GE L90 Instruction Manual page 530

CONTROL ELEMENTS
The CT failure function detects problems with system current transformers used to supply current to the relay. This logic
detects the presence of a zero-sequence current at the supervised source of current without a simultaneous zero-
sequence current at another source, zero-sequence voltage, or some protection element condition.
The CT failure logic (see later) is based on the presence of the zero-sequence current in the supervised CT source and the
absence of one of three or all of the three following conditions:
• Zero-sequence current at different source current (can be different set of CTs or different CT core of the same CT)
• Zero-sequence voltage at the assigned source
• Appropriate protection element or remote signal
Settings are described as follows. There are four CT FAIL functions with the breaker and half software option and two
without.
CT FAIL 1 FUNCTION
— Selects a FlexLogic operand to block operation of the element during some condition (for example, an
CT FAIL 1 BLOCK
open pole in process of the single pole tripping-reclosing). Local signals or remote signals representing operation of some
remote current protection elements via communication channels can also be chosen.
CT FAIL 1 3I0 INPUT 1
to the same source.
CT FAIL 1 3I0 INPUT 1 PICKUP
CT FAIL 1 3I0 INPUT 2
of the same CT. If 3I_0 does not exist at source 2, then a CT failure is declared.
CT FAIL 1 3I0 INPUT 2 PICKUP
CT FAIL 1 3V0 INPUT
5
CT FAIL 1 3V0 INPUT PICKUP
CT FAIL 1 PICKUP DELAY
5-344
— Enables or disables operation of the CT failure element.
— Selects the current source for input 1. The most critical protection element should also be assigned
— Selects the 3I_0 pickup value for input 1 (the main supervised CT source).
— Selects the current source for input 2. Input 2 should use a different set of CTs or a different CT core
— Selects the 3I_0 pickup value for input 2 (different CT input) of the relay.
— Selects the voltage source.
— Specifies the pickup value for the 3V_0 source.
— Specifies the pickup delay of the CT failure element.
Figure 5-197: CT failure detector logic
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS