Description

Table of Contents

Overview of 400V Anti-Islanding Protection Relay

This 400V Anti-Islanding Protection Relay fits small grid-connected systems of 400V low-voltage PV stations. It rapidly cuts off grid connection during islanding, isolating the station from power grid and protecting equipment and maintenance staff.
ASF-512H anti-islanding protection device boasts simple structure, easy operation and high reliability. Compact design facilitates installation and replacement.

Main Functions of Anti Islanding Protection Solar Inverter

Anti Island Protection Device Functions

Two-stage under/over frequency protection: Setting value and time of each stage can be adjusted independently. Separate control word enables function activation. Output supports under-frequency islanding separation, over-frequency generator tripping and standby unit under-frequency auto-start.
Two-stage under/over voltage protection: Each stage features independent adjustable setting and delay time. Function can be enabled via control word. Applicable for voltage-based separation, standby unit auto-start and over-frequency generator tripping.
Slip blocking function: Block output when slip exceeds preset threshold.
Voltage check closing function: Automatic closing output permitted when normal voltage is detected.
Two-stage reverse power protection
Rate of change of frequency protection

Measurement Functions

Measure bus frequency and rate of frequency change;
Measure bus voltage and rate of voltage change.

Communication Functions

Equipped with RS485 communication port for connection with monitoring system.
Supported protocols: ATN-101, MODBUS, IEC60870-5-103, IEC 61850

Monitoring Functions

Display voltage and frequency values;
Acquire status signals of circuit breakers, disconnectors and other switching devices.

Technical Specifications

Parameter	Specification
Rated System Voltage	400V AC (three-phase)
Rated Frequency	50Hz / 60Hz (selectable)
Voltage Input	400V AC (selectable, phase-to-phase or phase-to-neutral)
Current Input	1A or 5A (selectable)
Auxiliary Supply	110V DC / 220V DC / 220V AC (selectable)
Protection Functions	Overvoltage (59), undervoltage (27), overfrequency (81O), underfrequency (81U), ROCOF (81R), reverse power (32R), directional overcurrent (51V/67)
Trip Output	2 x Form C (changeover) relay outputs
Digital Inputs	4 (user-configurable)
Communication	RS-485 (Modbus RTU) / Optional Ethernet (Modbus TCP / IEC 61850)
Installation	Panel-mounted (144×144mm cutout)
Operating Temperature	-25°C to +70°C
Protection Degree	IP42 (front panel) / IP20 (rear enclosure)

400V Anti-Islanding Protection Relay Applications

400V anti-islanding protection relays are suitable for 400V grid-connected systems where compliance with local grid codes and interconnection standards is required. Their application depends on system configuration, protection scheme, and utility requirements.

400V Grid-Connected PV Systems

In 400V PV systems, the anti-islanding protection relay is typically installed at the Point of Common Coupling (PCC) — the interface between the PV system and the low-voltage grid.

Typical Architecture:

The relay monitors grid-side voltage, frequency, and power flow, and issues a trip command to the circuit breaker when islanding or abnormal grid conditions are detected. For larger commercial and utility-scale PV installations, an external relay provides independent, configurable backup protection beyond inverter-integrated functions, supporting redundancy and utility compliance requirements.

400V Distributed Generation

400V anti-islanding protection relays can be applied to distributed generation systems — including diesel generators, gas generators, CHP (combined heat and power) units, and other distributed energy sources — where anti-islanding protection is specified.

Application	Description
Small diesel/gas generators	Grid-connected backup or prime power generation
Distributed Energy Resources (DER)	BESS, microturbines, fuel cells requiring grid interface
Industrial captive generation	Factory-based generation with grid backup
Small-scale cogeneration	CHP systems feeding into low-voltage distribution

In these applications, the relay monitors frequency, voltage, and power flow, providing protection against abnormal conditions and ensuring safe disconnection when islanding is detected.

Small Hydropower Grid Connection

For small hydropower plants connected to 400V low-voltage distribution networks, anti-islanding protection is essential for safe grid interconnection. A 400V anti-islanding protection relay can be used in small hydropower applications where grid code compliance requires voltage and frequency-based disconnection protection. It provides undervoltage (27), overvoltage (59), underfrequency (81U), overfrequency (81O), and ROCOF (81R) detection to ensure the plant disconnects within the required time when abnormal grid conditions are detected. Integration with overcurrent protection schemes is typically required for a complete protection package.

Note: In 400V distributed generation applications, the anti-islanding protection relay can be deployed as an external protection relay at the PCC — either as primary anti-islanding protection or as backup to inverter-integrated protection, depending on project design and grid code requirements.

How Does a 400V Anti-Islanding Protection Relay Work?

The relay continuously monitors grid-side electrical parameters, compares them against configured thresholds, and issues a trip command when islanding or abnormal conditions are detected.

Step 1: Electrical Signal Acquisition

The relay acquires real-time data from the grid connection point:

Parameter	Purpose
Voltage (three-phase)	Over/undervoltage detection
Current (three-phase)	Power calculation, directional detection
Frequency	Over/underfrequency detection
Active power	Reverse power detection
Phase angle	Phase jump / out-of-step detection

Step 2: Protection Logic

The relay compares acquired values against configured thresholds and time delays.

Function	Trigger Condition
Overvoltage (59)	Voltage > set threshold (e.g., 110% of rated)
Undervoltage (27)	Voltage < set threshold (e.g., 80% of rated)
Overfrequency (81O)	Frequency > set threshold (e.g., 50.5Hz)
Underfrequency (81U)	Frequency < set threshold (e.g., 49.5Hz)
ROCOF (81R)	Frequency change rate exceeds threshold
Reverse Power (32R)	Power flows from generator to grid
Directional OC (51V/67)	Directional or voltage-restrained overcurrent

Step 3: Islanding Detection

When one or more protection conditions are met and the time delay elapses, the relay confirms islanding or abnormal grid condition.

Detection method:

Passive detection: Voltage/frequency deviation beyond set thresholds

Step 4: Trip Command

Upon confirmation, the relay:

Activates trip output (contact closes)
Sends trip signal to circuit breaker
Disconnects generation from the grid
Records event with time stamp and fault data

Operating Sequence

The detection and trip sequence typically completes within 200ms to 2 seconds, per grid code requirements.

Low-Voltage Anti-Islanding Protection Device – Setting List

No.	Name	Range	Step	Remark
1	Under Frequency Setting
1.1	1st Stage Under Frequency	1/0	–	1: Enable, 0: Disable
1.2	2nd Stage Under Frequency	1/0	–	1: Enable, 0: Disable
1.3	Slip Blocking for Under Frequency	1/0	–	1: Enable, 0: Disable
1.4	Undervoltage Blocking for Under Frequency	1/0	–	1: Enable, 0: Disable
1.5	1st Stage Time Delay	0.1s～120.00s	0.01s	–
1.6	2nd Stage Time Delay	0.1s～120.00s	0.01s	–
1.7	1st Stage Setting Value	45.00Hz～50.00Hz	0.01Hz	–
1.8	2nd Stage Setting Value	45.00Hz～50.00Hz	0.01Hz	–
1.9	df/dt	0.00Hz/s～4.00Hz/s	1.00Hz/s	–
2	Over Frequency Setting
2.1	1st Stage Over Frequency	1/0	–	1: Enable, 0: Disable
2.2	2nd Stage Over Frequency	1/0	–	1: Enable, 0: Disable
2.3	Undervoltage Blocking for Over Frequency	1/0	–	1: Enable, 0: Disable
2.4	1st Stage Time Delay	0.1s～120.00s	0.01s	–
2.5	2nd Stage Time Delay	0.1s～120.00s	0.01s	–
2.6	1st Stage Setting Value	50.00Hz～55.00Hz	0.01Hz	–
2.7	2nd Stage Setting Value	50.00Hz～55.00Hz	0.01Hz	–
3	Undervoltage Setting
3.1	1st Stage Undervoltage	1/0	–	1: Enable, 0: Disable
3.2	2nd Stage Undervoltage	1/0	–	1: Enable, 0: Disable
3.3	1st Stage Time Delay	0.1s～120.00s	0.01s	–
3.4	2nd Stage Time Delay	0.1s～120.00s	0.01s	–
3.5	1st Stage Voltage Value	5.00V～120.00V	0.01V	–
3.6	2nd Stage Voltage Value	5.00V～120.00V	0.01V	–
4	Overvoltage Setting
4.1	1st Stage Overvoltage	1/0	–	1: Enable, 0: Disable
4.2	2nd Stage Overvoltage	1/0	–	1: Enable, 0: Disable
4.3	1st Stage Time Delay	0.1s～120.00s	0.01s	–
4.4	2nd Stage Time Delay	0.1s～120.00s	0.01s	–
4.5	1st Stage Voltage Value	5.00V～120.00V	0.01V	–
4.6	2nd Stage Voltage Value	5.00V～120.00V	0.01V	–
5	Auto Closing Setting
5.1	Switch Auto Closing	1/0	–	1: Enable, 0: Disable
5.2	Voltage Check Before Closing	1/0	–	1: Enable, 0: Disable
5.3	Closing Time Delay	0.1s～120.00s	0.01s	–
5.4	Upper Voltage Limit	5.00V～120.00V	0.01V	–
5.5	Lower Voltage Limit	5.00V～120.00V	0.01V	–
6	1st Stage Reverse Power Setting
6.1	1st Stage Reverse Power Enable	1/0	–	1: Enable, 0: Disable
6.2	Reverse Power Time T1	0.1s～120.00s	0.01s	–
6.3	Reverse Power Value P1	0.05P1～0.2P1	0.01	–
7	2nd Stage Reverse Power Setting
7.1	2nd Stage Reverse Power Enable	1/0	–	1: Enable, 0: Disable
7.2	Reverse Power Time T2	0.1s～120.00s	0.01s	–
7.3	Reverse Power Value P2	0.05P2～0.2P2	0.01	–
8	Frequency Disturbance Setting
8.1	Frequency Disturbance Enable	1/0	–	1: Enable, 0: Disable
8.2	Disturbance Time Delay	0.1s～120.00s	0.01s	–
8.3	dF/dT1	0.05Hz/s～9.99Hz/s	0.01Hz/s	–
9	General Setting
9.1	Voltage Protection Plate Enable	1/0	–	1: Enable, 0: Disable
9.2	PT Broken Line Detection	1/0	–	1: Enable, 0: Disable
9.3	Undervoltage Blocking by PT Broken	1/0	–	1: Enable, 0: Disable
9.4	Two-element Wiring Mode	1/0	–	1: Enable, 0: Disable
9.5	380V Voltage System	1/0	–	1: Enable, 0: Disable
9.6	1A Current System	1/0	–	1: Enable, 0: Disable
9.7	Undervoltage Blocking Value	5.00V～120.00V	0.01V	–

Outline and Installation Dimensions of Anti Islanding Protection in Solar Inverter

FAQ：400V Anti-Islanding Protection Relay

What is a 400V anti-islanding protection relay?

A：A 400V anti-islanding protection relay is a microprocessor-based protection device designed to detect islanding and other abnormal grid conditions in distributed generation systems connected to 400V low-voltage networks. It continuously monitors voltage, frequency, power, and phase angle, and issues a trip command to the circuit breaker when abnormal conditions are detected, disconnecting the generation from the grid.

Where is a 400V anti-islanding relay used?

A：It is used in 400V grid-connected systems — including PV installations, small diesel/gas generators, CHP (combined heat and power) systems, energy storage systems, and small hydropower plants. Its application depends on the project protection scheme and local grid code requirements.

Can this relay be used for 400V grid-connected PV systems?

A：Yes. The 400V anti-islanding relay is typically installed at the Point of Common Coupling (PCC) between the PV system and the low-voltage grid, providing independent backup protection beyond inverter-integrated functions for larger commercial and utility-scale PV projects.

What protection functions does the 400V relay provide?

A：It provides the following protection functions: overvoltage (59), undervoltage (27), overfrequency (81O), underfrequency (81U), ROCOF (81R), reverse power (32R), and directional overcurrent (51V/67).

How does the relay disconnect a 400V distributed generator from the grid?

A：When islanding or abnormal conditions are detected, the relay confirms the protection condition, activates the trip output contact, and sends a trip signal to the circuit breaker at the PCC, disconnecting the generation from the grid.

Can protection thresholds and time delays be configured?

A：Yes. All protection thresholds and time delays are user-configurable via the front panel interface or PC software to meet specific project requirements and grid codes.

What information is required to select a 400V anti-islanding relay?

A：Selection requires: system voltage and frequency, CT ratio at the PCC, applicable grid code requirements (e.g., IEEE 1547, IEC 62116, or local regulations), required protection functions, and communication needs (Modbus or IEC 61850).

Can you provide technical drawings, settings and testing support?

A：Yes. We provide complete technical documentation including datasheets, wiring diagrams, dimensional drawings, setting guides, and compliance certificates. Our engineering team also offers setting calculation, secondary injection testing, and on-site commissioning support.

Get Technical Quote

Provide the following for a tailored quote:

Project name & location
System voltage & frequency
Generation type (PV, diesel, gas, CHP, hydro, other)
System capacity / generator rating
Applicable grid code (if known)
Required protection functions
Communication protocol
Quantity

2 reviews for 400V Anti-Islanding Protection Relay | Low-Voltage Grid Protection

xiao zhang – June 3, 2026

This 400V anti-islanding protection device features quick fault response and outstanding anti-interference capacity, reliably cutting off distributed generation under islanding conditions to guarantee grid safety, widely used in low-voltage photovoltaic power stations.
Rated 5 out of 5

Jack – June 4, 2026

Great for retrofitting old switchgear — minimal wiring changes needed.

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400V Anti-Islanding Protection Relay | Low-Voltage Grid Protection