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Transmission line Protection Relay panel-1A transmission line, installed in wide area for its characteristics, is a power system facility that transfers power from generation to a customer.
 
Thus, compared to other power system facilities, transmission lines face more frequent accident rate due to natural disasters such as thunder and snow storm. It is important due to its effect on power transfer and degree of stability when there are changes of power flows. Thus it needs a protection function with stability of protective system.
 
In Korea, transmission line voltage levels are mainly 154 kV and 354 kV. In order to support development of the industry which needs electrical power, 756 kV line also constructed and operated.
 
In transmission line protection panel, there is a function that uses PCM current differential function (87T) and back-up function which uses 3 steps (zone 1, 2, 3) distance protection scheme.
 
GABO’s transmission line protection panel has a combination of main protection relay (7SD522) and back-up protection relay (7SA522) made from SIEMENS.
  PCM COMMUNICATION FUNCTION
 
Through communication between relays at both ends, it checks differential current of transmission lines, deciding any existence of accidents.
Therefore multi-functional support of communication is a very important factor to support flexible application of current differential protection function.
  REDUNDANCY OF COMMUNICATION LINE
 
Local/Remote communication line enables redundancy. In 2 terminal systems, it offers as main/ back-up line. In 3 or more terminals it offers Ring/ Chain Topology.
chain topology
   
  MULTI TERMINAL TRANSMISSION LINE PROTECTION FUNCTION
 
By providing general 2 terminal transmission line protections and multi terminals more than 3 terminals protection function, we provide facility’s credibility and efficiency in operation.
   
  345 [KV] TRANSMISSION LINE PROTECTION PANEL
 
345 [kv] transmission line protection panel Due to high voltage level, 345 [kv] transmission line protection panel is applied with duplication system.
In order to guarantee credible function, it has redundancy by having two transmission lines. (Protection panel composed of current differential relay and distance relay)
   
  SHORT TRANSMISSION LINE PROTECTION PANEL
 
Along with development of the industry and urban areas, transmission lines have been buried in underground as built in short distance. That could cause problems of independence characteristics setting and disturbance in credibility of function.
Hence, a short transmission line protection panel has two types of protection relays, main and back-up. Like main protection relay, it uses current differential functions. And backup protection relay uses distance protection function and current differential function.
   
  DIFFERENTIAL CURRENT RELAY(7SD5x)
 
- For a remote PCM communication between relays located at both ends, CCITTG. 703 and IEEE C37.94 standard applied.
- Designed to meet redundancy communication function for maintenance of protection function when a communication error occurs.
- In 3 or more terminals, a redundancy communication function offers Ring/Chain Topology.
- In multi terminal differential current protection, it supports up to 6 terminals.
- Differential current protection could be applied also on transmission line including a transformer.
- Built in high sensitive protection function for detecting high impendence ground fault.
- Applied with synchronizing differential protection through communication delaytime compensation between relays located in remote ends.
   
  CHARACTERISTICS OF CURRENT DIFFERENTIAL PROTECTION
 
According to the ratio of restraint current and differential current, it is divided into trip area and non-trip area. In restraint current, it offers stable restraint current factor by considering current transformer error, synchronization error and CT saturation.
   
  MAIN FUNCTION
 
- Current differential function (an independent protection function on each phase)
- Auto compensation function on difference between CT ratios
- Current transformer open detection possible both in one pole/ three pole
- Fault location function
- Function to prevent mal-function through many fault detection
- Selection of one pole/three pole trip function
- Event recording function (trip, alarm, fail, etc)
- Using any portable computing device, setting and fault analysis function(Analysisprogram(DIGSI),comradefileconversionfunctionispossible)
- PCM telecommunication function between remote end relays.
- Charging current compensation function
- Auto-reclosing function
- User defined logic (CFC-continuous function chart)
- Self diagnosis function
- Metering function (current, voltage, active power, reactive power)
   
  CHARACTERISTICS OF DISTANCE RELAY (7SA5x)
 
- Distance protection which could be applied up to 3 terminals transmission lines network
- Distance protection having 5+1 zone which could be set as forward/reverse and non- directional protection zone
- Polygonal characteristics and MHO characteristics selection
- Prevention of impedance over-reach by heavy load current
- Selection of mutual impedance compensation on parallel transmission line
- Built in high sensitive protection function for detecting high impedance ground fault
- Detection of current transformer saturation and compensation of errors occurring
   
  CHARACTERISTICS OF 5+1 ZONE IMPEDANCE
 
  By calculating impedance using voltage and current, 5+1 impedance zone which divided into forward and reverse direction could be provided. Also as characteristic curve, both polygonal characteristics and MHO characteristics are built-in to provide selections to users.
   
  MAIN FUNCTION
 
  - 5+1 step distance protection function (independent protection function on each phase)   - Auto reclosing function  
  - Weak source protection function   - Power Swing Blocking/ Out of Step Tripping  
  - STUB protection function   - Synchronization detection function and single pole/multi pole auto reclosing function  
  - Single pole/ multi pole current transformer open detection function   - Additional various fault detection functions  
  - Selectable One pole/ 3 poles Trip function   - Metering function (current, voltage, active/reactive power, etc)  
  - Event recording function (Trip, Alarm, Fail, etc)   - Using any portable computing device, setting and fault analysis function(Analysis program (DIGSI), comrade file conversion function is possible)  
  - Out of step detection   - Directional comparison protection  
  - Switch-onto-fault protection   - User defined logic (CFC-continuous function chart).  
  - Fault location function   - Self diagnosis function  
   
  TRANSMISSION LINE PROTECTION PANEL TECHNICAL SPECIFICATION/STANDARD
Index Item Specification
Current differential ralay Distance relay
Rating Power Supply Voltage Input   DC : 125[V], AC : 230[V] (Frequency 50/60[hz])
Power Consumption   12[W], 17[VA]
Analog Current   1[A], Burden : 0.05[VA]
  5[A], Burden : 0.3[VA]
Power   80/125[V], Power Consumption ≤ 0.1[VA]
Digital input   Number of digital input : 8/16/24
  Voltage Range : 88~300[VDC]
  8/16/22/24
Digital output   Number of digital output : 7~31
  Allowable Current : Continus(5[A]), 30[A](0.5[sec])
  15~43
Communication Communication Port   RS-232, RS-485, Ethernet, FO(Fiber Optic)
Protocol   Profibus , DNP3.0, IEC61850, TCP/IP
Time Synchronization   DCF77/IRIG-B/SNTP