transforming know-how into solutions. siemens . · pdf fileintern © siemens ag 2014 alle...

Intern © Siemens AG 2014 Alle Rechte vorbehalten. Answers for energy.

Transforming know-how into solutions. Siemens Transformers.

SITRAM® DRY Cabinet, Frame und Smart

© Siemens AG 2014 All Rights reserved.

May 2014Seite 2 Energy Transmission Transformer

Scope of Activities / Portfolio of Transformer Service

Online Monitoring

Condition Assessment & Diagnostic

Consulting & Expertise

Spare Parts & Accessories

Maintenance & Lifecycle Extension

Repair & Retrofit

Transport, Installation & Comissioning



Structure of Transformers

Transformer wood

LaminatedpressboardPressboard

Insulating paper

Transformer oil Grain-orientedelectrical steel

Gasket material

Copper winding

Coating

Transformers are comprised substantially of organic materials



Ageing processes of transformer insulation system

The ageing of oil and cellulose is strong depending from each other

Moisture Oxygen Temperature

Oil/Cellulose - Insulation

Chemical degradation, acids, peroxides, ...

add. water, oxygen

Accelerated Agingof Insulation

Mechanical Degradation Dielectric Degradation

Lightning-Switching-Impulses Insulation failure Short Circuits



Ageing in transformers

The service life of a transformer is determinedby the life its solid insulation

End of life is reached as soon as the mechanicalstrength has lost 50% of initial value which commonlyappear at degree of polymerization (DP) values < 200 ( -75%) (IEEE C57.91-1995)



Ageing processes in the solid insulation

Paper ageing duration until a DP value of 150 is reached (end of life) at 120ºC depending on humidity content in the paper



Moisture in transformers

• Ageing of solid insulation

• Diffusion of moisture from the external environment:

• Free breathing systems with poorly maintained air dehumidifier

• Damaged gasket

Cause of moisture

A sustainable low water content in the cellulose and insulating oil extend the life of the transformer considerably.



Overview options for actions

If the latest transformer oil analysis reports high water content and/or low breakdown voltage:

The customer has six options, each with different characteristics and consequences:

1. Do nothing

2. Retrofill

3. Conventional dehydration

4. Field vacuum dehydration

5. Oven drying

6. Stationary transformer drying



Options for actions (1)

Option Process description Conclusion1. Do nothing This is as simple as the results are predictable:

continuous degradation and failure of the unit. Waterin the paper insulation breaks down the designedvalue of the insulation, resulting in premature failure, outage and replacement.

Inexpensive at first, thenextremely costly

2. Retrofill Exchange the wet oil with dry oil. The problem: themoisture is still bound deep within the transformer`sinsulation/paper. So after the retrofit the moisture will slowly leach from the paper into the new oil. Eventually, high moisture will reappear in testing. In the end, this approach treats the symptom but doesnot solve the problem.

Moisture remains in the paperThe risk is unchanged andhidden behind temporary goodoil values after processingOuttake costs

3. Conventionaldehydration

This temporary solution circulates and heats thetransformer oil, removing the moisture from the outerlayers of the insulation. However, most of themoisture stays deep within the paper. After removal ofthe dehydration unit, the moisture will slowly leachfrom the paper into newly processed oil. Over time, this will lower the breakdown voltage again.

Only temporary good resultsMoisture remains in the paperHigh power consumptionRisk is unchanged and hiddenbehind temporary good oilvalues after processing



Options for action (2)

Option Process description Conclusion4. Field vacuum

dehydration(LFH)

In the transformer tank is rated for full vacuum, thetransformer can be de-energized and disconnected fromthe system. Typical approaches heat up the core an coilassembly by heating the circulated oil. After reaching thenominal temperature, the unit is drained and placedunder vacuum. The combination of heat and vacuumbegins to remove moisture from the internal componentsincluding the paper. For full and proper moisture removal, this process requires constant or periodic application. It isalso recommended that a cold trap be utilized to measurethe amount and rate the moisture removal.

Process can take from days toweeksUnit stays de-energizedAfterwards, has to be refilled withoil and electrically testedVacuum in the tank could lead thefailure in the sealingsHigh outage costsVery effective at moisture removal

5. Oven Drying Wet transformers can be dried in an oven - just as in thefactory during initial assembly. Of course, this meansdisconnecting the transformer and transporting it to a drying oven. There it has to be drained and put in theoven for a period of days or weeks, until it finallybecomes dry. Afterward, the transformer must be refilled, the previous steps repeated in reverse, and (eventually) the power turned back on.

Effective for small distribution TX, but very costly in time and moneyfor bis units (transportation costsfor shipping to repair shop)

6. Stationarytransformerdrying device

A small, highly efficient unit is permanently placed on theenergized transformer and slowly but continuouslyremoves the moisture from the oil and paper completely.

Low cost, low risk. Maximum benefit. It`s just that simple.



Conclusion regarding drying of transformers

• Oil has the property to absorb only a lowwater quantity (<2%)

• The main part of moisture remains in the solid insulation and this acceleratesthe irreversible degradation of thecellulose.

• Conventional drying methods arecausing only a temporary reduction ofmoisture in oil

Continuous oil dehydration is necessary to ensure moisture removal from the paper insulation



What is molecular sieve?

A molecular sieve is a material containing tiny pores of a uniform size that is used as an adsorbent for gases and liquids.

Internal surface of the content of 3 cartridges amount approx. 25 km2



Experimental result (1) SITRAM® DRY in operation



Experimental result (2) SITRAM® DRY in operation

Temperature entry[ºC]Moisture entry [ppm]Temperature entry[ppm]H2O-Adsorption [Liter]

H2O

-Ads

orpt

ion

[Lite

r]

Moi

stur

ein

oil

[ppm

]; Te

mp.

[°C

]



SITRAM® DRY Stationary Drying SystemTwo product versions for all standard applications

• Target segment: Power transformers withconservator oil level of min. 2.5 m above ground

• Typical application: Power generation andTransmission Utilities/Industry

• Water capacity: 3 x 3 liter• PLC functionality

• Target segment: Distribution transformers withconservator oil level of min. 1.5 m above ground

• Typical applications: D-Utilities and Industry• Water capacity: 2 x 1.5 liter• PLC functionality

SITRAM® DRY Cabinet/Frame SITRAM® DRY SMART



SITRAM® DRY VersionsMain Customer Benefits

• Graded product approach

• Reduced total costs of ownership and higher availability- Automatic cartridge replacement signal- Self-monitoring of pump and moisture sensors - Leakage control (optional at SITRAM® DRY Cabinet)- Potential free alarm contact (live contact) to SCADA

• Extended field of application: ambient temperature range (-20ºC to +60ºC)



• Power transformers with conservatoroil level of min. 2.5 m above ground

• Typical application: Power generationand Transmission Utilities/Industry

• With transformers far away- From the daily access of their

personnel, - E.g. substation transformers

• Who set a high value on- The protection of their device- Information about the operation

conditions

SITRAM® DRY Cabinet The unit for customers with special requests

Speziell for customers, … Target Segment



• Automatic reaction if an error occurs• In case of an error, avoidance of leakage by

- Closing the magnetic valves- Switching off the pump

• Actual information about the operatingconditions and the measurement values bytext messages

• Recording and storage of measurementdata by data logging

• Good overview about the operatingconditions by enhanced visualization

Customer‘s benefits



• Message via text message and Panel• SITRAM® DRY continues in operation

• Stop of pump operation• Magnetic valves get closed to avoid a

leakage of oil

Functions with and without stop of operation

Leakage inside/outside, pump error Control of moisture/pressure sensors



Cartridge Saturation

• Detailed display about the cartridge saturation• Error message if the cartridges are saturated• Text messages



Four different text messages in German orEnglish• Error leakage inside / outside• Pump error• Transmission of measurement values

- SITRAM DRY operating condition- Temperatures, absolute moisture in ppm

and relative moisture as aw-value at theinlet and the outlet

• Cartridges saturated

SMS with information about operating conditionsand error messages



• Storage of the measurement values withtime stamp- Absolute moisture in ppm- Relative moisture as aw-value- Temperature of the transformer oil

• Acces with Ethernet connection using a common web browser

Data Logging



SITRAM® DRY VersionsCartridge Saturation and Exchange

• Message for cartridge exchangeIf the incoming transformer oil is higher than 10 ppm and the cartridges aresaturated a signal for cartridge exchange will automatically occur on the plc.

• Operating experienceFor a wet transformer the sets of cartridges last for:- 6 months for the first set- 12 months for the second set- 18 months for the third and all other setsThese values depend strongly on different parameters like the size of thetransformer, the oil volume, the moisture in the oil, the load and thetemperature in the transformer.



SITRAM® DRY CabinetHow to install SITRAM DRY at the transfomer?

Pipe connectionto transformer

Pipe connectionfrom transformer

Electrical connection



SITRAM® DRY CabinetGeneral Overview and monitoring functions

Control box with PLC

Moisture in oil sensor

Vent tank with vent valve

Oil filter

Cartridges



SITRAM® DRY CabinetLeakage Monitoring

Leakage control

Vent valve



Examples of installation

transforming know-how into solutions. siemens . · pdf fileintern © siemens ag 2014 alle...

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