, the DL normally open contact disconnects the tripping circuit and the DL normally closed contact closes to prepare for the next closing. The closing process of the circuit breaker is the same, so I won't go into details here.
Disconnecting the trip current with DL normally open contacts is to prevent the trip coil TQ from burning out due to adhesion of the trip outlet contact (because the heat capacity of TQ is designed according to short-term electrification); Second, if the tripping outlet contact disconnects the tripping current, it is easy to burn the contact due to the lack of arc breaking ability of the contact, which lays a hidden danger for the next protection tripping (or closing) and is not easy to be found.
02, monitoring circuit
The above circuits can't meet the actual needs. The basic requirements of the above control loop should reflect the position and state of the circuit breaker and the integrity of the tripping and closing loop. Therefore, we added TWJ and HWJ to the circuit to monitor the integrity of the trip circuit and the closed circuit. It is shown in green in the figure. HWJ and TWJ respectively monitor the closing and opening of relays.
When the switch is in the off position, the normally closed contact of DL is closed, the circuit where TWJ relay is located is connected, TWJ acts, the normally open contact of TWJ at the bottom of this drawing is closed, the off indicator is on, the reaction circuit breaker is in the off position, and the closing circuit is good. Similarly, when the closing indicator light is on, it means that the circuit breaker is in the closing position and the trip circuit is in good condition.
Is there a question to think about at this time? When the opening monitoring circuit is connected, a current flows through the closing coil HQ, will it lead to the circuit breaker closing by mistake?
The answer is no, because the current-limiting resistor R is connected in series in the opening monitoring circuit, the current flowing in the circuit will be very small, which is lower than the starting current value of the closing coil HQ, so it will not close.
03, tripping and closing to keep the cycle.
During the open and close operations, the remote close/open command is generally a high-level pulse of several hundred milliseconds. In order to prevent the pulse from failing before the end of the switch operation and ensure the completion of the switch operation, it is necessary to add a holding loop. Intuitively speaking, it is to prevent the tripping and closing outlet contact from being disconnected before the DL auxiliary contact, which leads to the incomplete opening and closing action, so the tripping and closing self-holding loop is added. See the blue part of the picture for details. Where HBJ and TBJ represent closed and tripped latching relays respectively, and S 1 represents the travel node of the energy storage spring.
During closing operation, HBJ relay is turned on and HBJ normally open contact is closed. At this point, whether the closing outlet contact is disconnected or not, the closing circuit will be connected through the HBJ contact to complete the closing operation. At this time, whether the closing outlet contact is disconnected before the DL auxiliary contact will not affect the closing of the circuit breaker. In the same way.
However, adding HBJ relay has a disadvantage. After the closing command HBJ is given, the on-off of the closing circuit is completely determined by the auxiliary contact DL. If the spring fails to store energy, the normally closed contact of DL will always be closed, and the closing current will always exist, which is easy to burn HQ, so it is necessary to connect the trip node S 1 of the spring in series.
04. Turn off the relay (KKJ)
Generally speaking, there are three ways to open and close circuit breakers: local manual operation, remote control and automatic control of protection devices. The control loop should have the function of distinguishing the action of the protection device from the manual operation of the circuit breaker, so a closing relay (KKJ) should be added. See the purple part in the picture for details.
As mentioned earlier, manual closing/remote closing/reclosing is not a contact. Combined with the purple part in the figure, we can see that:
CHJ is the reclosing contact, TJ is the protection tripping contact, and YHJ is the remote closing contact.
YTJ is the remote opening contact, HHJ is the closing relay, and QK is the switch operating handle.
Briefly introduce QK switch handle.
When the handle is far away, ③ ④ and ⑤ ⑤ contacts are connected, and remote control operation can be carried out.
When the handle position is local closing, ① and ② contacts are connected to complete local closing operation.
When the handle position is in the local brake opening, ⑦ ⑧ the contact is connected to complete the local brake opening operation.
The KKJ relay in the picture is a two-position relay. When manually (remotely) turned on, KKJ relay will act, set to "1" and keep it off. When the switching/remote closing contact is closed, KKJ relay returns, sets "0" and remains closed.
Because of the diode (unidirectional conduction), CHJ and TJ will not trigger KKJ relay, and KKJ is used to judge whether it is normal opening and closing operation or tripping and closing action when the protection device fails. When the normal opening and closing operation, KKJ strain, when the protection trip, KKJ should be the same. KKJ's normally open contacts are used for "emergency master" signals and reclosing devices.
05. Anti-jump circuit
The so-called anti-jump is not to prevent "jumping", but to prevent "jumping". Jump refers to the process that the circuit breaker repeatedly jumps-closes-jumps-closes-jumps for some reason. The reasons for the jump are as follows:
Jumping will lead to multiple shocks of fault current, damage the circuit breaker and even explosion. See the red part of the figure for the anti-jump circuit, in which TBJV is the anti-jump relay.
When the protection device acts, the current flows in the trip circuit, and the normally open contact of TBJ in the trip prevention circuit is closed. At this time, if the closing contact is stuck and the closing command is issued all the time, the circuit of the closing contact →TBJV→TBJ will be connected, and the voltage of the anti-trip voltage relay TBJV will be self-maintained. The self-maintained TBJV contact will be closed, and the normally closed contact of TBJV next to HBJ will be disconnected, thus cutting off the closing circuit and preventing the circuit breaker from "tripping".
If there is no opening command when tripping, after the breaker is opened, the tripping circuit is disconnected by the DL normally open contact, and the TBJ current coil loses power. At this time, because the closing contact has been disconnected, the TBJV voltage cannot be self-maintained and reset. TBJV recloses, and the closing circuit is good, which will not affect the next trip.
From the above action process, it can be seen that the essence of anti-trip is "anti-closing", which keeps the circuit breaker in the "tripping" state. The anti-trip is started by the tripping circuit anti-trip current relay TBJ and maintained by the closing circuit anti-trip voltage relay TBJV.
Let's think about two questions, okay?
1. Will the existence of anti-trip circuit affect the normal closing?
It will not affect the normal closing, because in the process of normal opening and closing, TBJ will start the anti-trip circuit after issuing the opening instruction, and will keep the trip circuit at the same time. After the trip is completed, the auxiliary contact DL will cut off the trip circuit, and the TBJ will be powered off and exit the trip prevention circuit. Normal shutdown will not be affected at this time.
2. Will the auxiliary contact D 1 open the trip circuit before TBJ starts the trip prevention circuit?
If TBJ doesn't move quickly, it can't be closed and the anti-jump circuit can't be started, so the sensitivity of TBJ anti-jump relay must be very high. The TBJ current coil connected to the trip circuit requires a small voltage drop when it is disconnected, and the regulations stipulate that it cannot be greater than 5% of the rated voltage of the control power supply. The rated working current of TBJ current coil should not be greater than 50% of the tripping current to ensure the reliable operation of TBJ when tripping.
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