Ground fault detector for T1 span equipment

A method of detecting a ground fault in a telecommunications network, wherein said network includes a central office, a network interface unit, a first and second pair of simplex transmission cables coupled between said network interface unit and said central office, and a repeater coupled to said first and second transmission cables, said method comprising, in combination:

• providing in said repeater a transformer comprising a core, a first coil coupled to said first pair of simplex cables, a second coil coupled to a detector device, said first and second coils configured to impose a signal from said first coil on to said second coil, a third coil, and a fourth coil;
• measuring a differential current between said third coil and said fourth coil, said transformer core saturating if said differential current exceeds a predetermined threshold and thereby preventing said first coil from imposing a signal on said second coil;
• applying said detector device to detect a signal level on said second coil;
• in response to said signal level being lower than a predetermined level, determining that a ground fault condition exists;
• and
• alerting said central office of said ground fault condition.

In telecommunications facilities comprising in combination:

• a central office;
• a network interface unit;
• a transmit span and a receive span between said central office and said network interface transmitting to and receiving from said network interface unit data over said transmit span and receive span;
• a repeater including a ground fault detector comprising in combination:
• a regenerator circuit coupled to said transmit span;
• a transformer comprising:
• a first, second, third and fourth coil, said first coil coupled to said regenerator circuit, said third coil coupled via a first and a second inductor to said transmit span, said fourth coil coupled via third inductor and a fourth inductor to said receive span;
• and
• a core, said core substantially saturated when a current differential between said third coil and said fourth coil exceeds a predetermined threshold, said saturated core preventing said first coil from imposing a test signal on said second coil;
• and
• a detector unit detecting a level signal on said second coil.

In a telecommunications network including a central office, a network interface unit, a transmit span and a receive span between said central office and said network interface unit transmitting to and receiving from said network interface unit data over said transmit span and said receive span, a repeater with a ground fault detector comprising, in combination:

• a transformer comprising a core, a first coil, a second coil, a third coil and a fourth coil;
• said third coil being coupled via first and second inductors to said transmit span;
• said fourth coil being coupled via third and fourth inductors to said receive span;
• when a current differential between said third and fourth coils exceeds a predetermined threshold, said core being substantially saturated and preventing a test signal from passing from said first coil to said second coil;
• and
• a detector for detecting a signal level on said second coil.

A method of detecting a ground fault in a telecommunications network, said telecommunications network including a central office, a network interface unit, transmit and receive lines carrying data signals between said central office and said network interface unit, and a repeater coupled to said transmit and receive lines, said method comprising, in combination:

• providing in said repeater a transformer comprising a core, a first coil, a second coil, a third coil and a fourth coil, said transformer core substantially saturating in response to a current differential of higher than a predetermined threshold between said third and fourth coils, and said transformer being configured to impose a signal from said first coil to said second coil unless said transformer core is substantially saturated;
• coupling said first coil to a signal generator;
• coupling said second coil to a detector device;
• coupling said third coil via a high impedance a.c.-blocking device to said transmit lines;
• coupling said fourth coil via a high impedance a.c.-blocking device to said receive lines;
• applying said signal generator to impose a test signal on said first coil;
• applying said detector device to detect a signal level on said second coil;
• in response to said signal level being lower than a predetermined level, determining that a ground fault condition exists;
• and
• alerting said central office of said ground fault condition.

A method of detecting a ground fault in a telecommunications network, said telecommunications network including a central office, a network interface unit, transmit and receive lines carrying data signals between said central office and said network interface unit, said method comprising, in combination:

• providing a transformer comprising a core, a first coil, a second coil, a third coil and a fourth coil, said transformer core substantially saturating in response to a current differential of higher than a predetermined threshold between said third and fourth coils, and said transformer being configured to impose a signal from said first coil to said second coil unless said transformer core is substantially saturated;
• coupling said first coil to a signal generator;
• coupling said second coil to a signal level detector;
• coupling said third coil via a high impedance a.c.-blocking device to said transmit lines;
• coupling said fourth coil via a high impedance a.c.-blocking device to said receive lines;
• applying said signal generator to impose a test signal on said first coil;
• applying said signal level detector to detect a signal level on said second coil;
• in response to said signal level being lower than a predetermined level, determining that a ground fault condition exists;
• and
• alerting said central office of said ground fault condition.