Date Code 20011026 Introduction 1-7
SEL-321/321-1 Instruction Manual
Applications Key Specifications
Short Transmission Lines
• Twenty-cycle polarizing memory duration
Permissive Overreaching Transfer
Tripping Schemes (POTT)
• Current reversal guard logic
• Open breaker echo keying logic
• Weak- and zero-infeed logic
• Time-step distance backup
Directional Comparison Unblocking
Tripping Schemes (DCUB)
• Includes all POTT logic
• All loss-of-channel logic inside the relay
• Time-step backup
Permissive Underreaching Transfer
Tripping Schemes (PUTT)
• Supported by POTT logic
• Time-step backup
Directional Comparison Blocking Trip
Scheme (DCB)
• Current reversal guard logic
• Carrier coordinating timers
• Carrier send and receive extend logic
• Zone 3 latch eliminates the need for offset
three-phase distance elements
• Time-step backup
Zone 1 Extension Schemes
• Settable Zone 1 extension multiplier
• Settable Zone 1 extension enable delay
Direct Underreaching Transfer
Tripping Schemes (DUTT)
• SEL
OGIC control equations program which
elements key direct trip
Other Features
• Fault locator
• Metering
• Automatic self-testing
• Forty event report summaries stored in non-volatile memory
• Three general purpose timers
• Five choices for controlling the trip circuits
• Trip circuit monitoring
• Hardware options for inputs, output contacts, and rear-panel terminals
Electronic-Level Input Option
The SEL relay instruction manuals address standard current (1 or 5 A) and voltage (67 V) inputs.
If you ordered your SEL relay with an electronic-level input option, references in the instruction
manual to Current Inputs and Voltage Inputs should be noted accordingly. Since the input
circuits are designed to accept electronic levels, do not subject them to Dielectric Strength,
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