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7SG14 Duobias-M-200 Commissioning
These ensure a 1:1 ratio between the injected phase and the relay setting.
Note, the LV interposing CT multiplier could be set to 3.0 for test purposes to reduce the test current requirements
if the test set has limited range.
Select Instruments Mode and select the following display.
W1 Relay Currents
0.00
0.00
0.00 x In
Switch on and increase the value of the test current until the highset relay operates, record the value in Table 2.
Operation of the Differential Highset on phase A is indicated by illumination of the appropriate LED. Check that
the contacts operate on all the output relays selected for this function, both trip and alarm. (Note that the
differential will also operate). Repeat the test for other phases if required and record the results.
9.6 Restricted Earth Fault (87REF)
Refer to the calculated setting data and check that the relay has the correct settings for each of REF protections.
Measure the resistance of the REF series setting resistors and adjust each one to match the REF setting data.
Record the values in Table 6.
This should be done in two stages: A by current injection or B - By application voltage.
A - Current Injection by test set
Inject the REF inputs with the CT's disconnected and record the pickup values in Table 6. The setting resistor
should be temporarily be shorted out to allow injection from digital test set.
B – Applied Voltage using Variac
Follow safety procedure to ensure no other personnel can come into contact with secondary wiring during this
test. Tests are carried out with the current transformers connected in idle shunt to the REF parallel leg. Apply
voltage across the REF parallel leg input via the test block or lead and connect an a.c. voltmeter to verify the
voltage applied. Slowly increase the applied voltage and note the voltage required for the REF protection to
operate on the voltmeter. Ensure that appropriate LED's illuminate and selected output relays operate.
9.7 Over Fluxing or Volts per Hertz Protection (24)
The testing of over fluxing element requires a variable voltage source.
The settings are set in terms of nominal voltage and frequency. Application of a voltage of nominal voltage and
frequency represents 100% or 1 per unit. Apply the required settings prior to testing.
24IT – inverse time
The inverse V/f element is best tested at the settings selected that constitute the overall inverse characteristics.
The seven setting points require the voltage to be calculated to check for pickup with nominal frequency applied.
The voltage may be raised or the frequency dropped to determine the pickup of the Volts per Hertz settings
applied. Usually it is easier to increase the voltage while applying h nominal frequency.
Record the results in Table 6
24 DTL – definite time
The voltage required for operation should be calculated and tested. The pickup and operate time should be
recorded for each stage used.
9.8 Thermal Overload (49)
The thermal pickup and operating time should be checked. The thermal overload equations for calculating the
operate time are:
©2010 Siemens Protection Devices Limited
Chapter 7 Page 10 of 20
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