MICROENER MM30-D - Operation and Algorithms; Reference Input Variables; Input Quantities; Mains Frequency and Phase Currents

MM30-D
Doc. N° MO-0037-ING
Rev. 4
Date 24.02.2003
Copyright 2010 - Microener
Pag
5
of
36
2.2 – Operation and Algorithms
2.2.1 – Reference input variables
Display
Description
Setting Range
Step
Unit
NodAd 1
Identification number for connection serial communication
1 - 250
1
1
Fn 50 Hz
Mains frequency
50 - 60
10
Hz
In 500Ap
Rated primary current of the phase C.Ts.
1 - 9999
1
A
On 500Ap
Rated primary current of the C.Ts. or of the tore C.T.
detecting earth fault current
1 - 9999
1
A
Im 1.0In
Motor full-load current (p.u. of phase C.Ts. rated current)
0.1 – 1.5
0.01
In
Ist 6Im
Motor starting current (p.u. of motor full load current)
0.5 – 10
0.1
Im
tst 5s
Motor starting time
1 – 120
1
s
Itr0.5Ist
Switch-over current for control of two-step motor starter
(p.u. of motor starting current)
Dis – 0.1 – 1
0.1
Ist
tTr 6s
Max switch-over time from start-up
0.5 – 50
0.1
s
2.2.2 – Input quantities
2.2.2.1 – Mains Frequency
The relay can operate either in 50Hz or 60Hz systems.
The rated Mains Frequency “ Fn “ must be set accordingly.
2.2.2.2 – Phase Current inputs
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 we have
to input the value of the Rated Primary Current “ In “ of the phase C.Ts.
For the Phase Current inputs, 1A or 5A configuration can be selected by moving the jumpers J1
and J2 provided on the C.T. input card (See § 18).
Example :
 Phase CTs 1500/5A and Core Balance CT 100/1A
 Set In = 1500A and On = 100A
 Configure CT input card with jumpers J1, J2 in the 5A position.
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:
 
0IIII 1
0CBA

- When no Earth Fault exists (I
0
= 0)
   
CABCBA
III 0III 2 
The earth fault protection element is independently supplied by the residual current coming either
from the residual connection of the 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.