IMC are undertaking a study, partly funded by the ECSC, into 'Improvement of Efficiency and Reliability for Underground Communications' the principal objective of which is improved communications, particularly for isolated workers and emergency operations.
Progress has been made on background collaborative research into existing communications systems, potential technologies evaluation and a study of emergency escape preparedness in coal mines. Reports of relevant emergency incidents from around the world have been collated and examined. This has highlighted that rescue organisations need self contained, lightweight and reliable systems whereas mine operators primarily require mine wide evacuation communication systems. Changing mining methods are increasing the dependency on existing underground communications systems for safeguarding lone workers, improving communication coverage for operational and evacuation announcement and emergency escape in the event of an incident. Newer communications systems are invariably more vulnerable to failure and damage.
Other research in this field centres on establishing the feasibility of mains-borne signal propagation in a working mine. Evaluation tests along underground power distribution cables using a non-contacting inductive coupler have successfully demonstrated the basic technique, though there remain a number of practical problems. Nevertheless, tests at four underground test locations spaced some kilometres apart along the underground power line network, established that the coupling efficiency was adequate to maintain two way test communications. These tests were repeated through transformers and switchgear with the same results.
Laboratory based tests on other forms of mains cable (not individual phase) coupling arrangements proved less effective. It is established that for data transmission the European wide low speed data network communication system standard protocol is most suitable. It is uniquely designed for transmission along power cables and commercially developed supporting hardware is starting to become available using proprietary power line communications technology.
New Test Apparatus for High Current, Low Voltage Applications
New electrical equipment intended for use in explosive atmospheres has to comply with the safety requirements of the ATEX Directive. Low voltage equipment can be certified intrinsically safe if it passes a European standard test method, provided the current is also low. Some low voltage equipment, such as miners' battery-powered cap-lamps, fails this test because the test apparatus overheats with currents greater than two amperes, even if an incendive spark is not produced. A simple, reliable and reproducible ignition test, or a method of assessing ignition capability, is needed if such equipment is to be shown to comply with the Directive.
HSL has started a new project, part funded from the European standards, measurement and testing research programme, involving collaboration with PJB (Germany), LOM (Spain). The aims are to study existing intrinsic safety test methods, evaluate the consequences of using higher currents then to develop a test method suitable for high current low voltage circuits and draft a procedure for its use.
The first phase of the project has been completed and involved a survey of all known work involving high currents. On completion of the survey, the next phase of the work has been agreed. This will involve further modifications to the standard IEC apparatus and also incorporate a thermal dissipation device for the tungsten contact wires developed at LOM.
Slack rope protection
Slack rope detection for mine shaft winding systems was one of the major recommendations of the Safe Manriding in Mines reports of 1976 and 1980 but subsequent trials failed to come up with a reliable solution. It has never been considered safe to include the device in winder emergency trip systems.
HMIM offered mine operators and equipment manufacturers pump-priming funding for a collaborative research project to examine whether advances in technology would now allow the development of a reliable system, suitable for direct rope and multi-rope friction winders, to protect against slack rope and to detect overloads. Davis Derby are co-ordinating the research with substantial inputs from Midlands Mining, RJB Mining and Barker davies.
The project started in February 1998 with an investigation of the reliability and accuracy of the existing technology and improvements to the sealing of the strain gauge and the strain gauge amplifier. The effects of non-destructive testing of the suspension link on the strain gauge and associated amplifier have also been investigated.
The intention is to develop a simple, low cost compression type load cell for multi-rope friction winders and provide enhanced features for the data transmission system and logic controller interface on the surface. The work is continuing.