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Authors: Joerg Huemer Uwe Eickelbeck Siemens AG Energy Sector Power Generation Division

Generator Modernization – Implementation of Harmonized EU Directives for Improved Safety

Power Gen Europe 2014 June 3-5, 2014 Cologne, Germany

siemens.com/energy

AL: N; ECCN: N Unrestricted © Siemens AG 2014. All rights reserved. Page 2 of 12

Table of Contents

1 Abstract .................................................................................................................. 3

2 Background ............................................................................................................ 3

3 Zone Classification ................................................................................................. 4

4 Application of ATEX Directives (Examples) ........................................................ 6

4.1 Single Tower Gas Dryer ......................................................................................... 7

4.2 Liquid Level Detector Rack ................................................................................... 8

5 Modernization Measures ........................................................................................ 9

6 Summary .............................................................................................................. 10

7 References ............................................................................................................ 10

8 Disclaimer ............................................................................................................ 11


1 Abstract

Hydrogen is an ideal generator coolant for medium and large-sized turbo generators, having

good heat transfer characteristics and low windage losses. But to maintain these advantages,

the hydrogen must be handled carefully, with the necessary attention to safety measures.

In this respect, the hydrogen filling and venting process of the generator as well as proper

operation play a very important role in the prevention and handling of possible explosive

atmospheres.

It is mandatory to implement the requirements of international standards such as ATEX

Directive 94/9/EC [1] and IEC60034-3 [2] to ensure safe and reliable operation of the power

plant. In the context of legacy plants, it is necessary to define which measures can be

implemented to meet the latest safety requirements.

The technical and legal background, boundaries and implementation strategies will be

presented as well as typical examples from executed projects.

2 Background

The hydrogen gas used for cooling certain generator designs can mix with air to form an

explosive gas mixture. Such mixtures can occur when the hydrogen gas is deliberately vented

to the atmosphere via the turbine building roof or if hydrogen escapes uncontrolled through

leaks (e.g. at breakable connections). Special precautions must therefore be taken to comply

with valid explosion protection requirements to prevent a potential explosion in hazardous

areas.

Generators, exciter and auxiliaries (hydrogen supply, waste gas system, seal oil system and

stator water system) are in their majority installed in machine houses.


Fig. 1: Overview of generator auxiliaries including gas dryer and liquid level detector rack

The generator area including its auxiliary systems is divided into different explosion

protection zones resulting in different requirements for transmitters, actuators, and their

electrical wiring.

The areas outside these zones are not subject to explosion protection requirements.

3 Zone Classification Explosion hazard areas are divided into zones to simplify the selection of suitable components

and to facilitate the correct design of electrical installations.

For hydrogen and other gases, the applicable zones are:

■ Zone 0 Place in which an explosive atmosphere consisting of a mixture with air

of flammable substances in the form of gas, vapor or mist is present

continuously or for long periods or frequently. (not applicable to the

generator area)

■ Zone 1 Place in which an explosive atmosphere consisting of a mixture with

air of flammable substances in the form of gas, vapor or mist is likely

Liquid

Level

Detector

Rack

Gas Dryer


to occur occasionally in normal operation. (e.g. H2 bottle rack, zone

diameter 0.5 m plus 0.5 m for zone 2)

■ Zone 2 Place in which an explosive atmosphere consisting of a mixture with

air of flammable substances in the form of gas, vapor or mist is not

likely to occur in normal operation but, if it does occur, will persist for

a short period only.

■ No zone

In zones 0 and 1, the only electrical devices that may be used are those which are explicitly

approved for that zone and for which an ATEX certificate has been issued. In zone 2,

electrical devices may be used that comply with the standard safety requirements and for

which at least a supplier's declaration is present.

Transmitters approved for a more restricted zone may also be installed in a less restricted

zone.

The calculation of the leak jet extension of 0.5 m is based on IEC / DIN EN 60034-3 [2]:

• if the uncontrolled losses exceed 18 m3 NTP within 24 hours, action shall be taken to

reduce those losses

• the calculation was based on the "worst-case" scenario of a leak of 18 m3 NTP within

24 hours at one single point of release

Controlled and uncontrolled losses can be defined as follows:

Controlled losses are those volumetric flows which are used e.g. for measurements and which

are subsequently vented to the environs via the roof. Uncontrolled hydrogen losses include

those losses which are incurred as a result of small leaks in various locations, and also include

those losses which are incurred when hydrogen diffuses to the outside of the generator

through seals, or, in the case of water-cooled generators, to the stator water cooling system

through Teflon hoses and bolted joints.

The following figure illustrates the extent of the explosion zone depending on the volume

flow derived from the IEC limit of 18 m³ NTP per 24 hours.


Fig. 2: Classification of hydrogen reactions based on reaction velocity [3]

4 Application of ATEX Directives (Examples) In general there are different strategies that need to be followed in order to ensure human

safety during operation of systems where hydrogen occurs or at least could occur. These

targets in accordance with the ATEX directives are:

■ to prevent the formation of an explosive atmosphere

■ to prevent the ignition of an explosive atmosphere

■ to minimize the consequences of an explosion to a harmless degree

The first two targets can be addressed by ATEX-compliant design of the respective systems,

while as regards the third target provisions need to be made to ensure that, for example,

operating staff is made aware of hazardous areas (e.g. by markings on the ground or labelling

of affected systems). Here the focus will be on compliant design.


4.1 Single Tower Gas Dryer

In order to keep humidity in the generator low, the generator gas dryer is continuously passed

through with the hydrogen from the generator during operation. The dried hydrogen is fed

back to the generator. This situation leads to the assumption that the definition for ATEX

zone 2 is valid at all detachable connections. Fig. 3 shows an example of the gas dryer as well

as the explosion zone drawing showing the superjacent explosion zone clouds which together

form the overall explosion zone.

Fig. 3: Example of ATEX zoning: generator single tower gas dryer

All electrical components located within the overall explosion zone must be of explosion-

proof design and certified accordingly. Unlike components located in explosion zone 1, in

zone 2, electrical devices may be used that comply with standard safety requirements and for

which at least a supplier's declaration is present. Nevertheless, the challenge should be not to

place electrical components within the overall zone at all, since most ATEX-certified

components involve added cost depending on which kind of equipment is used.


4.2 Liquid Level Detector Rack

The liquid level detectors, located on a wall-mounted rack, detect all kinds of liquids present

inside the generator. These liquids are usually oil or water. Fig. 4 shows quite a simple

version for use with hydrogen-cooled generators. Generators with a water-cooled stator

require a more sophisticated system, since water poses a much higher risk to the operability of

the generator.

Fig. 4: Example of ATEX zoning: liquid level detector rack

Since it is sometimes necessary to open the isolation valves of the liquid detectors even when

the generator is operating, a small amount of hydrogen may leak at these points.

Consequently, the outlets of the liquid level detectors form an explosion zone 1. Fig. 4 shows

how zone 1 and zone 2 overlap in this configuration. The detectors themselves, being located

in zone 1, must be certified accordingly.


5 Modernization Measures As the auxiliaries can have a relatively long service life, they may comprise technology that is

either no longer state of the art or may not be compatible with current codes and standards

such as the ATEX Directive 94/9/EC [1] and IEC60034-3 [2].

Amendments made to the explosion protection codes and standards in the meantime, as well

as technical progress, may make it advisable to modernize older generator auxiliaries.

In addition, operation of older technology and material can lead to increased maintenance or

repair costs and may result in delays for procuring spare parts.

The ATEX conformity of operating plants must be checked and if necessary established.

Responsibility for implementing explosion protection measures in all operating plants rests

with their operators.

Modernization and establishing ATEX conformity may make it necessary to replace entire

generator auxiliary systems which are not in compliance with the latest explosion protection

requirements by new explosion-protected systems. Thanks to the modular approach of

Siemens generator auxiliary systems, substituting individual components is no problem.

Although it is possible to recondition entire skids and refurbish the legacy instrumentation

circuits (sensors, wiring, etc.), it may be more expedient to replace complete skids.

Substituting whole systems provides the following benefits:

■ current state of the art & explosion-protected design

■ higher availability

■ reduced risk of potential personal injury or damage in the plant

■ compact design delivered ready to connect

■ shorter modification times

■ easier procurement of spare parts


6 Summary

ATEX regulations apply to nearly all assembly groups of the hydrogen and hydrogen/water-

cooled generator, and therefore the ATEX zoning has to be clearly defined when designing

generator instrumentation and auxiliary systems. In this respect ATEX zoning for the

different components is very helpful, providing visual information about how further design

improvement is possible. The zone extension of 0.5 m derives from the theoretical approach

of calculating the leak jet range. Boundary conditions for the calculation are taken from the

“worst case scenario” (18 m³ NTP uncontrolled hydrogen losses within 24 hours) as described

in IEC / DIN 60034-3 [2].

SIEMENS is able to deliver modularized generator auxiliary systems which are in compliance

with harmonized EU directives, e.g. ATEX, including plant-specific planning, installation and

commissioning. Substituting completely modularized auxiliary skids can, on the basis of a

holistic safety assessment, be a better and simpler solution than replacing individual

components.

7 References [1] ATEX Directive 94/9/EC of the European Parliament and the Council, 23 March 94

[2] IEC 60034-3: Rotating electrical machines – Part 3: Specific requirements for cylindrical

rotor synchronous machines Fifth Edition 2005-02

[3] Bildung und Ausbreitung zündfähiger Wasserstoff-Luft Gemische aus postulierten

Leckagen im Generatorbereich, Dr. Tilman Diesselhorst, Peter Schönfeld, Dr. Klaus

Friedrich Freudenstein, VGB PowerTech e.V., 12/2006


8 Disclaimer

These documents contain forward-looking statements and information – that is, statements

related to future, not past, events. These statements may be identified either orally or in

writing by words as “expects”, “anticipates”, “intends”, “plans”, “believes”, “seeks”,

“estimates”, “will” or words of similar meaning. Such statements are based on our current

expectations and certain assumptions, and are, therefore, subject to certain risks and

uncertainties. A variety of factors, many of which are beyond Siemens’ control, affect its

operations, performance, business strategy and results and could cause the actual results,

performance or achievements of Siemens worldwide to be materially different from any

future results, performance or achievements that may be expressed or implied by such

forward-looking statements. For us, particular uncertainties arise, among others, from changes

in general economic and business conditions, changes in currency exchange rates and interest

rates, introduction of competing products or technologies by other companies, lack of

acceptance of new products or services by customers targeted by Siemens worldwide,

changes in business strategy and various other factors. More detailed information about

certain of these factors is contained in Siemens’ filings with the SEC, which are available on

the Siemens website, www.siemens.com and on the SEC’s website, www.sec.gov. Should one

or more of these risks or uncertainties materialize, or should underlying assumptions prove

incorrect, actual results may vary materially from those described in the relevant forward-

looking statement as anticipated, believed, estimated, expected, intended, planned or

projected. Siemens does not intend or assume any obligation to update or revise these

forward-looking statements in light of developments which differ from those anticipated.

Trademarks mentioned in these documents are the property of Siemens AG, its affiliates or

their respective owners.


Published by and copyright © 2014: Siemens AG Energy Sector Freyeslebenstrasse 1 91058 Erlangen, Germany

Siemens Energy, Inc. 4400 Alafaya Trail Orlando, FL 32826-2399, USA

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All rights reserved. Trademarks mentioned in this document are the property of Siemens AG, its affiliates, or their respective owners.

Subject to change without prior notice. The information in this document contains general descriptions of the technical options available, which may not apply in all cases. The required technical options should therefore be specified in the contract..

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