Device and method for eliminating transformer excitation losses
The invention is a device and method for eliminating core excitation losses in a distribution transformer when the transformer is not supplying power to loads. The invention consists of sensors, a control circuit, a user interface and a power contactor. The power contactor is connected on the line side of a transformer and is opened or closed automatically based on preprogrammed time or load criteria determined by the control circuit. In one operational mode and when the transformer is disconnected from the line, the control board generates low power pulses at the transformer load connection points in order to “search” for loads. If a load is detected, the transformer is reconnected by way of contactor closure. If the transformer load drops to zero, for a predetermined amount of time, the transformer is again disconnected and the pulsed load search is reestablished.
1. A smart load detection circuit for selectively controlling a connection between a power supply and one or more loads electrically coupled to the power supply at a load point, the smart load detection circuit comprising:
a current sensor configured to be disposed in a current path between the power supply and the load point;
a controller including:
a control circuit configured to receive a current indication from the current sensor, determine a no-load condition from the current indication, and issue an open connection command signal at a control output of the control circuit in response to a no-load condition determination; and
a pulse generator configured to issue a pulse for reflection from the load point to the control circuit, the control circuit configured to receive a reflected pulse, determine a load condition, and issue a close connection command signal at the control output of the control circuit;
a contactor having control input coupled to the control output of the control circuit, the contactor being configured for coupling between the power supply and the load point and operative to electrically disconnect the power supply from the load point in response to the open connection command signal received at the control input and to electrically connect the power supply to the load point in response to the close connection command signal received at the control input.
2. The smart load detection circuit of claim 1 , further comprising a distribution transformer coupling the power supply to the load point.
3. The smart load detection circuit of claim 1 , wherein the distribution transformer is single phase distribution transformer.
4. The smart load detection circuit of claim 1 , wherein the distribution transformer is a three-phase distribution transformer, the smart load detection circuit being associated with one of the phases.
5. The smart load detection circuit 1 , further comprising an isolation transformer coupled between the pulse generator and the load point.
6. The smart load detection circuit 1 , wherein the contactor has a control coil and one or more electrical contacts configured to selectively establish an electrical connection between the power supply and the load point, the one or more electrical contacts being controllable by the control coil of the open and close connection command signals provided at the control input.