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Inspection of SF6 Gas Density Relay

SF6 gases are increasingly used in a variety of high-voltage electrical equipment due to their excellent insulation and arcing properties. Become the preferred insulation and arcing medium for today's high-voltage equipment. In order to ensure the safe operation of high-voltage equipment, the density and water content of SF6 gas must be strictly monitored. SF6 density relay is used in high-voltage electrical equipment, SF6 gas density monitoring of a device, it is for the electrical equipment gas leakage situation, timely issued alarm signal, latching signal. Can be timely and effective to avoid the occurrence of accidents, to ensure the safe operation of high-voltage electrical equipment. However, the SF6 density relay installed in the field because often do not move, over time, there will be inflexible movement, poor contact and other phenomena, and some will be due to the impact of environmental conditions caused by the temperature compensation performance, resulting in SF6 density relay misalignment. To this end, SF6 density relays must be regularly (generally prescribed for 1 to 3 years) for on-site inspection and prevention.

In a general closed container, the SF6 gas pressure at a certain temperature can represent the SF6 gas density, so in order to unify the standard, it is customary to take the SF6 gas pressure at 20 degrees Centigrade as the representative value of its corresponding density. Therefore, the SF6 density relays are scaled at the SF6 gas pressure at 20 degrees Centigrade. The test of the SF6 density relay is in effect a test of the action pressure at 20 degrees Centigrade. There are several ways in which SF6 density relays can be tested.

1. Use the SF6 device inflating process to inspect the SF6 density relay

This method is mainly used in the field, when the SF6 equipment is installed, the body is inflated, the density relay is proofread by the inflatable process (the contact action situation / pressure gauge indication value), this method is simple and practical, can initially judge the SF6 density relay, but there are several problems.

(1) Affected by temperature.SF6 gas storage cylinder SF6 gas is stored in liquid form, when the equipment is filled with SF6 gas, from liquid into gas, absorb energy, in a very short period of time into the equipment SF6 gas temperature and ambient temperature is very different, and SF6 density relay for a long time outdoor, the same as the ambient temperature, which is equivalent to different temperature SF6 gas density relay testing, it is difficult to ensure the accuracy of the test. Using the reading of SF6 pressure gauge as a reference value, the test method for comparison has a large error.

(2) The SF6 density relays are mainly used in the buck process, which is not in line with the actual situation and affects the accuracy.

2. Use the SF6 equipment degassing process to inspect the SF6 density relay

This method has the same problem as the first two in the inflatable process, and the released gas needs to be recovered with a special gas recovery device, the procedure is complex, generally not used.

3. Test the SF6 density relay in the constant greenhouse

This method of testing is carried out at a constant temperature (200 degrees Centigrade), eliminating the temperature error brought about by the inspection, high accuracy, but the inspection time is long, the need to establish a special temperature laboratory, the general site does not have the conditions, mainly used in manufacturers.

4. The SF6 density relay is inspected by temperature and pressure correction method

(1) This method is generally suitable for field applications and is currently the most used method. It is the use of SF6 gas degassing process to test it, but not the use of SF6 equipment body gas, but made into a special device in the field. During the inspection, the SF6 gas density relay is isolated from the body using a special valve of the device body, and then connected to the SF6 gas density relay inspection equipment for inspection. The pressure at the SF6 density relay is accurately measured and the ambient temperature is recorded simultaneously, and the movement pressure at 20 degrees Centigrade is converted.

(2) The keys to this method are:

1) The pressure (recording ambient temperature) when measuring the action of the SF6 density relay must be accurate;

2) Pressure/temperature conversion should be performed.

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Lanso Instruments INC.
233 W 1st St #210, North Vancouver, Canada
233 W 1st St #210, North Vancouver, Canada