Specifications

7SR242 Duobias Description Of Operation

3.3.2 Time Delayed Derived Earth Fault Protection (51N)

Optionally two time delayed derived earth fault elements are provided, each can be selected to either winding 1 or

winding 2.

51N-n Setting sets the pick-up current level.

A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is

selected from IEC, ANSI or user defined curves using 51N-n Char. A time multiplier is applied to the

characteristic curves using the 51N-n Time Mult setting. Alternatively, a definite time lag delay (DTL) can be

chosen using 51N-n Char. When Delay (DTL) is selected the time multiplier is not applied and the 51N-n Delay

(DTL) setting is used instead.

The 51N-n Reset setting can apply a definite time delayed or ANSI (DECAYING) reset. The reset mode is

significant where the characteristic has reset before issuing a trip output – see ‘Applications Guide’.

A minimum operate time for the characteristic can be set using the 51N-n Min. Operate Time setting.

A fixed additional operate time can be added to the characteristic using the 51N-n Follower DTL setting.

Operation of the time delayed earth fault elements can be inhibited from:

Inhibit 51N-n A binary or virtual input.

51N-n Inrush Action: Inhibit Operation of the inrush detector function.

General Pickup

51N-n

51N-n Setting

51N-n Charact

51N-n Time Mult

51N-n Min Operate Time

Wn-IL1

Wn-IL2

Wn-IL3

51N-n Delay (DTL)

51N-n Follower DTL

Pickup

trip

Inhibit 51N-n

51N-n Element

Enabled

Disabled

81HBL2

51N-n Inrush

Action

Off

Inhibit

51N-n Reset

Figure 3-8 Logic Diagram: Derived Time Delayed Earth Fault Protection