Impact of impedance unbalance on the efficiency of electricity transmission and distribution - A case study

Abstract

This article is devoted to the analysis of the possible influence of impedance asymmetry on the efficiency of electricity transmission and distribution in the electricity system in Slovakia, at a voltage level of 110 kV -400 kV, using synchronic phasor monitoring results. For simplicity of calculations, in practice, the impedance imbalance from mutual interfacial inductive capacitances bonds is neglected. In this way, the 3-phase network is interpreted as symmetrical in the calculations. In this case, it is possible to determine only some components of losses (ohmic losses, corona loss, leakages, etc). The influence of impedance asymmetry can be quantified by calculation using the results of the monitoring of the synchronous phasors of selected electricity system elements (OHL, transformer, choke) or by 3-phase modelling of real system elements. frequency to test the transformer for induced over voltage test, and its characteristics is analysed.

New Methods for Specification Latent Losses for Electricity Transmission by Overhead Lines

“…The calculation of the operating impedance and admittance matrices results from the 3-phase impedance [Z ABC ] and admittance [Y ABC ] matrix of the individual phases in general of the 3*n-conductor system with ground ropes in the matrix form, which content their own (again ground) and inter-phase inductive and capacitance bonds between all conductors. For the calculation of impedance and admittance matrices, the following input data are required: mast configuration, voltage level, conductor length, phase and ground conductor type, geometric distribution of phase wires at masts, type and number of masts, amount of power transmitted by line [4,5,6,12].…”

The impact of the construction of the new 400 kV transmission power lines between Slovakia and Hungary on the cross-border transmissions

“…These new 400 kV power lines will increase the transmission capacity of the international cross-border profile Slovakia -Hungary and relieve existing inter -national power lines 448 Gabčíkovo (SK) -Győr (HU) and 449 Levice (SK) -Göd (HU) on this profile as well as relieve the inter -national power line 440 Vel'ké Kapušany (SK) -Mukachevo (UA) on the cross-border profile Slovakia -Ukraine. Specifically, new 400 kV cross-border transmission lines are [8,9]:…”

“…Percentage changes of active powers on individual cross-border power lines with Czech Republic and Poland after the application of the corresponding reconfiguration are defined in SEPS dispatching instruction No. 2/6, [10]. This solution easily allows to set the incoming value of active power from abroad (from the direction of the Czech Republic and Poland) and to monitor changes not only on the cross-border profile Slovakia -Hungary and Slovakia -Ukraine, but also on the national transmission power lines.…”

“…The main purpose of the reconfiguration in 400 kV substation Lemešany is the current reduction (decrease of the transmitted active power) on the 400 kV power line 440 Vel'ké Kapušany (SK) -Mukachevo (UA). Based on the load flow calculations of the TS SR, it was found that due to this reconfiguration it is possible to reduce the loading of the power line 440 by ≈ 30 % from the value of the transmission in the basic connection of topology, which represents a decrease of the transmitted active power by ≈ 200 MW depending on the conditions in the TS SR. As a result of this topology change, there is an increase of active power flows on the cross-border power lines 448 Gabčíkovo (SK) -Győr (HU) and 449 Levice (SK) -Göd (HU), totalling by about 200 MW depending on the conditions in the TS SR [10].…”

“…These values approximately correspond with the values given in the dispatching instruction No. 2/6 [10], which will be achieved after the reconfiguration in 400 kV substation Lemešany considering the actual topology of the TS SR without new Slovak -Hungarian power lines. Construction and further operation of the new cross-border power lines to Hungary could lead into the situation, that for some operational states of the TS SR, it would not be necessary to perform the reconfiguration in 400 kV substation Lemešany as often as nowadays.…”