Howard Medium Power Substation User Manual

Page 13

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Medium Power Substation Transformers

Document 2.4.06, Revision 4

June 2013


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


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.