Patent EP-1361637-A2 (EP)
Inventor: DUFFY HUGH
IPC: H02H9/02
Filed: 1996-09-12
Abstract: An overcurrent protection system which will give a rapid response to relatively small
overcurrents. In a first aspect, the system, as illustrated in Figs. 1a and 2a, can be connected
between an electrical power supply 102,12 and an electrical load 112,26 to form an operating
circuit. When so connected, the system protects the circuit from overcurrents, has a normal
operating condition and a fault condition, and comprises: a circuit interruption element 108,24
having a normal state which permits the flow of a normal current, I NORMAL , when the system is in
the normal operating condition, and a fault state which permits the flow of at most a reduced
current, substantially less than I NORMAL , when the system is in the fault condition; and a control
element 104, connected in series with the circuit interruption element, the control element
having a variable resistance which is low when the current in the system does not exceed the
normal current, I NORMAL , by a predetermined current amount, and increases by at least a
predetermined resistance amount when the current in the system exceeds the normal current,
I NORMAL , by the predetermined current amount; the circuit interruption element changing from its
normal state to its fault state, thereby causing the system to change from its normal operating
condition to its fault condition, when the resistance of the control element has increased by the
predetermined resistance amount. In a second aspect, the system, as illustrated in Figs. 1c and
4, can be connected between an electrical power supply 102,12 and an electrical load 112,26 to
form an operating circuit. When so connected, the system protects the circuit from overcurrents.
The system has a normal operating condition and a fault condition, and comprises: a circuit
interruption element 108 having, a normal state which permits the flow of a normal current,
I NORMAL , when the system is in the normal operating condition, and a fault state which permits
the flow of at most a reduced current, substantially less than I NORMAL , when the system is in the
fault condition; a control element 104, connected in series with the circuit interruption element,
and having a control element deenergized state when the current in the system does not exceed
the normal current, I NORMAL , by a predetermined current amount, and a control element energized
state when the current in the circuit has exceeded the normal current, I NORMAL , by the
predetermined current amount; a bypass element 106, connected in parallel with the series
combination of the control element, the circuit interruption element, and the load, and having a
bypass deenergized state which permits the flow of at most a reduced bypass current through the
bypass element, and a bypass energized state which permits the flow of a substantially increased
bypass current through the bypass element; and with the circuit interruption element changing 
from its normal state to its fault state when the bypass element changes from its bypass
deenergized state to its bypass energized state, and the bypass element changing from its bypass
deenergized state to its bypass energized state when the control element changes from its control
element deenergized state to its control element energized state, thereby causing the circuit to
change from its normal operating condition to its fault condition.