IL 44-751-1
Instruction Leaflet
Page 4 November, 2001
Ratings
The type DTW tap changer is available in one basic current rating and is offered with several
different electrostatic shielding and insulation options. Table 1 presents the various rating options.
Table 1. DTW Ratings
Test/ Parameter
Rated Value
Ref. Dimension
on Tap Changer
Voltage Class
See note 3
N/A
Phase to ground and phase to phase:
Lightning Impulse
60 Hz. Power Frequency
See note 3
N/A
Between Adjacent contacts:
Lightning Impulse
60 Hz. Power Frequency
220 kV
70 kV
(A-B, B-C, C-D,
D-E, E-F, F-A)
1
Short circuit current
10,000 A r.m.s.
N/A
Rated Current
2
850 A
N/A
1
See Figure 2
2
Based on a steady state contact temperature rise of 15
°
C at a continuous current equal to 120%
of rated current.
3
The dielectric withstand from tap deck to ground and from phase to phase is very much
dependent on the electrical clearance distances which are maintained by the transformer design.
See also Electrostatic Shielding and Insulation (page 9).
Figure 2.
