6.5 STANDARD LOGIC EQUATION TEMPLATES

OneLiner provides logic equation template for a number of logic schemes, as described in the IEEE Guide for Protective Relay Applications to Transmission Lines, Standard C37.113-1999:

• Direct Under-reaching Transfer Trip (DUTT)

• Permissive Under-reaching Transfer Trip (PUTT)

• Permissive Overreaching Transfer Trip (POTT)

• Directional Overreaching-Under-reaching Transfer Trip (POTT-PUTT)

• Directional Comparison Blocking (DCB)

Users can use these logic equation templates as-is or make further customization to describe the actual logic scheme.

Logic diagrams and trip equation for these five “standard” schemes are shown in this section with the following variable naming convention. (You are not obligated to follow this naming convention.)

• RU: Under-reaching elements

• RO: Over-reaching elements

• REV: Reverse looking elements

• _FAR: Suffix for relay elements at the line far end

• _NEAR: Suffix for local relay elements

Each of the under-reaching and over-reaching elements can be:

1. Zone-1, -2, -3 or -4 phase or ground distance elements, or

2. Forward- or reverse-looking directional overcurrent elements, or

3. A combination of these through logical ‘AND’ and ‘OR’ operators.

Note: Even though reverse-looking directional ground overcurrent elements are not explicitly available in OneLiner now, the user can model them by adjusting the characteristic angle of the directional element.

In the diagrams boxes labeled ‘TX’ and ‘RX’ are the transmitter and receiver, respectively. The transmission time delay is not shown explicitly.

The following constants are used in logic equation templates:

• Tx: Transmission time delay constant

• Tr: Drop-out timer constant

• Tc: Pickup timer constant