The analysis of technical requirements for renewable energy sources grid integration was performed by DSO named AB ESO. The case study was performed using EA-PSM. Study had included reactive power and voltage control, voltage sag evaluation, harmonic load flow study, harmonic losses analysis, grid optimization through power losses, short circuit analysis and protection coordination.

Renewable energy sources grid integration questions are analysed in a case study according to standards requirements: EN 50160 “Voltage characteristics of electricity supplied by public distribution networks”, IEC 61000-3-7 “Limits – Assessment of emission limits for the connection of fluctuating installations to MV, HV and EHV power systems”, IEC 61400-21 “Measurement and assessment of power quality characteristics of grid connected wind turbines”.

Fig. 1 Network voltage limit reach due to Wind turbine generation
Fig. 1 Network voltage limit reach due to Wind turbine generation

Case study analyses voltage at the buses in the network, which are depicted in Fig. 1. Standard EN 50160 limits bus voltage to ±10%, however requirements are increased due to network planning transition from GOST to IEC standards. The voltage limits are +6%/-10%. Study revealed network topology, parameters and load influence to the maximum power of renewable energy sources connected to the grid.

The 80kW renewable energy source or distributed generator do not match standard requirements due to network voltage increase more than +6% (voltage marked in red color).The variation of load and generation could lead to voltage drop below required limits. Increase in loading and disconnection of the generator at the same time, results in bus voltage decrease up to 84÷85% of its nominal value, as depicted in Fig. 2.

High load value and low voltage at the consumer requires change of the transformer tap position. DSO increases voltage by changing the position of the transformer tap changer. However reduced load and increased generation increase voltage in the network to more than +10% from nominal value. The situation depicted in Fig. 3.

Fig. 2. Network voltage lower limit reach due to Wind turbine disconnection
Fig. 2. Network voltage lower limit reach due to Wind turbine disconnection
Fig. 3. Wind generation combination with rise of position of 10/0.4kV transformer tap changer
Fig. 3. Wind generation combination with rise of position of 10/0.4kV transformer tap changer

EA-PSM software allows calculate possible network load, generation, topology combinations within couple of minutes and asses the network voltage quality as well as losses under all possible network operation conditions.

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