ABB HU Instruction Leaflet

Effective: February 1999
Supersedes I.L. 41-347.12B, Dated November 1998
( | ) Denotes Change Since Previous Issue
CAUTION
!
Before putting relays into service, remove all
blocking which may have been inserted for the
purpose of securing the parts during shipment,
make sure that all moving parts operate freely,
inspect the contacts to see that they are clean
and close properly, and operate the relay to
check the settings and electrical connections.
APPLICATION
These relays have been specially designed and
tested to establish their suitability for Class 1E appli-
cations. These relays have been specially designed
and tested to establish their suitability for Class 1E
applications in accordance with the ABB Power T&D
Company program for Class 1E Qualification Testing
as detailed in bulletin STR-1.
"Class 1E" is the safety classification of the electric
equipment and systems in nuclear power generating
stations that are essential to emergency shutdown of
the reactor, containment isolation, cooling of the
reactor, and heat removal from the containment and
reactor, or otherwise are essential in preventing sig-
nificant release of radioactive material to the environ-
ment.
The types HU and HU-1 relays are high-speed relays
used in the differential protection of transformers.
These relays can be applied where the magnetizing
inrush current to the transformers is severe.
All possible contingencies which may arise during installation, operation or maintenance, and all details and
variations of this equipment do not purport to be covered by these instructions. If further information is
desired by purchaser regarding this particular installation, operation or maintenance of this equipment, the
local ABB Power T&D Company Inc. representative should be contacted.
Printed in U.S.A.
ABB Automation, Inc.
Substation Automation & Protection Division
Coral Springs, FL
Allentown, PA
Current transformer ratio error should not exceed
10% with maximum symmetrical external fault current
flowing and the maximum symmetrical error current
which is flowing in the differential circuit on external
faults should not exceed 10 times relay tap setting.
The HU-1 relay has three restraint transformers and
associated rows of taps; whereas, the HU relay has
one less restraint transformer and two rows of taps.
Otherwise the two relays are identical. Three-winding
banks normally require the HU-1 relay, although the
auto-transformer application uses the HU if the ter-
tiary is not loaded.
Both the HU or the HU-1 are available with a sensitiv-
ity of either 30% or 35% times tap. The 30%-sensitiv-
ity relay satisfactorily handles up to 15% mismatch
(e.g. ± 10% transformer tap changing plus 5% ct mis-
match). The 35%-sensitivity relay handles as much
as 20% mismatch. See figure 7 for a comparison of
the characteristics of the two sensitivities. Any of the
relays may be recalibrated
either
Ordinarily the 30%-sensitivity relay will suffice; how-
ever, where ct mismatch is abnormally high or where
the transformer tap-changing range exceeds
this calibration may be too sensitive.
CONSTRUCTION
The types HU and HU-1 relays consist of a differen-
tial unit (DU), a harmonic-restraint unit (HRU), an
indicating instantaneous trip unit (IIT) and an indicat-
ing contactor switch (ICS). The principal parts of the
relay and their locations are shown in figures 1, 2, 3,
and 4.
Type HU and HU-1
Transformer Differential Relays
(Class 1E Applications)
in the field to obtain
characteristic.
Instruction Leaflet
41-347.12C
10%,