.LEPSE.UsersGuide.Implementation_Notes

Information

I To start working with LEPSE, firstly you need to determine the values of model element's parameters. All variables are presented in basic per-units (p.u.b.) of measurement - so you need to choose 2 basic values: basic power and basic voltage , for example: 1000 MVA and 340 kV.

The next stage is to calculate values of parameters in p.u.b. with the use of well known formulas. Here are examples of some parameter's conversion from per-units or named units (Om, MVA, MW etc) to basic per-units. An example for all parameter's calculations is presented in Excel-file "Conversion".

- reactivity of synchronous generator (xd, xq, x'd, etc);

- reactivity of transformer;

- reactivity of power transmission line;

- reactivity of external power system;

- reactivity of shunt reactor;

- reactive conductivity of load.

All the active resistances in basic per-units can be calculated in th same way, except resistances of field and damper windings, which can be calculeted dy the formulas below.

It should be noted that in most cases there is a necessity to equivalent power system grid to simplify dynamic model. In these case several power transmission lines, transformers, generators and loads can be equivalented into one. It is taken into account in "Conversion" file.

II Every scheme needs infinite bus - "big" equivalent generator. It's parameters can be easily calculated using the same method as for a conventional generator. The defining initial parameter for this calculation is the total short-circuit power , which defines the total power of external system and is determined by the following formula:

,

where Isc - nominal short-circuit cut-off current; Uline - nominal phase-to-phase voltage of the line. If there are several lines of communication with the external power system, the short-circuit power is determined by summing the calculated Ssc value for each line.

Then the infinite bus is equivalent to the number of generators required to provide the total short-circuit power. It is normal, for example, if infinite bus is equivalent to 50 generators of 500 MVA nominal power.

To get quasi-steady-state condition, you need to manually set a dummy load at the infinite power bus connection point so that the power system maintains a balance between generation and consumption. This balance can be easily monitored by the slip value s of the equivalent generator of the external power system - ideally, it must be near zero.

III To investigate transient processes, certain emergency events are needed. Simple switching off (on) is specified by three parameters - time of the element's shutdown (TLineOff, TtOff etc), duration of shutdown (dTLineOff, dTtOff etc) and the degree of its shutdown (Koff) . The latter means either the shutdown of a part of the generation/load, or the shutdown of one circuit or one transformer of the equivalent power line and equivalent transformer, respectively. In real power energy systems the main reason of emergency shutdown is short circuit, which is simulated by ShortCircuitShunt switching on. There are 4 main parameters of ShortCircuitShunt: reactive, active conductivity of short sircuit, time of its start and duration. The fifth parameter, total conductvity of short circuit, is useful, when you need to save the same degree of voltage drop duiring short circuit, varying the ratio between its active and reactive components. To simulate repeated short circuit, you need another ShortCircuitShunt model. The second power transmission line shutdown after its automatic reclosing can be simulated with the help of TLineOff_1, dTLineOff_1 and Koff_1 parameters.

IV LEPSE allows to investigate different means of increasing dynamic stability. The first of them is the changement of Automatic Voltage Regulator (AVR) control coefficients in Excitation_Regulator model as well as setpoints of field forcing, which is realised by logical_switch implementation in AVR model. The second one is series or parallel electrical breaking, Electrical_Braking and Electrical_Braking_Parallel accordingly, which efficiency depends on their active resistanse value. The third mean is fast turbine valving control or turbine fast valving (defined by T_regOff, T_regOn, Aimp, Timp, dTimp values) as well as automatic speed controller (ASC) parameters changement (Sigma and TauCup). The fourth mean is automatic reclosing, which was mentioned before. Finally, the fifth way to increase dynamic stability is generation or load reduction or disabling.