Omicron CP CR500, Руководство пользователя

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CP CR500
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6.2 The
Δ
Tan Delta" or "TIP-UP" Test
In IEC 60894 the "
Δ
Tan Delta" test and in IEEE 286 the "Tip-up" are described.
Both
Δ
Tan-Delta and Tip-up are an indirect way of determining if partial
discharges (PD) are occurring in a high voltage stator winding. Since PD is a
symptom of many winding insulation deterioration mechanisms, the described
tests can indicate if many failure processes are occurring. In addition to its use
as an off-line maintenance test, the tests are widely used by stator coil and bar
manufacturers as a quality control test to ensure proper impregnation by epoxy
and polyester, during coil manufacture.
6.2.1 Purpose and Theory
At low voltages, the PF and DF are not dependent on voltage. However, as the
AC voltage is increased across the insulation in a form wound coil, and if voids
are present within the insulation, then at some voltage partial discharges will
occur. These discharges produce heat, light and sound, all of which consume
energy. This energy must be provided from the power supply.
Consequently, in a coil with delaminated insulation (perhaps due to long term
overheating), as the voltage increases and PD starts to occur, the DF and PF
will increase above the normal level due to dielectric loss, since the PD
constitutes an additional loss component in the insulation. The greater the
increase in PF and DF, the more energy that is being consumed by the partial
discharge.
In the tip-up test, the PF or DF is measured at a minimum of two voltage levels.
The low voltage DF, DF_lv, is an indicator of the normal dielectric losses in the
insulation. This is usually measured at about 20 % of the rated line-to-ground
voltage of the stator. The voltage is then raised to the rated line-to-ground
voltage, and DF_hv is measured. The tip-up is then:
The higher the tip-up, the greater is the energy consumed by PD. Sometimes
the PF or DF are recorded at several different voltage levels, and several
different tip-ups are calculated between different levels. By plotting the tip-up as
a function of voltage, the voltage at which PD starts is sometimes measurable.
If the PF or DF is measured in percent, then the tip-up is in percent.
Tip-up = DF_lhv - DF_lv