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ABB safety PLC enables SIL3 protection for mine hoist systems

Close cooperation between ABB’s mine hoist and safety PLC teams has resulted in a portfolio of systems, called ABB Ability™ Safety Plus for hoists, that meet the highest SIL3 safety integrity level in mine hoists.

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A safety programmable logic controller (PLC) has enabled a series of mine hoist systems to recently attain the highest SIL3 functional safety certification. The three functional safety systems cover speed and position monitoring, additional protections using emergency stop functionality that incorporates mine shaft safety devices and a SIL 3-certified mine hoist brake system.

Speed and position monitoring

The new ABB Ability™ Safety Plus for hoists, SIL 3 Hoist Monitor (SPHM) provides accurate safely limited speed, position control, acceleration and deceleration for a mine hoist, replacing a traditional system. It uses PROFINET/PROFIsafe safety encoders connected to the AC500-S safety PLC.

SPHM is implemented using safe function block diagrams and Structured Text programming languages. Using Structured Text in safety programming reduces the development time because you can be much more flexible when creating complex safety logic, such as safe supervision of the speed, position, acceleration and deceleration of the mine hoist.

In addition, fast safe floating-point calculations and trigonometric functions enable the mine hoist to run extremely quickly, often up to 20 meters per second (m/s). This significantly increases the mine hoist productivity without compromising on functional safety.

Using the PLC’s high-performance safety calculations when controlling a hoist running at 20 m/s, requires a very fast feedback from the encoder. This can be easily implemented using PROFINET/PROFIsafe communication between the safety encoder and AC500-S safety PLC.

The AC500-S included within SPHP protects against overspeed and over- or under-winding by running within safe limits set by the control system. Should the control system fail to stay within the pre-defined safe speed, position, acceleration or deceleration range, the Safety Plus Hoist Monitor triggers the safe machine stop and applies the mine hoist brakes to bring the hoist to a safe stop. For drum hoists, additional safety protection is provided for functions such as correct coiling supervision and clutch monitoring.

Tim Gartner, Global Product Manager, Mine Hoist Electrical
“We were able to work very closely with our colleagues in ABB safety PLC business to ensure that we realized the extremely powerful functionality built within the AC500-S safety PLC. With SIL3 certification, the key differentiation is that hoist users now have less probability of failure compared to previous systems as all components are certified with clearly defined probabilities of failure per hour.”

Protection using emergency stop functionality

An advanced version of SPHM, called the Safety Plus Hoist Protector (SPHP), also SIL 3, is available which uses emergency stop functionality, specifically tailored for the given mine hoist installation and customer functional safety requirements. The AC500-S safety PLC, within the SPHP, provides a safe, flexible configuration, with pre-certified functional safety protections.

Examples of mine hoist safety protections include shaft and underground level emergency stop controls, such as gate monitoring and emergency stop push buttons connected to AC500-S safety PLC. When the mine hoist is stopped, personnel need to be able to enter and exit the hoist system safely, without the possibility of inadvertent hoist movement. Often there is also a need to safely override the system from the operator control room and carry out a manual, step-by-step safe control to a particular mine level.

Safety braking system

SIL 3 certified Safety Plus Brake System (SPBS) features up to four completely independent and redundant mechanical and hydraulic systems. Each system (channel) is controlled by a separate AC500-S safety controller, making up a complete SIL 3 brake system. Four separate safety brake channels, with each simultaneously receiving a signal from an independent safety encoder or other safety controllers, are needed to satisfy advanced SIL 3 functional safety requirements in mine hoists.

To synchronize multiple safety controllers, safe communication with more than one master system is required. To address this ABB provides safety CPU modules that function as both a safety controller and a safety device using PROFINET/PROFIsafe shared device functionality.

While other mine hoists feature safety-related controllers that are compliant with local regulations, ABB is the first company to achieve global SIL product certification of the entire mine hoist safety control system prior to its installation. Mine hoist users benefit from knowing in advance that the equipment and systems are already pre-certified and verified to be compliant with the machinery functional safety standards.

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