Pilot Protection Schemes Simulator

Zone 1 Zone 2 Zone 3 (Fwd) Zone 4 (Rev) Breaker Closed Breaker Open Comm Signal

Protection Zone Characteristics

Zone 1: Typically set to 80-90% of the protected line length. Provides fast, instantaneous tripping for faults within this range. It is *underreaching* to avoid operating for faults beyond the remote bus.

Zone 2: Typically set to 120-150% of the protected line length. It *overreaches* the remote bus to ensure coverage for all line faults. Operates with a time delay (e.g., 0.3-0.5s) to coordinate with Zone 1 at the remote end. Used for primary protection in pilot schemes and as backup.

Zone 3 (Forward): Reaches further than Zone 2, often covering the protected line plus the next line section. Operates with a longer time delay (e.g., 0.6-1.2s). Provides remote backup for faults on adjacent lines or if remote breakers fail. Can be used for *forward* directional supervision.

Zone 4 (Reverse): Typically set with a reach similar to Zone 3 but looking *backwards* from the relay location. Used primarily to determine if a fault is *reverse* (behind the relay). Essential for directional comparison schemes (DCB, DCUB) to prevent tripping for external faults.

Sequence of Events

Assumed Time Delays

Relay Pickup:
ms
Zone 1 Trip:
ms
Zone 2 Trip Delay:
ms
Zone 3 Pickup Delay:
ms
Zone 4 Reverse Delay:
ms
Communication:
ms
Breaker Operation:
ms
Coordination:
ms

Trip Equation

Define custom trip logic using zone pickup and trip signals:

Available Bits:

  • Local Relay Bits:
    • Z1PU, Z2PU, Z3PU, Z4PU: Zone pickup signals (fault detected in zone)
    • Z1, Z2, Z3, Z4: Zone trip signals (zone timer expired)
    • Z4RPU: Zone 4 reverse pickup (fault detected behind relay)
    • COMM: Communication signal received from remote relay
    • COMM_TX: Communication signal sent to remote relay
    • DTT_RX: Direct transfer trip received from remote relay
  • Remote Relay Bits (prefixed with R_):
    • R_Z1PU, R_Z2PU, R_Z3PU, R_Z4PU: Remote relay zone pickup signals
    • R_Z1, R_Z2, R_Z3, R_Z4: Remote relay zone trip signals
    • R_Z4RPU: Remote relay Zone 4 reverse pickup
    • R_COMM_TX: Communication signal sent by remote relay
  • Operators:
    • +: OR operation
    • *: AND operation
    • !: NOT operation (negation)

Trip Equation:

Determines when the local relay will trip its breaker:

  • Z1 + (Z2PU * COMM) - Trip on Zone 1 OR (Zone 2 pickup AND communication)
  • Z1 + (Z2PU * !Z4RPU) - Trip on Zone 1 OR (Zone 2 pickup AND NOT Zone 4 reverse pickup)

COMM Bit Equation:

Determines when the relay sends its COMM bit to the other relay:

  • POTT: COMM_TX = Z2PU * Z3PU - Send COMM bit when forward fault detected (Zone 2 AND Zone 3)
  • DCB: COMM_TX = Z4RPU - Send COMM bit when reverse fault detected (Zone 4 Reverse)
  • DCUB: COMM_TX = !Z4RPU - Send COMM bit when no reverse fault detected (NOT Zone 4 Reverse)
  • PUTT: COMM_TX = Z1 - Send COMM bit when Zone 1 trips

The COMM bit in the trip equation represents the communication signal received from the remote relay, which is determined by the remote relay's COMM_TX equation.

Scheme Descriptions:

POTT (Permissive Overreaching Transfer Trip):
POTT uses Zone 3 for directional supervision and to send permissive signals (COMM Eq: `COMM_TX = Z3PU`). The relay trips on Zone 1 or when it detects a forward fault and receives a permissive signal (Trip Eq: `Z1 + (Z3PU * COMM)`). If comms fail, it relies on Zone 1 protection.

PUTT (Permissive Underreaching Transfer Trip):
PUTT uses underreaching Zone 1 to trigger permissive signals (COMM Eq: `COMM_TX = Z1`). If a relay detects a fault in Zone 1, it trips instantly and signals the other end. The remote end trips instantly if it sees the fault in Zone 2 and receives the permissive (Trip Eq: `Z1 + (Z2PU * COMM)`). Otherwise, relies on Zone 1 only.

DCB (Directional Comparison Blocking):
DCB trips on forward Zone 2 detection (Trip Eq: `Z1 + (Z2PU * !COMM)`) unless a blocking signal is received from the remote end. Blocking is sent if a reverse fault is seen (COMM Eq: `COMM_TX = Z4RPU`). The trip logic requires *no* blocking signal received. Zone 1 trips instantly regardless.

DCUB (Directional Comparison Unblocking):
DCUB normally blocks tripping. A relay sends an unblocking signal when *no* reverse fault is detected (COMM Eq: `COMM_TX = !Z4RPU`). Tripping occurs if the local relay sees a forward fault (Z2PU) *and* receives the unblock signal (Trip Eq: `Z1 + (Z2PU * COMM)`).

DTT (Direct Transfer Trip):
DTT is a direct command initiated by external logic or another relay function (COMM Eq: `COMM_TX = Z1`). The receiving relay trips directly upon receiving the DTT signal (Trip Eq: `Z1 + COMM`). Zone 1 trips instantly regardless.

Zone Pickup and Trip Variables

Note: Communication delay (currently ${config.times.comm}ms) is the time it takes for the COMM bit to be received after being sent by the remote relay.