BS 7744:1994

Committees responsible
National foreword
Introduction
Section 1. General
1.1 Scope
1.2 Normative references
1.3 Definitions
Section 2. General test requirements
2.1 Test methods
2.2 Arrangement of the insulator for the test
2.3 Requirements for the test circuit
Section 3. Salt fog method
3.1 Salt solution
3.2 Spraying system
3.3 Conditions before starting the test
3.4 Preconditioning process
3.5 Withstand test
3.6 Acceptance criteria for the withstand test
Section 4. Solid layer method
4.1 Composition of the contaminating suspension
4.2 Main characteristics of the inert material
4.3 Application of the pollution layer
4.4 Determination of the degree of pollution of the
      test insulator
4.5 Test procedure
4.6 Withstand test and acceptance criteria
Section 5. Withstand characteristic of insulators
5.1 Determination of the withstand characteristics of
      insulators
Annexes
A. (informative) Method for checking the uniformity
      of the layer
B. (informative) Additional recommendations concerning
      the solid layer method procedures
C. (informative) Information to check equipment for
      artificial pollution tests
Tables
1. Salt-fog method: correspondence between the value
      of salinity, volume conductivity and density of the
      solution at a temperature of 20 deg C
2. Correspondence between the solution temperature
      and the factor b
3. Approximate correspondence between the SD and
      sigma 20 for kaolin compositions
4. Main characteristics of kaolin used in the solid
      layer suspension
Figures
1. Ripple amplitude and actual mean voltage, measured
      on a resistive load absorbing 100 mA
2. Voltage drop and voltage overshoot and leakage
      current
3. Typical construction of fog spray nozzle
4. Test layout for inclined insulators
A.1 Arrangement of the probe electrodes
A.2 Circuit diagram of the meter
B.1 Determination of layer conductance and evaluation
      of its rise time Tc = t2 - t1
C.1 (Provisional)

Provides a methodology for undertaking tests but world experience is too limited to know if these procedures cover all voltages adequately.