ABB HU Instruction Leaflet page 19

b. After the dropout has been measured, the
unit should operate at 25% or higher of tap
value current without the polarization test.
Pickup value should then remain within this
value until the polarization current is applied
again.
c. Upon polarizing the unit, the unit will operate
at a value of current greater than 25% of tap
value current but not greater than 31% of tap
value current.
B) Differential Unit (DU)
Set the adjustable resistor at top of the relay in the
approximate center of its range. Open the SPDT
switch and close the SPST switch and pass I
times tap value polarizing current. This current
should be applied for a very short period of time and
it should be suddenly interrupted. Adjust right-hand
shunt of lower polar unit until it trips with I
tap value amperes. Lower I
value current and adjust right-hand shunt until unit
resets. If polar unit resets before 15% of tap value
current, no adjustments are necessary to the left-
hand shunt. Repeat these steps until the lower polar
unit will pickup at 30% of tap value current and reset
for values of tap value current greater than 15%.
Indicating Instantaneous Trip (IIT)
Initially adjust unit on the pedestal so that armature
fingers do not touch the yoke in the reset position
(viewed from top of switch between cover and
frame). This can be done by loosening the mounting
screw in the molded pedestal and moving the IIT in
the downward position.
1. Contact Wipe - Adjust the stationary contacts so
that both stationary contacts make with the mov-
ing contacts simultaneously and wipe 1/64" to 3/
64" when the armature is against the core. This
can be accomplished by inserting a 0.0125 thick
gage between the armature and core and adjust-
ing the stationary contacts until they just touch
the moving contacts.
2. Target - Manually raise the moving contacts and
check to see that the target drops at the same
time as the contacts make or up to 1/16" ahead.
The cover may be removed and the tab holding
the target reformed slightly if necessary. Care
should be exercised so that the target will not
drop with a slight jar .
= 20
ac
= 30% of
ac
gradually to 15% of tap
ac
3. Pickup - With switch open, pass I
tap value current and adjust core of the instanta-
neous trip unit until it picks up. The target should
drop freely.
Harmonic-Restraint Unit (HRU)
Close SPST switch and close SPDT switch to posi-
tion 2. Short out I ammeter. Adjust direct current
LR
until Idc reads 0.8 times tap setting. Gradually
increase alternating current until upper polar unit
operates with I reading between 1.3 and 1.8 times
ac
tap setting. The percent second harmonic in the
wave may be derived by the use of the formula:
% second harmonic = ----------------------------------- -
I
ac
This formula is plotted in curve form in figure 17 for
I = 4 amperes.
dc
Percentage Slope Characteristic (DU)
Close SPST switch and close SPDT switch to posi-
tion 1. Set I to zero and I
ac
current. Then adjust I
ac
Adjust resistor t top of relay until lower polar unit
operates. Interchange lead positions to terminals 5
and 7 and repeat the above test. The lower polar unit
should operate between the limits of:
I =4 times tap value current
ac
I =9 to 10 times tap value current
LR
Trip condition can best be determined by holding I
at 4 times tap value current and varying I
adjusting I . If I is too low the contacts will be
SR LR
closed when the currents are first applied. Hence,
I should be increased until the contacts open and
LR
then decreased until contacts close.
The adjustment of the resistor will have some effect
on the pickup of the unit. Hence, polarize the circuit
and recheck the pickup. If necessary readjust shunts
to obtain a pickup of 30% of tap value current and
dropout of 15% or greater of tap value current. If
shunts are changed, check to see that above read-
ings are obtained on the higher restraint currents. If
necessary readjust resistor and repeat procedure
until the unit operates within the specified limits.
Apply I = .56 time tip value and vary I
ac
ing I until lower polar unit operates. The lower
SR
polar unit should operate between following limits.
41-347.12C
= 10 times
ac
47 I
dc
1.11 I
+
dc
to 5.5 times tap value
SR
to 4 times tap value current.
LR
by adjust-
LR
ac
by
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