Recent Observations and Maintenance Issues

related to

1.3 kW @ 4.5 K Helium Plant for SST-1

Vipul L. Tanna

On behalf of SST-1 Cryo Team

Institute for Plasma Research, Bhat, Gandhinagar (INDIA)

Contact: vipul@ipr.res.in1

SST-1 Cryogenics Team

Dr.-Ing. V.L. Tanna

Head, SST-1 Cryogenics

Mr. J.C. Patel

(ME / Cryo)

Mr. R. Sharma

(ME / Cryo)Mr. G.L.N. Srikanth

(BE / ME)

Mr. A. Garg

(BE / ME)

Mr. J. Tank

(ME / IC)

Mr. P. Panchal

(M. Tech / IC)

Mr. D. Sonara

(BE / EC)

Mr. R. Panchal

(BE / IC)Mr. R. Patel

(BE / IC)Mr. G. Mahesuriya

(BE / IC)

Mr. K. Patel

(Diploma / ME)Mr. D. Christian

(BE / EE)

Mr. N. Bairagi

(M.Phil. / Phy.)

Mr. H. Nimavat

(M.Sc. / Phy.)Mr. P. Shah

(Diploma / ME)

Dr. Subrata Pradhan

SST-1 Project Leader

Mr. G Purwar

(Diploma / EE)

SST-1: India’s First Successful Superconducting Tokamak

Presently, it is in fully operating conditions

With SST-1, India has become the SIXTH nation in world to have superconducting Tokamak

Device supporting advanced superconductivity, cryogenics & fusion relevant experiments3

4

Typical Plasma Shot in SST-1

(IP = ~75 kA / 330 ms with ECRH Fundamental Mode at 1.5 T)

Outline

� Brief : 1.3 kW @ 4.5 K Helium plant system at IPR

� Glimpse of Helium plant and other Cryo sub-systems for SST-1

� Preventive maintenance activities during 2009-2010

� Major areas of maintenance

(a) Impurities pollution and pressure drop

(b) Electrical motors at compressors station

� Recent observations during Helium plant operation

� Different activities conducted to understand the Problem

� Understanding and resolution of the problems (with ALAT help)

� Helium plant performance after maintenance

� Future possible task (If required)

� Summary

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Brief : 1.3 kW @ 4.5 K Helium plant system at IPR

� HRL is based on modified Claude cycle.

� Refrigeration power of 650 W @ 4.5 K and

� 7 g-s-1 liquefaction capacity.

� The operational features of HRL are,

� Control cool-down of SCMS

� Two-phase helium operation

� Cold circulation mode,

� Controlled warm up of SCMS,

� Handling transient events in Tokamak

like, Quench of SCMS and Emergency

shut down with safety.

� A cold circulator (CC) acts as booster

device

� Supercritical helium flow 300 g-s-1 at 0.4

MPa and 4.5 K.

� MCD as thermal buffer to damp out all the

transients produced during SST-1 operation

and to provide LHe to CLs (Volume: 2500 L)6

Oil Removal SystemHelium Screw Compressors

Main Purifier HRL Cold-Box

Glimpse of SST-1 Helium Plant System

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Helium Cold Box + MCD IFDC systemTop Closure View of IFDC

Helium Gas Balloon

LN2 Sub-cooler Vessel

Glimpse of SST-1 Helium Plant System

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Preventive Maintenance of HRL was conducted in Winter 2010

The main objectives of such activities were as follows,

[1] Checks and calibration of Instrumentation and diagnostics

[2] Replacement of degraded components with new spares

[3] Demonstration of Supercritical Helium operation

[4] Compressor-C Tuning

[5] HRL capacity tests before and after of Maintenance

IPR has awarded a contract with the Original Equipment Manufacturer i.e.

M/s. Air Liquide DTA France to conduct the Preventive Maintenance Activities

IPR Cryo team as well as AL experts have successfully completed this task in 35

days in two phases

Highlights of Preventive Maintenance of 1.3 kW @ 4.5 K HRL

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[a] Purifier Heater Regeneration replacement

[b] Purifier Filter Cartridge replacement

[c] Internal T-sensors replacement of cold-box

[d] Compressor-C Tuning

T-sensor Replacement Tuning of Compressor-C slide valve

Purifier Heater Replacement

Some of the Examples of Maintenance of HRL

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Liquification Mode

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Liq

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Watt Flow(g/s)

Refrigeration Mode

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Pure Refrigerator Mode:

V=170.8 V X I=6.56 A = 1120 W

Pure Liquefaction Mode:

V=100.66 V X I=3.8 A = 388 W + 9.7 g/s

Mixed Mode:

V=131.2 V X 5.01 A = 657.3 W + 7 g/s

Mixed Mode

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Results: Performance Test Before Maintenance

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Results: Performance Test After Maintenance

Liquification

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Refrigeration Mode

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3:00

3:20

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Mixed Mode

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0:01

0:11

0:21

0:31

0:41

0:51

1:01

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1:41

1:51

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Pure Refrigerator Mode:

V=170.9 V X I=6.5 A = 1110 W

Pure Liquefaction Mode:

V=118.5 V X I=4.58 A = 542.7 W + 8.32 g/s

Mixed Mode:

V=132.0 V X 5.07 A = 670 W + 7 g/s

LN2 Storage and Distribution

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LN2 Requirements (1.5 bar(a); 79K):

• Radiation Shield : 350 l/h – 1450 l/h

• CLB, Cryo-transfer lines: 95 l/h

• Liquid Helium Plant : 110 l/h

• On-line Purifier : 110 l/h

• NBI system : 225 l/h – 400 l/h

LN2 Storage :

• Total Storage : 105 m3

• 3# tanks 35 m3 each

• Vacuum + Perlite Insulated

• Max operating pressure 2.75 barg

• Max Discharge rate 2000 l/h

LN2 Distribution:

• Main Transfer Lines ( 250 m )

• Phase separator/ Sub-cooler Dewar

• LN2 Distribution and Return lines

• N2 Gas vent lines

• Instrumentation and Control1000 l storage Dewar for NBI system

HIGH PRESSURE STORAGE AREA

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High pressure storage system (HPSS) at 150 bar

• 2# of 25 m3 SS tanks, associated valves, instrumentation and piping

Medium Pressure storage system (MPSS) at 14 bar.

• 4# of 68 m3 tanks (1 SS; 3 CS), associated valves, instrumentation and piping.

The interconnecting pipe-lines, between the compressors, HPSS, MPSS, purifier and cold-

box ( over distance of ~250 m)

4# gas bags (40 Nm3 each) and a recovery compressor for emergency He gas recovery

High Pressure He Gas Storage Tanks Medium Pressure He Gas Storage Tanks

Warm Gas Management System

Major issues faced related to Maintenance

� Higher Pressure drop across Purifier caused by Impurities pollution

� High pressure drop across Turbine A (outlet) and B (inlet)

� Electrical Motors of Helium Screw Compressors

Basic Protocols to be strictly followed:-

(a) Quality of Process Helium gas

(b) Pre-commissioning and Regeneration of system

(c) Lubrication Oil replacement at Compressors station

(d) Oil quality as well as quantity

(e) Charcoal replacement at ORS

(f) Filters cartridge replacement at ORS, Purifier and CB

(g) Adequate Greasing of Electrical Motors (frequency, weight, type) 15

Impurities and Pollution in the Process: Basic Observation

“Within 3 – 4 days of HRL operation, pressure drop across

purifier and cold-box were observed more than 1 bar”

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Efforts made to understand Impurities and Pollution in the Process

�Replacement of Breox Oil at Compressors station

�Regeneration of Charcoal at ORS

�Observations on Filter Cartridges

�Replacement of Charcoal Powder

�Cleaning of Filters Cartridge (Ultrasonic and Chemical)

�Chem Lab test of Samples of Oil and Charcoal Powder

Even after above efforts, the problem did not resolve !

ALAT, France (OEM) help and expertise were requested 17

IR Spectrum of Breox- B35 Oil (Lubricant) in Compressors Station

It shows the oil quality is better

There is no formation of Acetaldehydes as k = 1750 cm-1

there is no significant peak observed

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Old Charcoal from ORS

System

2006 Year Charcoal

Oil Traces found from Old

Charcoal from ORS System

2006 Year Charcoal

Charcoal Adsorber Analysis

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Oil observed even in 3rd Cartridge

Oil sight glass level (Malfunction

Drain switch)

Configuration as mentioned in Original kit: AO-AA-AA

Recommended by ALAT : AA-AA-AX

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Outcome of ALAT Expertise Report

1. Over-filling of Oil at Primary Oil Separator (POS) was found due to faulty Oil level sensor

2. Oil pollution was detected starting from 3rd Coalescer to 230 m long HP line

3. Filters configuration was not appropriate: AO-AA-AA instead of AA-AA-AX

4. At the drain of Main purifier, Oil residue were found

5. At the Turbine Bearing filters Oil was collected (20 – 30 ml)

Resolution towards the Problems

1. Appropriate level of Oil at Primary Oil Separator was ensured

2. Additional Two filter cartridges were installed at POS to increase its filtration capacity

3. Faulty Oil level sensor suggested to be replaced with bigger and clear one

4. Filter cartridges at ORS were replaced with AA-AA-AX type

5. IR spectrum of oil residue at the drain of purifier was studied

6. Cold-Box Filters were replaced and nearby area were chemically cleaned

7. Turbine Bearing filters area were cleaned and replaced by new filters

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About 40 days of continuous operation of HRL and

The pressure drop across Purifier and cold-box was

constant about 0.34 bar during the whole campaign .

Electrical Motors Issue

HRL has Fimet Make (315 kW/ 440 V AC/ 50 Hz/ Asynchronous Motors

Ambient Temperature, Greasing cycle and Vibrations need to be looked carefully

Electrical as well as Mechanical Damages found almost once in 1.5-2 years

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Electro-Mechanical Failure of Motors

� We have total 03 numbers of 315 kW induction Motors connected with the

Helium screw compressors

� Two Motors run at a time and the third one is redundant

Recommended Procedure and Protocols while operating Motors

1. Screw Compressor Motor Coupling with shaft alignment

2. Appropriate cycle of Grease applied to Motors (every 500 h operation, 40 g)

3. Appropriate choice of Grease (GHY 176, Kulber make, Germany)

4. Routine checks of Electrical winding resistance and Megar Insulation checks

5. Checks on incoming line voltage and current measurement

6. Measurement on phase imbalance current in Motors

Specifications of Consumables of Compressors Station

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Every 500 h / Monthly operation� Check compressors filters

� Check Grease in Motors

� Check Motor Vibration� Check oil level in compressors

HRL Maintenance Schedule / Protocols

Daily (if operated)� Check display

and take log

readings

� Weekly Oil drain at 3rd Coalescer

Every 4000 h / Annual operation� Overhauling of Motors

� compressors filters

� Check Grease in Motors

� Check Motor Vibration

� Check oil level in compressors

� Check Interconnection leaks� Instrumentation calibration

Every 8000 h / Annual operation� Overhauling of Motors

� compressors filters

� Check Grease in Motors

� Check Motor Vibration

� Check oil level in compressors

� Check Interconnection leaks

� Checks & Replacement of Turbine Filters

� Checks & Replacement of Charcoal in ORS

� Oil level and re-filling of Oil � Instrumentation calibration

Every 24,000 h Operation� Check for overall integrated piping, interconnections for leaks

� Plan for complete Preventive Maintenance for whole Plant system� Check for integrity of Compressors station (bearing change if it is essential)

Summary

� Over years of experience, the SST-1 Cryo team had learnt lessons from different critical

maintenance related issues e.g. control of impurities pollution, reliable operation of

electrical motors.

� The recent pressure drop across purifier was analysed and that was due to the oil

impurities pollutions due to the fact that

(a) Over-filling of Oil in Primary Oil Separator (POS)

(b) Malfunction of Oil drain switch

(c) Providing additional Filter Cartridges in POS system

(d) Right configuration of Filters Cartridges in ORS : AA-AA-AX

� For reliable operation of HRL on months duration, strict maintenance as a part of

preventive maintenance as per schedule shall be strictly followed. Regular Oil check up at

the 3rd coalescer will help and if required then it is to be drained frequently.

� Quantity and Quality of consumables (Oil, Grease, etc.) used shall be appropriate.

� Adequate Spares Inventory must be there to take up any Maintenance related tasks.

� Looking at the experimental results on HRL plant performance during (Sept-Oct-2014.

Presently, HRL is running like a text book fashion delivering 1300 W @ 4.5 K cold capacity

on months together non-stop operation 27

Acknowledgement

Root cause of all the problems were understood and resolved

successfully by IPR SST-1 Cryo Team in collaboration with ALAT on

very urgent basis.

Outcome of ALAT Report: Oil Drain from POS was found dirty and

suspected to be malfunctioning

A special Thanks goes to ALAT Team for their continuous help and

support.

We sincerely grateful to our IPR Director (Prof. D. Bora) for taking

keen interest in resolving this issue.

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Many Thanks

for

your Kind Attention

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