Ground fault detection circuit

• US 6,188,203 B1
• Filed: 08/18/1997
• Issued: 02/13/2001
• Est. Priority Date: 11/01/1996
• Status: Expired due to Term

• Current Assignee: Safran Power UK Ltd.
• Original Assignee: Lucas Aerospace Power Equipment Corp. (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Rice, Kevin E., Roseman, Ronald W.
• Primary Examiner(s): PONOMARENKO, NICHOLAS
• Application Number:
  US09/414,039
• Time in Patent Office: 1,275 Days
• Field of Search: 322/18, 322/25, 322/27, 322/37, 322/19, 322/28, 361/20, 361/101
• US Class Current: 322/25
• CPC Class Codes: F02N 11/04 the motors being associated with current generators
• CPC Class Codes: H02H 7/06 for dynamo-electric generators; for synchronous capacitors
• CPC Class Codes: H02P 2101/30 for aircraft
• CPC Class Codes: H02P 9/30 using semiconductor devices

Abstract

A controller for a starter/generator used with an aircraft engine, includes means for monitoring field return current in a generator field winding; means for monitoring generator voltage; and microprocessor control means for adjusting generator field current as a function of the field current and voltage and field return current. The field return current and output voltage monitoring functions allow for open field, field integrity, over voltage, field weakening and torque limiting functions to be realized in an integrated programmable system configuration.

Claims

1. Apparatus for detecting a ground fault in a generator circuit a load is connected to the generator by a first conductor, being a feeder line and having a feeder current, and a second conductor, being a return line having a return current, comprising:

a sensing means coupled to each conductor for detecting instantaneous changes in feeder current and return current, where said sensing means producing a first output that corresponds to instantaneous changes in feeder current, and a second output that corresponds to instantaneous changes in return current;

a differential circuit for differentially combining said first and second outputs and producing a third output for indicating when the ground fault is detected based on a difference between said first and second outputs, and;

a control means for monitoring said third output and de-energizing the generator when the ground fault is detected.

2. The apparatus of claim 1 wherein said differential circuit differentially combines said first and second outputs to reject common mode disturbances that could otherwise cause a false ground fault indication.

3. The apparatus of claim 1 wherein said differential circuit comprises a first differential amplifier having a non-inverting input connected to said first output and an inverting input connected to said second output and producing a first differential output related to difference between said feeder and return currents.

4. The apparatus of claim 3 wherein said circuit comprises a second differential amplifier connected in a complementary manner to said first differential amplifier having a non-inverting input connected to said second output and an inverting input connected to said first output and producing a second differential output related to the difference between said return and feeder currents.

5. The apparatus of claim 4 wherein said first and second differential outputs are coupled to a common node to produce said third output, wherein said third output is related to an absolute value of the instantaneous difference between said feeder and return currents.

6. The apparatus of claim 1 wherein said third output indicates magnitude of a ground fault based on the instantaneous difference between said feeder and return currents.

7. The apparatus of claim 1 wherein said sensing means comprises

a first current transformer for detecting instantaneous changes in the feeder current and producing a pulsed output corresponding to the instantaneous change in the feeder current and

a second current transformer for detecting instantaneous changes in the return current.

8. The apparatus of claim 7 wherein said transformers are connected to complementary inputs of said first and second differential amplifiers.

9. The apparatus of claim 7 wherein said first and second current transformers are connected to complementary inputs of said first and second differential amplifiers to produce said third output with said third output being related to the absolute value of the peak voltage difference between said feeder and return current transformer voltage signals.

10. The apparatus of claim 1 wherein said control means comprises a built in test (BIT) circuit connected to said differential circuit by which the control means can determine the operability of said differentially combining circuit independent of the application of a test signal.

11. The apparatus of claim 10 wherein said differential circuit comprises a first differential amplifier having a first amplifier output that is related to the difference between said feeder and return currents, and said BIT circuit comprises a summing node coupled to said first amplifier output and a reference so that said node voltage indicates a failure of the amplifier by a static change in the voltage level at said node.

12. The apparatus of claim 11 comprising a second differential amplifier having a second amplifier output that is related to the difference between said first and second conductors'"'"' currents, said second amplifier output being coupled to said summing node so that said node voltage indicates a failure of said first or second amplifier by a static change in voltage level at said node.

13. Apparatus for detecting a ground fault in a circuit which has a load connected to a D.C. generator by a first conductor being a feeder line and having a feeder current and a second conductor being a return line and having a return current, comprising:

a first current transformer coupled to said feeder line, said first transformer producing a first voltage pulse in response to an instantaneous change in the feeder current;

a second current transformer coupled to said return line, said second transformer producing a second voltage pulse in response to an instantaneous change in the return current;

a first differential amplifier having an inverting input and a non-inverting producing an output relative to the difference of the voltages at the inverting and non-inverting inputs;

a second differential amplifier, having an inverting input and non-inverting input producing an output relative to the difference of the voltages at the inverting and non-inverting inputs;

means for connecting the inverting input of said first differential amplifier to said first current transformer and receiving said first voltage pulse;

means for connecting the non-inverting input of said first differential amplifier to said second current transformer and receiving said second voltage pulse;

means for connecting the inverting input of said second differential amplifier to said second current transformer and receiving said second voltage pulse;

means for connecting the non-inverting input of said second differential amplifier to said first current transformer and receiving said first voltage pulse;

a first summing node connected to the output of said first differential amplifier and the output said second differential amplifier whereby the existence of a ground fault may be detected;

a built in test (BIT) circuit connected to the outputs of said differential amplifiers wherein the operability of said differential amplifier circuits can be tested independent of the application of a test signal, said BIT circuit comprising a second summing node coupled to said first differential amplifier output, said second differential amplifier output and a reference voltage whereby the second summing node voltage indicates a failure of said first or second differential amplifier by a static change in the voltage level at said second summing node;

a sample and hold circuit coupled to said first summing node;

a control means for monitoring said first and said second summing nodes and de-energizing the generator when either the ground fault is detected or the failure of the apparatus is detected.