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Monitoring devices perform a wide range of functions for protecting people and machines: Residual current monitors (RCMs) enable the detection of system malfunctions and facilatate troubleshooting before the protective device is switched off, which increases plant and operating safety, and cuts costs.
Plant safety and operating safety are becoming increasingly important alongside the protection of personnel. Shutdowns due to the unexpected tripping of protective devices cause high costs. It is possible to detect residual currents in the electrical installation before the protective device responds.
Residual current monitors (RCM) monitor residual current in electrical installations and issue a signal when the residual current exceeds a set value.
RCMs are used primarily in plants where a fault should result in a signal but not in disconnection. This enables plant operators to detect faults and eliminate their causes before the protective devices disconnect the installation, which increases plant and operating safety and cuts costs.
The summation current transformer detects all conductors required to conduct the current, i.e. including the neutral conductor where applicable. In a fault-free system, the magnetizing effects of the conductors through which current is flowing cancel each other out for the summation current transformer, i.e. the sum of all currents is zero. If a residual current is flowing due to an insulation fault, a residual magnetic field is left in the core of the transformer and produces a voltage. This voltage is evaluated using the electronics of the RCM. The switched contact can be used e.g. to operate an acoustic/optical signaling device, a higher-level control system or a circuit breaker.
Voltage relays are used for device and plant protection, supplying emergency light devices and the detection of N-conductor breaks and short-time voltage interruptions.
They are available as undervoltage, overvoltage and under/ overvoltage relays. The devices are equipped with different functions, depending on their intended use, and comply with the pertinent regulations.
Current relays monitor single and three-phase systems for the flow of current in emergency lighting installations and the load of motors. They are available as undercurrent, overcurrent and under/overcurrent relays.
In the mixed operation of electric hot water and electric storage heaters, the priority switch interrupts the charging procedure of the storage heater if hot water is required during the low-tariff time, thus limiting the connected load in compliance with BTO § 6. The control circuit terminals must be sealable.
Reduction of the connection fee, which depends on the maximum load to be supplied (BTO, German Federal Regulation on Tariffs § 6 Section 4), when used in systems with continuous-flow heaters and electric storage heaters where the continuous-flow heaters are switched with priority.
Fuse monitors serve to monitor all types and versions of melting fuses that cannot be equipped with a fault signal contact. This enables integration in fault signaling circuits or a central alarm in order to improve plant availability.
Phase monitors monitor the voltages in three-phase system and signal the power failure of one or more phases over a floating contact. Phase sequence monitors monitor the phase sequence in three-phase systems and signal any changes in the phase sequence – change of rotating field – over a floating changeover contact.
Insulation monitors are used for the protection of persons against ungrounded systems – IT systems. The insulation resistance of the system being monitored is measured against ground.
These types of measurements are specified according to DIN/VDE 0100-410 – Erection of power installations up to 1000 V – Protection against electric shock.
Medical premises require additional protective measures against the occurrence of excessively high touch voltages.
In rooms that conform to Group 2 of DIN VDE 0100-710, any interruption to the examination and /or treatment of patients would place those patients at risk.
This is prevented through the use of changeover and monitoring units. These monitor the insulation resistance of the non-grounded IT system, the load current and the temperature of the transformer. A warning signal is output if the limit values are exceeded. This function is carried out by an insulation monitor.
In addition, a special voltage relay monitors the voltage of the power supply and switches to a second power supply if it falls below the specified limit values.