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MR-REF & MR-REF3 Technical Manual
Issue 3, November 2013
1. P&B MR-REF & MR-REF3
P&B Protection Relay's MR-REF & MR-REF3 is a highly sophisticated microprocessor based feeder protection
relay, specifically designed to be used on low or medium voltage feeders as an integral part of any type or
manufacture of distribution equipment.
MR-REF & MR-REF3 monitors the earth current/s by means of conventional ring type current transformers with
typically 1A or 5A secondary outputs. This measured current is then used by the MR-REF & MR-REF3 to determine
tripping or alarm functions in order to interrupt the main switching device and protect the circuit or transformer from
damage.
The MR-REF & MR-REF3 is a withdrawable, easily installed package. The MR-REF & MR-REF3 with the 4 x relay
output option can be used as a replacement for older MREF relays by removing the relay module from the
switchgear mounted casing and fitting the new MR-REF & MR-REF3 in its place some wiring changes are required
to ensure compatibility.
All setting parameters are programmed independently for each unit via the integral keypad and liquid crystal display
on the front plate or via any of the communication ports and PC based software package available for the Vision
series of products.
During operational conditions the LCD also gives access to accurate load, statistical and fault data such as; Earth
Phase Amps, Time to Trip, In Service Hours, Number of operations.
Tri-Colour Light Emitting Diodes mounted on the front plate give immediate visual indication of the breaker status i.e.
HEALTHY / IRF / INHIBIT and ALARM / FAULTY / HEALTHY conditions.
The MR-REF & MR-REF3 can also be integrated onto an RS485 based network. This allows measured, statistical
and status information from the relay to be reported to a remote central communicating system.
Pages 25 to 27 can be used as a template for your relay settings schedule.
Summary of Contents for MR-REF
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