1.2 UR OVERVIEW
1 GETTING STARTED
1.2 UR OVERVIEW
1.2.1 INTRODUCTION TO THE UR RELAY
Historically, substation protection, control, and metering functions were performed with electromechanical equipment. This
first generation of equipment was gradually replaced by analog electronic equipment, most of which emulated the single-
function approach of their electromechanical precursors. Both of these technologies required expensive cabling and auxil-
iary equipment to produce functioning systems.
Recently, digital electronic equipment has begun to provide protection, control, and metering functions. Initially, this equip-
ment was either single function or had very limited multi-function capability, and did not significantly reduce the cabling and
auxiliary equipment required. However, recent digital relays have become quite multi-functional, reducing cabling and aux-
iliaries significantly. These devices also transfer data to central control facilities and Human Machine Interfaces using elec-
tronic communications. The functions performed by these products have become so broad that many users now prefer the
term IED (Intelligent Electronic Device).
It is obvious to station designers that the amount of cabling and auxiliary equipment installed in stations can be even further
reduced, to 20% to 70% of the levels common in 1990, to achieve large cost reductions. This requires placing even more
functions within the IEDs.
Users of power equipment are also interested in reducing cost by improving power quality and personnel productivity, and
as always, in increasing system reliability and efficiency. These objectives are realized through software which is used to
perform functions at both the station and supervisory levels. The use of these systems is growing rapidly.
High speed communications are required to meet the data transfer rates required by modern automatic control and moni-
toring systems. In the near future, very high speed communications will be required to perform protection signaling with a
performance target response time for a command signal between two IEDs, from transmission to reception, of less than 5
milliseconds. This has been established by the Electric Power Research Institute, a collective body of many American and
Canadian power utilities, in their Utilities Communications Architecture 2 (MMS/UCA2) project. In late 1998, some Euro-
pean utilities began to show an interest in this ongoing initiative.
IEDs with the capabilities outlined above will also provide significantly more power system data than is presently available,
enhance operations and maintenance, and permit the use of adaptive system configuration for protection and control sys-
tems. This new generation of equipment must also be easily incorporated into automation systems, at both the station and
enterprise levels. The GE Power Management Universal Relay (UR) has been developed to meet these goals.
L90 Line Differential Relay
GE Power Management