Event under the auspices of the Ministry of Economy of Slovak Republic

Increasing the efficiency of electricity transmission in the transmission system

Ľuboš Pavlov
VUJE, a.s.

Ľuboš Skurčák
VUJE, a.s.

Juraj Altus
Žilinská Univerzita v Žiline


     Last modified: 2017-06-16

Abstract
Increasing the efficiency of electricity transmission in the transmission system
Ľuboš Pavlov (VUJE, a.s.), Jozef Lago (VUJE, a.s.), Juraj Altus (KVES)
The article discusses the possibility of increasing the efficiency of electricity transmission in the Slovak transmission system by determining losses due to impedance imbalance of selected electrical components (transformers, overhead lines and compensation reactors) of transmission system as generally unbalanced system.
Reducing losses of electricity should be a permanent effort of TSO-transmission system operator (220 kV, 400 kV), but also operators of DS-distribution system (22 kV, 110 kV). The issue of reducing losses in all developed economic countries, which joined the Paris Convention on Climate closely linked to increasing energy efficiency. Increasing energy efficiency in transmission and distribution of electricity is not a new issue neither in the Slovak Republic. This issue is addressed in the law no. 321/2014 Coll. and the Energy Efficiency Action Plan of the Slovak Republic, which combines the requirements of Directive 2002/36 / EC on energy services as well as new requirements of Directive 2012/27 / EU on energy efficiency. In accordance with the new Directive 2012/27 / EU is part of the Third Action Plan already area of transformation, transmission and distribution of energy (reducing the energy intensity of electricity transmission and distribution), the savings achieved on the transmission and distribution can be partially counted towards attaining the objectives of savings energy.
Reducing losses of electricity and their quantification is a very complicated task that is resolved in practice for many years. In their assessment, however, often they appear some inconsistencies, the cause of which is unknown. Leaving aside the operating conditions, measurement of transmitted energy calculation methodology and similar causes, there is also the fact of hidden losses. For the operator there is therefore a need to find out as they happen, how big they are and how can be presence of these losses reduced or eliminated. Progress in measuring or computing brings new opportunities for a more accurate analysis of total losses of electricity and its individual components. One of the components of total losses of electricity losses are caused by imbalance stars phasor of voltages and currents.
Losses in networks voltage level EHV and HV are determined by physical formulas using measured values of active power and voltage of individual network elements and the actual network parameters. These values in practice provide various measuring devices. Generally, there are electricity meters. These devices allow you to record effective values of the above parameters. At present, it is possible to realize a vector record of these electrical parameters. Vector report will provide a more complete picture of electrical quantities recorded in the form of phasor. Phasor values of electrical parameters allow detailed quantification, but also present an analysis of individual components of the loss of electricity to any element in the transmission system. To determine the total losses in the transmission system there are several possible methods. The loss of any member of the transmission system on the basis of the measured phasor values calculated from the difference of the phasors of the column vector of the apparent performance of the start and end node of the equation (1):

(1)

As previously mentioned in the text, total losses in the transmission system are expressed as the sum of several components losses. One of the components of total losses are losses caused by imbalance in the transmission system. Loss of asymmetry can then be divided into losses due to impedance and operational imbalance. Transmission system consists of a set of three-phase, impedance balanced and impedance unbalanced electrical machines (power transformer), equipment (instrument current and voltage transformers, disconnectors, lightning arresters), regulatory (protection and automation) and compensation (choke) equipment in substations, which are mutually interconnected by unbalanced or balanced external and cable wiring.
The total loss by asymmetry of the apparent power in the branch (element) of the transmission system is determined by the difference in general non-symmetrical apparent power at the start and end node to which the branch (element) is connected by the equation (2):
(2)
Calculation of losses by own impedance asymmetry depends on the input parameters of TS type elements. Each TS type element (power lines, transformer and compensation choke) affects the size of impedance imbalance losses by different design layout and location. It is therefore necessary to set the input parameters for the calculation of losses by own impedance imbalance (Tab. 1)
Tab. 1 Input parameters for calculating losses by own impedance imbalance
TS type element Input parameters
Line - Line type,
- Voltage level,
- Line length,
- Type of phase and ground wire,
- geometric distribution of phase conductors on the mast,
- type and number of masts,
- size of transmitted power in line
Transformer - nameplate data of transformer (hour angle, transformer ratio, a no-load current and short-circuit current)
- type transformer,
- arrangement of the core of transformer.
Compensation choke - geometrical arrangement,
- constructive arrangement,
- connection of the compensation choke in the transmission system

 

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