Current limiting technology providing safe restoration of supply and switching on LV networks
SafeON™ is a proprietary arrangement of current and voltage pulses available through patented arc-less switching technology.
In certain circumstances, a member of the public or Network Operator staff may expect that exposed conductors will be dead after a fault has occurred. Until now this assumption was correct, however automated reclosers are now being installed on the LV Networks. These automated devices will attempt to re-energise a circuit once the specific reclose time has elapsed. The switching equipment within the ALVIN family comprises of semiconductor devices that allow full control over the applied voltage and resulting current, prior to full switching operations, SafeON™ Warning pulses are sent down the cable. Those pulses have limited energy and activation time.
The graph below illustrates how those pulses are formed during the SafeON™ Warning operation. Internal thyristors switch on the circuit just before the zero-crossing and increase the energy levels with every half cycle up to the level of current or voltage pre-programmed by the operator. The duration of those pulses can also be set by the Customer.
Once the SafeON™ Warning pulses have been injected down the cable, ALVIN Reclose™ will initiate the SafeON™ Making sequence. This, as shown in the figure below, aims for a “soft start” for the connected load. Thyristors are switched just before the zero-crossing in the first half-cycle. The current amplitude is measured and compared with required limits, assuming the current is within the safe range the thyristors are switched earlier than previously to allow more volts to be supplied to the load. The resulting current is measured and checked against customer requirement figures and whether it is within the ideal range. If the thyristors are able to conduct for a full cycle, then the ALVIN Reclose device will close the contactor to make the circuit.
If at any time, flowing current is higher than expected, the whole process is interrupted and the switching operation is stopped. The ALVIN Reclose device can be programmed to perform one or all of the following operations: