ABB REC650 ANSI - Page 665

For inverse time characteristics a time will be initiated when the current reaches the set
pickup level. From the general expression of the characteristic the following can be seen:
( )
- × - ×
æ ö
æ ö
× ç ÷ =
ç ÷
ç ÷
è ø
è ø
P
op
i
t B td C A td
Pickupn
EQUATION1642 V1 EN (Equation 76)
where:
t
op
is the operating time of the protection
The time elapsed to the moment of trip is reached when the integral fulfils according to
equation
77, in addition to the constant time delay:
- × ³ ×
æ ö
æ ö
ç ÷
ç ÷
ç ÷
è ø
è ø
ò
0
P
t
i
C dt A td
Pickupn
EQUATION1643 V1 EN (Equation 77)
For the numerical protection the sum below must fulfil the equation for trip.
( )
=
D × - ³ ×
æ ö
æ ö
ç ÷
ç ÷
ç ÷
è ø
è ø
å
1
P
n
j
i j
t C A td
Pickupn
EQUATION1644 V1 EN (Equation 78)
where:
j = 1 is the first protection execution cycle when a fault has been detected,
that is, when
> 1
i
Pickupn
EQUATION1646 V1 EN
Dt
is the time interval between two consecutive executions of the
protection algorithm,
n is the number of the execution of the algorithm when the trip time
equation is fulfilled, that is, when a trip is given and
i (j) is the fault current at time j
For inverse time operation, the inverse time characteristic is selectable. Both the IEC and
ANSI/IEEE standardized inverse time characteristics are supported.
1MRK 511 287-UUS A Section 19
Time inverse characteristics
659
Technical manual