Siemens 7SR242 Duobias, Technical Manual

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Chapter 1) 7SR242 Duobias Description Of Operation
©2015 Siemens Protection Devices Limited Chapter 1 Page 43 of 60
3.12 Voltage Protection: Neutral Overvoltage (59N)
Optionally two Neutral Overvoltage (or Neutral Voltage Displacement) elements are provided.
One of the elements can be configured to be either definite time lag (DTL) or inverse definite minimum time
(IDMT),
59NIT Setting sets the pick-up voltage level (3V
0
) for the element.
An inverse definite minimum time (IDMT) can be selected using 59NIT Char . A time multiplier is applied to the
characteristic curves using the 59NIT Time Mult setting (M):
1
M
t
Vs
3Vo
op
Alternatively, a definite time lag delay (DTL) can be chosen using 59NITChar . When Delay (DTL) is selected the
time multiplier is not applied and the 59NIT Delay (DTL) setting is used instead.
An instantaneous or definite time delayed reset can be applied using the 59NIT Reset setting.
The second element has a DTL characteristic. 59NDT Setting sets the pick-up voltage (3V
0
) and 59NDT Delay
the follower time delay.
Operation of the neutral overvoltage elements can be inhibited from:
Inhibit 59NIT A binary or virtual input.
Inhibit59NDT A binary or virtual input.
User Inhibit Reylogic (graphical logic).
It should be noted that neutral voltage displacement can only be applied to VT arrangements that allow zero
sequence flux to flow in the core i.e. a 5-limb VT or 3 single phase VTs. The VT primary winding neutral must be
earthed to allow the flow of zero sequence current.
Figure 3-19 Logic Diagram: Neutral Overvoltage Element