Phase Balance Protection Relay

Phase Balance Protection Relay
Posted on Posted in Protection Relays


DIN rail mounting protection relays for use in single and three phase systems. Available in 55mm x 112mm or 100 x 112mm DIN rail cases.


For over protection, under protection and combined under & over protection available in AC current AC voltage & frequency versions. Millivolt trip, DC voltage trip, Reverse Power, Phase sequence & Phase balance relays also available in our extensive range of protection relays.

Selection Guide

M200-PB1 Detects phase loss & phase unbalance
M200-PB2 Detects phase loss, phase imbalance & symmetrical undervoltage

Typical Applications

The M200-PB1 can detect the following conditions in 3 phase 3 or 4 wire systems. Phase unbalance, Phase loss, Phase Reversal, Phase Sequence. The phase balance relays are used to detect phase loss and unbalance in systems using motors, generators, heater elements, transformers etc. A phase unbalance as small as 10% in a 3 phase motor can cause the temperature in the motor winding to increase by more than 120%, correct setting of the PB1/PB2 will ensure that this does not occur. Protection against open phase regenerated voltage created  if a single phase should fail is also provided. Customer adjustment of unbalanced voltage between 5 to 15% is provided along with time delay adjustment of 200mS to 10 seconds. If the system being monitored is healthy, the relay is energised, red LED illuminated, if there is a phase unbalance greater than the preset level or phase loss/reversal occurs, the relay de-energises after the time delay period. The M200-PB2 provides all the protection features of the PB1 with the additional benefit of having symmetrical under voltage protection. This means that if all 3 phase voltages remain balanced, but drop below a preset voltage, the relay will de-energise. The under voltage is internally set, for standard units it is set at 85% below the nominal voltage but this value can optionally be between 70 and 90%.

Technical Specifications

Rated value Un 57.8 < 500V ±25%
Frequency 50 / 60 / 400Hz
Burden <2VA
Overload 1.5 x Un 2 x Un
Range Adjustment 5% to 15% unbalanced voltage
Repeatability Better than 0.5% of full span.
Undervoltage PB2 only, preset 85% of nominal voltage
(optional 90% to 70%)
Time delay Adjustable 200ms to 10 seconds
Self powered
WEIGHT&CASE Approx 0.4kg. 55mm case

Ordering Information

Product Code Un Input Freq Option
M200-PB2 415V 50Hz Under volts at 70%


1 Adjustable time delay max 30 seconds
2 Internal under voltage set between 90% and 70%
3 Calibration at nominal Hz 35…450Hz
4 Calibration at temperature other than 23ºC

Connection Diagrams