Voltage Protection: Neutral Overvoltage (59N); Figure 3.12-1 Logic Diagram: Neutral Overvoltage Element - Siemens 7SR224 Description & Operation

(1) Description of Operation 7SR224
3.12 V P
OLTAGE
Two Neutral Overvoltage (or Neutral Voltage Displacement) elements are provided.
59N Voltage Source setting selects the source of the residual voltage to be measured. The voltage is
measured directly from the Vx input or derived from the line voltages where suitable VT connections
are present. The relay utilises fundamental voltage measurement values for this function.
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
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):
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
59NDT Delay the follower time delay.
Operation of the neutral overvoltage elements can be inhibited from:
Inhibit 59NIT
Inhibit59NDT
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.
Page 38 of 66
: N
ROTECTION EUTRAL
t
op
A binary or virtual input.
A binary or virtual input.

Figure 3.12-1 Logic Diagram: Neutral Overvoltage Element

O (59N)
VERVOLTAGE
) for the element.
0
⎡ ⎤
M
=
⎢ ⎥
[ ]
s
−
⎢ ⎥
3Vo
⎣ 1 ⎦
Vs
©2009 Siemens Protection Devices Limited
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