🗊Презентация General terms of transmission lines performance and simulation

General terms of transmission lines performance and simulation Prof. Evgeniy (Eugen) SHESKIN SPbPU, Institute of Energy and Transport Systems

Topics Power Systems Structure and Basic Elements AC Transmission Lines Modeling Classification Of Transmission Lines Typical Parameters Of Transmission Lines AC Transmission Lines Performance In No-Load Modes AC Transmission Lines Performance Under Load Conditions Power Transfer and Stability Considerations Reactive Power Demand Tasks

1. Basic Circuit Elements

1. Phasor Notation sinusoidally varying voltage is represented as an arrow of constant length, spinning around at the constant frequency ω; we can ignore this circular spinning to the extent that it will be the same for all quantities, and they are not spinning in relation to each other (only when f = const!).

1. Power System Structure Main elements: 1. Generators; 2. Transformers; 3. Transmission lines.

1. Control Structure Things we can control: Power flows; System frequency; Node voltages.

2. AC Transmission Lines Modeling To develop performance equations and models for transmission lines; To examine the power transfer capabilities of transmission lines as influenced by voltage, reactive power, and system stability considerations; To examine factors influencing the flow of active power and reactive power through transmission networks; To describe analytical techniques for the analysis of power flow in transmission systems.

2. AC Transmission Lines Modeling Series Resistance (R). The resistances of lines accounting for stranding and skin effect are determined from manufacturers’ tables. Shunt Conductance (G). The shunt conductance represents losses due to leakage currents along insulator strings and corona. In power lines, its effect is small and usually neglected. Series Inductance (L). The line inductance depends on the partial flux linkages within the conductor cross section and external flux linkages Shunt Capacitance (C). The potential difference between the conductors of a transmission line causes the conductors to be charged; the charge per unit of potential difference is the capacitance between conductors

2. AC Transmission Lines Modeling AC transmission line tower construction defines its electric parameters. AC transmission line electric parameters define its performance in various under-voltage conditions.

2. AC Transmission Lines Modeling

2. AC Transmission Lines Modeling The constant Zc is called the characteristic impedance and γ is called the propagation constant. The constants у and Zc are complex quantities. The real part of the propagation constant у is called the attenuation constant α, and the imaginary part the phase constant β.

2. AC Transmission Lines Modeling The power delivered by a transmission line when it is terminated by its surge impedance is known as the natural load or surge impedance load (SIL).

2. AC Transmission Lines Modeling

3. Classification of TL by Length Short lines: lines shorter than about 100 km (60 mi). They have negligible shunt capacitance, and may be represented by their series impedance. Medium-length lines: lines with lengths in the range of 100 km to about 300 km (190 mi). They may be represented by the nominal π equivalent circuit. Long lines: lines longer than about 300 km. For such lines the distributed effects of the parameters are significant. They need to be represented by the equivalent π circuit. Alternatively, they may be represented by cascaded sections of shorter lengths, with each section represented by a nominal π equivalent.

4. Typical Parameters

5. Performance of a TL (no-load) (a) Receiving end is opened (IR=0)

5. Performance of a TL (no-load) Voltage profile

5. Performance of a TL (no-load) (b) Line connected to sources at both ends

5. Performance of a TL (no-load) Voltage profile

6. Performance of a TL (under load) (a) Radial line with fixed sending end voltage; load PR+jQR.

6. Performance of a TL (under load) (b) Line connected to sources at both ends

7. Power Transfer and Stability Considerations Let δ be the angle by which ES leads ER

7. Power Transfer and Stability Considerations

8. Reactive Power Demand

9. Tasks

10. Answers

Thank you for your attention!