ABB ret650, Applications Manual

Page: 160 / 392

8.3.3.6 Settings for two step residual overvoltage protection
M13853-21 v13
Operation : Off or On
UBase (given in GlobalBaseSel ) is used as voltage reference for the set pickup
values. The voltage can be fed to the IED in different ways:
1. The IED is fed from a normal voltage transformer group where the residual
voltage is calculated internally from the phase-to-earth voltages within the
protection. The setting of the analog input is given as
UBase =Uph-ph.
2. The IED is fed from a broken delta connection normal voltage transformer
group. In an open delta connection the protection is fed by the voltage 3U0
(single input). Section
Analog inputs in the Application manual explains how
the analog input needs to be set.
3. The IED is fed from a single voltage transformer connected to the neutral point
of a power transformer in the power system. In this connection the protection
is fed by the voltage UN=U
0
(single input). Section Analog inputs in the
Application manual explains how the analog input needs to be set.
ROV2PTOV will measure the residual voltage corresponding to the nominal
phase-to-earth voltage for a high-impedance earthed system. The measurement will
be based on the neutral voltage displacement.
The setting parameters described below are identical for the two steps ( n = step 1
and 2). Therefore the setting parameters are described only once.
OperationStepn : This is to enable/disable operation of step n.
Characteristicn: Selected inverse time characteristic for step n . This parameter
gives the type of time delay to be used. The setting can be, Definite time or Inverse
curve A or Inverse curve B or Inverse curve C or Prog. inv. curve . The choice is
highly dependent of the protection application.
Un> : Set operate overvoltage operation value for step n , given as % of residual
voltage corresponding to UBase :
( ) ( )
% 3 U UBase kV
> ×
IECEQUATION2290 V1 EN-US
(Equation 38)
The setting depends on the required sensitivity of the protection and the type of
system earthing. In non-effectively earthed systems, the residual voltage cannot be
higher than three times the rated phase-to-earth voltage, which should correspond
to 100%.
In effectively earthed systems, this value depends on the ratio Z0/Z1. The required
setting to detect high resistive earth faults must be based on network calculations.
tn : time delay of step n , given in s. The setting is highly dependent on the
protection application. In many applications, the protection function has the task to
prevent damage to the protected object. The speed might be important, for
Section 8
1MRK 504 169-UEN A
Voltage protection
154 Transformer protection RET650 2.2 IEC
Application manual