GB/T 7409.2-2020Excitation systems for synchronous machines—Part 2: Models for power system studies (English PDF)

3.1 Main voltage control

The link of comparing the actual measured value of the synchronous generator terminal voltage with the given value and adjusting the excitation output with appropriate control rules in accordance with its deviation.

NOTE: its main functions also include load current compensation, excitation feedback link and power system stabilizer (PSS) functions.

3.2 Auxiliary limiters

The limiting link in the excitation regulator other than the main voltage control.

NOTE: it includes V/Hz limiter, over excitation limiter, maximum current limiter, stator current limiter and under excitation limiter, etc.

3.3 Maximum current limiter

Under any operating conditions, the output current of the excitation system is instantaneously limited to not exceed the specified maximum value.

3.4 Volts per hertz limiter; VEL

An additional unit or function in a voltage regulator that prevents the voltage-to-frequency ratio of a synchronous machine or its connected transformer from exceeding an allowable range.

3.5 Over excitation limiter; OEL

An additional unit or function in a voltage regulator that limits the output current of the excitation system to an allowable value.

3.6 Stator current limiter; SCL

An additional unit or function in a voltage regulator that limits the stator current within an allowable value by adjusting the reactive component of the stator current of the synchronous generator during over excitation or under excitation.

3.7 Under excitation limiter; UEL

An additional unit or function in a voltage regulator that limits the reactive power of the synchronous generator to no less than a specified value under different active loads.

4.1 DC Exciters

In recent years, although DC exciters have been rarely used in new units, some synchronous machines are still equipped with such exciters. Figure 2 is a schematic diagram of an DC exciter using separately excited windings, and Figure 3 demonstrates the model of the exciter. In the model, the constant KE of the self-excited magnetic field of the AC and DC exciters is used to describe the characteristics of the exciter with self-excited components. Please be noted that when adopting the separately excited exciters, KE = 1.

XE---rectifier load factor, which is proportional to the commutation reactance of the voltage source and current source, or the combined equivalent commutation reactance of the voltage and current source, see Appendix H. Fe---commutation pressure drop coefficient, see Appendix H. Xgamma---commutation reactance. KI---current loop input constant. KP---voltage loop input constant.

Uf max, Uf min---maximum and minimum voltage output by the excitation system.

Ur max, Ur min---maximum and minimum output of the regulator UFE max---exciter magnetic field current limiting parameter.

UP+, UP----at the rated voltage of the generator, the maximum and minimum no-load output voltage of the potential source exciter. KG---feedback gain of the inner loop magnetic field regulator. KR---gain of voltage measurement link.

KZ---static difference compensation coefficient of the control link, which is generally set to the reciprocal of the proportional gain KS of the control link. TR---time constant of terminal voltage converter and load current compensator. XP---rectifier load factor of potential source converter, see Appendix H. KMAX---proportional gain constant coefficient, which is generally set to 1,000,000.

KA, KA1, KFF, KV, KAP, KAD, KAI, KB, KBP, KBI---voltage regulator gain constant. KF, KH---gain constant of excitation feedback link.

TB1, TB2, TC1, TC2, TA, TB, TAD, TG---voltage regulator time constant. TF---time constant of excitation feedback link. XC, RC---current and power compensator gain constants.

UA max, UA min, UA1 max, UA1 min, UA2 max, UA2 min, UB max, UB min, UD max, UD min, UI max, UI min---voltage regulator amplitude limiting values.

KL1---over excitation instantaneous limit gain.

UL1R---over excitation instantaneous setting value. KPSS, KS1, KS2, KS3---power system stabilizer gain.

TS1, TS2---time constant of power system stabilizer signal measurement link.

TW1, TW2, TW3, TW4---time constant of DC blocking link of power system stabilizer.

TP1, TP2, TP3, TP4, TP5, TP6, TP7, TP10, TP11---power system stabilizer time constant. A1, A2, M, N, TP8, TP9---power system stabilizer filter parameters. USS max, USS min---power system stabilizer output amplitude limiting values.

USI1 max, USI1 min, USI2 max, USI2 min---power system stabilizer input amplitude limiting values.

UfB, IfB, RfB UefB, IefB, RefB---respectively: generator magnetic field voltage, field current and field winding resistance reference value, exciter field voltage, field current and field winding resistance reference value.

UVF_REF---fixed value amplitude limiting value (expressed by the per-unit value of the rated value). Kinv, Kcool---heat accumulation and heat dissipation integral coefficient. KexpVEL---inverse time characteristic exponential coefficient of V/Hz limiter.

UVFL_th---inverse time timing start setting value of V/Hz limiter (expressed by the per-unit value of the rated value).

UVFL_rth---action return fixed value of V/Hz limiter (expressed by the per-unit value of the rated value).

UREF max---output maximum setting value of V/Hz limiter (expressed by the per-unit value of the rated value). KexpOEL---inverse time characteristic exponential coefficient of OEL limiter.

Ifth---inverse time limit timing start setting value of OEL limiter (expressed by the per-unit value of the rated value, and the setting value setting can be found in Appendix I).

Ifn---heat accumulation rotor current reference value of OEL limiter (expressed by the per-unit value of the rated value, and the setting value setting can be found in Appendix I).

Ifrth---inverse time limit setting value of OEL (expressed by the per-unit value of the rated value, and the setting value setting can be found in Appendix I).

If max---maximum magnetic field current setting value allowed by OEL (expressed by the per-unit value of the rated value, and the setting value setting can be found in Appendix I). C---upper amplitude limiting value of heat accumulation integral.

P, Q---active power and reactive power of the generator (expressed by the per-unit value of the apparent rated value).

IP, IQ---active current and reactive current of the generator (expressed by the per-unit value of the apparent rated value). delta---generator power angle.

Ue---exciter voltage after commutation reactance (expressed by the per-unit value of the generator air gap magnetic field voltage).

UREF---voltage regulator setting value (determined in accordance with the initial conditions). Upss---output of power system stabilizer.

Upss1, Upss2, Upss3---outputs of the power system stabilizer intervening in the main voltage control at different positions. UERR---deviation signal of the voltage control channel. Uess---output of excitation feedback link. Uie---a signal proportional to the exciter magnetic field current. UC---voltage measurement and compensator output. UA---output of voltage correction link.

USI1, USI2---input signals of power system stabilizer. fG---generator frequency (expressed by the per-unit value of power frequency 50 Hz). UVF_REF---fixed value output of V/Hz limiter. UVFL---output of V/Hz limiter.

UVFL1, UVFL2, UVFL3---outputs of V/Hz limiter intervening in the main voltage control at different positions. SOEL---OEL action flag bit (expressed by 0 and 1). UOEL---inverse time limit output of OEL limiter.

UOEL1, UOEL2, UOEL3, UOEL4, UOEL5---outputs of OEL limiter intervening in the main voltage control at different positions.

USCL1, USCL2---outputs of SCL limiter adopting the superposition mode to intervene in the main voltage control at different positions.

USCLind, USCLcap---SCL delayed phase side limit output and advanced phase side limit output.