Core Technical Specifications

• Model: LQPSC 0.4KV/4000A

• Phase Configuration: Three-phase

• System Voltage: 380V AC

• Rated Current (400V Side): 4000A

• Per-Phase Current: 1000A

• Tripping Current: 1250A

• Testing Transformer Current: ≥4500A

• Tripping Off Current: 1500A

• Protection Principle: 1.1× rated current

Primary Application

Protection and control of 400V LV side input for regulator front pole installations in power distribution systems.

Protection System Design

Current Settings & Coordination

Protection Philosophy

• 1.1× Rated Current Principle:

• Primary protection setting for transformer circuits

• Prevents overcurrent during voltage regulator adjustments

• Mitigates station transformer overload risks

• User-Adjustable Settings:

• Configurable trip values based on actual load profiles

• Customizable protection thresholds for specific applications

System Architecture

• Main Circuit Protection:

• Three-phase circuit breaker (4000A rating)

• 4500A testing capacity for transformer inputs

• 1500A tripping capacity for fault isolation

• Secondary Loop Protection:

• LV busbar subdevices (1000A configurable rating)

• 1250A maximum operating current capacity

• Integrated current-limiting protection

• Coordination Logic:

• Selective tripping hierarchy

• Time-current coordination

• Load-dependent protection settings

Protection Scenarios

Industrial Applications

• Power substation LV distribution

• Transformer station input protection

• Industrial plant main switchgear

• Voltage regulator front-end protection

• Heavy-current manufacturing facilities

Design Features

• Intelligent Protection: Adaptive 1.1× current principle with manual override

• High-Current Capacity: 4000A main bus with 4500A testing capability

• Modular Design: Configurable subdevices for secondary loops

• Visual Indicators:

• Load status indicators

• Protection activation signals

• System health monitoring

• Safety Interlocks:

• Preventive blocking during maintenance

• Voltage presence indicators

• Key-operated control transfer

Installation Requirements

Protection Configuration Protocol

1. Determine transformer rated current (In)

2. Set protection threshold at 1.1× In

3. Configure LV subdevices at 1000A base rating

4. Set maximum operating current at 1250A (1.25×)

5. Calibrate tripping mechanism at 1250A

6. Verify coordination with upstream devices

7. Implement user-specific adjustments as needed

Compliance Standards

• IEC 61439-1: Low-voltage switchgear assemblies

• IEC 60255: Electrical relays

• IEC 60947-2: Circuit-breakers

• IEEE C37.20: Switchgear standards

• ANSI/IEEE C37.13: Low-voltage AC power circuit breakers

Designed for critical transformer protection applications with configurable protection parameters.