18
Setting voltage Pick-up voltage at relay input
Test number (V) terminals (27 & 28) (V)
MVTU 11 MVTU 12 MVTU 11 MVTU 12
1 210 400 Z Z
2 216 410 Z + 1 ± 1 Z + 2 ± 1
3, 4, 5 222 420 Z + 2 ± 1 Z + 4 ± 1
6 258 480 Z + 10 ± 2 Z + 17 ± 2
7 396 710 Z + 39 ± 3 Z + 66 ± 4
The drop-off voltages should be within 5% of the pick-up values.
MVTU 13 and MVTU 18 neutral displacement relays
A series dropper resistor of approximately 50kΩ should be inserted in series with the
input terminals 27 and 28 to allow sufficient sensitivity in the setting range when
using a 0 – 240V variac supply, see Figure 1 for the test circuit.
Check that the trip indicator is reset and slowly increase the ac input voltage until the
trip indicator operates. Record the pick-up value.
Slowly lower the voltage, checking to see when the trip indicator can be reset.
This is the drop-off value and should be recorded.
Alternatively, the pick-up and drop-off states can be determined by connecting an
ohmmeter across the contacts.
Repeat the test for each of the settings shown in Table 1.
The allowable errors on the voltage settings are ±2% on the lowest setting and ±4%
on all other settings.
(No allowance has been made for instrument errors.)
The drop-off value should be within 5% of the pick-up value.
4.5.5 Timer setting check
It is recommended that all MVTU relays are tested on the following timer settings:
1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7, 8.8, 9.9 seconds. The circuit diagrams for these
tests are shown in Figures 1, 2 and 3.
The applied voltage levels should be greater than 10% above and 10% below any
convenient voltage setting.
MVTU 11 – undervoltage
Remove the ac supply from 10% above the voltage setting to zero volts,
simultaneously starting the timer. The timer stop contacts should be connected to the
relay output contacts. The allowable errors in the timer settings are ±3% or 70ms
whichever is the greater.
MVTU 12 – overvoltage and MVTU 13 – neutral displacement
Apply the ac supply from zero to 10% above the voltage setting, simultaneously
starting the timer. The timer stop contacts should be connected to the relay output
contacts. The allowable errors in the timer settings are ± 3% or 70ms whichever is
the greater.
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