CHAPTER 5: SETTINGS CONTROL ELEMENTSL60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL 5-3115The CT failure function detects problems with system current transformers used to supply current to the relay. This logicdetects 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 theabsence 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 signalSettings are described as follows.CT FAIL 1 FUNCTION — Enables or disables operation of the CT failure element.CT FAIL 1 BLOCK — Selects a FlexLogic operand to block operation of the element during some condition (for example, anopen pole in process of the single pole tripping-reclosing). Local signals or remote signals representing operation of someremote current protection elements via communication channels can also be chosen.CT FAIL 1 3I0 INPUT 1 — Selects the current source for input 1. The most critical protection element should also be assignedto the same source.CT FAIL 1 3I0 INPUT 1 PICKUP — Selects the 3I_0 pickup value for input 1 (the main supervised CT source).CT FAIL 1 3I0 INPUT 2 — Selects the current source for input 2. Input 2 should use a different set of CTs or a different CT coreof 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 — Selects the 3I_0 pickup value for input 2 (different CT input) of the relay.CT FAIL 1 3V0 INPUT — Selects the voltage source.CT FAIL 1 3V0 INPUT PICKUP — Specifies the pickup value for the 3V_0 source.CT FAIL 1 PICKUP DELAY — Specifies the pickup delay of the CT failure element.Figure 5-178: CT failure detector logic CT FAIL 1 EVENTS:DisabledRange: Disabled, Enabled
