Download Technical inspection of remote power supply systems

Mathematical Methods in Science and Engineering
Technical inspection of remote power supply
systems for microgrid development
Stanislav A. Eroshenko, Vladislav O. Samoylenko, Alexander O. Egorov, Pavel. V. Kolobov,
Darina A. Firsova, Ekaterina M. Eroshenko

considered as an alternate plan. The very system combines
generators, running on fossil fuel, and/or renewable energy
sources and storage systems.
However, it is necessary to carry out complex technical
inspection in order to choose the plan of power supply system
development in the given location [3].
The methodology of technical inspection of remote
customers’ power supply system is provided in the paper.
Much attention is paid to the metering experiment, including
data analysis and processing.
The case study provides deep analysis of the results,
obtained during technical inspection of remote power supply
system, located in northern Ural.
Abstract— the paper provides extended discussion about the
procedure of remote areas’ electrical supply systems technical
inspection, made in an effort to reveal energy quality and reliability
problems of power supply systems. Technical inspection is carried
out in order to determine prospective alternatives of existing power
supply system development. The paper focuses on the possibility of
distributed generation implementation for the purpose of power
quality and supply reliability improvement in terms of remote
territory, located in Far North region.
Keywords— technical inspection, remote areas, power quality,
reliability of power supply, distributed generation.
I. INTRODUCTION
T
HE main tasks set before power grid companies are to
provide end users with electric energy of required quality,
to reduce long line power losses, to optimize loading of 610 kV distribution network [1], to improve consumers
electricity supply reliability in case of line fault.
The problem dealing with reliable supply of electric energy
with required qualitative parameters is of great importance for
grid companies, providing power supply for remote rural users
[2]-[5]. Taking into account that 6-10 kV feeders can be
considerably long (several tens of kilometers), the voltage may
reach unacceptably low levels during peak load hours [3].
Moreover, the power of new consumers to be connected
(remote from main 110(35) kV substation) is strictly limited
owing to insufficient carrying capacity of existing grids.
Consequently, there are several problems, regarding remote
rural areas power supply [4], namely:
1) Impermissible voltage reduction at the consumer side.
2) Intolerably high 6-10 kV feeders’ technical power losses.
3) Low reliability due to the lack of backup systems.
In order to solve above-mentioned problems the next
alternatives are considered: to develop existing network
infrastructure or to put into operation distributed generation
unit, providing reliability and quality of power supply [5]. The
construction of hybrid power supply system is frequently
II. TECHNICAL INSPECTION PROCEDURE
According to the methodology, provided in the paper,
complex technical inspection of remote power supply systems
is multistage [6]. Firstly, it is necessary to evaluate existing
supply system, namely:
1) to evaluate the structure of energy consumption;
2) to analyze external power supply system;
3) to evaluate power supply system modes of operation.
This stage is mostly composed of initial data gathering and
analyzing. This information can be found in power utilities’
reporting documents. Generally, the initial information
includes energy consumption data, electrical supply system
data, distribution lines and power equipment data, the
information about energy consumption structure and main
electrical load units [7].
The analysis of listed above data gives the possibility to
estimate energy consumption dynamics and reveal distinctive
features of power supply system’s operation modes.
At the next stage, it is necessary to make a set of
measurements in the given power supply system, including
load curves and power quality parameters identification.
Special consideration must be given to the number of
measuring devices and time of a single measurement interval.
It is necessary to evaluate:
1) power supply center operation mode;
2) operation mode of the backbone network;
3) distribution substations’ operation modes;
4) loading conditions of the power equipment;
5) power quality parameters;
6) statistic parameters of power system operation.
To determine prospective plan of power supply system
This work was supported by the Ural Federal university.
S.A. Eroshenko (phone: +7(312)0333335, fax: +7(343)359-16-15, e-mail:
[email protected]), V.O. Samoylenko (e-mail: [email protected]),
A.O. Egorov (e-mail: [email protected]), P.V.Kolobov (e-mail:
[email protected]), D.A. Firsova (e-mail: [email protected]), E.M.
Eroshenko (e-mail: [email protected]) are with Ural Federal
University named after the first President of Russia B. N. Yeltsin,
Ekaterinburg, Mira Street, 19, Russian Federation.
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Mathematical Methods in Science and Engineering
development with account of energy quality and reliability
requirements, as well as to carry out investment feasibility
study for distributed generation implementation, it is essential
to perform permanent monitoring of power supply center
(main substation) and backbone network modes of operation.
Local (internal) measurements are necessary to develop
recommendations for the given power supply system. At the
same time the overall clear picture of power supply system
mode of operation is not provided with these measurements.
The measurements are to be carried out using power quality
analyzing devices and are to be made in accordance with
national or international standards [8-9]. For example, in
Europe energy quality indices are regulated by EU 50160
“Voltage characteristics of electricity supplied by public” [8].
In this work, the experiments were conducted in
conformance with national standard [9]. The voltage, phase
currents and power parameters, controlled within minute
intervals, included:
 line and phase voltages;
 zero-phase-sequence voltages and negative-sequence
voltages;
 voltage unbalance ratio;
 voltage oscillograms, harmonic distortion;
 voltage nonsinusoidality ratio;
 phase currents;
 zero-phase-sequence current and negative-sequence
current ;
 phase current unbalance;
 current oscillograms and harmonic distortion;
 current unsinusoidality ratio;
 active and reactive power, electric power;
 power factor.
Additionally, the statistic parameters and dynamic changes
of observed values were estimated too.
parameters of the power transmission.
2. Electrical measurements of load curves and power quality
parameters.
№1252 160 kVA
10/0.4 kV
50 mm2
0.44 km
Substation
35/10 kV
Inc. cub.
10 kV
70 mm2
57 km
50 mm2
0.54 km
50 mm2
0.06 km
CB-1
№135 100 kVA
10/0.4 kV
50 mm2
0.07 km
№1223 170 kVA
10/0.4 kV
50 mm2
0.06 km
№1232 100 kVA
10/0.4 kV
№1254 250 kVA
10/0.4 kV
50 mm2
0.66 km
50 mm2
0.66 km
50 mm2
0.18 km
Fig. 1 Сase study 35/10 kV network
The measuring points, duration and purposes of the
measurements for each point are listed in Table 1.
Within the framework 10/0.4 kV №135 measurements were
not carried out because of its weak influence on total load
curve and close location to 10 kV sectionalizing point.
TABLE 1
MEASUREMENT ALLOCATION
№ Measurement point
Time
III. THE EXPERIMENT DESCRIPTION
The remote territory under consideration is supplied by
10 kV overhead distribution line (Fig. 1). The line extends
from 10 kV bus section located at 35/10 kV main substation to
sectioning point with the overall length of 56 km. The
distribution line is made of AS-50 mm2 wire (aluminum-steel).
There are six single-transformer distribution substations at
the given location: №1232/100 kVA, №1254/250 kVA,
№1223/170 kVA,
№1244/160 kVA,
№1252/160 kVA,
№135/100 kVA. The total transformer power is 930 kVA,
including consumer substation №135/100 kVA.
Speaking about reliability, there are I-category consumers at
the given territory: fire station, rural health post, kindergarten.
They are to be supplied with two or more independent power
sources. The great deal of electrical load is domestic.
Technical inspection of electrical equipment, located at the
very settlement includes:
1. Visual examination of 10 kV distribution feeder at
35/10 kV substation, 10/0.4 kV distribution substations and
0.4-10 kV internal networks of remote territory under
consideration in order to control technical construction
ISBN: 978-1-61804-256-9
№1244 160 kVA
10/0.4 kV
1
2
3
4
5
6
7
8
91
35/10 kV substation,
10 kV line cubicle,
secondary circuit
0.1 kV
10 kV
sectionalizing point,
0.22 kV relay
protection circuits
10/0.4 kV substation
№1254, 0.4 kV
transf. bushing
10/0.4 kV substation
№1223, 0.4 kV
transf. bushing
10/0.4 kV substation
№1232, 0.4 kV
transf. bushing
10/0.4 kV substation
№1244, 0.4 kV
transf. bushing
10/0.4 kV substation
№1252, 0.4 kV
transf. bushing
House,
0.22 kV inresidential network
5 days
1 day
Obtained data
- 10 kV bus section parameters;
- load curve of «line-settlement»
system;
- parameter variation, curve
characteristics.
- 10 kV supply system “input”
parameters;
- 10 kV line operation parameters;
- 10 kV network parameters.
1 day
- load curve;
- 0.4 kV network parameters
1 day
- load curve;
- 0.4 kV network parameters
1 day
- load curve;
- 0.4 kV network parameters
2 days
- load curve;
- 0.4 kV network parameters
2 days
- load curve;
- 0.4 kV network parameters
1 day
- operation mode parameters “at
the customers side”
Mathematical Methods in Science and Engineering
morning on business days. However, the weekly peak loading
conditions occur in the evening on weekends. The curve of
reactive power consumption is uniform with single surges,
caused by electric motors starting.
The daily average active power equals 109.8 kW, reactive
power – 39.6 kVAr, total power – 117.0 kVA. The active
power ranges within 65.9 – 183.7 kW.
The line voltage profile is presented in Fig. 3. The line
voltages vary from 10.23 kV to 10.81 kV. The daily average
line voltage equals to 10.53 kV. The voltages are symmetrical.
In general, the loads characteristics are uniform for all
phases. The average asymmetry is about 10 %. It is caused by
unbalanced distribution of consumers’ single-phase loads
between different phases in 0.4 kV network.
IV. MEASURED RESULTS
A. Main substation mode
The active and reactive power curves for 10 kV feeder are
illustrated in the Fig. 2. The list of the consumers forming
active power curve is the following:
 lighting load;
 household appliances: satellite equipment, computers;
 small heating devices (electric kettles, irons);
 big heating devices (boilers, electric ovens);
 induction motors: machine tools, electric saws, pumps,
water-towers, fridges;
 cellular communication stations;
 distribution line losses and contact losses.
The list of the consumers, forming reactive power curve is
the following:
 power units and chargers for modern household
appliances;
 induction motors: machine tools, electric saws, pumps,
water-towers;
 welders;
 cellular communication stations and signal retransmitters;
 distribution line losses and transformer losses.
Lighting and distributed low-rated power devices tend to
predominate in the loading structure. They have active
consumption characteristics and cause daily peak in the
B. Backbone network operation mode
In order to estimate operation mode of the backbone 10 kV
network the additional measurements have been made at the
end of 10 kV line in secondary circuits of 10 kV sectionalizing
point.
Having no access to the current transformers’ and voltage
transformers’ secondary windings, the current measurements
were carried out in control cabinet of sectionalizing point. The
clamp meters were connected to internal circuits of two
current relays in two phases. The phase voltage was measured
at the terminals of the automatic breaker of control cabinet.
Fig. 2 Active and reactive power flow curves at the beginning of 10 kV feeder
Fig. 3 Line voltages curves at the beginning of 10 kV feeder
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Mathematical Methods in Science and Engineering
Fig. 4 Active and reactive power flow curves, measured at 10 kV feeder terminals
Fig. 5 Line voltages, measured at 10 kV feeder terminals
As a result, it can be stated that the line voltage, measured
at 10 kV sectionalizing point, lies in the range of 9.8 – 10.4
kV, that meets voltage magnitude requirements (Fig. 4). The
daily average voltage levels are 10.47 kV for distribution line
sending end and 10.12 kV – for receiving end.
In this way, the average voltage drop across the given
10 kV line is about 0.35 kV. The length of the line is 56 km and
the loading factor of the line is nearly 0.1.
The relation between measured power flows in the
beginning and in the ending of the given 10 kV line (Fig. 5)
arises from current and voltage transformers inaccuracy. This
inaccuracy mainly occurs at the sectionalizing point where
there is no energy accounting circuits provided. Current
transformer’s secondary windings have 10R accuracy rating,
which corresponds to 10% error.
Another source of inaccuracy at the sectionalizing point is
the configuration of relay protection circuits working on a.c.;
such circuits contain a great number of non-linear elements.
The power losses are to be subdivided on three main types,
namely: series losses (load losses), shunt losses (leakage
currents), contact losses, commercial losses (measurement
inaccuracy, caused by current transformers low loading
conditions) [10]-[12]. Load losses, which were calculated in
accordance with measured data, equal to 8.6%. Leakage
currents are about 1%. Moreover, it was estimated that
commercial losses and contact losses are about 4.5%. In this
way, the total line losses equal to 14.1%.
supply system of the remote territory will be further described
using measurements made at distribution substation №1254.
Final conclusions, made for distribution substation №1254,
are suitable for other distribution substations too.
Low-rated household devices predominate in load structure
of the given substation. This loads result in morning peak
loads. In addition, there is motor load with approximately
12 kW active power consumption. Active and reactive power
curves are given in Fig. 6.
Phase voltages range from 226 V to 245 V, that exceeds
voltage level standard requirements. The daily average phase
voltage is 235 V. The graph illustrating phase voltages is
represented in Fig. 7.
The phase loads are not uniform. Phase asymmetry results
in rapid deterioration of transformer isolation and worsening
of electric power quality in each phase.
V. CONCLUSION
The paper presents methodology of electrical measurements
for remote power facilities. The analysis of residential
consumers operating conditions and energy quality rates is
made to develop recommendations for power quality and
reliability improvement. The main statistical rates of remote
territory operation are provided in the Table 2.
The 10 kV power supply network of the given remote
settlement provides electrical energy quality in compliance
with [8-9] and operates in a symmetrical three-phase mode.
Taking into account the overall length of the overhead 10 kV
distribution line, which equals to 56 km, the level of the power
losses in the line is satisfactory.
C. Internal power supply system operation mode
The operation modes of 10/0.4 kV grid of internal power
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Mathematical Methods in Science and Engineering
Fig. 6 Distribution substation load curve
Fig. 7 Distribution substation voltage profile
It was also observed that load phase balance is inadmissible.
Thus, it is recommended to reconnect a share of load to other
phases.
The main challenge of remote customers power supply is
low reliability. In case of distribution line fault, consumers are
not supplied within the repair time period.
In this case, distribution generator implementation becomes
the question of growing importance. Basing on the metering
data the capacity of the generator, which will be installed at
the remote settlement, is assessed to be 500 kVA taking into
account winter peak loads.
TABLE 2
POWER SUPPLY PROBLEMS
Parameter
Value
Property
Customer side voltage (0.22 kV network)
Minimal, V
222,0
High
Maximal, V
251,3
Inadmissible
Admissible
Average, V
236,3
10 kV line losses
Load losses, %
8,6
Admissible
leakage currents, %
1,0
Low
Contact losses and
commercial losses, %
4,4
Admissible
Total losses, %
14,0
Admissible
ACKNOWLEDGMENT
The authors express their gratitude for being supported by
Ural Federal University. The authors appreciate the
contribution of Open Joint-Stock Company «Interregional
Distributive Grid Company of Urals» dealing with assistance
in measurements made at 10 kV power facilities within
research and development work.
Load curve uniformity
Minimal α, %
18,3
Average α, %
20,7
Low
Admissible
REFERENCES
Load current asymmetry
Maximal I2 , %
58,2
Inadmissible
Average I2 , %
35,6
Inadmissible
[1]
[2]
It is important to note that the increased voltage level is
observed due to low loading conditions and 10/0.4 kV
transformers NLTC systems, switched to winter position. The
latter represents atypical problem of remote consumers power
supply.
ISBN: 978-1-61804-256-9
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