Siemens Reyrolle 7SR5, Руководство пользователя

Страница: 167 / 504

Parameter:
Setting
•
Default setting:
80 V
This is the operating voltage threshold of the element. The element will pickup if the voltage falls below
this value. This should be set to suit the individual application.
Parameter:
Hysteresis
•
Default setting:
3 %
This sets the drop-off threshold for the undervoltage element. The element will pickup if the voltage falls
below the setting and will reset when the voltage recovers to the s hysteresis voltage. This setting
is a percentage of the undervoltage setting.
The default setting of 3 % is generally enough to avoid chatter of the element but care may be required
for settings which are close to the nominal value otherwise the element may not reset when the voltage
recovers to nominal value as the voltage is still in the hysteresis window.
Parameter:
Delay
•
Default setting:
0.1 s
This is the time delay setting for the DTL element. This should be set to suit the individual application.
Parameter:
UV Guard Inhibit
•
Default setting:
Yes
This setting selects whether operation is blocked for measured voltages below setting.
Settings Example
2-stage undervoltage protection
This example shows settings that could be applied for a 2-stage undervoltage protection application.
This example applies settings to detect a condition of 10 % reduction in supply voltage compared to nominal
as a standing level which may indicate a voltage control failure but also detects a 30 % reduction in voltage
between any phases more quickly to allow remedial actions such as a supply changeover. The actions should
not be initiated for a loss of supply which could result from a grid supply trip which is assumed to be handled
separately. This example considers device settings for the 27Vx elements but does not cover I/O mappings and
tripping logic.
•
First stage
To detect a -10 % deviation in the voltage compared to the expected 110 V phase to phase secondary
nominal voltage allowing for a voltage controller which would be expected to correct this deviation in
less than 2 seconds.
Threshold = 110 ⋅ 0.9 = 99 V
Time delay must be greater than 2 seconds. Choose 3 s.
Choose a suitable element: 27Vx-1
•
Second stage
To detect a -30 % deviation in the voltage compared to the expected 110 V phase to phase secondary
nominal voltage allowing only for transient conditions and fault clearance and meeting the customers’
expectations for supply changeover which will allow 1000 ms.
Threshold = 110 ⋅ 0.7 = 77 V
Time delay specified as 1000 ms.
Choose a suitable element: 27Vx-2
•
Immunity to Loss of Supply
Set UV guard to a low level that would not be expected unless the system is dead. Choose 5 V.
Protection and Automation Functions
5.4 27Vx Undervoltage Protection – Vx
Reyrolle 7SR5, Transformer Protection Device, Device Manual 167
C53000-G7040-C015-1, Edition 11.2019