Any power Supply and Distribution Systems are chosen with suitable protective measures depending on the requirement of reliability, criticality of the equipment and process, considering the possibility of Insulation Faults and basic fault protections. The protective Earthing is a common practice for any System.
A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an overcurrent protection device (fuse, circuit breaker) that disconnects the power supply.
a) IT System – All active parts are insulated from earth or one point of supply is connected to earth through sufficiently high impedance. The exposed non-current carrying conductive parts of the electrical installation are earthed individually or collectively.
b) TN System –One point of the supply is directly earthed. The exposed non-current carrying conductive parts of the installation are connected to that point by protective conductors.
c) TT System – One point of the supply is directly earthed. The exposed non-current carrying conductive parts of the installation are connected to earth electrodes, which is/are electrically independent of the earth electrode of the system.
Insulation Fault and Residual Current
An insulation fault may be due to insulation deterioration:
An insulation fault between live conductors becomes a short-circuit. In the above cases, a fault results in current flow to earth. This earth-fault current, which does not return through the live conductors, is the resultant of the instantaneous currents flowing in the live conductors is the "residual current", which quantifies the level of Human protection/safety.
Residual Current Monitoring Device
The AC and pulsed DC sensitive residual current monitor RCMA420-D (Type A) from Bender is designed for fault and residual current monitoring in earthed power supply systems (TN and TT systems) where an alarm is to be activated in the event of a fault, but disconnection must be prevented. In addition, the device can be used to monitor the current in single conductors, such as PE conductors, N-PE connections and PE-PAS connections. Due to the use of measuring current transformers, the device is nearly independent of the load current and the nominal voltage of the system.
Typical application fields are: Residual current monitoring in earthed two, three or four conductor systems; construction site equipment; current monitoring of single conductors de-energized under normal conditions; socket-outlet circuits for devices which are operated unattended for a long time and which may not fail; alarm systems; safety devices.
Residual Current Monitoring System
BENDER presents the world's first multichannel, AC/DC sensitive, residual current monitoring system
The availability and reliability of the power supply is vital not only for the efficiency and productivity of our customers processes but also for the safety of traffic engineering and public facilities. Within the framework of preventive maintenance it is therefore very important that power supplies be continuously monitored to ensure that faults can be recognized and localized at an early stage.