Saturating time-delay transformer for overcurrent protection
AssigneeThe United States of America as represented by the United States Energy Research and Development Administration
InventorWalter F. Praeg
Life of this patent
Estimating the term…
Abstract
Electrical loads connected to d-c supplies are protected from damage by overcurrent in the case of a load fault by connecting in series with the load a saturating transformer that detects a load fault and limits the fault current to a safe level for a period long enough to correct the fault or else disconnect the power supply.
Claims9
An apparatus for protecting an electrical load connected to a d-c supply from damage from overcurrent in case of a load fault comprising:
- a. a transformer having a primary winding, a secondary winding, and a ferromagnetic core capable of maintaining inductive coupling between the primary winding and the secondary winding, the primary carrying the load current and the ferromagnetic core in magnetic saturation from magnetic flux set up in the ferromagnetic core by the load current;
- b. a bias supply connected electrically to the secondary winding and supplying a current to the secondary winding in a direction to saturate the ferromagnetic core, the current in the secondary winding producing an mmf greater in magnitude and opposite in direction to the mmf produced by the load current, the net mmf placing the saturation of the core at a value near the knee of the B-H curve and in saturation;
- c. a filter connected between the bias supply and the secondary winding to isolate the bias supply from pulses generated in the secondary winding by changes in load current through the primary winding;
- d. a crowbar connected across the d-c supply;
- and
- e. a time-delay circuit connected to the crowbar and to the transformer and responsive to changes in the transformer that indicate a fault to apply a delayed triggering signal to the crowbar after a predetermined time interval, thereby making the crowbar a short circuit and protecting the load.
An apparatus for protecting from damage by overcurrent an electrical load that is supplied with a load voltage by a d-c supply, the apparatus comprising:
- a transformer having a primary winding, a bias winding, and a signal winding, the windings all coupled inductively to each other by a ferromagnetic core, the primary winding connected in series with the d-c supply and the load to form a series circuit, The core in magnetic saturation when carrying a load current in a normal amount;
- an ignitron connected across the d-c supply, the ignitron having an ignitor electrode to trigger conduction;
- a time-delay circuit connected to the signal winding and the ignitor electrode and responsive to a signal from the signal winding to effect a time-delayed triggering of conduction of the ignitron;
- a bias supply connected through a filter to establish a bias current in the bias winding in a sense to saturate the core in opposition to the normal load current and to leave the core in saturation near the knee of the B-H curve;
- a triggered spark gap having a first electrode, a second electrode, and a triggering electrode, the first electrode connected to a first terminal of the electrical load, the triggering electrode connected to the signal winding to initiate conduction from first electrode to the second electrode in response to a signal from the signal winding;
- a capacitor connected to the second electrode and to a second terminal of the electrical load to form with the electrical load, the first electrode, and the second electrode a simple series circuit;
- and
- a d-c power supply connected in parallel with the capacitor to charge the capacitor to a voltage that is opposite in sense to the load voltage and smaller in magnitude than the load voltage.
Dependencies are inferred from the claim text.