August, 1991
Supersedes Descriptive Bulletin 41-123M
pages 1 and 2, dated January, 1991
Mailed to: E, D, C/41-100C
Micro-51
Micro-511FT
Features
•
Eight selectable curves
•
Wide current tap ranges
•
Exceptional setting resolution
•
Self-powered, low burden
ABB
Power T&D Company Inc.
Relay Division
Coral Springs, FL
Allentown, PA
Single Phase
Device Number: 50/51
•
Transient and EMI immunity
•
Total-drawout construction
•
Retrofit existing CO installations
•
2 year warranty
Descriptive Bulletin
41-123M
Page 1
CIRCUIT
U
SHIELD
@
Types MICRO-51 and
MICRO-511FT
Microprocessor-Based
Time-Overcurrent
Relays
Application
Micro-51 microprocessor-based overcurrent
relays are used for phase and ground overcur
rent protection in utility, industrial. and com
mercial electrical power systems. The Micro-51
operates from conventional 5A or 1 A second
ary current transformers. The relay is self-pow
ered from the current; therefore, there is no
continuous drain on the control voltage supply.
Settings are made by front panel switches.
Eight time-current curves are built-in, select
able on the front panel:
Inverse
Long Time Inverse
Very Inverse
Long Time Very Inverse
Extremely Inverse Long Time Extremely
Definite Time
Inverse
Short Time Inverse
Wide current tap ranges with exceptional set
ting resolution are offered: 1.5-12A in 0.25A
increments, and 0.3-2.4A in 0.05A increments.
The time dial is adjustable from 1 to 10 in
increments of 0.1.
An instantaneous element is standard. Instan
taneous pickup is adjustable from 1 to 20 multi
ples of the time-pickup, in increments of 0.1
multiples. The instantaneous unit may be dis
abled by setting the pickup to zero.
The Micro-51 can be set for operation on a 50
Hz or 60 Hz system by positioning an internal
link.
The Micro-51 has three electrically isolated
normally-open output contacts: Time trip, Inst.
trip, and trip alarm.
A led is provided on the front panel to indicate
when the cc;rrent is above the pickup setting.
Two targets are provided for Time and Instan
taneous trip indication. Target operation is by
trip circuit current. Reset is manual by a front
panel magnetic device.
The Micro-51 has self-diagnostics that continu
ously perform functional checks when the input
current to the relay is above a minimum level.
The integrity of the ROM, RAM, EEPROM, and
anaglog elements are monitored. A red led on
the front panel indicates the detection of a
problem.
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