Basler PRS 250 Synchronous Relay Maintenance and Replacement Guide

Phase angle window set too small (increase to ± 15 ° for trial operation)

Input common terminal not connected or PT polarity reversed (resulting in a phase difference of 180 °, theoretically exceeding the maximum ± 20 °)

Solution process: First, measure whether the bus side voltage is within the input range (such as 120V ± 10%), and then measure the generator side voltage; Use an oscilloscope to check the phase difference between the two waveforms and confirm if it is within the set window.

Fault 2: Relay frequently engages and releases (shaking)

Possible reason: The slip frequency is close to the upper limit of 0.5Hz and fluctuates, causing the relay to switch back and forth at the boundary; Or voltage fluctuations cause the difference to oscillate around 6.6%.

Countermeasure: Reduce the slip to 0.2-0.3Hz and increase the phase angle window appropriately (such as from 10 ° to 15 °) to increase the hysteresis margin. Additionally, check if the power supply is pure and add an isolation transformer if necessary.

Fault 3: A huge surge current occurs after closing the circuit

Root cause: Although the relay is closed, the actual phase angle at the moment of closing exceeds the tolerance - because there is a delay from the relay action to the closure of the main contact of the circuit breaker (including the action time of the intermediate relay and the mechanical time of the closing coil). If the total delay is 150ms and the slip is 0.3Hz (corresponding to a phase angle change of about 16.2 °), the phase angle window needs to be set to 20 ° and the slip should be kept below 0.2Hz.

Corrective measures: Use an oscilloscope to record the time difference between the relay closing contact signal and the circuit breaker auxiliary contact signal, infer the actual closing angle, and adjust the window.

Fault 4: Relay failure at low temperature (environment below -20 ° C)

PRS 250 is rated up to -40 ° C, but if moisture freezes inside the control cabinet, it may affect terminal insulation or cause potentiometer jamming. It is recommended to install a heater inside the cabinet in cold regions and set the temperature controller to+5 ° C.

Life management and spare parts replacement solutions

6.1 Normal lifespan

Solid state relays have no mechanical wear and tear, and their expected lifespan mainly depends on the aging of internal electrolytic capacitors and optocouplers. In general industrial environments, no replacement is required for 15-20 years. But it is recommended to conduct a functional test every 5 years: simulate various out of limit conditions to confirm that the relay is correctly locked; Measure whether the output voltage and phase angle setting values drift (the potentiometer may change slightly due to vibration).

6.2 Direct Replacement Models

If PRS 250 is discontinued, a new generation of synchronous inspection relays from Basler can be considered, such as Basler SCP-250 (with a wider slip range of 0.1-2Hz) or Basler BE1-25 (digital, programmable). However, when replacing, attention should be paid to:

The definition of the wiring terminal may be different and needs to be re crimped;

Digital relays require an external auxiliary power supply (PRS 250 self powered), while BE1-25 requires 24/48/125VDC power supply.

The software settings interface may increase debugging complexity, and maintenance personnel need to be trained.

6.3 Precautions for Purchasing in the Second hand Market

Considering that PRS 250 is no longer a mainstream new product, some suppliers offer "refurbished/inventory" products. When purchasing, the following should be requested:

Factory test report (including verification data for phase angle, voltage, and frequency)

Inspect the appearance for signs of erosion

Is the mechanical stop of the potentiometer intact (to avoid internal open circuit)

Safety operation and compliance reminder

CSA certification indicates that the relay complies with relevant electrical standards in Canada and the United States, but it still needs to follow local regulations (such as NFPA 70E) for live working when in use.

As the relay does not have a built-in fuse, a 1A slow melting fuse should be added to the external voltage input circuit to prevent the spread of faults in case of PT short circuit.

If the output contact is used for DC inductive loads (such as contactor coils), it must be connected in parallel with a freewheeling diode (DC) or an RC absorption circuit (AC), otherwise it may cause contact adhesion or internal semiconductor damage due to back electromotive force.