Apparatus protecting a synchronous machine from under excitation

• US 5,264,778 A
• Filed: 12/31/1991
• Issued: 11/23/1993
• Est. Priority Date: 12/31/1991
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Mummert, Charles R., Kimmel, Donald S., Markus, David R., Eichler, Kenneth M.
• Primary Examiner(s): KINCAID, KRISTINE LYNN
• Application Number:
  US07/815,676
• Time in Patent Office: 693 Days
• Field of Search: 322/22, 322/23, 322/24, 322/25, 322/28, 322/33, 322/46, 322/47, 322/59, 322/90, 322/99, 322/14, 322/15
• US Class Current: 322/25
• CPC Class Codes: H02H 7/065 against excitation faults
• CPC Class Codes: H02P 9/30 using semiconductor devices
• CPC Class Codes: Y10S 174/17 in an electric power conversion, regulation, or protection system

Abstract

Apparatus for protecting a synchronous generator from under-excitation, includes a limiter implemented as part of a microprocessor based voltage regulator. The limiter selectively characterizes one or more limiting parameters, such as, system stability, machine capability and loss of field protection, as straight line segments in the real/reactive power plane to provide versatile, easily modified limits on excitation.

Claims

1. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine and

minimum excitation means including characterizing means characterizing as a function of real and reactive power a machine capability limit and a system stability limit, and means monitoring said excitation and applying to said voltage regulator a signal which increases excitation when said excitation is below either said stability limit or said machine capability limit.

2. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine and

minimum excitation means including characterizing means characterizing as a function of real and reactive power a machine capability limit and a system stability limit, and means monitoring said excitation and applying to said voltage regulator a signal which increases excitation when said excitation is below either said stability limit or said machine capability limit, wherein said characterizing means characterizes said machine capability limit as at least one first line segment, and said system stability limit as at least one second line segment which intersects said first line segment.

3. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine;

minimum excitation means including characterizing means characterizing as a function of real and reactive power a machine capability limit, and means monitoring said excitation and applying to said voltage regulator a signal which increases excitation when said excitation is below said machine capability limit; and

means monitoring cooling effectiveness of said synchronous machine, and wherein said characterizing means includes means adjusting said characterizing of said machine capability limit in response to said means monitoring cooling effectiveness of said machine.

4. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine; and

minimum excitation means including digital processor means characterizing as a function of real and reactive power in at least one first straight line segment a minimum limit on said excitation, and means applying to said voltage regulator a limit signal which increases excitation when said excitation is below said minimum limit, wherein said processor means includes means characterizing a system stability limit on minimum excitation as at least one second straight line segment, and wherein said means applying to said voltage regulator a limit signal which increases excitation comprises means which increases excitation when said excitation is below said system stability limit.

5. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine; and

minimum excitation means including digital processor means characterizing as a function of real and reactive power in at least one first straight line segment a minimum limit on said excitation, and means applying to said voltage regulator a limit signal which increases excitation when said excitation is below said minimum limit, wherein said processor means includes means characterizing a machine capability limit on minimum excitation as at least one second straight line segment, and wherein said means applying to said voltage regulator a limit signal which increases excitation comprises means which increases excitation when said excitation is below said machine capability limit.

6. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine; and

minimum excitation means including digital processor means characterizing as a function of real and reactive power in at least one first straight line segment a minimum limit on said excitation, and means applying to said voltage regulator a limit signal which increases excitation when said excitation is below said minimum limit;

wherein said processor means includes means characterizing a machine capability limit on minimum excitation as at least one second straight line segment which intersects said at least one first straight line segment; and

cooling means monitoring cooling effectiveness of said synchronous machine and wherein said processor means includes means adjusting said characterizing of said machine capability limit in response to said cooling means.

7. Apparatus for controlling a synchronous machine connected to an electrical power grid, said apparatus comprising:

a voltage regulator controlling excitation of said synchronous machine to regulate voltage on the machine; and

minimum excitation means including digital processor means characterizing a loss of field limit on minimum excitation as a function of real and reactive power in at least one straight line segment which closely correlates with said trip function characteristic with a selected margin, and means applying to said voltage regulator a limit signal which increases excitation when said excitation is below said loss of field limit.