Ground fault protection relay
mZAZ-Io ground-fault protection is dedicated to be used in protection systems of HV network with solidly earthed neutral point (with Io1, Io2 and Uo inputs) or in MV network characterised by isolated neutral system (with Io3 and Uo inputs). The device belongs to the mZAZ family of protection relays whose integrates the functions of measuring, protection, control and recording.

Manuals, diagrams, technical details


Product description

Protection set

50N/51N ground overcurrent
51N ground overcurrent, inv. time characteristic
67N/59N ground overcurrent directional, def.-time or inv.-time characteristic
67N/59N ground overcurrent with directional interlock, def.-time or inv.-time characteristic
59N residual overvoltage
21N admittance-based directional or non-directional
81 frequency -based, ferroresonance detection function
32N directional residual power protection
62 external protection

Main features

  • 4 measuring inputs (Io1, Io2, Io3, Uo)
  • Two binary inputs for external protection purposes or to block selected protection functions or to acknowledgment of relay pick-up signalling
  • 7 programmable relay outputs
  • BZ “watchdog” contact for device failure signalling purposes or lack of aux. voltage signalling purposes
  • 4 settings banks
  • Trip pulse forming
  • SMiS software enabling full operation of the device by PC computer
  • Indicating of key device statuses
  • Measuring of current input values
  • Event recorder
  • Samples and magnitudes values recorder
  • Last disturbance parameters recorder
  • Self-control of proper operation of relay
  • Real time clock
  • Remote communication with PC computer or with supervise and control system in RS-485 standard
  • Protection against unauthorized access
  • Digital technology ensures high accuracy, stability and dependability of the relay

SMiS software provided with each device allows to: protection functions configuration, read and write of protection settings, acknowledgment of relay pick-up signal and browsing relay recorded data.


Rated measuring current

I01n=1A, I02n=5A,

I03n=0,5A or 5A

Rated measuring voltage U0n 100V
Rated frequency 50Hz
Auxilliary voltage Upn (24V, 48V/60V)DC,
(110V, 230V)DC/AC
Control voltage acc. to aux voltage
Setting range of threshold values:
ground current threshold value for HV systems (0,01 ÷ 30,00)Ion
ground current threshold value for MV systems (5÷500)mA
or (50÷5000)mA
residual voltage threshold value (0,01 ÷ 0,99)Uon
admittance threshold value Yor = (0,05 ÷ 50,00)mS
or Yor = (0,5 ÷ 500,0)mS
Characteristic angle of operating characteristic
MV protection function  0…90° (cap. direction)
HV protection function 0…90° (ind. direction)
Operating characteristics direction

from the busbars

to the busbars                                                                              unidirectional

Accuracy of current inputs if I=I0n 1%
Accuracy of voltage input if U=U0n 0,5%
Accuracy of admittance measuring 2,5% ± 0,01mS
Accuracy of angle measuring 2,5˚
Accuracy of time measuring 1% ±10ms
Burden in measuring inputs ≤0,5VA/input
Burden of supply module ≤6W
Continuous measured current 4In
Thermal withstand (1s) 80In
Dynamic withstand 200In
Relay outputs data:
Max. breaking capacity by 250V DC
– resistive load 0,3A
– inductive load of L/R ≤40ms 0,1A
Max. breaking capacity by 250V, 50Hz
– inductive load, cosϕ=0,4 3A
Continuous contact carry 6A
Ambient temperature (operation) (253÷328)K/(-20÷55)°C
Ambient temperature (storage) (248÷343)K/(-25÷70)°C
Humidity (with no condensation) ≤80%
Ingress protection degree IP40
Weight ~0,7kg
Dimensions (height x width x depth) 75 x 100 x 120 mm
Electromagnetic compatibility acc. to EN 60255-26
Insulation according to EN 60255-27

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