Element Blocking
The undervoltage elements can be blocked by
Binary Input Inhibit
and
VT Supervision
. This func-
tionality should be checked.
Element
BI Inhibits
VT Supervision
27-1
27-2
27-3
27-4
Check correct indication, trip output, alarm contacts, waveform record.
When testing is complete reinstate any of the disabled functions.
Undervoltage Guard
If any 27 undervoltage element is set to be inhibited by the
UV Guard
element, this function should be
tested.
Connect the test voltage inputs to suit the installation wiring diagram utilizing any test socket facilities avail-
able. It may be useful to temporarily map an LED as
General Pickup
to assist during testing.
UV Guard
operation will reset the
General Pickup
if no other element is operated. This LED should not be set as
Hand Reset
in the output matrix.
Starting from nominal voltage, apply a step decrease to the applied voltage to a level below the 27 under-
voltage setting but above the 27UVG setting such that an undervoltage element operation occurs. Slowly
reduce the applied voltage until the 27 undervoltage element resets, this can be detected by the
General
Pickup
LED reset if no other element is operated (this includes any undervoltage element which is not
UV
Guarded
).
Phase
Setting (Volts)
Tolerance
V Element Used
for Test
Blocked Volts
Notes
UVG
27Vx Undervoltage Protection – Vx
27Vx elements operate similarly to the 27 elements but are applied to the fourth voltage input Vx.
Where more than one 27Vx undervoltage elements are being used with different settings, it is convenient to
test the elements with the lowest settings first. The elements with higher settings can then be tested without
disabling the lower settings.
Note that if the voltage is reduced below the
UV Guard
setting threshold, the function may be blocked.
Current inputs are not required to stabilize the relay during voltage element testing.
Single phase voltage should be connected to the Vx input directly. If the DTL is short, starting from nominal
voltage, slowly decrease the applied test voltage until the
Pickup
LED (temporarily mapped) is on. Record the
operate voltage. The LED should light at setting Volts ± 5 %. Slowly increase the input voltage until the LED
extinguishes. Record the reset voltage to check the
Hysteresis
setting. If the DTL is long, the operate level
should be checked by applying a voltage of 90 % of setting voltage. Check hysteresis by resetting element to
the operate level setting plus the
Hysteresis
setting.
Connect the relevant output contact(s) to stop the test set. Step the applied voltage to a level below the
setting. The test set should be stopped at the operate time setting ± 5 %.
When testing is complete reinstate any of the disabled functions.
Setting
(Volts)
DTL (sec) Hyst.
D.O.
(calcu-
lated)
P.U. Volts D.O Volts Op. Time
@ 0.5 ⋅ V
set
(UV)
UV Guard Tolerance
9.10.4
Functional Tests
9.10 Protection Functional Tests
424
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
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