Howard Medium Power Substation - Manual (Page 13)

Medium Power Substation Transformers
Document 2.4.06, Revision 4
June 2013
13
6. Using the fish wire, carefully pull the draw-lead
through the bushing, taking care not to damage
the insulation on the lead.
7. Install the bushing mounting hardware and
fully tighten by alternately tightening opposite
corners. For bushings with porcelain flange and
clamping flange, torque hardware to 8 ft-lbs.
For bushings with metal flange, tighten until the
bushing flange has contacted the bushing boss
and lock washers are flattened.
8. Rotate the terminal until the steel pin pressed
in the draw lead seats in the slot inside the
porcelain top end. With the pin seated in the
groove, approximately 1/2 inch of thread should
protrude above the porcelain top. If the lead
appears to be too short, a problem may exist
that should be corrected before proceeding.
9. Apply a thin coating of petroleum jelly to the top
surface of the terminal cap sealing gasket and
press the coated surface into the gasket recess
in the terminal cap.
10. Remove the fish wire taking care to prevent
the draw lead from slipping back inside the
porcelain bushing.
11. Install the terminal cap on the draw lead
terminal and hand tighten, being careful to
keep the steel pin seated in the slot inside the
porcelain top.
12. verify that the gasket is properly seated and the
terminal cap is centered on the porcelain.
13. Torque the terminal cap to 35 ft-lbs.
14. Test for gasket leaks by pressurizing the
transformer with dry air or nitrogen to a
pressure of approximately 2-3 PSIG and
applying a soap bubble solution.
Installation of Condenser Bushings
If condenser type bushings are furnished, install them
according to the instruction literature shipped with the
bushings. These instructions will cover installation
maintenance, and use of the power factor test terminal.
vacuum Oil Fill Process
This procedure is for the vacuum oil filling of a
transformer. This procedure applies for transformers
which have been shipped dry air filled. It also applies
if the oil level in the transformer has been lowered to
a level that exposes part or all of the coils to air at any
time during the installation of the transformer.
Every container or tote of transformer fluid used in the
filling process should be visually inspected and tested
for water and other possible contaminants before
proceeding with the filling process.
1. Check all radiators to be sure the radiator valves
are in the open positions and to verify that all
the radiator flanges are tightened.
2. Check all high voltage bushing bolt flanges and
all low voltage bushing bolt flanges and be sure
all are properly tightened.
3. If the manhole access cover has been removed
for any reason verify that the bolts securing the
manhole cover(s) are properly tightened.
4. Connect the vacuum pump suction line to the
tank cover fitting. If the transformer has an OlTC
then vacuum must be applied to the OlTC tank
at the same time as the main tank is vacuumed.
Connect vacuum lines and pull a vacuum on the
OlTC tank.
5. Connect the oil fill line to the tank at the bottom
drain valve connection.
6. Start the vacuum pump.
7. When the vacuum level inside the tank reaches
500 microns (500 milliTorr) start timing and
when this vacuum level has been maintained for
12 hours the oilfilling may be started. Fill rate to
be 30 – 40 gpm.
8. Continue to fill until the oil fill gauge registers
slightly above the 25 C oil level.
9. After the oil filling has been completed continue
to hold the vacuum level for 1 additional hour.
10. The vacuum pump may now be stopped. Use
dry nitrogen to vent the transformer tank.
11. After the transformer has been filled with oil
it should be allowed to sit for 24 hours before
energizing in order to allow bubbles of gas
(which have been pulled out of solution by the
vacuum filling process) to be reabsorbed by the
oil.
12. At any time during the installation of the
transformer if the oil level in the transformer
has been lowered to a level that exposes part or
all of the coils to air, the oil must be completely
removed and the above procedure followed.