System and method for synchronizing an auxiliary electrical generator to an electrical system

• US 7,877,169 B2
• Filed: 08/21/2007
• Issued: 01/25/2011
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: EI Electronics LLC (Hubbell, Inc.)
• Original Assignee: Electro Industries/Gauge Tech
• Inventors: Slota, Frederick B., Chen, Henry (Ying Hong)
• Primary Examiner(s): Bahta; Kidest
• Application Number:
  US11/894,553
• Publication Number:
  US 20090055031A1
• Time in Patent Office: 1,253 Days
• Field of Search: 700/286, 702/61, 340/635, 361/65, 361/42, 361/47
• US Class Current: 700/286
• CPC Class Codes: H02J 3/42 with automatic parallel connection when synchronisation is achieved

Abstract

There is provided herein methods and apparatus for apparatus for controlling the interconnection of an auxiliary AC generator with an electrical system, such as an electrical distribution system, e.g., a utility grid. A measuring circuit measures the frequency of an auxiliary AC generator and the phase angle between one voltage phase of the generator and the correspondent voltage phase of the electric utility'"'"'s electricity supply lines, i.e., the grid, each of which are averaged and filtered. The measured frequency of the auxiliary AC generator is matched to the frequency of the electrical system and the measured phase angle of the generator is matched to the electric utility'"'"'s electricity supply lines. Once matching is achieved to within a defined tolerance, interconnecting contactors are closed.

Claims

1. A method for controlling the interconnection of an auxiliary AC generator with an electrical distribution system in an intelligent electronic device for monitoring electrical parameters of the electrical distribution system, the method comprising:

determining a frequency of the auxiliary AC generator by;

(a) detecting a rising edge zero-crossing of a reference line voltage of the electrical distribution system in two consecutive waveform cycles;

(b) determining a time value associated with the detected rising edge zero-crossings in the two consecutive waveform cycles; and

(c) computing a time difference value between the respective time values associated with the detected rising edge zero-crossings in the two consecutive waveform cycles;

adjusting the frequency of the auxiliary AC generator until a phase angle difference between the auxiliary AC generator frequency and a frequency of a corresponding phase of the electrical distribution system is determined to be within a defined tolerance; and

closing a set of interconnecting contactors to connect the auxiliary AC generator to the electrical distribution system when said phase angle difference is determined to be within the defined tolerance.

2. The method according to claim 1, further comprising:

(d) repeating steps (a)-(c) over a predetermined number of consecutive cycles to yield a single averaged time difference value;

(e) filtering the averaged time difference value to yield a filtered time difference value; and

(f) computing the frequency of the auxiliary AC generator as;

frequency(aux)=1/[filtered time difference value].

3. An intelligent electronic device (IED) operative to control the interconnection of an auxiliary AC generator with an electrical distribution system, the IED comprising:

at least one analog sensing circuit for measuring generator and line frequency of the electrical distribution system;

at least one A/D converter;

at least one zero-crossing detector;

a processor, operatively coupled to the A/D converter, wherein the processor is programmed to measure voltage, current, power and energy parameters and being further programmed to determine a frequency of the auxiliary AC generator and said electrical distribution system, said processor being operatively coupled to said at least one zero-crossing detector, said processor being further programmed to measure a difference in phase angle between the auxiliary AC generator and line voltages associated with said electrical distribution system;

means for adjusting the frequency of the auxiliary AC generator;

means for determining when the measured difference in phase angle between the auxiliary AC generator and the line voltages associated with said electrical distribution system is determined to be within a defined tolerance;

means for closing a set of interconnecting contactors to connect the auxiliary AC generator to said electrical distribution system responsive to said means for determining; and

integrated display means for displaying instantaneous phase, frequency, and phase-angle difference values.

4. The IED according to claim 3, further comprising a program product operable with the IED for automatically controlling the auxiliary AC generator to synchronize the auxiliary AC generator with said electrical distribution system at a point in time when the phase angle difference value is within the defined tolerance, the program product storing instructions operable with the processor to cause said IED to perform the steps of:

outputting a first analog control signal to a first input of the auxiliary AC generator to adjust the frequency of the auxiliary AC generator;

determining when the frequency and phase of the selected voltage phase of the auxiliary AC generator and a corresponding voltage phase of said electrical distribution system are synchronized to within the defined tolerance; and

outputting a second control signal to interconnect contactors to couple the auxiliary AC generator to said electrical distribution system.

5. An IED for monitoring electrical parameters of an electrical distribution system and for controlling the interconnection of an auxiliary AC generator with the electrical distribution system, the IED comprising:

a meter module coupled to a three-phase power electrical system for measuring respective voltages, harmonics, voltage sags and surges, associated with each phase of the three-phase power electrical system; and

a synchronization module for controlling the interconnection of said auxiliary AC generator to the three-phase power electrical system, said synchronization module being coupled to said meter module for receiving parameters associated with a selected phase of the three-phase power electrical system for performing said synchronization, wherein the synchronization module, further comprises;

a zero-crossing detector module configured to receive a voltage of said auxiliary AC generator, having a voltage phase which corresponds to said selected phase of the three-phase power electrical system and further configured to output a zero-crossing time of said auxiliary AC generator voltage;

a frequency computation module for computing an auxiliary AC generator frequency; and

a phase angle computation module for receiving, as a first input, said zero crossing time of a voltage associated with a selected phase of the three-phase power electrical system and for receiving, as a second input, said zero-crossing time of said voltage of said auxiliary AC generator and computing a phase-angle difference value therefrom.

6. The IED according to claim 5, further comprising a counter for calculating generator frequency and power system line frequency.

7. An IED according to claim 5, further comprising:

display means for displaying an instantaneous phase, frequency, phase-angle difference values and a visual indication of when said phase angle difference value, is within a defined tolerance; and

means for outputting a control signal to synchronize said auxiliary AC generator with the three-phase power electrical system upon determining that said computed phase angle difference is within said defined tolerance.

8. An IED comprising:

at least one analog sensing circuit for measuring generator and line frequency of an electrical distribution system;

at least one A/D converter;

at least one zero-crossing detector;

a processor, operatively coupled to the A/D converter, said processor programmed to measure voltage, current, power and energy parameters and being further programmed to determine a frequency of said generator and said electrical distribution system, said processor being operatively coupled to said at least one zero-crossing detector, said processor being further programmed to measure a difference in phase angle between said generator and line voltages associated with said electrical distribution system.

9. An IED of claim 8, wherein the measured phase difference in phase angle is an analog value.

10. An IED of claim 8, wherein the measured phase difference in phase angle is a digital value.

11. An IED of claim 8, further comprising a display for providing a graphical display of said phase angles, said generator frequency and said electrical distribution system frequency.

12. An IED of claim 8, further comprising an Ethernet connection for coupling said IED to an external module.