GENERATOR SEAL OIL SYSTEM

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   1:- Introduction of generator seal oil system.
   2:- Calculation & parameters for example.
   3:- DCS snap view & some important images.


INTRODUCTION / GENERAL DESCRIPTION
1:- A turbo generator for a generating unit can not operate without this system.
2:- It prevents the leakage of gas (Hydrogen or Carbon dioxide) along the generator rotor shaft where it passes through the casing.
3:- To prevent hydrogen coming into contact with oxygen in the atmosphere (hydrogen oxygen mixture is highly explosive).
4:- Hydrogen leakage is prevented by providing gas tight housing at the generator end shields (mounted between end shields bearing either end of the stator).
5:- Some gas leak through the annular gap between shaft and stator housing, to
prevent hydrogen leakage from this gap, high pressure oil film is provided continuously.
6:- So the shaft seals are supplied with pressurized seal oil to prevent hydrogen escape at the shaft.
7:- The pressure of the seal oil film is greater than the hydrogen gas pressure inside the turbo generator. So no hydrogen gas is escaping from the turbo generator housing (a constant DP is maintaining between hydrogen pressure & seal oil supply pressure).
8:- The shaft seal are supplied with required seal oil from an exclusive closed loop oil circuit.
9:- The oil in the seal oil system is the same as that used in the turbine generator journal bearing and turbine governing system.
10:- System is designed such that all the oil does not allow to mix together.
11:- Most of the oil flows towards the bearing and is drained into the main drain oil header.
12:- A small quantity of oil is flowing towards the hydrogen side.
13:- Seal oil system continue running if hydrogen or carbon di-oxide is present inside the turbogenerator.


SHAFT SEAL GENERAL DESCRIPTION
1:-The shaft seal consists of seal liner, lined with Babbitt metal and pressed against the collar of the rotor or   on the rotor.
2:-The liner is kept pressed to the shaft collar or on the shaft by thrust oil pressure, pumped into the   chamber between the seal body and the liner.
3:- The seal liner is enclosed in seal body.
4:- Seal oil is fed to the seal body and flows to the liner to form an oil film between babbit and shaft collar.
5:- Oil wipers are provided for catching the oil at both end and drained in to the system.
6:- The oil which flow towards the generator hydrogen side passes into seal oil drain called hydrogen side seal oil drain.
7:- The oil which flows towards the bearing (air side oil drain) mixed with oil discharge from generator bearing  and goes back to the main oil tank, called seal oil air side drain.
8:- Most of the oil flows towards the bearing and is drained into the main drain oil header.
9:- A small quantity of oil is flowing towards the hydrogen side.
10:- Oil is supplied from two sources (as per design of system) first is from governing oil system (turbine lub oil system) & second is from oil pumps provided for seal only that purposes.
11:- The seal system is free to move axially to take up any movement due to thermal expansion of rotor.

Figure - Seal ring 


figure- oil catcher


SEAL OIL SYSTEM
1:- AC seal oil pump supplied oil from the seal oil tank and feeds it to the shaft seals through coolers and filters.
2:- After sealing the seal oil drain towards hydrogen side and air side through the annular gap between the   shaft and seal ring.
3:- Air side seal oil is returned in to the seal oil tank through a float valve.
4:- Oil drained on the hydrogen side first flows into the pre-chamber and then flow into the intermediate oil   tank before returning the seal oil tank.
5:- The seal oil tank is kept under vacuum to prevent deterioration of hydrogen purity in the generator.
6:- The gas entrapped in the oil & removed, so seal oil pump supply only degasses oil only.
7:- For oil circulation 100 % capacity screw type pumps, AC motor & DC motor are provided.
8:- A vacuum pump is provided for maintaining specified vacuum in seal oil tank and is kept in operation when   either of the seal oil pumps is running.
Figure- Seal a general view 


Figure -Generator shaft expansion

# EXAMPLE

(For KWU 250 MW unit)
Seal oil supplied after PRV 9.0 to 11.0 Kg/cm²
Seal oil after DPR      5.5 kg/cm²
Hydrogen pressure in generator 4 kg/cm²
Differential pressure (DP) 5.5 - 4 = 1.5 kg/cm²
(DP maintain 1.2 to 1.5 kg/cm²)
(For LMW/LMZ 210 MW unit) 
Hydrogen pressure   3.5 kg/cm²
Seal oil pressure   4.1 to 4.4 kg/cm²
Quantity of seal oil required   80 LPM
Quantity of seal oil flowing towards hydrogen side   1-2 LPM
Pressure of thrust oil   1 to 2.2 kg/cm² 
# Two types of seal are used
Thrust face type (thrust type seal)
Floating ring type (ring type seal, 210/250 mw unit occupied with this).

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