Electrical Excitation System References
Industry Codes and Standards
National Electrical Manufacturers Association
NEMA MG 1 Motors and Generators
Institute of Electrical & Electronics Engineers
IEEE Std 421.3-1997 Standard Definitions for Excitation
Electrical Excitation System Definitions
Automatic Control: In excitation control system usage, automatic control refers to maintaining synchronous operation of the machine terminal voltage at a predetermined level without operator action, over the operating range of the synchronous machine.
Brushless Exciter: An alternator-rectifier exciter employing rotating rectifiers with a direct connection to the synchronous machine field thus eliminating the need for field brushes.
Ceiling Current: The maximum direct current which the excitation system is able to supply from its terminals for a specified time.
Ceiling Voltage: The maximum direct voltage which the excitation system is able to supply from its terminals under defined conditions.
Discharge Resistor: A resistor that, upon interruption of excitation source current, is connected across the field windings of a synchronous machine or an exciter to limit the transient voltage in the field circuit and to hasten the decay of field current of the machine. Also, it is used during synchronous machine start-up process.
Excitation Power Current Transformer: The elements in a compound source-rectifier excitation system which transfer electrical energy from the synchronous machine armature current to the excitation system at a magnitude and phase relationship required by the excitation system.
Excitation Power Potential Transformer: The element or elements in a compound source-rectifier excitation system which transfer electrical energy from the synchronous machine armature terminals to the excitation system at a magnitude and phase relationship required in the excitation system. Also, the element or elements in a potential source-rectifier excitation system which transfer electrical energy either from the machine terminals or from an auxiliary bus to the excitation system at a magnitude level required by the excitation system.
Excitation System: The equipment providing field current for a synchronous machine, including all power, regulating, control, and protective elements.
Excitation System Stabilizer: An element or group of elements that modify the forward signal by either series or feedback compensation to improve the dynamic performance of the excitation control system.
Exciter: The equipment providing the field current for the excitation of a synchronous machine.
Limiter: An element of the excitation system which acts to limit a variable by modifying or replacing the functions of the primary detector element when predetermined conditions have been reached.
Notes: Examples: (1) An under excitation limiter prevents the voltage regulator from lowering the excitation of the synchronous machine below a prescribed level. (2) An over excitation limiter prevents the voltage regulator from raising the excitation of the synchronous machine above a level which would cause a thermal overload in the machine field. (3) A volts per hertz limiter acts, through the voltage regulator to correct for a machine terminal voltage to frequency ratio that is considered abnormal. (4) Other types of limiters may be used to control various quantities, such as, rotor angle, excitation output, etc.
Manual Control: In excitation control system usage, manual control refers to maintaining synchronous machine terminal voltage by operator action.
Note: Manual control means may include an exciter field rheostat, controlled rectifiers, or a dc regulator controlling either exciter field current or exciter output voltage, or other means that do not include regulation of synchronous machine terminal voltage.
Power System Stabilizer: An element or group of elements that provide an additional input to the regulator to improve power system performance.
Note: A number of different quantities may be used as input to the power system stabilizer, such as, shaft speed, frequency, synchronous machine electrical power, and etcetera.
Synchronous Machine Regulator: A regulator that couples the output variables of the synchronous machine to the input of the exciter through feedback and forward controlling elements for the purpose of regulating the synchronous machine output variables.
Voltage Regulator: A synchronous machine regulator that functions to maintain the terminal voltage of a synchronous machine at a predetermined value, or to vary it according to a predetermined plan. It is usually addressed as AVR (Automatic Voltage Regulator)