Description

The ASB‑4401H is a digital distribution transformer protection relay designed for medium‑ and low‑voltage distribution transformer applications in substations. It integrates overcurrent, earth fault, overload, voltage, transformer body and temperature protection with measurement, control and communication functions in one compact device.

Key Features

• Distribution transformer protection
• Overcurrent protection
• Earth fault protection
• Overload protection
• Overvoltage and undervoltage protection
• Transformer body protection
• Transformer temperature protection
• Voltage circuit supervision
• Real-time measurement
• Fault recording
• Remote monitoring and setting

Measurement and Monitoring

The ASB-4401H can provide real-time monitoring of electrical operating conditions, including:

• Phase current
• Voltage
• Frequency
• Protection status
• Alarm status
• Fault information
• Transformer operating conditions

This allows operators to monitor distribution transformer operating conditions from the protection device or through the connected monitoring system.

Communication Functions

• The device supports three communication modes: RS-485, CANbus, and Ethernet (to be specified at the time of ordering);
• The device uploads real-time data, including measurement data, waveform data, faults, alarm signals, and all protection settings, configurations, and coefficients; it supports remote online modification of settings and activation/deactivation of protection functions;

Event Logging and Fault Recording

Monitoring Functions

• This device measures analog parameters including current, voltage and frequency.
• It collects digital signals such as status of circuit breakers, energy storage devices, disconnectors and remote/local mode. Circuit breaker closing and opening controls are also available.

What Is a Distribution Transformer Protection Relay?

A distribution transformer protection relay is a protection and control device used to detect electrical faults and abnormal operating conditions in distribution transformers. Compared with protection systems for large power transformers, distribution transformer protection generally emphasizes overcurrent, earth fault, overload, voltage and temperature protection, with the exact configuration depending on transformer capacity, voltage level, grounding method and application.

The ASB-4401H integrates these functions into one numerical relay, reducing the need for multiple separate protection devices in distribution transformer applications.

Distribution Transformer Protection Functions

Distribution Transformer Protection Applications

10kV Distribution Transformers

• Dedicated protection for 10kV distribution transformers in utility and industrial networks.

11kV Distribution Transformers

• Comprehensive protection for 11kV distribution transformers commonly used in regional distribution systems.

20kV / 22kV Distribution Transformers

• Protection solutions for 20kV and 22kV distribution transformers – subject to the specific model’s voltage rating.

33kV Distribution Transformers

• Protection for 33kV distribution transformers – to be confirmed based on actual technical specifications.

Industrial Distribution Transformers

• Reliable protection for transformers serving:

  • Manufacturing plants

  • Industrial facilities

  • Mining operations

  • Oil & gas installations

  • Commercial buildings

Box-Type / Compact Substations

• Protection and control for compact transformer substations and box-type substations, integrating seamlessly with MV switchgear for coordinated feeder and transformer protection.

Distribution Transformer Protection Scheme

Distribution Transformer vs Power Transformer Protection

Setting Table

No.	Description	Setting Range	Upload & Download Conversion Factor
1	Control Word 1	0000～FFFF	×1
2	Control Word 2	0000～FFFF	×1
3	Control Word 3	0000～FFFF	×1
4	Stage 1 Time Delay (Stage 1 Overcurrent Protection Delay)	0.00～120.00s	×100
5	Stage 2 Time Delay (Stage 2 Overcurrent Protection Delay)	0.00～120.00s	×100
6	Stage 3 Time Delay (Stage 3 Overcurrent Protection Delay)	0.00～120.00s	×100
7	HV Side Stage 1 Zero-sequence Current Delay	0.00～120.00s	×100
8	HV Side Stage 2 Zero-sequence Current Delay	0.00～120.00s	×100
9	LV Side Stage 1 Zero-sequence Current Delay	0.00～120.00s	×100
10	LV Side Stage 2 Zero-sequence Current Delay	0.00～120.00s	×100
11	Zero-sequence Overvoltage Delay	0.00～120.00s	×100
12	Overload Delay	0.00～120.00s	×100
13	Undervoltage Delay	0.00～120.00s	×100
14	Stage 1 Overcurrent Setting (Instantaneous Overcurrent Setting)	0.40～99.99A / 0.10～20.00A	×100
15	Stage 2 Overcurrent Setting (Time-limit Instantaneous Overcurrent Setting)	0.40～99.99A / 0.10～20.00A	×100
16	Stage 3 Overcurrent Setting (Overcurrent Protection Setting)	0.40～99.99A / 0.10～20.00A	×100
17	Overload Current Setting	0.40～99.99A / 0.10～20.00A	×100
18	Spare Setting (Original Startup Setting)	—	×1
19	HV Side Stage 1 Zero-sequence Overcurrent Setting	0.02～5.00A	×100
20	HV Side Stage 2 Zero-sequence Overcurrent Setting	0.02～5.00A	×100
21	LV Side Stage 1 Zero-sequence Overcurrent Setting	0.02～5.00A (HV Auxiliary Transformer) 0.40～99.99A (LV Auxiliary Transformer)	×100
22	LV Side Stage 2 Zero-sequence Overcurrent Setting	0.02～5.00A (HV Auxiliary Transformer) 0.40～99.99A (LV Auxiliary Transformer)	×100
23	Zero-sequence Current Blocking Setting (for Zero-sequence Overvoltage)	0.10～99.99A	×100
24	Undervoltage Setting	5.00～100.00V	×100
25	Negative-sequence Voltage Setting	5.00～100.00V	×100
26	Zero-sequence Overvoltage Setting	1.00～120.00V	×100
27	Zero-sequence Voltage Blocking Setting (for Zero-sequence Overcurrent)	1.00～120.00V	×100
28	Undervoltage Blocking Setting (for Overcurrent Protection)	5.00～100.00V	×100
29	Overvoltage Delay	0.00～120.00s	×100
30	Overvoltage Setting	20.00～120.00V	×100
31~48	Reserved	—	—

Outline and Installation Dimensions

   

How to Select a Distribution Transformer Protection Relay

1. Transformer Rated Voltage

Confirm HV voltage level is within relay range:

• 6 kV / 10 kV / 20 kV / 22 kV / 33 kV

2. Transformer Capacity

Match CT ratio and protection settings to transformer rating:

• 500 / 630 / 1000 / 1600 / 2500 / 5000 kVA

3. Grounding Method

4. Protection Functions — Checklist

5. Communication Requirements — Checklist

Required features: Telemetry, teleindication (SOE), telecontrol, remote setting, fault recording (COMTRADE).

6. Installation Space — Checklist

Summary Checklist

FAQ