Siemens SIPROTEC 4 7VK61 Manual Download

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For symmetrical voltages an increase of the positive sequence system corresponds to an AND gate of the
voltages. These stages are particularly suited to the detection of steady-state overvoltages on long, weak-
loaded transmission lines (Ferranti effect). Here too, the

U1>

stage (address 3732) with a longer delay time

U1>

(address 3733) is used for the detection of steady-state overvoltages (some seconds), the

U1>>

stage

(address 3734) with the short delay time

T U1>>

(address 3735) is used for the detection of high overvol-

tages that may jeopardise insulation.
Note that the positive sequence system is established according to its defining equation
U

·|U

+ a·U

+ a

·U

|. For symmetrical voltages this is equivalent to a phase-to-earth voltage.

The dropout to pickup ratio (address 3739

U1>(>) RESET

) is set as high as possible with regard to the detec-

tion of even small steady-state overvoltages. This parameter can only be altered in DIGSI at Display Additional
Settings.

Overvoltage negative sequence system U

The negative sequence voltage stages detect asymmetrical voltages. If such voltages should cause tripping,
set address 3741

U2>(>)

. If such conditions will only be reported, set address 3741

U2>(>)

Alarm

Only

. If only one stage is desired to generate a trip command, choose the setting

U>Alarm U>>Trip

. With

this setting a trip command is output by the 2nd stage only. If negative sequence voltage protection is not
required, set

OFF

This protection function also has two stages, one being

U2>

stage (address 3742) with a longer time delay

U2>

(address 3743) for steady-state asymmetrical voltages and the other being

U2>>

stage (address 3744)

with a short delay time

T U2>>

(address 3745) for high asymmetrical voltages.

Note that the negative sequence system is calculated according to its defining equation U

·|

+ a

·U

+ a·U

|. For symmetrical voltages and two swapped phases this is equivalent to the phase-to-

earth voltage value.
The resetting ratio can be changed

U2>(>) RESET

using the address 3749. This parameter can only be

altered in DIGSI at Display Additional Settings.

Overvoltage zero-sequence system

The zero-sequence voltage stages can be switched in address 3721

3U0>(>) (or Ux)

OFF

. In addi-

tion to this, you can set

Alarm Only

, i.e. these stages operate and also send alarms but do not generate any

trip command. If a trip command of the 2nd stage is still desired, the setting must be

U>Alarm U>>Trip

This protection function can be used for any other single-phase voltage which is connected to the fourth
voltage measurement input U

. Also see section

2.1.3.1 Setting Notes

at margin heading “Voltage Connec-

tion”.
This protection function also has two stages. The settings of the voltage threshold and the timer values
depend on the type of application. Therefore, no general guidelines can be established. The stage

3U0>

(address 3722) is usually set with a high sensitivity and a longer delay time

T 3U0>

(address 3723). The

3U0>>

stage (address 3724) and its delay time

T 3U0>>

(address 3725) enables a second stage to be imple-

mented with less sensitivity and a shorter delay time.
Similar considerations apply if this voltage stage is used for a different voltage at the measuring input U

The zero-voltage stages feature a special time stabilization due to repeated measurements allowing them to
be set rather sensitive. This stabilization can be disabled in address 3728

3U0>(>) Stabil.

if a shorter

pickup time is required. This parameter can only be altered in DIGSI at Display Additional Settings. Please
consider that sensitive settings combined with short pickup times are not recommended.
The drop out to pick up ratio can be changed

3U0>(>) RESET

using the address 3729. This parameter can

only be altered in DIGSI at Display Additional Settings.
When setting the voltage values please observe the following:

Functions
2.5 Under and over-voltage protection (optional)

108

SIPROTEC 4, 7VK61, Manual

C53000-G1176-C159-5, Edition 05.2018