DL/T 506-2018Method of humidity measurement of sulfur hexafluoride insulated gas in electrical equipment (English PDF)

1 Scope

This Standard specifies the method for measuring the humidity of insulated gas in sulfur hexafluoride electrical equipment.

This Standard is applicable to the measurement of the humidity of the insulated gas in sulfur hexafluoride electrical equipment in the type test, exit-factory test, handover test and preventive test. The mixed gas insulated electrical equipment can be implemented as a reference.

2 Normative References

The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) is applicable to this document.

DL/T 639 Safety and Protection Rules for Operation, Test and Maintenance

Personnel of SF6 in Electrical Apparatus

3 Terms and Definitions

For the purposes of this Document, the following terms and definitions apply.

4 Requirements for Humidity Meter

4.1 The used humidity meter shall meet the following requirements when the ambient humidity is 10°C~40°C:

--- The measuring range of the electrolytic humidity meter shall satisfy

1µL/L~1000µL/L.

--- Fiducial error: within the range of 1µL/L~30µL/L, it shall not exceed ±10%;

within the range of 30µL/L~1000µL/L, it shall not exceed ±5%.

4.2 The measuring dew-point range of the chilled dew-point meter shall satisfy 0°C~ -

70°C when the ambient temperature is 20°C; and the measurement error shall not exceed ±0.6°C.

4.3 The dew-point range of resistance capacitive humidity measurement shall satisfy

0°C~-60°C; and the measurement error shall not exceed ±2.0°C.

4.4 The humidity meter shall be checked and calibrated regularly; and the validity period of the calibration result certificate is one year.

5 Requirements for the Measurement Gas Circuit

System

5.1 The measuring pipeline must be made of stainless steel, copper or polytetrafluoroethylene, with a wall thickness of no less than 1mm and an inner diameter of 2mm~4mm. The inner wall of the pipeline shall be smooth and clean; and it is not allowed to use pipelines with strong water absorption capacity, such as rubber pipes and polyvinyl chloride pipes, etc.

5.2 The joints are required to be well sealed, clean, and free from damage and burrs.

It is made of stainless steel or brass, and it is forbidden to use iron joints.

6 Requirements for Measuring Ambient Temperature

and Humidity

6.1 The ambient temperature shall be between 10°C ~ 40°C (measure between 10°C and 30°C as much as possible).

6.2 The relative humidity shall be no greater than 85%.

10 Temperature Conversion of Measurement Results

10.1 Since the ambient temperature has a significant effect on the gas humidity in the equipment, the measurement results shall be converted to the value at 20°C in accordance with Appendix C.

11 Safety Precautions

11.1 Safety precautions shall be taken when testing the equipment while it is live.

11.2 During the test, the test site shall be ventilated.

11.3 The safety protection of test personnel shall be implemented in accordance with the relevant provisions of DL/T 639.

12 Report on Measurement Results

The report on measurement results shall include the following:

a) The name, model, exit-factory number, and exit-factory date of the tested equipment;

b) The name, model, exit-factory number, calibration date of humidity meter;

Appendix A (Informative)

Conversion Formula of Humidity Measurement

A.1 When measuring the humidity in the gas, it can be expressed in various measurement units. Such as dew point, saturated water vapor pressure, volume ratio, weight ratio, absolute humidity, relative humidity. The measured dew point can be used to convert between measurement units.

The symbols and meanings are as follows:

ed – saturated water vapor pressure under measuring dew point, in Pa;

NOTE: When the dew-point is lower than 0°C, if the condensate on the surface of the dew sensor is supercooled water, take the saturated water vapor pressure on the surface of the supercooled water; if the condensate on the surface of the dew sensor is ice crystals, take the saturated water vapor pressure on the ice surface.

Pt – total pressure of the measurement system, in Pa;

Vr – volume ratio, in µL/L;

Wr – weight ratio, in µg/g;

Mw – relative molecular mass of the water vapour;

Mt – relative molecular mass of the test gas;

es – saturated water vapor pressure of the water under the measuring temperature, in

Pa;

U – relative humidity, in %;

Ta – temperature of gas sample, in K;

dv – absolute humidity, in g/L;

SVP0 – saturated water vapor pressure under the measuring pressure, in Pa;

SVPa – saturated water vapor pressure under the atmospheric pressure, in Pa;

P0 – absolute working pressure in the equipment, in Pa;

Pa – atmospheric pressure, in Pa.

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