The density relay is one of the main components for monitoring SF6 electrical equipment. It monitors the pressure value of SF6 gas in real time, thus ensuring the insulation strength inside the electrical equipment.
Since it has an internal bimetal for temperature compensation, it can effectively prevent changes in gas pressure indication due to changes in ambient temperature.
The density relay can be divided into two parts: meter display and node signal. The meter display part indicates the internal air pressure of the electrical equipment, and the node signal part issues a low pressure alarm or low pressure blocking signal when the internal air pressure drops to a certain value.
In the "Electric Power Equipment Handover and Preventive Test Regulations" requires the SF6 relay to be calibrated after handover and overhaul as well as every 3 years.
This is because the SF6 relay long-term operation, due to a variety of reasons the performance may change, or even lose the role of guardianship.
However, because SF6 density of gas relay is installed with the switch in the field next to the body, it is not easy to disassemble and does not support disassembly, because frequent disassembly is easy to lead to interface damage and gas leakage, so the density relay calibration is recommended to be carried out directly in the field of.
1. The design of the three-way valve
In order to facilitate on-site calibration, while not disassembling the density relay, reducing the risk of equipment damage and gas leakage, it is recommended that the SF6 equipment be equipped with a three-way valve.
One interface is connected to the body for isolating the gas chamber of the body; one interface is used for installing SF6 relay; one interface with self-sealing function is used as field calibration port, testing and filling port.
2. Introduction of working principle
Density relay three-way valve in the normal working state, the cone valve and the gas inlet does not contact, the equipment gas interface of the gas path and density of gas relay, the sealing cover is tightened state, the inside of the sealing cover is installed to ensure that the three-way valve interface sealing reliable.
If the density of gas relay is calibrated or replaced, the body is isolated from the relay by adjusting the switch on the three-way valve to control the connection between the body and the relay.
Thus the relay will be independent, and then the calibration or replacement of the gas density relay will be completed step by step by deflating the SF6 relay with a standard meter.
With the application of the three-way valve, it is possible to calibrate the SF6 relay without disconnection and disassembly, making the field calibration of the density relay very simple.
At the same time, the calibration port on the three-way valve can be used as SF6 micro water, decomposition products, purity test, inflatable interface, and at the same time can unify the test and SF6 relay calibration port on different types of switchgear to ensure the safe and reliable operation of the power grid.
3. Standard of three-way valve
The design of the three-way valve has strict standards and needs to meet the following requirements.
(1) One-piece structure, stainless steel material.
(2) explosion-proof pressure test: under 4 times PN, the valve is normal, and under 32 times PN, the valve body appears damaged.
(3) Impact test: after 10,000 impacts, the leakage value is less than 1 × 10-8 mbar * L / s.
(4) Corrosive environment test: IEC60068-2-11 standard test.
(5) Technical specifications: Pressure rating of PN64.
(6) sealing performance: leakage rate
(7) Ambient temperature: -40～100℃.
(8) Impact resistance: 600m/s, 211ms.
Close the valve between SF6 equipment body and density relay, open the inflatable valve slowly for deflation, and directly measure the pressure signal of the output terminal with a multimeter.
When the pressure value of SF6 gas drops to the alarm value and blocking value respectively, read and record the external pressure gauge value respectively.
According to the ambient temperature at that time by the density following the "sulfur hexafluoride pressure and ambient temperature relationship chart" to check the SF6 relay action value, so as to achieve the purpose of calibration density relay.
SF6 equipment installation three-way valve can be non-stop, without disassembling the case, to complete the density relay calibration work; without power outages to replace the SF6 relay; convenient to measure the equipment micro-water test and replenishment of SF6 gas;.
At the same time to solve the SF6 gas density relay frequent disassembly caused by gas leakage phenomenon, and calibration without power failure, no need to disassemble the screws, one person can operate independently, effectively saving labor costs.