4
SME70-O-Manual-04-2020
M A I N F E A T U R E S
SME70-O panel
The panel is suitable for projecting assembly. The front includes signalling LEDs, the RS232 commu-
nication port is accessible by opening the front cover.
Sensors
3 outdoor integrated sensors for measuring phase currents and voltages
Residual voltage
The residual voltage is computed through vector sum of phase voltages.
Sensors connections
The sensors must be connected to the MA RJ45 connectors located inside the SME70-O panel.
Remote control unit
Remote control unit connections are implemented according with ENEL specification; they are abut-
ted to the terminal board MB at the factory according to the connection diagram inside the device
cover.
RS232 communication
The device provides a serial interface to allow a PC connection for installation, configuration, moni-
toring, firmware upgrade and diagnostic.
X21 and X22 jumpers realise, according to Cyber Security requiremments, the RS232 access protec-
tion against unwanted third parties manipulation.
X21
X22
Action
CLOSE
CLOSE
RS232 Read/Write
ENABLE
OPEN
OPEN
RS232 Read/Write
DISABLE
Binary input
In
Standard
mode, the reversal of the direction of directional earth fault (67N) can be enabled; in
voltage monitoring
mode the binary input may be used as trigger to acquire the state of the line
voltages.
F U N C T I O N C H A R A C T E R I S T I C S
SME70-O devices perform its fault detection functions based on measure of line currents and phase
voltages.
Earth single-phase fault
directional detection function
(67N)
The function detects the occurrence of earth faults both on insulated neutral networks and on com-
pensated neutral networks, without any need of changing settings when changing type of network.
The algorithm is based on the numerical analysis of signals (FFT) through fast sampling (64 samples
per period) and phase locking algorithm (PLL); in this way the quantities are correctly measured in
Through external signal from the remote control system, it is possible to control the reversal of the
reference direction in case of line feeding from the opposed side (secondary station bar tripping
directionality); the reversal signal is provided by the remote control system through the closing of a
contact connected to terminals 8 and 9 of the MB terminal board.
The fault signal (TS67AV) is provided to the remote control unit by the closing of a contact connected
to terminal 5 of the MB terminal board.
The sensitivity of the earth directional function depends on the extension of the line and on the neu-
tral status (insulated or with Petersen coil).
The setting is based on the adjusting of a
V
0
> residual voltage
[1]
threshold and a
I
0
zero sequence
current
[2]
.
The protective element detects the directional earth fault if all the following conditions occur:
• Residual voltage exceeds the
V
0
> threshold
• Residual current exceeds the
I
0
> threshold
• Residual current - residual voltage displacement inside the trip sector (
I
0
lags behind to
V
0
with
reversed direction disabled)
• All the above conditions were met for almost 80 ms
Double earth single-phase
or phase-phase (short circuit)
fault detection function (51)
The phase currents are measured and fault indication is provided when current in at least one phase
exceeds the set threshold a:
• 100...900 A for multi-phase faults (51)
• 10...600 A for double earth-phase faults (51N)
The fault signal (TS51A) is provided to the remote control unit by the closing of a contact connected
to terminal 2 of the MB terminal board.
Note 1 The residual voltage V
0
is the vector sum of the three phase voltages divided by three.
Note 2 The residual current I
0
is the vector sum of the three phase currents.
