SF6 gas has excellent insulating properties, arc extinguishing properties and stable chemical properties, and is widely used in high-voltage switchgear, while the density and purity of SF6 gas are directly related to the performance and reliable operation of the equipment.
For example, the leakage of SF6 gas will cause its density to decrease, and may increase the water content of the gas in the equipment, thus affecting the insulation performance and breaking performance of the equipment. In order to monitor the SF6 density of gas, high-voltage switchgear is equipped with the SF6 relay.
When the SF6 gas pressure drops to the first alarm value, the density relay acts to report the signal of the supplemental gas pressure; when the SF6 gas pressure drops to the second alarm value, the density relay acts to report the signal of the blocking pressure, and at the same time the switch jumps The closing circuit is disconnected to realize opening and closing blocking.
Due to various reasons, the performance of SF6 gas density relays may change during long-term operation, or even lose the monitoring function. For example, after a long period of inactivity, the action is stuck or inflexible, and the contact point is not in good contact.
In some cases, the temperature compensation performance will also deteriorate. When the ambient temperature changes, it may cause the SF6 gas density relay to malfunction. Therefore, it is very necessary to carry out the calibration in a timely manner, and the transmission test of the SF6 gas density relay and the background secondary device after the calibration is even more important.
However, there are many difficulties and safety hazards in the traditional SF6 relay transmission test in actual work. The specific status is as follows:
1. Open the rear junction box of the SF6 relay on site, and use the short-circuit wire to artificially short-circuit the corresponding alarm and blocking contacts to conduct the test. It is impossible to find that the SF6 relay meter pointer is stuck or other faults cannot rotate normally, and the contacts are not connected normally when indicating pass defects;
2. For the SF6 relay installed near the middle of the circuit breaker frame, the junction box is wrapped inside the frame, and even if the sealing plate is opened, the traditional short-circuit method cannot be used to open the junction box for transmission test.
It can only be used to discharge the wiring terminals in the upper-level mechanism box, and perform short-circuit test transmission. In this way, the defects of the alarm and the reverse connection of the locking contacts cannot be found, and it is impossible to realize the root transmission test. Invisibly buried more equipment safety hazards.
In order to solve the above defects and realize the function of carrying out the transmission test from the root of the SF6 relay, we have designed and developed the SF6 relay transmission test control valve after a lot of analysis and research.
1. Working principle
Install the control density valve at the check joint of the SF6 relay, close the valve at the circuit breaker body, and change the residual gas pressure value in the meter head of the SF6 relay through the control valve to turn on the alarm and lock contacts, and conduct a signal transmission test.
2. Working method
During the transmission test, first install the control valve on the SF6 relay verification connector, close the main gas valve of the circuit breaker body, and then slowly rotate the SF6 relay transmission test control valve.
When the SF6 gas in the table slowly drops to the alarm value, the alarm signal will be sent out. At this time, check the background signal, and if it is correct, continue to rotate the control valve until the gas pressure measuring device finds the pressure dropping to the lock value, and then carry out the corresponding lock transmission test.
3. Matters needing attention
Before the test, safety measures must be taken, the test procedures must be mastered, and corresponding test procedures should be formulated if necessary.
The on-site SF6 relay transmission test should be carried out in the case of equipment power failure, and the control power supply with the gas density relay must be cut off.
The corresponding wiring of the alarm and blocking contacts should be disconnected from the terminal block to prevent the formation of a loop with the secondary circuit and the use of signal lines, which will affect the transmission test and ensure that it does not affect the normal operation of other equipment.
4. Beneficial effects
It can timely find the defects and hidden dangers that the SF6 relay meter pointer cannot rotate normally, and the contacts are not normally connected during the indication, which cannot be found in the traditional SF6 relay transmission test.
Solved the problem that some circuit breakers cannot be driven due to the installation position of SF6 relays.
The function of carrying out the transmission test from the root of the SF6 relay is realized.