GUID-93ECF983-CCBB-4277-8E7B-7EC43743A375 V1 EN
Figure 320: Functional module diagram
V/f calculation
This module calculates the V/f ratio, that is, the excitation level from the internal induced
voltage (E) and frequency. The actual measured voltage (V
m
) deviates from the internal
induced voltage (emf) E, a value the equipment has to withstand. This voltage
compensation is based on the load current (I
L
) and the leakage reactance (X
leak
) of the
equipment. The leakage reactance of the transformer or generator is set through the
Leakage React setting in percentage of the Z base.
The internal induced voltage (E) is calculated from the measured voltage. The settings
Voltage selection and Phase supervision determine which voltages and currents are to be
used. If the Voltage selection setting is set to "phase-to-ground" or "phase-to-phase", the
Phase supervision setting is used for determining which phases or phase-to-phase
voltages ("A or AB", "B or BC" and "C or CA") and currents are to be used for the
calculation of the induced voltage.
Table 556: Voltages and currents used for induced voltage (emf) E calculation
Voltage selection setting
Phase supervision
setting
Calculation of internal induced voltage (emf) E
1)
phase-to-ground A or AB
E V I j X
A A leak
= × + × ×
( )
3 ( )
GUID-B567E82F-DDAB-4D87-A209-097D5FC072C6 V2 EN
phase-to-ground
B or BC
E V I j X
B B leak
= × + × ×
( )
3 ( )
GUID-551F8B8A-40D2-4D99-B20D-6FC433406EFF V2 EN
phase-to-ground
C or CA
E V I j X
C C leak
= × + × ×
( )
3 ( )
GUID-8B274F07-54A0-4CEC-9AAC-618F742D9EED V2 EN
phase-to-phase
A or AB
E V I I j X
AB A B leak
= + − × ×
( )
( ) ( )
GUID-BA2D5CDB-BC06-4F7E-A71F-A2BEFC10F5A2 V2 EN
Table continues on next page
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 643
Technical Manual
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