What Does a Solar PV Grid-Tie Protection Relay Include?

• A solar PV grid-tie protection relay, also referred to as a PV grid interconnection protection relay, is used to monitor operating conditions at the point of common coupling (PCC) between a photovoltaic (PV) system and the utility grid. It provides protection, control and disconnection functions in response to unintentional islanding, abnormal voltage or frequency and other specified grid conditions.
• A complete PV grid interconnection protection system typically includes anti-islanding protection, fault separation/interconnection protection and frequency and voltage protection and control. Power quality monitoring may also be incorporated. GoWatron provides the GWPR300-AIP, GWPR300-FS, GWPR300-FV and GWPR320-PQA for these applications. Depending on project requirements, these devices can be applied individually or integrated into the GWPC300-PVG PV Grid Connection Protection Panel.

1. Anti-Islanding Protection Relay

Typical Device: GWPR300-AIP Anti-Islanding Protection Relay

Anti-islanding protection is one of the key functions of a PV grid interconnection protection system. If the utility grid is de-energised because of a fault, outage or maintenance while the PV system continues to energise a local section of the network and its connected loads, an unintentional island may be formed.

The GWPR300-AIP monitors voltage, frequency, rate of change of frequency, power flow direction and other relevant electrical quantities at the PCC. When the configured anti-islanding criteria are met, the relay initiates tripping of the interconnection circuit breaker to disconnect the PV system from the utility grid.

Core Protection Functions:

• Overvoltage Protection (ANSI 59): Detects voltage above the configured threshold and operates after the specified time delay.
• Undervoltage Protection (ANSI 27): Detects voltage below the configured threshold and operates after the specified time delay.
• Overfrequency Protection (ANSI 81O): Detects system frequency above the configured upper threshold.
• Underfrequency Protection (ANSI 81U): Detects system frequency below the configured lower threshold.
  Rate of Change of Frequency Protection (ANSI 81R): Monitors the rate of change of frequency (ROCOF, df/dt) as one of the criteria for detecting abnormal grid conditions and unintentional islanding.
• Reverse Power Protection (ANSI 32): Monitors active power flow direction and detects undesired reverse power flow according to the configured pickup and time-delay settings.

The GWPR300-AIP is suitable for distributed PV systems, utility-scale PV plants and other grid-connected renewable energy applications. Protection functions, pickup settings and operating delays should be coordinated with the applicable grid code, utility interconnection requirements and project specifications, including relevant voltage and frequency ride-through requirements.

2. Fault Separation / Interconnection Protection Relay

Typical Device: GWPR300-FS Fault Separation / Interconnection Protection Relay

Fault separation/interconnection protection is used to disconnect a PV generating source from the relevant section of the grid when specified grid faults or abnormal operating conditions occur.

For example, when a distribution feeder fault is followed by automatic reclosing, continued energisation of the faulted feeder by a PV source may interfere with fault clearance and the reclosing sequence. The GWPR300-FS can use voltage, frequency, residual voltage and external status signals to implement the required interconnection disconnection logic.

Core Protection Functions:

• Residual Overvoltage Protection (ANSI 59N): Monitors residual voltage for earth-fault or abnormal earthing conditions.
• Undervoltage Protection (ANSI 27): Initiates disconnection when voltage falls below the configured threshold and the specified operating conditions are met.
• Overvoltage Protection (ANSI 59): Initiates disconnection when voltage exceeds the configured threshold and the specified operating conditions are met.
• Underfrequency Protection (ANSI 81U): Initiates disconnection when system frequency falls below the configured threshold and the specified operating conditions are met.
• Overfrequency Protection (ANSI 81O): Initiates disconnection when system frequency exceeds the configured threshold and the specified operating conditions are met.

The GWPR300-FS can be installed at the PV interconnection point, collector/step-up substation or associated utility substation. It can also be coordinated with circuit-breaker status, feeder protection, automatic reclosing and external binary signals. The need for a dedicated fault separation/interconnection protection relay depends on the interconnection voltage, network configuration, protection coordination scheme and utility requirements.

3. Frequency and Voltage Control Protection Relay

Typical Device: GWPR300-FV Frequency and Voltage Control Protection Relay

During grid-connected operation, system disturbances such as network faults, generation–load imbalance or loss of a power source may cause voltage and frequency to move outside their permitted operating ranges.

The GWPR300-FV continuously monitors voltage and frequency at the PCC. Based on configured thresholds, operating ranges and time delays, it provides the required protection and control functions. Depending on the application, the relay can initiate alarms, control commands or tripping.

Core Protection Functions:

• Overvoltage Protection (ANSI 59): Detects system voltage above the configured upper threshold and operates after the specified time delay.
• Undervoltage Protection (ANSI 27): Detects system voltage below the configured lower threshold and operates after the specified time delay.
• Overfrequency Protection (ANSI 81O): Detects system frequency above the configured upper threshold and operates according to the configured logic and time delay.
• Underfrequency Protection (ANSI 81U): Detects system frequency below the configured lower threshold and operates according to the configured logic and time delay.

The GWPR300-FV allows voltage and frequency protection thresholds and operating delays to be configured according to project requirements. Its protection logic can also incorporate circuit-breaker status and other control conditions. Settings should comply with the applicable grid code and utility interconnection requirements and should be coordinated with low-voltage ride-through (LVRT), high-voltage ride-through (HVRT) and frequency ride-through requirements.

4. Power Quality Analyser

Typical Device: GWPR320-PQA Power Quality Analyser

The GWPR320-PQA performs a different role from that of a protection relay. Protection relays are primarily responsible for detecting abnormal operating conditions and issuing protection and tripping commands, whereas the GWPR320-PQA is designed for continuous power quality measurement, event recording and data analysis at the PV interconnection point.

Core Monitoring Functions:

• Voltage and Current Measurement: Continuously measures three-phase voltage and current at the PV interconnection point.
• Power and Frequency Measurement: Measures frequency, active power, reactive power, apparent power and power factor.
• Harmonic and Interharmonic Analysis: Monitors voltage and current harmonics, interharmonics and total harmonic distortion (THD).
• Voltage Dip and Swell Monitoring: Detects and records voltage dips (sags) and voltage swells, including their magnitude and duration.
• Interruption Monitoring: Detects and records supply interruptions and associated power quality events.
• Voltage Fluctuation and Flicker Monitoring: Monitors voltage fluctuations and flicker for power quality assessment.
• Three-Phase Unbalance Monitoring: Monitors voltage and current unbalance in three-phase systems.
• Event Recording and Trend Analysis: Records power quality events and operating data for event analysis, historical trending and system assessment.

Depending on project requirements, power quality measurements may be specified with reference to IEC 61000-4-30, IEC 61000-4-7, IEC 61000-4-15, EN 50160, IEEE 519 and applicable local power quality requirements. The measurement class, harmonic range, interharmonic measurement capability and other performance parameters should be based on the actual specifications of the GWPR320-PQA.

5. GWPC300-PVG PV Grid Connection Protection Panel

For PV projects requiring an integrated grid interconnection protection solution, the above devices can be configured together within the GWPC300-PVG PV Grid Connection Protection Panel.

Main Configuration:

• GWPR300-AIP Anti-Islanding Protection Relay: Anti-islanding protection.
• GWPR300-FS Fault Separation / Interconnection Protection Relay: Fault separation/interconnection protection.
• GWPR300-FV Frequency and Voltage Control Protection Relay: Frequency and voltage protection and control.
• GWPR320-PQA Power Quality Analyser: Power quality monitoring and analysis.

The GWPC300-PVG integrates anti-islanding protection, fault separation/interconnection protection and frequency and voltage protection and control within a single panel. It also incorporates power quality monitoring. Depending on project requirements, the panel can provide interconnection circuit-breaker tripping and control, status monitoring, event recording and communication with the PV plant supervisory control and data acquisition (SCADA) system or substation automation system.

This integrated arrangement simplifies secondary-system engineering and panel assembly. It also facilitates site commissioning, operation and maintenance, as well as system communications. The GWPC300-PVG therefore provides a comprehensive protection, control and power quality monitoring solution for PV grid interconnection applications.