The one-and-a-half breaker scheme is a sophisticated configuration used in Extra-High Voltage (EHV) substations, crucial for modern power transmission networks. This scheme offers exceptional reliability and operational flexibility, making it ideal for critical transmission systems.
Key Features:
1. Configuration: Three circuit breakers manage two circuits, with the middle breaker shared.
2. Flexibility: Allows for maintenance and fault isolation without disrupting power supply.
3. Reliability: Ensures continuous operation even if one circuit breaker is out of service.
Interlocking Requirements:
Interlocking is vital for safe operation. Key aspects include:
1. Open and Closed Positions: Basic states of circuit breakers and isolators.
2. “Under Operation” State: A transitional, potentially dangerous state during switching.
3. Fully Open/Closed Positions: Definitive states ensuring complete isolation or connection.
Additional Interlocking Conditions:
1. Synchro Check Function: Ensures safe connection of energised sections.
2. Maintenance Mode: Special interlocks for safe maintenance operations.
3. Emergency Conditions: Overrides certain interlocks in critical situations.
4. SF6 Pressure Interlocks: Prevent operation if insulating gas pressure is low.
5. Local vs Remote Operations: Different interlocking rules based on control location.
Typical Configuration:
– Two overhead lines connected to three circuit breakers.
– Each line can be isolated independently.
– Middle breaker provides redundancy.
Operational States:
1. Normal Operation: All breakers in service.
2. Single Feeder Energised: One line in service, the other isolated.
3. Fault Scenarios: Isolation of faulted sections without total shutdown.
4. Emergency Conditions: Special operating procedures for critical situations.
The one-and-a-half breaker scheme’s complexity is balanced by its unparalleled flexibility and reliability, making it a cornerstone of modern EHV substation design.
Source: Electrical Engineering Portal
