Short-Time Protection (ANSI 51)
Introduction
Short-time protection protects all types of motor applications against short-circuit currents.
Short-time protection lets through motor starting currents but protects cables and motor starter devices and allows not to oversize them (useful for wide range settings devices).
Operating Principle
Short-time protection is definite time. It can be configured as the Isd pickup.
|
Item |
Function |
Description |
|---|---|---|
|
A |
Ir |
Overload or thermal protection pickup |
|
C |
Isd |
Short-time protection pickup |
|
D |
tsd |
Short-time protection fixed time delay |
Isd Pickup Setting Value
 |
The short-time protection pickup Isd is set by using a multi-position dial. The setting value is expressed in multiples of Ir. |
|
Step |
Action |
|---|---|
|
1 |
Set the long-time protection first: the setting pickup is Ir (A). |
|
2 |
Turn the Isd adjustment dial to the value required. The setting range is 5 to 13 x Ir in steps of Ir. |
|
3 |
Isd is set to Ir (A) x Isd setting. |
The precision range is +/-15%.
tsd Time Delay Value
The time delay cannot be adjusted.
-
The hold time is 20 ms.
-
The maximum breaking time is 60 ms.