Overview
The Distribution Automation System (DAS) is a system newly developed to provide remote control and supervising sectionalizers on a high-voltage distribution line for switching load current of the line either automatically or manually, thus providing automatic isolation of a faulty line section that enables the recovery of stable power supply to customers remaining on the line.
As the general concept for system construction of the DAS in Japan, three stages are referred to herein as shown in Fig. 1. Stage-1 DAS is without remote control and supervision functions. Stage-2 DAS is the most suitable stage for revealing to the customers the real advantages of the automation system. Remote control and supervision functions for line switches together with automatic sectionalization of faulty line sections are provided.2 Also, installation of the Stage-2 System is the shortest path to Stage-3 without making any large modifications on the Stage-2 System, and offering very easy understanding of the effectiveness of FDR (fault detecting relay) system incorporated in the Stage-1 System.
CPU: Central Processing Unit
CB: Circuit Breaker
RTU: Remote Terminal Unit
LP: Line Printer
VS: Vacuum Switch
TCM: Telecontrol Master Unit
HC: Hard Copier
FDR: Fault Detecting Relay
CD: Control Desk
FSI: Fault Section Indicator
SPS: Switch Power Supply
Stage |
System Description |
Main Equipment |
1 |
Automatic isolation of faulty section by combination of pole-mounted FDR and substation enclosing relay |
Reclosing relay, vacuum switch, switch power supply, fault detecting relay(FDR) |
2 |
Remote terminal unit, including FDR functions, is used as pole-mounted equipment, enabling remote control and supervision of the line switch |
Remote terminal unit (RTU) telecontrol remote unit (TCR), telecontrol master unit (TCM), and man-machine interface equipment together with Stage-1 equipment |
3 |
Computer system is introduced and linked to the Stage-2 System, which provides automatic operations by the computer |
CPU system together with Stage-2 equipment |
Fig. 1 Configuration of the three stages of DAS
Advantages and Configuration
The advantages of DAS are as follows:
•Reduced outage periods/customers.
•Route changing without power interruption during feeder or bank overloading DAS functions to monitor the distribution feeder and bank current on real time.
Therefore, DAS can maintain a balance in loading by route changing without power interruption should feeder or bank overloading occurs.
•Reduced personnel expense
DAS enables reductions of the number of service crew because the fault section can be isolated by remote-control facilities installed in a central station. Therefore, DAS provides a significant improvement in personnel expense.
•Rapid and accurate response to customers
As DAS can provide information of the site condition on real time, you can accurately reply to customers who have been deprived of service.
•Expansion to Customer Automation
DAS can be expanded to advanced functions such as load management, automation meter reading, and home automation in the future by using the signal transmission line of DAS etc.
Fig. 1 shows the configuration of the three stages of DAS.
Functions of the Three Stages DAS
Stage-l is composed of pole-mounted of pole mounted equipment (VS/FDR/SPS) and FSI in a substation. Fault Section Indicator (FSI), installed in substation and connected to CB, can detect a faulty section by the time lapse from enclosing until tripping of CB.
Stage-2 DAS has the following functions:
•Remote control of pole-mounted VS
•Monitoring of substation bank and feeder regarding their current, voltage, and relay operation
•Monitoring of VS status
•Information on faulty sections by color-CRT
•Recording of maintenance work data
The main functions of Stage-3 DAS are:
•Automatic fault detection, isolation, and restoration in case of substation and feeder fault. The most suitable procedure for restoration is calculated by the CPU, and restoration is performed automatically.
•As to overload and maintenance work, the procedure of changing the distribution network by considering the load balance is affected automatically and performed.
•Monitoring of substation and feeder is displayed in real time on graphic display with street map.
•Information on customers and facilities connection.
•Data recording and reporting by printer and color hard copier
•Simulation for operator training
Pole-mounted Equipment Interface
The Pole-mounted Vacuum Switch (PVS) is closed by excitation a coil when a voltage is applied and it stays closed state while the voltage is alive. The PVS is opened automatically when the voltage is lost due to de-excitation of the coil. The voltage is supplied by SPS and the PVS coil is excited when the Y contact of FDR is closed as shown in Fig. 2 below.
Conditions for Y relay excitation are shown in Fig. 2.
i)X-time (closing time) has passed after the voltage is applied to the PVS. ("a" contact of FDR is closed), or.
ii)FDR hundle is set at "MANUAL ON" position.
Y contact is opened when the FDR handle is set at "MANUAL OFF" position and PVS coil is not excited.
Fig. 2Pole-mounted equipment interface
Fault Detecting Relay for Radial System
The FDR can be used for both radial system and loop system. In radial systems, X-time (Closing time) count starts when the FDR detects the voltage of source side. PVS is closed after X-time and simultaneously Y-time (fault detecting time) count starts.
FDR shall be locked when the voltage is lost during the Y-time count. X-time and Y-time settings are satisfied with the following conditions:
X-time>Y-time>Time from detecting a fault until CB tripping (= Relay + CB operation time)
In radial system, faulty zone sectionalization procedure can be shown as Fig. 3.
Fig. 3Faulty zone sectionalization procedure by FDR in radial system
①CB"A" and all the PVSs except PVS"E" (normally opened on loop point) are closed during normal operation.
②A fault occurred in section C and CB "A" is tripped. PVSs "B", "C" and "D" are opened simultaneously because of a voltage drop in the feeder.
XL-time count of FDR for PVS "E" starts at that time as there is no voltage at one side.
③Power is supplied to section "a" by CB "A" first enclosing after the first recoding time of 15 sec. When FDR of PVS "B" detects the voltage at section "a", X-time count starts.
④Power is supplied to section "b" after X-time of 7 sec. by automatic closing of PVS "B" and Y-time count of 5 sec. starts simultaneously.
⑤Then, after a further X-time of 7 sec, power is supplied to section "c" by PVS "C" automatic closing and Y-time count starts.
⑥CB "A" is ret ripped as a fault occurred in section "c" breaking faulty current. PVS "C" is locked out in an open state as FDR of PVS "C" has detected no voltage within Y-time of 5 sec. PVS "D" is also locked out in open state as its FDR detects faulty voltage (30% of the rated voltage or more during 150 ms or more).
FSI counts the time between CB "A" reclosing until it retrips and FSI indicates section "c" as the faulty section basing on the time counted..
⑦CB "A" closes again (second reclosing) and power is supplied in sequence to the healthy sections on source the side of the faulty one.
⑧PVS "E" is closed after XL-time of 45 sec. and automatic power supply from another feeder for section "d" is achieved. X-time count does not start as PVS "D" has locked out and no power is supplied to the faulty section.
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