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At the vanguard of safety

SIL certified overspeed switch deployed – ThyssenKrupp Steel Europe is first off the line


In Short

  • Objective: Maximum safety for personnel and machine during defined operating statuses such as “safe standstill”, “safety limited speed” as well as when carrying out “maintenance work on live systems and components”
  • Implementation: Installed the SIL/PL certified electronic overspeed switch EGS(H)® 41 with integrated sensor (speed measurement), logic circuitry (speed evaluation) and actuator (speed switch)
  • Result: Reliable speed monitoring means the main electric drives do not need to be isolated from the power supply when changing a roll or rectifying faults. That not only reduces risks to the safety of personnel it also saves time and money
When work is being carried out to rectify faults, the EGS(H)® 41 in combination with the absolute encoder ASPAH 60 from Johannes Hübner Giessen quickly safeguards the operating modes "safely-limited speed" and "zero speed" to minimize risk.When work is being carried out to rectify faults, the EGS(H)® 41 in combination with the absolute encoder ASPAH 60 from Johannes Hübner Giessen quickly safeguards the operating modes "safely-limited speed" and "zero speed" to minimize risk.  
The coilbox in the hot strip mill operated by ThyssenKrupp Steel Europe AG.The coilbox in the hot strip mill operated by ThyssenKrupp Steel Europe AG.  
The hot strip mill II operated by ThyssenKrupp Steel Europe AG in Duisburg, Germany.The hot strip mill II operated by ThyssenKrupp Steel Europe AG in Duisburg, Germany.  

Systems operators are requested to observe increased safety regulations with regard to critical operating statuses. Leading the way, ThyssenKrupp Steel Europe AG installs the EGS(H)® 41 from Johannes Hübner Giessen. This is the only overspeed switch worldwide certified to Safety Integrity Level 2 as well as Performance Level d to ensure maximum safety.

Humans and machines face extreme conditions in heavy industry in particular. To comply with stringent safety regulations applicable to large industrial systems, operators implement protective measures as part of "functional safety" management procedures. These encompass the safety of the whole plant, which depends on the proper functioning of safety-related systems to reduce risks. Standards such as the international standards IEC 61508 and DIN EN ISO 13849 specify that plant systems must ensure their functions are performed under defined fault conditions with a defined high degree of probability. These functions must be executed flawlessly, in particular with regard to operating statuses such as "safe standstill" and "safely-limited speed" as well as when carrying out maintenance on "live" systems.

To guarantee maximum safety for these operating statuses in particular at the stands of the roughing train of the hot strip mill II, ThyssenKrupp Steel Europe AG installed an electronic overspeed switch that operates independent of the closed-loop speed control system. The Duisburg-based company is the first in Germany in which the EGS(H)® 41 produced by Johannes Hübner - Fabrik elektrischer Maschinen GmbH ensures an even higher level of plant safety. The device functions as a system with an integrated sensor (speed measurement), logic circuitry (speed evaluation) and actuator (speed switch). In this combination it is the first device on the market worldwide certified according to the international standard IEC 61508 up to Safety Integrity Level (SIL) 2 as well as to Performance Level (PL) d in accordance with DIN EN ISO 13849. "Functional safety means protecting life and limb by means of safe systems in our plant. With the introduction of this global innovation from Johannes Hübner Giessen we have responded to increased requirements with regard to safety of personnel, and we are more than meeting functional safety requirements" explains Svetlana Regner, responsible project manager in the field of Energy/Asset Management (EA) at ThyssenKrupp Steel Europe AG. 

Safe processes when performing maintenance

To date, it is only mandatory to install SIL components in new plants and systems. No such obligation applies when upgrading systems such as in the case of the hot strip mill II operated by ThyssenKrupp Steel Europe AG. Nevertheless, the Duisburg-based group decided to install the SIL certified EGS(H)® 41. The electronic overspeed switch helps their maintenance personnel to eliminate faults in the system significantly quicker. "We introduced a new safety concept in cooperation with the [German] Employer's Liability Insurance Association. This safety concept makes it necessary to precisely monitor the system with the Hübner device", according to Ms Regner. 

"It is not necessary to de-energize the electrically powered main drives when changing a roll if the operating speed of the system is monitored with the aid of this encoder. This practice protects the electrical components, because we do not have to switch the system back and forth at the contacts", says Ms Regner explaining the procedure. If it were necessary to continuously electrically activate the system, it would also be necessary to constantly switch the power components to and fro. It is expected that switching the electric components less will have a positive effect on contact wear. "The electronic components do not have to be replaced so often since the overspeed switch was installed. That saves both time and costs", added the project manager. With the EGS(H)® 41 installed the system supervisor is now able to quickly safeguard the operating modes "safely-limited speed" and "zero speed" to minimize risk.

New encoder and overspeed switch combined

The overspeed switch was attached to the equally new absolute encoder ASPAH 60 from Johannes Hübner Giessen. Based in Giessen, the company developed the absolute encoder specifically to fulfil the requirements of systems operating in heavy industry. And because the encoder is equipped with a parallel interface for the absolute value output (terminal box 1) as well as two additional electrically isolated incremental value outputs (terminal box 2) communications between the ASPAH 60 and the EGS(H)® 41 are ideal. The overspeed switch is equipped with four programmable switching outputs and equally two terminal boxes. Moreover, the encoder is housed in a robust casing to which it is possible to attach devices such as the SIL certified overspeed switch without any difficulty. 

Since its foundation in 1934 the company specializing in the fields of measurement, encoder and drive technologies has installed several thousand applications in heavy industry. Operating across the globe the Hessian-based company offers an all-round complete service from determining on-site installation conditions through to installing complete encoder systems for steel and rolling mills as well as container cranes, hydroelectric power plants, wind turbine generators, power systems and systems for use in mining and railway technology. 

High switching accuracy offers peace of mind 

ThyssenKrupp has trusted the reliable and long-lasting products from Johannes Hübner Giessen for more than 40 years and installs the encoder technology made in Gießen, Germany, in numerous manufacturing plants and sites worldwide. The Duisburg-based company became aware of the EGS(H)® 41 during a technical consultation. "As we were sounding out the market for a new encoder solution, Hübner was the only developer that offered a device for use in heavy industry, such as the hot rolling mill in our case. Hübner put in an enormous amount of development work during the following project phase to meet specific demands such as the shaft diameter and SIL 2 rating for the envisaged application."

The safety device is equipped with two separate electrically isolated switches to monitor speed; they can be programmed independent of one another to monitor overspeeds and underspeeds from 0.5 rpm. Electric isolation means there are two complete switches available. To achieve the same function with mechanical centrifugal switches it would be necessary to install two devices. Thanks to the setting "independent rotation direction" maintenance personnel are able to store different switching speeds for each switching point. To ensure it is possible to continuously monitor the safety functions incorporated in the device, the EGS(H)® 41 offers integrated standstill and slip monitoring functions as well as diagnostics switches. 

Internal diagnostics is a precondition for SIL 2 certification. All told, there are three diagnostics switches available: Two switches are fitted in series with both main switches. Another, separate switch is provided to facilitate enabling functions in the customer controls as required. The integrated overcurrent detection and the switching contact status monitoring functions monitor the switching contact current in both directions of flow. "Rapid overcurrent detection protects the switch and the series-connected fuse against damage in the event an inadvertent connection causes too much current to flow across the switch contacts", confirms Bernhard Herbst, project engineer at Johannes Hübner Giessen.

Tailored precisely to the customer's needs

The solution of choice for ThyssenKrupp Steel Europe is the B5 version of the SIL 2 certified overspeed switch, which is flange-mounted to the ASPAH 60 hollow-shaft device. The overspeed switch is available as B5 (flange), B35 (flange and foot) as well as a hollow shaft version. Furthermore, Hübner customers are able to choose between a supply voltage of 12 to 30 V DC or 100 to 240 V AC and between the versions with a switching voltage 0 to 30 V DC or 30 to 230 V AC/DC. 

Johannes Hübner Giessen produces other options tailored to customer's needs. "Our portfolio includes a variety of encoder solutions for heavy industry, all of which are individually adapted to meet specific customer requirements", explains project engineer Bernhard Herbst. "To achieve the best possible signal quality and a long service life it is important to choose the right devices and ensure optimum mechanical attachment of the devices to the system on site." The combination of encoder and overspeed switch fulfilled these requirements in the hot strip mill operated by ThyssenKrupp.

Before the EGS(H)® 41 was installed, personnel had to reckon with risks to safety time and again, such as the system starting up suddenly or the speed increasing abruptly as they carried out maintenance tasks or system setup work. The high switching accuracy of the device minimizes these risks. Hence, the first SIL certified overspeed switch produced in-house at Johannes Hübner Giessen fulfils an important objective: the safe operation of machines and systems.