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Position Indicator and Add-AMP
Capability
Regulators rated below 668 A include an ADD-AMP fea-
ture which permits additional current-carrying capabilities
at reduced regulation, as shown in Table 2, but not to
exceed 668 A. The ADD-AMP type adjustment is located
inside the position-indicator faceplate to prevent inadver-
tent adjustment. In addition, the SOFT-ADD-AMP feature
allows adjustment by way of the control keypad or inter-
face software. An optional ADD-AMP feature maximum
of 875 A is provided when specified for regulators rated
438–668 A.
The position indicator (see Figures 3 and 11) is mounted on
a junction box on the cover of the regulator and is directly
connected to the tap-changer by a flexible drive shaft
passing through the junction box and terminal board via a
sealing gland.
The indicator face is graduated in steps. Drag hands indi-
cate the maximum and minimum positions attained during
raise and lower operations. The drag hands are automati-
cally reset around the main hand position by operating the
drag-hand reset switch on the control front panel.
During forward power flow, the main hand of the position
indicator will be to the right of the neutral position when
the regulator is boosting. During reverse power flow, the
main hand will be to the left of the neutral position when
the regulator is boosting.
The ADD-AMP feature of VR-32 regulators allows increased
current capacity by reducing the regulation range. This is
accomplished by either setting limit switches in the position
indicator or enabling the SOFT-ADD-AMP feature (Function
Code 79) to prevent the tap-changer from traveling beyond
a set position in either raise or lower directions.
The limit switches have scales graduated in percent regula-
tion and are adjustable to specific values of 5, 6 1/4, 7 1/2,
8 3/4, and 10% regulation to alter the regulation range.
These percentages translate to tap position limitations of 8,
10, 12, 14, or 16 raise or lower. The five possible load cur-
rent ratings associated with the reduced regulation ranges
are summarized in Tables 13 and 14 (see Appendix). Higher
regulation ranges are realized in closed delta application.
When using the limit switches, a detent stop at each set-
ting provides positive adjustment. Settings other than
those stops are not recommended. The raise and lower
limits need not be the same value unless reverse power is
possible. The regulator will stay within the ADD-AMP limits
set forth by the control or the position indicator, whichever
limit is of a lower regulation percentage.
NOTE:
If the ADD-AMP limits have been programmed into the
control (soft ADD-AMP) and the limit switches have not
been set, it is possible to manually step the tap-changer
beyond the ADD-AMP limit. If the unit is switched back to
automatic mode, the control will step the regulator back
to within the ADD-AMP limits set in the control.
See also the
TROUBLESHOOTING
section of this manual
for position indicator replacement instructions.
Surge Protection
Series Arrester
All VR-32 Regulators are equipped with a bypass arrester
connected across the series winding between the source
(S) and load (L) bushings. This arrester limits the volt-
age developed across the series winding during lightning
strikes, switching surges, and line faults. The series surge
arrester can be seen in Figure 3. A heavy-duty MOV-type
series surge arrester of 3 kV offers series winding protection
on all regulators except those rated 22,000 V and greater,
which have a 6 kV MOV-type series surge arrester.
Shunt Arresters
A shunt arrester is a recommended accessory on the
VR-32 regulator for protection of the shunt winding. The
shunt arrester is a direct-connected arrester mounted on
the tank and connected between the bushing and ground
(earth). It is recommended that arresters be applied to all
non-grounded bushings.
For best results, locate these arresters on the mounting
pads provided on the tank near the bushing. Connect the
arrester and the regulator tank to the same ground con-
nection using the shortest cable possible. Shunt arrester
application data is listed in Table 3.
5
S225-10-30
!
SAFETY
FOR LIFE
TAbLE 2
ADD-AMP Adjustments
Regulation (%)
Current (%)
± 10.0
100
± 8.75
110
± 7.5
120
± 6.25
135
± 5.0
160
Recommended
Recommended
MOV Shunt
MOV Shunt
Regulator
Arrester
Regulator
Arrester
Voltage
Ratings
Voltage
Ratings
Rating
(kV)
Rating
(kV)
2500
3
4400
8
5000
6
5000
2
6600
20
27
7620
0
22000
27
8660
2
33000
36
000
5
34500
36
3800
8
TAbLE 3
Typical Shunt Arrester Application Data*
* Contact factory for specific shunt arrestor application ratings.