1.Directional Earth-Fault Protection; 2.Protection Signal Routing; 3.Indication And Control Connections - ABB REX 521 Technical Reference Manual, Standard Configurations

REX 521
10.1.3.1.
10.1.3.2.
10.1.3.3.
146
Protection Relay
Technical Reference Manual, Standard Configurations
Directional earth-fault protection
The neutral current can be measured with a cable current transformer and the
residual voltage can be measured with a set of voltage transformers in a open-delta
connection. In the REX 521 M01 it is suitable to use the directional earth-fault
protection with the sensitive current input. The rated values are 0.2 A/1 A.
In most cases, in compensated and isolated networks the directional earth-fault is
used if the sensitive requirements are high and the configuration of the network is
varying a lot.
The directional earth-fault function includes three protection stages: a low stage
Io>-> a high stage Io>>-> and an instantaneous stage Io>>>->. The protection is
based on measuring the neutral current Io, the residual voltage Uo and the phase
angle between these. An earth-fault stage starts if the neutral current and the residual
voltage exceeds the set values and the phase angle is within the specified operating
sector. The earth-fault function can also be configured to operate as a three-stage
residual voltage protection.
The basic angle of the function can be set to 0°, -30°, -60° or -90°. If the network to
be protected is compensated, the basic angle is normally set to 0°. When an isolated
neutral system is protected the basic angle is set to -90°. It is also possible to use an
external control signal BACTRL for selecting the basic angle (0°/-90°) to be
automatically determined by the earthing situation of the network. The operation
direction, forward or reverse, can be individually selected for the three stages.
The start value of the low stage Io>-> of the earth-fault protection should be set low
enough to fulfil the sensitivity requirements of the safety regulations. The
requirements regarding operate times are mainly fulfilled by the operation of the
high stage Io>>-> and instantaneous operation by the third stage Io>>>->. The
directional earth-fault protection in this example is configured with two stages,
Io>-> and Io>>->.
The settings for the earth-fault current protections can be found in
Main menu\Protection\Io>->\ ... \Io>>>->\.
Protection signal routing
The settings for the protection signal routing can be implemented as described in the
first application example (chapter 9.1.).
Indication and control connections
The connections for indication and control can be implemented as described in the
first application example (chapter 9.1.), except the signals for the open and close
buttons that in this example are connected to free the digital inputs for other
functionality. Local control can be executed via the HMI according to the
instructions in Operator's Manual (1MRS 751107-MUM).
1MRS 751802-MUM