IEEE 421.5-2005 pdf free

IEEE 421.5-2005 pdf free.IEEE Recommended Practice for Excitation System Models for Power System Stability Studies.
In addition, models for some supplementary discontinuous excitation controls are provided.
Most excitation systems represented by the Type AC and ST models allow only positive current flow to the field of the machine, although some systems allow negative voltage forcing until the current decays to zero. Special provisions are made to allow the flow of negative field current when it is induced by the synchronous machine. Methods of accommodating this in the machine/excitation system interface for special studies are described in Annex 6.
4. Synchronous machine terminal voltage transducer and current compensator models
Several types of compensation are available on most excitation systems. Synchronous machine active and reactive current compensation are the most comrnon Either reactive droop compensation and/or line-drop compensation may be used, simulating an impedance drop and effectively regulating at some point other than the terminals of the machine. The impedance or range of adjustment and type of compensation should be specified.
Droop compensation takes its name from the drooping (declining) voltage profile with increasing reactive power output on the unit. Line-drop compensation, also referred to as irans/órnzer-drop c’ompensasion. refers to the act of regulating voltage at a point partway within a generator’s step-up transformer or. less frequently, somewhere along the transmission system. This form of compensation produces a rising voltage profile at the generator terminals for increases in reactive output power.
A block diagram of the terminal voltage transducer and the load compensator is shown in Figure 4-I. These model elements arc common to all excitation system models described in this document, It is realized that, for some systems. there may he separate and different time constants associated with the functions of voltage sensing and load compensation. The distinction is not recognized in this model, in which only one time constant, TR, is used for the combined voltage sensing and compensation signal. Single-phase voltage and current sensing will, in cncral, require a longer time constant in the sensing circuitry to eliminate ripple.
When load compensation is not employed (Rc Xc 0), the block diagram reduces to a simple sensing circuit. The terminal voltage of the synchronous machine is sensed and is usually reduced to a dc quantity. While the filtering associated with the voltage transducer may be complex, it can usually be reduced, for modeling purposes, to the single time constant TR shown. For many systems. this time constant is very small and provision should be made to set it to zero.IEEE 421.5 pdf free download.