remote terminal unit for smart distribution

7/29/2019 Remote Terminal Unit for Smart Distribution

1/7

Electrical and Electronics Engineering: An International Journal (ELELIJ) Vol 2, No 1, February 2013

63

REMOTETERMINALUNIT FORSMART

DISTRIBUTION

P.Anil Kumar1 ,J.Shankar2 and G.Ashok Kumar3

1,2Annamacharya Institute of Tech&Science, Asst Professor, EEE Dept, JNT University,

Hyderabad,[email protected]

[email protected]

college of engineering & technology, Asst Professor, EEE Dept, JNT University,

Hyderabad,[email protected]

ABSTRACTDue to the increasing development of IT and communication technologies and the increasing trust in power

supply for people, the use of remote terminal units is becoming an important development direction of

distribution industry throughout the world. As an important part of the distribution system, the smart

distribution requires the terminal unit to realize information interaction and technique of the smart

distributed system. The traditional feeder terminal unit cannot meet the requirements and must be replaced

by the remote terminal unit. Firstly, the model of the intelligent distribution system is proposed. Secondly,

the model of remote terminal unit is constructed and its structure and function are presented. Finally, the

scheme of the remote terminal unit based fault detection, protection, location, isolation and restoration

algorithms for distribution system with remote terminal unit are presented.

KEYWORDS

smart distribution system; Remote terminal unit; fault location; fault isolation, load redirection protection

1.INTRODUCTION

In recent years, in order to achieve low-carbon power, many countries in the world has

accelerated the development of smart distribution technology and effectively promoted the

network's intelligence. The smart distribution has become the new trend of the future distribution

network development. In the face of new situation and new challenges, automation and

interactive are its main features. More efforts must be paid to upgrade distribution system from

the traditional distribution system to the efficient, economical, clean and interactive modern

distribution system and actively promote clean energy development. It focuses on the key

technology for intelligent distribution in power, transmission, substation, distribution,consumption,dispatching,communication information, etc.

The smart distribution is a critical part of the smart Distribution grid. The difference between the

traditional distribution and smart distribution is more serious in the distribution network. The

distribution network is a direct user-oriented, it is the key part to control and guarantee the quality

of the users power supply. The 95 percent of users power cuts are caused by the distribution


2/7


64

network. The 50 percent of the loss of power occurs in the distribution network. But the

intelligence and automation level of the current distribution network lags behind the transmission

network. So, the intelligent distribution network is an important part of smart Distribution. As the

presence of large distributed generations in smart distribution grid, after the distributed

generations are connected to the distribution network, the traditional distribution network is no

longer pure power single-supply, radiation-type power supply network. If the system faults, theamplitude, direction, distribution of the fault current and the action of auto-reclosing will be

affected by the distributed generations. So the traditional fault detection, protection, location and

reconfiguration methods for distribution network will be not valid.

To make the smart distribution system used widely, the fault detection and control methods mustbe redesigned. The structure of smart distribution network is more complex than the traditional

distribution network. The interactive features of the smart distribution network require a lot of

information exchange between the remote terminal units, the remote terminal units and the

distribution master station. The traditional centralized control methods of the distribution network

cannot meet the real-time requirements. The remote terminal unit needs to have informationinteractivity and distributed control to realize fault detection and control. It is urgent to study the

intelligent remote terminal unit for the smart distribution system which not only has real-timemonitoring function of running status and fault status, but also data processing and computing,

fault determination and treatment, fault isolation, load redirection, the restoration, healing and

local control capabilities through the information interaction.

2.STRUCTURE OF RTU FOR SMART DISTRIBUTION

Learning from the structure of the traditional distribution network and according to the

requirements of the smart grid, the smart distribution system is designed. It is mainly composed

of substation, switching station, ring main unit, pole- mounted switch, microgrid (MG), a

distributed generation (DG), feeders, intelligent remote terminal unit (IRTU), Global Positioning

System (GPS) and the communication network.

The distribution automation (DA) in the smart distribution System is changed into the advanced

distribution automation (ADA). The ADA is composed of the advanced distribution operation

(ADO) and the advanced distribution management(ADM).The ADO fulfills the distribution

supervisory control and data acquisition (DSCADA), feeder automation (FA), reactive power

control, DG dispatching, etc. The ADM looks the geographical image as the backgroundinformation to achieve data input, edit, query and statistical management of spatial and attribute

data and the network topology data of the distribution device.

The ADO system obtains the attribute and network topology data and the feeder breaker running

information from the ADM system. Through sending the operation commands to the switches,

the ADO system realizes the fault location, isolation and power restoration with ITU. The

structure of the ADO system is showed as figure 1. The substation and the ITUs are connectedinto a distributed control system via optical Ethernet.


3/7


65

Fig. 1. Structure of Smart Distribution System

3.STRUCTURE AND CHARACTERISTICS OF IRTU

3.1 Structure of IRTU

The primary functions of IRTU are status monitoring, fault detection, fault location, fault

diagnosis, information interaction and switching control. Through detecting the loss of voltage,

the over current and the transient and steady current and voltage of feeders, it determines the

position of faults and operates the corresponding switching, isolates faults and restores power

supply. The model of IRTU is showed as figure2.

Fig. 2. Structure of IRTU


4/7


66

3.2 Characteristics of IRTU

The ITU for smart distribution grid compared with the traditional FTU has the following

characteristics.

a. Realization of complete information interaction. Through the distributed control networkbased on fiber optic Ethernet and supplemented by microwave and power line carrier, one IRTU

exchanges the complete information with other IRTUs and control master. The information

includes not only node voltage, current, active power, reactive power, apparent power, power

factor, active power, reactive power, frequency, harmonics, voltage fluctuation, voltage flicker,

switch position signal, breaker failure signal , all the more off-limit signal, reclosing signal andfault recording signal, , but also protection and fault isolation output signal, network

reconfiguration and fault diagnosis decision-making signals, etc. Using the extensive interactive

information, the IRTU can improve the protection action speed and fault location accuracy, avoid

the false-operation or fail operation of protective relays.

b. Realization of distributed control. The IRTU performs the orders of protection tripping,fault location, restoration power and fault diagnosis decision. The remote control and remote

modulation order of the control master only plays a supporting role. This not only improves the

control of real-time, but also improves the distribution network reliability to avoid the control

failure of the whole network as a result of the control master fault.

c. Self-healing function. The IRTUs diagnosis functions not only conclude the IRTUs self-

healing function, but also conclude the self-healing function of the distributed control network.

When a failure IRTU is diagnosed, the IRTU is out of the network and its works are taken over

by nearby IRTU. When the distribution network is failure, the IRTU can automatically isolate

faults and restore power supply of the non-fault region to achieve the self-healing function of the

distribution network. Meanwhile, the IRTU can diagnose the devices of the local node. According

to the real-time information of the feeder and the devices, the IRTU predicts the weak links or the

possible fault links to warn in time and take appropriate defensive measure for the link.

4.PROTECTION AND CONTROL ALGORITHM

4.1 Protection Scheme

Because the current differential protection has the advantages of the simple, reliable and fast

protection and being immune from the power system disturbances, it is widely used in thetransmission network. With the successful application of the optical Ethernet and IRTU in the

smart distribution network, the current differential protection will become the best protectionalgorithm of the smart distribution network. But this algorithm will be invalid for the high

impedance fault. Meanwhile, since the large amount of information will be transmitted for this

method, when the communication network is congested, the protective time is too long to meetthe requirement of the distribution protection real-time characteristic. The direction current

protection overcomes the shortcomings that the conventional current instantaneous trip protection

cannot protect the whole line. The direction of components installed by the end of fault lines is


5/7


67

sensitive to the method of tuning. Only the protection which direction is opposite to the

downstream protection will act, so the protection has selectivity. As the input voltage value is

close to zero or very small in three-phase faults, known as "dead time voltage", the protection

cannot act. If there are disturbances during the communication process, the downstream current

direction received by the IRTU may be opposite to the actual current direction and the fail

operation of the local protection will happen. In order to improve the reliability of protection, themain protection selects the current differential protection and the direction current protection.

After performing the "or" operation to the outputs of the two protection, the final protection

output is achieved. The over-current protection is selected as the backup protection. When the

communication network faults, the conventional current instantaneous trip protection performs

the main protection.

Figure 3 shows a 10kV smart distribution grid with distributed generations. The opening loop

point is the breaker 10. One IRTU is set on every breaker or section switch.

The direction current protection works as follows: The direction from the bus to feeders is set asthe positive direction and the direction from feeders to the bus is set as negative. When the k1 of

the BC section faults, the IRTU2 and IRTU3 can all feel the fault current, but their currentdirections are all the positive direction, the downstream IRTU2 will lock the upstream IRTU1

through communication network, the protection of the IRTU 1 does not operate. If the DG

capacity is small, the IRTU3 doesnt feel the fault current and doesnt send the blocking signal tothe IRTU2. The protection of the IRTU2 acts. If the DG capacity is large, the IRTU3 can feel the

fault current, but the direction of the felt fault current is negative. The IRTU3 doesnt send the

blocking signal to the IRTU2. The protection of the IRTU2 still acts. When the k3 of the AH

section faults, if the DG capacity is small, the IRTU1-9 all dont feel the fault current, the

corresponding protections dont act. If the DG capacity is large, the IRTU4-9 all dont feel thefault current, the corresponding protections dont act. The IRTU1-3 all feel the fault current, but

their current direction are all negative and the corresponding protections dont act. The IRTU13

feels the fault current and the current direction is positive. The downstream IRTU14 doesnt feel

the fault current, it doesnt send blocking signal to the upstream IRTU13. So, the protection ofIRTU13 acts. Thus, whether the adjacent feeder or local feeder faults for the smart distributiongrid with distributed generations, the direction current protection can all operate correctly

Fig. 3. Protection structure of smart distribution


6/7


68

The current differential protection works as follows: When the k1 of the BC section faults, the

current of the IRTU1 is compared with the received current sum of the current of RITU2 and the

current of LD1 through communication networks, the difference doesnt exceed the setting value,

the protection of the ITU1 doesnt act. The current of the IRTU2 is compared with the received

current of IRTU3 through communication networks and the difference exceeds the setting value,

the protection of the IRTU2 acts. The current differences of other protection all doesnt exceedthe setting value, they doesnt act.

After protection action, there is a period of delay. Then, the corresponding protection starts the

automatic reclosing and the corresponding switch is closed. If the IUT doesnt detect the fault, the

fault type is transient fault and the distribution network comes back to work. If the IRTU stilldetects the fault, the fault type is permanent fault. The corresponding protection acts again and

the corresponding breaker is opened.

After the protection action, through the communications network, the corresponding IRTU

informs the downstream distributed generations to exit from the distribution network, theupstream distributed generations still run. For example, when the k1 faults, the IRTU2 sends the

remote control command to the IRTU5 and IRTU15 to make the DG1 and DG2 exit from thedistribution network. When the k2 faults, the ITU4 doesnt send the remote control command to

the IRTU5 and the DG1 still works.

4.2 Fault isolation and power restoration

When the permanent fault occurs at the k1 of the BC section, the IRTU2 opens and locks the

breaker 2. Meanwhile, the IRTU2 sends the opening and locking command to the IRTU3 and the

breaker 3 is opened and locked. So, the fault isolation is achieved. The CD section is not the faultsection and needs to restore power supply. The IRTU4 and RITU6-9 will send restoration power

supply command to the IRTU10 at the new power system side. The IRTU10 closes the loop

switch 10 and the CD section is supplied by the new power system 2. When the k2 faults, the

IRTU6 and IRTU7 judge that the fault point is located between node 6 and node 7, but theswitches in node 6 and node 7 are the section switch which cannot cut off fault current. The IRTU6 sends the direct jumping command to the IRTU 4 and the IRTU4 opens the breaker 4. If the

IRTU6 detects non-voltage in the feeder, opens the section switch 6. After a period time delay,

the breaker 4 is reclosed. Then the section switch 6 is closed. If the fault is transient, the

distribution network comes back to work. If the fault is permanent, the IRTU6 feels the fault

current again and sends the direct jumping command to the IRTU 4. The breaker 4 is opened.

When the IRTU6 detects non-voltage in the feeder, the section switch 6 and the switch 7 is

opened. So, the fault isolation is realized. When the IRTU4 and IRTU7 detect the section switch

6 and switch 7 is opened reliably, send reclosing command to the IRTU4. The breaker 4 is closed

again and the section between node 4 and node 6 is restored power supply. Meanwhile, the

IRTU7 sends the restoration power supply command to the IRTU10 and the loop switch 10 is

closed. The section between node 7 and node 10 is restored power supply.

4.3 Network reconfiguration and protection resetting

When the k1 in the section BC faults, the breaker 2 and breaker 3 isolate the fault section and the

CD section is supplied by the power system 2. The network reconfiguration is easy. To the

distribution network with more power sources and more branches, the load level, load amount,


7/7


69

the tolerant current capacity of the feeder and the power source capacity must be considered

integrally. Through interacting information between the ITUs, the new network structure is

constructed by using the genetic algorithm. The network reconfiguration is realized.

After network reconfiguration, the relationships between the ITUs are changed. For example,

when the k1 in the section BC faults, before network reconfiguration, the node 4 is upstream nodeof node 6 and the node 6 is upstream node of node 7. After network reconfiguration, the node 4 is

download node of node 6 and the node 6 is downstream node of the node 7. In the direction

current protection, the scheme that the downstream node felt the fault current locks its upstream

node protection must be modified. The modified scheme is that the node 4 locks the node 6 and

the node 6 locks the node 7. So the protection resetting is realized.

5.CONCLUSIONS

Aiming at the traditional feeder terminal unit (FTU) does not meet the requirements of smart

distribution grid, the intelligent remote terminal unit (IRTU) for the smart distribution grid is

designed. In addition to the functions of FTU, through information interaction, the IRTU canachieve relay protection, fault location, fault isolation, network reconfiguration, power restoration

and fault diagnosis of the feeders. The corresponding algorithm is discussed in detail. Through

the simulation analysis, the protection and location algorithm of the IRTU is verified. The results

show that the protection algorithm achieves a high accuracy.

6.AUTHORS BIOGRAPHY

1P.Anil Kumar was born in 1985. He received the B.Tech. & M.Tech degrees in

electrical engineering from the Dr.Paul Raj Engineeting College, Bhadra chalam,

Khammam Dist, A.P, in 2006 and 2011 respectively. Currently, he is the Assistant

Professor in the Department of Electrical Engineering, ANNAMACHARYA

INSTITUTE OF TECHNOLOGY & SCIENCE

2J.Shankar was born in 1984. He received the B.Tech. degree in electrical

engineering from the Dr.Paul Raj Engineeting College, Bhadrachalam,in 2006 &

M.Tech degree in Power Electronics From PRRM Engg college in 2011 respectively.

Currently, he is the Assistant Professor in the Department of Electrical Engineering,

ANNAMACHARYA INSTITUTE OF TECHNOLOGY & SCIENCE.

3G.Ashok Kumar. He received his B.Tech degree in electrical engineering from the

from Aizza college of engineering & technology,Mancherial and M.Tech degree

Electrical Power Engineering from JNT University,Hyderabad. Currently, he is theAssistant Professor in the Department of Electrical Engineering, Aizza college of

engineering & technology

remote terminal unit for smart distribution

Documents