ABB PR521 Protection Relay

ABB PR521 Protection Relay Supplier & Exporter in India

ABB PR521 Self-Supplied Protection Relay for HD4 and VD4 Circuit Breakers

ABB PR521 is a microprocessor-based protection relay used with ABB medium-voltage circuit breakers for feeder and transformer protection. It was mainly fitted with ABB HD4/R, HD4/S, VD4/R and VD4/S circuit breakers in medium-voltage switchgear up to 24 kV.

One of the main advantages of the PR521 is its self-powered design. The current sensors connected to the relay provide both the measurement signal and the energy required for protection operation. This makes the PR521 suitable for installations where a separate auxiliary supply for the protection relay was not available or was not preferred.

Today, most requirements for ABB PR521 come from plants, substations and industrial users maintaining older ABB switchgear. Buyers may be looking for an ABB PR521 replacement relay, PR521/LSI spare, PR521/LSIG protection relay, PR521/DK unit or a suitable solution for an existing HD4 or VD4 circuit breaker.

ABB has discontinued the PR521 range, so the complete details of the existing relay and circuit breaker should be checked before offering a replacement.

ABB PR521 Models

The principal PR521 protection versions are PR521/LSI and PR521/LSIG. ABB’s current service documentation also identifies a PR521/DK version used with HD4 and VD4 side-version circuit breakers.

ABB PR521/LSI – 1VCF349899S0121

PR521/LSI is intended for phase overcurrent protection.

Protection functions include:

• ANSI 51 time overcurrent protection
• ANSI 50 short-circuit / instantaneous overcurrent protection
• Two-phase or three-phase protection depending on the number of current sensors connected
• Adjustable protection thresholds
• Adjustable trip delays
• Fixed-time and inverse-time protection characteristics

ABB PR521/LSIG – 1VCF349899S0122

PR521/LSIG includes the phase protection functions of the LSI version along with earth-fault protection.

Protection functions include:

• ANSI 50 phase short-circuit protection
• ANSI 51 phase overcurrent protection
• ANSI 51N earth-fault overcurrent protection
• Internal earth-fault measurement using the vector sum of the phase sensors
• Connection for an external earth-fault toroid where required
• Adjustable operating thresholds and time delays

ABB PR521/DK – 1VCF349899S0123

ABB service documentation also lists PR521/DK for HD4 and VD4 side-version circuit breakers. When enquiring for this version, the complete relay code and circuit-breaker details should be provided because PR521/DK requirements are normally connected with existing or older ABB switchgear installations.

Technical Specifications

• Product: Microprocessor-based protection relay/protection trip unit
• Product family: ABB PR521
• Main protection versions: PR521/LSI and PR521/LSIG
• Additional service version: PR521/DK
• Application: Medium-voltage circuit-breaker protection
• Compatible breaker families: ABB HD4/R, HD4/S, VD4/R and VD4/S
• Maximum circuit-breaker rated voltage: Up to 24 kV
• Protection functions: ANSI 50, 51 and 51N depending on version
• Protection arrangement: Two-phase or three-phase
• Power supply: Self-supplied through current sensors
• Minimum current for self-supplied operation: Approx. 0.2 × In on at least one sensor-equipped phase
• Current sensor secondary rating: 1 A
• ABB current sensor primary ratings: 40 A, 80 A, 250 A and 1250 A
• External earth-fault toroid secondary rating: 1 A
• External earth-fault toroid burden: 1 VA
• Operating frequency: 45 Hz to 66 Hz
• Continuous overload withstand: 1.5 × In
• Overload withstand: 6 × In for 200 seconds
• Short-time withstand current: 25 kA for 1 second
• Protection setting: Front DIP switches
• Circuit-breaker tripping: Opening solenoid operated directly by the PR521
• Remote opening input: Available
• Operating temperature: -5°C to +40°C
• Storage temperature: -40°C to +90°C
• Relative humidity: Up to 90% without condensation
• Degree of protection when mounted with front protection: IP42

Features

• Self-powered protection: Does not depend on a separate auxiliary supply for its basic protection operation.
• Phase overcurrent protection: Provides overload and short-circuit protection for medium-voltage feeders and transformer circuits.
• Earth-fault protection: Available with the PR521/LSIG configuration.
• Adjustable trip settings: Protection thresholds and operating times can be selected from the front of the unit.
• Fixed and inverse-time curves: Allow protection settings to be matched to the requirements of the connected system.
• Two or three current sensor operation: Can be applied according to the breaker and protection arrangement.
• External earth-fault toroid connection: Useful where more sensitive earth-fault protection is required.
• Direct breaker tripping: The relay operates an opening solenoid connected directly to the circuit-breaker mechanism.
• Current sensor supervision: Incorrect current sensor selection is indicated through the alarm indication.
• Designed around ABB MV breakers: Commonly associated with HD4 and VD4 circuit-breaker installations.

Applications

ABB PR521 protection units are commonly found in older:

• Medium-voltage distribution switchboards
• ABB HD4 circuit-breaker panels
• ABB VD4 circuit-breaker panels
• Primary distribution substations
• Secondary distribution substations
• Industrial MV switchgear
• Transformer protection panels
• Medium-voltage feeder protection
• Utility distribution systems
• Factory electrical distribution networks
• Infrastructure power distribution systems
• Existing ABB switchgear refurbishment projects
• Circuit-breaker maintenance and modernisation requirements

ABB PR521 for Existing HD4 and VD4 Switchgear

A large number of PR521 enquiries today are not for new projects. They come from users who already have an ABB HD4 or VD4 breaker fitted with PR521 and need to restore the panel after the existing protection unit has failed or become unreliable.

For these requirements, simply mentioning “ABB PR521” may not be enough. The protection version, current sensors, breaker model and existing wiring arrangement can affect the replacement solution.

For faster identification, buyers should share:

• PR521 version – LSI, LSIG or DK
• Complete ABB ordering code
• Photograph of the existing PR521 nameplate
• Circuit-breaker model
• HD4 / VD4 breaker rating
• Rated voltage
• Current sensor rating
• Existing protection settings, if available
• Quantity required
• Project / end-user location

ABB PR521 Replacement Requirements

ABB PR521 is now an obsolete protection unit and ABB no longer lists it as a normally available standard product. ABB’s service documentation specifically states that replacement is not one-to-one and can require rebuilding or modification of the existing arrangement.

Because of this, ABB PR521 replacement for HD4 circuit breaker or ABB PR521 replacement for VD4 circuit breaker requirements should be checked against the complete existing breaker configuration before ordering.

This is particularly important for old switchgear where the objective is to keep the existing breaker and panel in service rather than replacing the complete switchboard.

Looking for ABB PR521 Protection Relay?

We handle enquiries for ABB PR521 legacy protection relay requirements, PR521/LSI, PR521/LSIG, PR521/DK, ABB PR521 replacement units and protection solutions for existing HD4 and VD4 circuit breakers.

Send the complete relay model, ordering code, breaker details and nameplate photograph along with the required quantity and destination country for quotation and availability checking.