Download International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.2, pp. 1765-1770

International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
An Internet Protocol Quality of Service
Algorithm for the Protection of Smart
Power Systems
1
V.ARULKUMAR and 2S.THANGAVEL
1
[email protected], [email protected]
Abstract— The paper proposes a new concept of protection
philosophy for Distribution Grids with high penetration of
renewable energy. Conventional protection concepts are
normally based on protection schemes that consist of definite or
inverse time overcurrent relays. In future power systems, these
schemes can lead to high fault clearing times, unselective
tripping and massive Bus disconnections, which are not
acceptable in a deregulated multi owner energy market. This
work proposes an efficient intelligent communication based
protection algorithm that implements different multi
functional protection principles supported by blocking
schemes. The real time organization of both the hardware
architecture and communication infrastructure of the
protection algorithm is illustrated in detail. Special emphasis is
given to the network reconfiguration scenario cases and
detailed simulation results of such illustrative studied cases are
provided. The new protection strategy guarantees protection
selectivity and provides Bus unit availability during and after
the fault. The intelligent algorithm is applied on existing
Distribution network and meaningful conclusions are derived.
It is shown that the algorithm enables a uniform fault clearing
time (in the order of 78 ms) for all the geographically dispersed
circuit breaker positions. The overall combination of this setup
is assumed in the MATLAB/Simulink platform and the output
parameters are investigated with the existing topology.
Index Terms—Communication based protection, DG
availability, intelligent algorithm, and Utility Power Grid.
I. INTRODUCTION
The formal construction of electrical power systems is
such that the electric force is generated in large generating
stations at a relatively modest act of key locations. Yet, over
the last decade, a number of genes have contributed to an
increased interest in Distributed Generation (DG) [14]
systems. Also, the cost of the distribution technology
decreases and the cost of the transmission technology
increases; this fact draws the interest of the governments and
utilities to invest in renewable resources like wind and solar
energy, fuel cells etc.
The effects of DG on an existing distribution network
could be plus or minus depending on the location and the size
of the generators installed. Nevertheless, the integration of
large DG units may negatively impact Important distribution
and transmission grid features such as local power flow,
protection and fault current level [13],
Stability [9], voltage control, grid losses, power quality,
islanding detection [17] etc. These problems have been
extensively explored in the literature. For illustration, in
voltage boost and power quality issues due to the
implementation of DG are discussed in particular. A portion
of this aforementioned effect, DG connection can endanger
the proper operation of the security system and undoubtedly
changes the fault current amplitude. Specifically, the interface
between DG-unit and the grid strongly determines the
donation of the fault current. Directly connected DG unit does
contribute to the fault current, whilst inverter coupled DG unit
hardly contributes to the fault current rise [8]. Moreover,
large contributions to the fault current may cause the grid’s
equipment rating to be transcended. In these situations fault
current limitation is necessary. Since significant contributions
of the DG-units to the fault currents affect the measured
currents by the protective devices, applied protection systems
in the distribution grid are affected as easily. This leads to
incorrect operation of the shelter system and cause fault
detection and selectivity problems.
The larger the DG penetration level in a distribution grid,
the more difficult the modeling and analysis of the
short-circuit behavior of the organization. Hereafter, this
number will for sure continue to farm and make an
impingement along the distribution network protection.
Taking into account the growing penetration levels of DG,
distribution grid protection becomes an important matter in
the future power systems. The current protection philosophy
relies on the usage of current based time graded relays and
associated DG protection. This is effective protection for
passive distribution grids. Still, with the increasing number of
DG-units in the distribution system, the protection philosophy
1765
Arulkumar and Thangavel
An Internet Protocol Quality of Service Algorithm for the Protection of Smart Power Systems
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
needs to be reconsidered and adapted. The demand for this
adaptation depends on the penetration level and the
engineering of the DG units. This impact leads to fault current
detection failure or unjustified switching off of a goodly
portion of a tributary. Therefore, the need of migration
towards intelligent protection strategies is unavoidable. This
paper deals with the application of a general IP QoS algorithm
that converts the grid structure from radial to closed-loop just
before the isolation of the faulty segment of the network.
For this purpose the network is divided into zones. The
division of the network into zones has also been applied in
other algorithms, so far [16]. The major thought behind this
algorithm is that for specific types of protection one model is
employed. The time setting for the overcurrent protection, for
example, is the same for all zones and the coordination is
achieved by using blocking functions that switch off the zone
in which the fault current occurs. Similar approach applies to
other types of protection. It is demonstrated that, the IP QoS
algorithm guarantees the protection selectivity, is capable of
enhancing the accessibility of the DG-units during and after
the fault and ensures a fast protection speed performance by
minimizing the fault clearing time.
locations along each of them, to accommodate the
conventional protection scheme. The installation of primary
interface units i.e., current interface units (CIUs), voltage
interface units (VIUs) and circuit breaker interface units
(BIUs) at the locations where instrument transformer
equipment already exists is proposed. Therefore, time
stamped digital samples of current and voltage measurements
acquired from multiple locations are provided to create a
sophisticated protection algorithm. This proposed strategy
implies that there is no need of installation of additional
instrument transformers, except for the cases in which voltage
transformer (VT) equipment is required.
The assumptions taken into consideration regarding the
time delay components of the total fault clearing time are
defined according to Fig. 1. The following assumptions have
been considered regarding the latency values of each separate
delay component:
Sensor delay (CIU, VIU): 5 ms
Communication delay: 5 s/km (negligible)
Central protection unit (CPU) delay: variable type of
delay, dependent on the modeled protection principle
BIU delay: 15 ms
CB delay due to contact opening: 53 ms
II. THE ALGORITHM
In distribution networks with high penetration of DG, it is
very likely that during faults maloperations take place, which
result in massive DG disconnections. Furthermore, in some
cases relay tripping times should be so high that might exceed
the critical clearing time of some generators, which finally
results in increasing generators’ rotor speed and losing their
stability. The feeder/substation oriented fully centralized
protection concept is analyzed for the Dutch distribution
network located in the province of Flevoland. The generators
are modeled in detail and after the fault occurrence, the
stability can also be observed. More about the network
modeling and data can be found in [16][11][12]. The present
protection system with respect to the stability and false
tripping has been also investigated in detail. Critical clearing
times (CCTs) for all generators have been determined and it
was found that present protection scheme is vulnerable to
maloperations and stability of generators for some cases
cannot be attained [16], [12]–[3]. In [18], [3], [4] CCTs of the
generators have been a subject of investigation during variety
of faults applied at different locations. The result of this was
that in some scenarios the critical clearing time is exceeded
and some DGs lose their stability [16], [4]. Besides, the
observed scheme is vulnerable to false tripping. Present
problems may be resolved by applying additional protection
issues. However, these solutions could be temporary as the
network may increase by applying new DGs that would cause
additional problems and increasing costs. The feeders are
equipped with instrument transformers and relays at several
Fig. 1 Delay components of the total fault clearing time.
The hardware and communication infrastructure
organization of the fully centralized protection scheme for
distribution network is depicted in detail in Figs. 2. The red
dots indicate the location of the sensors and the circuit
breakers. Each feeder is divided into zones and the locations
of the primary interface units indicate the borders of each
separate zone. The protection strategy is realized in a way that
when a fault current occurs, the requested signals are
transferred to the CPU where the main algorithm is located
and a specific zone is disconnected. The protection principle
makes use of different relay algorithms [1] and for the
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Arulkumar and Thangavel
An Internet Protocol Quality of Service Algorithm for the Protection of Smart Power Systems
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
Fig. 2 Substation oriented hardware organization for distribution network.
studied scheme in Figs. 2 a combination of Line differential
protection (PLDF), busbar differential protection (PBDF) and
directional overcurrent protection (PDOC) are applied.
III. PROTECTION SETTINGS OF THE IMPLEMENTED
FUNCTION
By means of communication based transmission, sensors
provides the actual voltage and current values obtained by the
current and voltage transformers to the overcurrent and
directional blocks that work in the central integrated
algorithm. Directional overcurrent functionality has been
trained for specific measurement points. The overcurrent
block detects an overcurrent and provides instantaneously an
active signal when a threshold value is surpassed. The
directional block detects whether the direction of the force
that belongs to the fault current is in forward or reverse
charge. The relays are set in the forward direction, thus active
signals are generated when the error is in the forward steering.
More about the performance of the applied directional
overcurrent protection can be found in [18]. The protection
settings for some functions are given in the
In this scheme, blocking signals has been applied among
different blocks to enhance the protection reliability. The
binary signals generated by PDOC blocks are used for
blocking the function of upstream PDOC blocks.
The overall binary status signals of the blocks generate the
final trip signals, which are transferred back. Fig. 3 depicts the
block representation of the functions that make use of the
blocking signals. The applied blocking scheme is necessary in
order to obtain the correct coordination with respect to which
zones should be blocked and which circuit breakers should be
triggered. Besides, the applied logic is simple and can be
easily implemented in practice
Particular relay functions are executed based on specific
settings. The applied functions based on the differential
protection principle utilize percentage restraint differential
protection logic and particularly make use of a single-slope
characteristic. The applied differential protection functions
are separated into two categories. Line differential protection
functions represented by F1, F2 and F3 are applied to detect
the section of the parallel connected cables located in feeder
ZPD 2.07, namely zones 1, 2 and 3. The typical recommended
value for the pickup current of the line differential protection
logic ranges between 20 to 50% of the nominal current value.
The setting of the pickup current used in the simulations is set
to 30% of the nominal line current.
The Busbar differential protection functions represented by
F4, F5 and F16, are applied to protect the bus bars
corresponding to the protection zones 4, 5 and 16
accordingly. The recommended value of the pickup current of
the Busbar differential protection logic is between 80 and
100% of the highest nominal primary current of all current
transformers connected to the protected Busbar. The setting
of the pickup current used in the performed short-circuit
calculations is 90% of the maximum CT primary nominal
current connected to the bus bar. The settings of the
directional overcurrent based functions and differential
protection functions are fully described in [1].
IV. SIMULATION RESULTS
In order to validate the selectivity and speed performance of
the proposed IP QoS algorithm, detailed simulation studies
are carried out. Since the observed network is to isolate
neutral point, the protection scheme has been tested for three
and two phase faults at the borders of each separate protection
zone (covering both DG penetration levels) and the accuracy
of the new protection algorithm has been validated. The
system is subjected to various faults at different locations, as
shown in Fig.2. Simulations have been performed for
different DG penetration levels, % and %. In this paper only
PL1 level will be presented and one example of the applied
algorithm. All other results and the performance of the
algorithm can be found in [18]. Additionally, the other cells
denote the disconnection times of the DG-units (all in
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Arulkumar and Thangavel
An Internet Protocol Quality of Service Algorithm for the Protection of Smart Power Systems
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
seconds) and the corresponding triggered function, which
initiates a specific disconnection with the corresponding
disabled DGs. Fault initiation is at 100 ms for all case
scenarios. Fault clearing time is the total time covering the
time delays of the total path from the instant of the fault
inception (sensor time delay) to the instant of the fault clearly
(circuit breaker contact opening time delay). This is
represented in Fig. 4. The fault locations and types, the
triggered functions, the triggered circuit breakers and their
corresponding tripping and total fault clearing times (all in
seconds) are presented for all case scenarios.
Fig. 3 Block representation of the functions that make use of blocking
signals
The evaluation of the intelligent protection scheme shows
that for all fault locations correct functions are executed and
corresponding circuit breakers are triggered. It is additionally
observed that for all scenario cases, the faulty section is
isolated in less than 78 ms, providing a high percentage of the
DG-units to remain connected to the network and support it
during and after the disturbance. Simulation results verify that
the new protection scheme is highly beneficial in case of a
high number of DG-units connected to the network. Since the
protection scheme speed performance has been significantly
improved, the fault zone of the network is isolated quickly and
there is no problem of interference related to the coordination
between the network protective functions and the interconnect
protection of the DG-units[2].
For all the studied cases, DG-units are disconnected by the
transferred trip command of the activated function and not by
the locally installed DG interconnect protection (under
voltage protection). Therefore, the locally installed DG
interconnects protection units (under/over voltage) can be
mainly used as backup, in case the remote
communication-based trip command fails. As it can be seen,
the DG-units connected to the sound sections of the grid
always remain connected to the network because the total
fault clearing time is shorter than the DG disconnection time
of its interconnect protection. Another significant observation
is that false tripping does not take place in both cases on the
DG penetration level. The problem of false tripping is
completely eliminated by applying directional elements in the
protection logic of the software based protection
functionality, which runs in the CCUs. One of the most
significant observations is that the IP Qos algorithm is
designed in a way that it prevents the loss of a complete
feeder. A feeder is divided into several zones and the
algorithm is additionally capable of keeping the healthy zones
of a feeder in operation. This is done by changing the status of
the switch ties between neighboring feeders from radial to
closed-loop operation, 15 ms before the isolation of the faulty
segment. The grid structure restores to its pre-fault radial
operation, after the successful fault clearance.
A simulation model is done with the help of MATLAB
R2013a software. These generating stations are connected to
the load is connected to the substations. The total length of the
distribution system is 450 km. The communication port
measures the grid voltages and current values. The measured
data are sent to the smart monitoring display modeled in
Visual Basic. The occurrence of faults will be cleared
automatically when this algorithm is executed. Node id
indicates the zone in which the fault has been created. The
measured fault information is sent to the control unit and a
communication delay is noticed. The control unit processes
the information regarding the fault and depending distribution
station by means of circuit breaker, Busbar and
four substations. Different upon the fault the control unit
instructs the circuit breaker to isolate the faulty region.
There is also a small communication delay between Circuit
Breaker control and the control unit. The fault clearing time
varies according to the zone.
Fig.5 Fault Clearing Time
Fig. 5 Shows Node 1,2,3,4 and 5, the Node1 measures the
fault, Node 2 the fault data in transferring to the CPU, Node
1768
Arulkumar and Thangavel
An Internet Protocol Quality of Service Algorithm for the Protection of Smart Power Systems
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
3 identified the Fault area, Node 4 sends the identified the
Fault area to the C.B unit and Node 5 Trip the Circuit
Breaker. We can also see that the fully integrated protection
algorithm enables a uniform fault clearing time in the order
of maximum 78 ms for all the geographically dispersed
circuit breaker locations. One of the most significant
observations is that the protection algorithm is designed in
such a way that it prevents the loss of a complete feeder. A
feeder is divided into several zones and the algorithm is
additionally capable of keeping the healthy zones of a feeder
in operation.
V. DISCUSSION
The distribution grid is predominantly a cable grid.
These types of grids have a different behavior in faulted
situations than distribution grids consisting of overhead
lines. This behavior might ask for a different protective
strategy. The artificial ring is created in order to avoid the
possible islanding. This can be considered as switching-in a
fault current for a short period of time, and possible
consequences like resonance or overvoltage in the circuit
due to prestrike effects have not been observed. Another
solution would be to re-connect the created island after fault
isolation. This will require an additional algorithm to
synchronize both sides in order to avoid possible inrush
currents due to voltage and phase differences at the tieswitch poles [5]. No cost analysis of the real implementation
of this methodology has been done in this work as it was
beyond the scope of this project. However, the installation
costs of the new equipment are related to the costs of the
communications infrastructure, hardware architecture,
software applications, and costs of IEDs etc.
VI. CONCLUSION
The paper proposes a general feeder/substation-oriented
fully centralized protection scheme that can be implemented
on an arbitrary network. The real implementation of the
proposed protection strategy reflects an intelligent protection
scheme, which makes use of smart hardware sensors,
redundant
communication
infrastructure,
standard
communication protocols, and flexible multi-functional
software algorithms [15]. The performance of the algorithm
is validated by the aid of the distribution network. From the
simulation results of the developed protection concept,
meaningful conclusions can be summarized:
 Assures protection scheme selectivity
 Ensures a fast protection speed performance by
minimizing the fault clearing time, which satisfies the needs
of grid transient stability and prevents DG transient
instabilities
 Eliminates the problem of false tripping by means of
incorporating directional elements in the protection
functionality and eliminates the conventional relay time
coordination via utilization of redundant and reliable
communication links.
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Arulkumar and Thangavel
An Internet Protocol Quality of Service Algorithm for the Protection of Smart Power Systems
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.2, pp. 1765-1770
ISSN 2078-2365
http://www.ieejournal.com/
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