The ZCPSCH Scheme Communication Logic provides high-speed teleprotection functions that enable instantaneous fault clearance for transmission line faults. By exchanging protection signals between line terminals, the function significantly reduces fault clearing time and improves overall power system stability.

The ZCPSCH function supports a comprehensive range of industry-standard communication-assisted protection schemes, including:

Permissive Underreaching Transfer Trip (PUTT)
Permissive Overreaching Transfer Trip (POTT)
Blocking schemes
Delta-based blocking schemes
Unblocking schemes
Direct intertrip schemes

When equipped with the integrated LDCM (Line Data Communication Module), the REC670 can use its built-in communication interface for reliable teleprotection signaling without requiring additional communication hardware.

Key Benefits
Instantaneous fault clearing for transmission line faults
Improved power system stability
Reduced fault duration and equipment stress
Multiple teleprotection schemes to suit different network requirements
Integrated communication using the optional LDCM module
Current Reversal and Weak-End Infeed Logic (ZCRWPSCH)

The ZCRWPSCH function enhances communication-assisted distance protection by providing advanced current reversal and weak-end infeed logic.

This function operates in conjunction with the distance protection and scheme communication functions and is not intended for standalone operation.

Current Reversal Logic

Following fault clearance, power flow may reverse, creating conditions that could lead to incorrect teleprotection operation.

When a current reversal is detected, the function automatically:

Blocks transmission of teleprotection signals to the remote terminal
Prevents unintended permissive tripping at the local terminal
Maintains the blocking condition for an appropriate time interval to ensure secure protection operation

This feature prevents false trips caused by transient current reversals after fault clearing.

Weak-End Infeed Logic

When a fault occurs on a transmission line with a weak infeed source, the remote terminal may not contribute sufficient fault current for conventional protection to operate correctly.

After verifying a weak-end infeed condition, the function can:

Retransmit the received teleprotection signal back to the initiating terminal
Issue local tripping commands
Support phase-selective tripping for single-pole and two-pole breaker applications
Identify faulted phases using integrated undervoltage detectors

This functionality ensures dependable fault clearance even when one end of the transmission line supplies only limited fault current.

Key Benefits
Secure operation during current reversal conditions
Reliable protection for weak-source transmission systems
Prevention of unwanted teleprotection operations
Support for phase-selective tripping
Improved dependability of communication-assisted distance protection
Local Acceleration Logic (ZCLCPSCH)

The ZCLCPSCH Local Acceleration Logic provides accelerated fault clearing when a dedicated communication channel between line terminals is unavailable.

Although it cannot completely replace communication-assisted protection, the function significantly improves fault clearing speed under predefined operating conditions.

The logic supports two operating methods:

Zone Extension Acceleration

When coordinated with the automatic reclosing function, the protection zone can be temporarily extended following a fault, allowing faster fault clearance and improved system restoration.

Loss-of-Load Acceleration

The function can also accelerate protection operation based on loss-of-load current detection, enabling rapid tripping when sudden load loss indicates fault conditions.

Advantages
Faster fault clearance without teleprotection communication
Improved network stability during communication outages
Enhanced coordination with automatic reclosing
Reduced fault duration and improved service continuity

While local acceleration cannot provide the same level of selectivity as communication-assisted protection schemes, it offers an effective alternative for increasing protection speed when communication channels are unavailable or temporarily out of service.

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