VACUUM OVEN PROCESS
After and connections are made, the entire job has to be heated to higher temperature of 100 degree centigrade to reduce the water contain in the insulation level.
Vacuum oven consist of a heating chamber vapor condenser ,vacuum pump, exhaust condenser ,water storage tank ,refrigeration tank , water circulation pump, vacuum sensor.
After completion of connection the core and winding are kept on trolley and kept in oven.
Minimum clearances of 200 mm shall be maintained between the transformer and the heater to avoid damage of the winding.
The over door shall be soaked between 70 to 90 degrees centigrade temperature shall be maintained constantly until the min IK values are obtained as given below.
HV-LV 500M OHMS AT 70
HV–EARTH 500M OHMS AT 70
LV-EARTH 500M OHMS AT 70
To heat the job vacuum is employed the working procedure of vacuum oven is as follows.
1.Load the job make sure the sensor position ,close the door and tighten the door properly .
2.Set the control thermostat at 100 degree centigrade .
3.Check the sufficient water level in the tank check oil level in the vacuum and roots pump.
WORK INSTRUCTION FOR VACUUM OVEN
A. Heating phase
B.-valve open : Scavenging valve
C.-valve close : Drain valve ,oil line valve, airing valve , gauge valve , vacuum valve ,throttling valve , drying valve .
D. Switch on the circulation fan of chamber switch on heater and cover heater.
E. When job temperature reaches to 100 degree centigrade , steel counting heating time for minimum 4 hours and maximum depends on job .
F. In mean time switch on water chiller temperature of water reduce from 25-10 degrees in 3-4 hours .
G. Switch on water circulating pump at the same time heating continuous same time heating is begin continued for minimum 4 hours.
a. As soon as heating time of 4 hours is over.
b. Valve open : Vacuum valve
c. Condensate valve
Valve close : drain valve , oil line valve, airing valve, throttling valve , scavenging valve .
Switch of the air circulating van
Switch on water circulating pump ordinary water
And Switch on vacuum pipe
Observe the reading
Vacuum indicator shows reading of vacuum from 250 mbar to 0.1 mbar
When vacuum level reach to 40 mbar throttling valve gets off due to setting of 40 mbar is done in vacuum control
At evening 1 hour drain out the condensate water from tank
Close condensate valve ,open valve, airing valve and drain the water through drain valve.