MICROENER MC20-X/10-4, Operation Manual

Page: 6 / 35

MC20-X/10-4
Doc. N°
MO-0352-ING
Microener - Copyright 2010 FW 720.07.01 Date 09.04.2008 Rev. 1 Pag. 6 of 35
2.2 - Operation and Algorithms
2.2.1 - Reference Input Values
Display Description Setting Range Step Unit
I1 100 A Rated Primary current of phase C.T. 1 - 9999 1 A
I2 1 A Rated Secondary current of phase C.T. 1 - 5 1/5 A
Io1 100 A
Rated Primary current of the tore C.T. detecting earth fault
current.
1 - 9999 1 A
Io2 1 A
Rated secondary current of the tore C.T. detecting earth fault
current.
1 - 5 1/5 A
In 100 A Reference primary current of the relay 1 - 9999 1 A
Freq 50 Hz System rated frequency 50 - 60 10 Hz
2.2.2 - Input quantities
2.2.2.1 - Mains Frequency (Freq)
The relay can operate either in 50Hz or 60Hz systems.
The rated Mains Frequency “ Freq “ must be set accordingly.
2.2.2.2 - Phase Current inputs (I1)
The relay directly displays the r.m.s. value of the Phase Currents “ IA “, “ IB ”, “ IC ” flowing in the
Primary of the input Current Transformers and refers all its measurements to that value.
To make the relay properly working with any C.T., when programming the relay settings, input the
value “I1“ of the primary current of the phase C.Ts
Only phase A and C currents are measured, whereas the current of the phase B is computed as
vector summation of the currents of the other two phases.
The algorithm is based on the following considerations coming from well-known vector relations
among the three-phase currents and the zero sequence current.
- In any circumstance – currents balanced or not, sinusoidal or not – it is always true that:
 
0 I I I I 1
0 C B A
   
- When no Earth Fault exists (I
0
= 0)
 
 
C A B C B A
I I I 0 I I I 2
     
The earth fault protection element is independently supplied by the residual current coming either
from the residual connection of 3 system C.Ts. or from the core balance C.T.
If any Earth Fault is experienced (I
0

0) the Earth Fault Protection Element trips independently
from the phase current measuring elements.
If no Earth Fault is present (I
0
= 0), the equation (2) is valid, no matter if currents are balanced or
not, sinusoidal or not.
The third phase current is calculated, in real time, as vector summation of the other two-phase
currents.
During Faults:
A) Single phase to earth Fault Trip of the earth fault element directly measuring the Residual
Current.
B) Two Phase Fault In any case one of the currents directly measured is involved, so
the relay trips correctly.
C) Two Phase to Earth Fault Same as A + B
D) Three Phase Fault All the three currents are correctly measured (in any case two
directly).