Directional Overcurrent Protection, Ground
Overview of Functions
The Directional overcurrent protection, ground function (ANSI 67N):
•
Detects short circuits to ground affecting electric equipment
•
Ensures selective ground-fault detection for parallel lines or transformers with infeed at one end
•
Ensures selective ground-fault detection in cable runs with infeed at both ends or in lines connected to
form ring topologies
Structure of the Function
The Directional overcurrent protection, ground function can be used in protection function groups which
provide zero-sequence current and zero-sequence voltage measurements. 2 function types are offered:
•
Directional overcurrent protection, ground – advanced (67N Dir.OC-gnd-A)
•
Directional overcurrent protection, ground – basic (67N Dir.OC-gnd-B)
The basic function type shall be used for standard applications. The advanced function type provides more
functionalities and is intended for more sophisticated applications.
Both function types are preconfigured by the manufacturer with 2 Definite-time overcurrent protection
stages and 1 Inverse-time overcurrent protection stage.
In the advanced function type Directional overcurrent protection, ground – advanced, the following stages
can operate simultaneously:
•
A maximum of 4 Definite-time overcurrent protection – advanced stages
•
1 Inverse-time overcurrent protection – advanced stage
•
1 Logarithmic inverse-time overcurrent protection stage
•
1 Logarithmic inverse time with knee-point overcurrent protection stage
•
1 User-defined characteristic curve overcurrent protection stage
In the basic function type Directional overcurrent protection, ground – basic, the following stages can
operate simultaneously:
•
A maximum of 4 Definite-time overcurrent protection – basic stages
•
1 Inverse-time overcurrent protection – basic stage
and
, the stages not preconfigured are shown in gray. Apart from the
operate-delay characteristic curve, the stages are similar in structure.
The general functionality includes the direction determination and the measured-value selection (only
advanced function). They take place on the functional level and have a uniform effect on the stages (see
and chapter
). This ensures that all stages of the function receive the
same measured current value and the same direction result. Each stage can be set to work in forward or
reverse direction.
The group indication output logic generates the following group indications for the protection function by the
logic OR from the stage-selective indications:
•
Pickup
•
Operate
7.7
7.7.1
7.7.2
Protection and Automation Functions
7.7 Directional Overcurrent Protection, Ground
700
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
Summary of Contents for 6MD85
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