The Phase Failure Relay is a critical point of failure in any automatic power control system; if the relay itself fails, the system will act as if a real power failure has occurred, causing unnecessary interruption of the load. As the relay is connected to the supply for prolonged periods, and can be subject to power surges and harmonic distortions, failure often occurs, but the risk is normally accepted as being unavoidable, - until now.

The Triplex Power Control Ltd Phase Failure Relay is unique; although a signal is reliably given if mains failure does occur, it will not be given if any part of the device itself fails.

This characteristic is achieved by the use of triplicated circuitry, as used on aircraft systems. Three independent monitoring circuits, each with a far higher reliability than any standard unit, interconnect when plugged into the base unit, so that the overall output responds only to two or more of the three circuits that are in agreement. Even if a fault does occur in one unit it will not cause a malfunction, but will be indicated as a “mismatch” of the three plug-in units, either by direct observance of the indicating lights on the individual items, or remotely by the use of the simple monitoring circuit included. Correction can be made later, without causing a break in the supply.

Replacement of existing PFRs with the Triplex unit is direct and easy, as all the connection terminals are in similar relative positions to those of most standard PFRs. The Triplex units can tolerate very high levels of harmonic distortion, power surges and sustained overvoltage, and true “off” delays of up to 6 seconds are available, so that added timers are not necessary.

The Triplex Phase Failure Relay Specification

General description

The complete assembly comprises of three separate voltage-sensing units, plugged in to a common base unit. The three-phase voltage to be monitored is connected directly to the base unit, and output contacts are provided in the same manner as a standard PFR, to indicate loss or presence of supply, i.e. 11 & 12 closed if no supply, and 11 & 14 closed if supply is healthy. The complete unit is therefore a direct replacement for normal 3-wire type PFRs, and ideal for controlling automatic change-over systems in buildings with critical supply requirements.

Internal arrangement

Each of the plug-in units monitors the voltage between two different phases, i.e. the inputs of the three devices are delta-connected to the supply by the base unit. The duplicated output contacts of each of the three plug-in units are, interconnected by the base unit, such that the output contacts 11, 12, and 14 represent the status of any two plug-in units that are the same.

Thus if an internal fault did occur in one unit, causing that to differ from the other two, or even if one unit is removed completely, the output indication is still according to the remaining two units and is therefore correct. However if one phase is lost, two units will detect a reduced voltage, and the output contacts will correctly indicate failure of supply. Delay of contact response after loss of supply is set in the plug-in units, (true off delay). Standard periods available are 1,2,4,& 6 seconds.

Technical specification for base unit type PF 100, with three MF100 or MF101 plug-in units fitted.

  Mounting; DIN or G rail. Dimensions, 106mm high along 104mm of rail.
  Depth from mounting surface of rail; 132mm Weight; 650g approx.
  Input; 3-phase 400V, 50 – 400 HZ. Max continuous voltage 440V
  Power dissipation @ 400V ; < 6W total.
  Ambient temperature 0 – 400 DegC.
  Output contacts; 1A @ 240Vac or 30V dc resistive loads.

Operation

 3 phase input to be fused at maximum of 2A.
  With applied voltage above 380V between all pairs of phases, contacts 11 & 12 will change over to 11 & 14. Green and red lamps lit on all three plug-in units.
  If voltage between two or more phases drops below 290v, contacts revert to 11 & 12.
  If voltage waveform distorted, values may differ; contact us for technical assistance.
  Time delay for opening; when input drops from 415v to below 290v, true off delay to operate contacts (seconds) as marked on MF units. Tolerance -10 to +20%
  Note that time delay will reduce if initial voltage below 400V.
  Lamp indications. Green = supply live. Red = voltage on internal relay.
  If either lamp of any one plug-in unit differs from the other units when supply is above 380v, that unit must be replaced.
  This will not affect output contacts from terminals 11,12,14 if performed whilst unit energised, provided that the two identical units remain in place at all times.

Plug-in units

  Two types of plug in device can be used with the PF 100 base unit.
  These operate the main contacts in an identical manner, but differ in the type of auxiliary contacts connected to the terminals 21,31,41.
  MF 100 has N/C auxiliary contacts. The contacts of the three units can be connected in parallel, by linking terminals 21,31,41 and also 22,32,42, so that if any one unit indicates failure, the circuit between terminals 21 and 42/44 is made.
  MF101 has N/O auxiliary contacts. The contacts of the three units can be connected in series, by linking terminals 31,41 and also 24,34, so that if any one unit indicates failure, the circuit between terminals 21 and 42/44 is opened.
  If individual monitoring of the units is required, all links can be removed

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Datasheet

Specification