Overcurrent

Automatic testing of positive/negative/zero sequence overcurrent characteristics

Overcurrent is used for automatic testing of directional and non-directional overcurrent relays with auto-assessment of the trip time characteristic, the directional boundaries of the current stages, and the pick-up/drop-off ratio. With its flexible directional boundary definition it is also perfect for testing the characteristic of steady-state ground fault relays.

The test module supports directional sector definition and any number of line, ground, positive sequence, negative sequence, and zero sequence elements. For each element the trip characteristic can be individually selected and displayed in the I/t diagram and the directional diagram.

In Overcurrent, the set of test shots can be defined concurrently for all desired fault loops. This is
possible for the following fault types:

Line-to-line fault
Line-to-ground fault
Line fault with suppressed residual current (for individual phase testing without ground
starting)
Negative sequence
Zero sequence

The software overlays the characteristics of each of the elements in both the I/t diagram and the
directional diagram. This includes all of the elements which respond to the type of fault applied.
For each test shot an assessment of the relay’s performance is made based on the allowable
tolerances for the measurement of the current and the operating time.

Key features

Unrestricted characteristic element definition (characteristic type, directional sector)
Assessment for each test shot considering all active elements
Simultaneous availability of all element types and characteristics
Testing of all fault types and loops together in one test module
Definition of test point sequences (in terms of fault type, current magnitude variation, and current angle variation)
Testing of the pick-up/drop-off characteristic with automatic assessment
Testing with or without load current
Automatic reporting

The time characteristics can either be entered directly in current/time tables or based on a wide range of pre-defined relay and recloser characteristics. Hierarchically structured templates for the following relay characteristics are included: inverse-time characteristics as defined by IEC 60255-4 (BS 142), IAC type characteristics, and relay specific curves based on the IEEE equation (PC37.112). Variants of these characteristics support commonly used relay types. Additional variants may be added to the template file, including curves digitized with the Overcurrent Characteristics Grabber. PTL test templates add relay-specific support by mapping the relay settings to the overcurrent module parameters and providing sample test sequences.