IEC IEEE 65700-19-03-2014 pdf download.Bushings for DC application.
4 Ratings
4.1 Rated voltages
4.1.1 Rated continuous DC voltage
The rated continuous DC voltage is the maximum continuous DC voltage assigned to the bushing by the manufacturer for specified operating conditions.
4.1 .2 Rated peak voltage
The rated peak voltage is the maximum value of the combination of DC voltage plus peak AC voltage that the bushing is required to withstand under the specified operating conditions.
4.2 Insulation levels
According to IEC 60071 -5 the insulation levels for bushings used in DC applications do not generally follow the standard values of insulation level given in IEC 60071 -1 . The purchaser shall specify the insulation levels. The methods of calculation for test voltages are given in the relevant clauses of this standard.
4.3 Rated currents
The definition of rated current depends on the bushing application. If the bushing is one for pure DC application, the ratings are defined in 4.3.1 . If the bushing is one for combined voltage application, the ratings are defined in 4.3.2.
4.3.1 Pure DC applications
4.3.1.1 Rated continuous DC current
The rated continuous DC current is the maximum continuous direct current that the bushing is required to carry under the specified operating conditions.
4.3.1.2 Rated DC overload current
The rated DC overload current is the maximum direct current that the bushing is required to carry for a stated duration of time and ambient temperature. The purchaser shall specify the current magnitude, duration and frequency of occurrence.
4.3.2 Combined voltage applications
In these applications, the bushing is usually required to carry AC current.
4.3.2.1 Rated continuous AC current
The rated continuous AC current is the r.m.s. equivalent of the actual current wave shape (including fundamental and harmonic frequency components) that the bushing is required to carry based on the DC rated load current commutated with zero commutating reactance.
4.3.2.2 Rated AC overload current
The rated AC overload current is the maximum alternating current that the bushing is required to carry for a stated duration of time and ambient temperature. It shall be the r.m.s. equivalent of the actual current waveshape that the bushing is required to carry based on the DC rated overload current commutated with zero commutating reactance.
4.3.2.3 Rated momentary (short-time) current
The rated momentary short-time current is the current flowing through the bushing at the major peak of the maximum cycle as determined from the envelope of the current wave. This current is expressed as the root mean-square value including the DC component. Duration of momentary current shall be 1 s unless otherwise specified.
4.4 Rated frequency
Rated frequency is the frequency of the AC system to which the bushing is connected. Rated frequency for bushings for pure DC application is “DC”.
4.5 Pollution parameters
The purchaser shall specify the minimum creepage distance or the minimum USCD (see IEC 6081 5-1 ) or, alternatively, the degree of pollution severity.
For indoor bushings, the minimum USCD value shall be 1 7 mm/kV.
If artificial pollution tests are required, they shall be performed in accordance with 1 0.1 .
NOTE Values for USCD and k d for outdoor bushings are under consideration by IEC TC 36: Insulators.
5 Operating conditions
5.1 General
Bushings conforming to this standard shall, unless otherwise stated, be suitable for operation at rated values under conditions defined in IEC 601 37 and summarized as follows:
a) The ambient air temperature is within the limits specified in Table 1
b) Altitude does not exceed 1 000 m.
c) The temperature of the transformer insulating oil in which the oil end of the bushing is immersed is within the limits specified in Table 1 .
d) The temperatures and temperature rises of external connections and metal parts in contact with insulating materials do not exceed the limits given in Table 2 of IEC 601 37:2008.
e) No moisture condensation is present on the outer surface of the indoor part of outdoorindoor bushings, indoor bushings and indoor-immersed bushings.IEC IEEE 65700-19 pdf download.