h 
microprocessor logic and supervision 
RACID Three- phase time overcurrent relay with phaseand earth fault overcurrent was introduced 1981 
RACID Microprocessor time overcurrent relay 
RACIF- is a low-power version of RACID and it 
performs the same protection functions. This relay does 
not need auxiliary power supply since it is self-powered 
from the CT's. An electromagnetic indicator stores 
phase and trip indications also after loss of power 
supply. 
RACIF power supply independent three-phase and 
ground overcurrent relay 
Fault localisation 
The fault localisator RANZA was introduced 1983. In 
RANZA for the first time a truly numerical approach 
was used to calculate the distance to fault. The 
measuring signals were stored in a memory and the a 
system algorithm was used to calculate the distnce3 to 
fault with a much better accuracy, +- 2 %, than was 
previously possible with analogue electronics. The 
measuring principle is shown below. 
RANZA fault locator measuring principle 
Numerical line distance protection 
The world’s first fully numerical line distance 
protection terminal, RELZ 100 was introduced 1986. 
This was also the first multifunction relay, where a 
number of functions were integrated. 
• Full scheme line distance relay with 5 zones 
• Load compensated operation 
• Phase selector 
• Power swing blocking 
• Disturbance recorder- 1 ms resolution 
• Event recorder 
• Over-current 
• Fault locator 
• Built-in protection communication schemes 
• Serial data communication with two ports for 
monitoring and control 
• etc 
RELZ 100 Line distance terminal 
5 NUMERICAL PROTECTION AND CONTROL 
CONCEPT SERIES 500 
The 500 series protection and local control terminals 
were introduced 1994. To really take advantage of the 
modern microprocessor technology, the 500 series of 
microprocessor based protection and control equipment 
has been designed with a platform concept. The 
platform consists of a number of hardware modules for 
analogue inputs and A/D conversion, a main processing 
module, dc/dc supply module and a number of flexible 
input and output modules. Communication modules, for 
example a 56/64 kbit communication module for 
differential protection is also included in the platform. 
The platform incorporates an extensive library of 
Line section length = L
Fault distance = F
pZL
Z Z
UA
I I
(1-p)ZL
I
RF7 
protection and control software functions, monitoring 
functions and communication functions. 
Thus, it is technically possible to integrate the 
protection and control functions, for example in a bay 
terminal for a power line. It is easy to see that the 
different control and protection functions are using the 
same information from the primary equipment and have 
many similarities, or that some functions are redundant. 
By co-ordinating these main functions and integrating 
them when possible, the functionality and performance 
of the control and protection system can be increased. 
The integration can both decrease the required wiring 
and space and increase the overall reliability and 
availability together with reduced investment and 
operation cost. Of paramount importance is then how 
the basic power system requirements on dependability, 
security, fault tolerance and availability can be 
achieved. 
Series 500 object terminal concept 
The designation terminal is used instead of relay, 
protection or control device, since today many functions 
can be integrated in the terminal. Thus, the terminal can 
be used as a line protection terminal with ancillary 
functions. It can also be used as terminal for local 
control or as an object terminal, where both control and 
protection, etc. is included as an object terminal. or coordinated in various degrees for automated substations, 
or as replacement for conventional centralised RTUs 
standard PC or telephone modem, without the need for 
additional equipment. Various software programs, such 
as REVAL disturbance evaluation, RCALC setting 
calculation and RESDA Expert programs in Windows 
will furthermore enhance the capability of the 
information handling 
Hardware modules 
The basic object terminal is provided with a CPU 
module and DC/DC converter. In addition a number of 
various input and output modules can be installed in the 
terminal. The number of modules depends on the size of 
the mechanical housing. The housing can be a 1/2, 3/4 
or 1/1 19” rack, 6 U high (247 mm) with depth 245 mm 
Functional library 
The terminals can be loaded with a number of modular, 
type tested software function blocks as shown below 
Future
Etc
Interlocking
Apparatus control
Fuse failure
o/c protection
Synchro- and dead-line-check
Breaker failure protection
Auto-reclosing
Line differential protection
Earth fault o/c protection
Distance protection
PROTECTION AND
CONTROL FUNCTIONS
Protection and control functions 
Future
Etc
Optional I/O units
Fault location
Operating values I, U, P, Q, f
Real time clock
Event recording
Disturbance recording
Self-supervision
Remote communication
Man-Machine Interface
MONITORING AND
AUXILIARY FUNCTIONS
Monitoring and auxiliary functions
Functional configuration 
The various functions are arranged as individual blocks, 
that can be combined either as predetermined schemes 
or custom designed utilising function block 
programming. This means that an output signal from 
one function can be used as an input signal to another 
function. These function blocks include all protection 
functions, tripping and autoreclosing logic, all control 
functions for apparatus control and interlocking, binary 
inputs and outputs as well as a logical function library 
with AND, OR and Time Delayed elements (0-50 
seconds with 5 ms resolution). 
As an example each distance zone can be programmed 
individually and also accessible individually in the 
logic. External (or internal) signals can be used to block 
or enable the auto reclosure. 
The Configuration can be made according to the 
application requirements 
The protection and control functions can be integrated 
in the terminal in a very cost efficient way 
SYNCH
CHECKOK
BLOCK
AR
AR CLOSE CB
AR CB READY
AR INHIBIT
AR P3PH
&
INTL
Q1-OP Q0-ITL
Q2-OP
Q3-OP
Q4-OP
CLOSE
SWICON
CLOSE
SEL-CLOSE
SEL-OPEN
SY-OK INTLOCK
Protection functions Control functions
Co-ordination of protection and control functions
To allow the user to take advantage of the 
configuration flexibility, a Computer Aided Tool 
(CAP 535) for PC is available. 8 
The tool CAP 535 is based on the IEC standard 1131-3, 
and allows the user to configure the terminal using 
graphic symbols, which makes the handling of the 
configuration tool very simple 
6 THE 500 SERIES TERMINALS 
The first terminals in series 500 were introduced in 
1994. The terminals could perform both protection and 
control functions. A large functional library is available. 
Some examples: 
• Three/four/five zone distance protection 
• General fault criteria 
• Three-phase trip 
• High set inst. O/C protection 
• Scheme communication 
• Fuse failure supervision 
• Switch-onto-fault facilities 
• Four parameter setting groups 
• Restricted settings by local HMI or BI 
• Local information on: 
- Service value of I, U, P, Q, f, R, X 
• Status of I/Os and internal logics 
• Fault locator with U&I phasors 
• Stub protection
• Under- and overvoltage protection
• Breaker failure protection 
• Event recorder 
• Disturbance recorder
• Automatic reclosing-1/3 phase 
• Up to 3/6 I/O modules 
• Synchro check, energising check and phasing 
• On line control functions 
• Simulation logics 
• System supervision functions 
• - overload 
• - broken conductor 
• - loss of voltage 
• Remote serial communication 
• PC programs for information handling 
• etc 
Line distance terminals 
REL 501 Line distance terminal for distribution 
REL 511 Line distance terminal for subtransmission 
REL 521 Line distance terminal for transmission 
The characteristic is shown below 
1996 a high speed distance terminal REL 531 was 
introduced. The high speed distance algorithm is based 
on ∆Ι and ∆ U. Together with a very fast phase selector 
based on the same principle as RALDA travelling wave 
detector, single phase tripping time < 1 cycle is 
achieved 
REL 531 High speed distance protection 
REL 531 characteristic 
Line differential terminals 
Also in 1994 a new concept for differential relaying 
was introduced. The communication between the 
terminals was utilising 56/64 kbit digital 
telecommunication, replacing the previous pilot wire 
relays. 
E 
C 
REL521
E 
C 
REL511
E 
C 
REL501
ZM 1
ZM 2
ZM 5
ZM 4
ZM 3
E
C
REL531 
< Z: Zone 1 
 <= 85%
HS
<= 9 
REL 551 Line differential terminal with current 
functions 
REL 561 Line differential terminal with current and 
voltage functions. (Distance back-up available) 
A breaker terminal was introduced 1994. The breaker 
terminal cointains breaker oriented functions 
• Auto reclosure, 
• Synchro check, 
• Breaker failure etc 
REB 551 Breaker terminal 
In 1996 a dedicated control terminal REC 561 was 
included in the 500-series. This terminal has control 
oriented functions
• Control of up to 12 bays / 24 apparatuses 
• Interlocking 
• Synchro- check and energising 
• Auto-reclosing of up to 12 breakers 
• Configurable logic 
• Pole discordance protection 
• Fuse failure protection
• Breaker failure supervision 
• Loss of voltage supervision 
• Disturbance recorder 
• etc 
REC 561 Control terminal 
Transformer terminal 
In 1998, a transformer terminal was included in the 500-
series. The operate time of the differential function is 
around 21 ms. The terminal comprises all required 
hardware and software elements for protection and 
control of 
• big power transformers 
• three-phase and single phase auto-transformers 
• shunt reactors 
• groups with generators and step-up transformers 
• special transformers 
• tap changers 
• etc. 
RET 521 Transformer terminal 
In 2000, a general differential protection was 
introduced. The operate time of the differential 
function is typical 12 ms. The current transformer 
requirement is < 2 ms to saturation. The application 
area is: 
• Busbars 
• Autotransformers 
• Generators 
• Motors 
• Shunt Reactors 
• Shunt Capacitors 
. 
RED 521 General differential protection 
Application of RED 521 1½ Breaker Stations with 
up to 6 diameters 
E 
C 
REL561
E 
C 
REL551
E
C
 REB 551 
E
C
 REC 561 
E
C
 RET 521 
E
C
 RED 521 
ZA
ZB10 
7. THE INTELLIGENT SUBSTATION 
 POSSIBILITIES AND BENEFIT 
The described terminals can be used as stand alone 
units, with or without the use of serial communication 
or computers. The full benefits of the new technology 
will however be obtained in the fully automated 
substation 
Depending on requirements and customer preference the 
architecture can be designed from a totally distributed 
concept with one terminal per bay with integrated 
protection and control, to a sectionalised or centralised 
concept where one terminal for control functions is 
connected to several bays. In all alternatives the 
protection, monitoring and the database is always 
distributed in each terminal. This means that almost all 
protection, monitoring and control functions can be 
distributed to the line and breaker terminals. 
The information transfer within the substation is 
structured on three levels. The station bus is a Local 
Operative Network (LON), with a speed of 1,25 Mega 
bits/s, which transfers the information between the 
object terminals. There is no specific master node, or 
central bus master. All nodes can communicate directly 
with each other, over an optical star coupler, which of 
course increases the fault tolerance. The Gateway for 
the remote control is connected to the LON bus and 
converts the required information to a remote protocol, 
for example IEC 870-101 
The Spa bus or IEC 870-103 is used for monitoring 
information. 
Automated substation
8 SUMMARY 
It is impossible to describe the vast range of protection 
equipment that ABB has developed during 100 years. 
However, one has to be impressed with the innovative 
and creative engineers, which has developed, designed 
and manufactured relay protection during the 
electromechanical, static and microprocessor era. 
 To sound historic 
Never has so many had so few to thank for, that 
electric power have been safely delivered for over 100 
years.