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50 Instantaneous Overcurrent – Phase
Overview of Functions
Time overcurrent protection is used to provide:
•
Short circuit detection in electrical equipment
•
High speed highset overcurrent protection of plant where appropriate
•
Coordinated operation with other devices using current and time graded settings
Structure of the Function
The instantaneous overcurrent function element has group dependent settings. These settings can be
different in each settings group – group numbers (Gn) 1 to 4.
This function corresponds to the logical node
A50PTOC*
in IEC 61850.
The function monitors the primary system current using the 3 phase CT inputs e.g. CT1/2/3.
The basic time overcurrent protection function (50) is summarized below:
•
Current measurement is based on either fundamental or RMS current
•
Operation with a definite time delayed (DTL) characteristic
•
Outputs are provided for each phase
The basic function is non-directional but can be directionalized. This requires 3 phase VT inputs e.g. VT1/2/3.
Each 50 function element can be set to operate for forward current, reverse current or independently of
current direction. Directionalized functionality is controlled by the outputs of the 67 function element.
•
Provides information regarding flow direction of phase current for selective application of overcurrent
protection
•
Ensures selective fault detection for parallel lines or transformers with infeed at one end
•
Ensures selective fault detection in cable runs with infeed at both ends or in lines connected to form ring
topologies
Where directionalized overcurrent protection is used, correct operation is dependent on valid information
being received from the VT inputs, operation of each directionalized element will be affected if a VT fuse fails.
When a fuse failure is detected, 60VTS function, each element can be selected to either ignore the VT failure,
switch to non-directionalized operation (which does not require VT inputs) or be inhibited.
When installed in power transformer circuits increased currents may be measured by the overcurrent function
during switch in of the transformer. Each element can be set to be inhibited when inrush current is detected,
(see
6 Supervision Functions , section 81HB2 Inrush Current Detection).
Elements can be mapped to start
79 Automatic Reclosing
by selection of the element as a
79 PF
Trigger
within the 79 function element menus. For advanced autoreclose applications each element can be
selected to be inhibited during delayed autoreclose shots of a multi-shot sequence.
Where significant distributed generation is installed in the power system network, load current may flow in
the reverse direction to normal operation, this is not fault current but may be in excess of low directionalized
overcurrent settings. Each element can be set to be inhibited during periods of low reverse load current flow,
(see
5 Protection and Automation Functions , section 21LB Load Blinder).
5.11
5.11.1
5.11.2
Protection and Automation Functions
5.11 50 Instantaneous Overcurrent – Phase
204 Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019