DEMA CPM 310 G, User Manual

Page: 78 / 225

- 78 -
Protection
Can be set as “Active” or “Passive”, to have the
protection into or out of service
I
Θ
>
This abbreviation stands for the Thermal Protection Set
Current and is calculated by dividing the rated current
of the protected equipment to nominal current of the
CTs. In practice, the I
Θ
> value is determined as
follows: For a 34.5 kV / 0.4 kV 1,600 kV·A PT with CTs
of 30 A / 5 A ratio, The I
r
of PT is 26.8 A, which
corresponds to 0.89 I
n
of CTs (26.8 A / 30 A).
So I
Θ
> = 0.89 I
n
is appropriate.
The setting range for I
Θ
> is (0.10 – 3.20) I
n
.
T
e
This abbreviation represents the heating constant in
minutes. T
e
value is obtained empirically (usually by the
equipment manufacturer)- by measuring the time that
the equipment heating reaches %63 of the maximum
heating allowed, when loaded with I
Θ
> = I
r
. T
e
variable
can be set in the range of (1 - 200) minutes.
k
This variable lets the user to multiply the tripping
threshold. The actual effect of this variable can be
evaluated from the formula to decide what value it
should be set in the allowed range of (1.00-1.50).
Trip Θ
Trip Θ value is the maximum heating percentage
allowed before tripping.
Trip Θ
is set to typical %100
by default, on the other hand, CPM 310 G provides the
user the flexibility to set this value between %50 and
%200 to fulfill the requirements of exceptional
applications. When the calculated heating percentage
reaches the set
Trip Θ
value, the circuit breaker will be
tripped to prohibit more heating of and possible
damage to the equipment protected.
Trip Θ threshold can be used as an alarming function
alternatively, when automatic tripping is not desired.
To employ the function in this way, a programmable
output with
Trip Θ
function appointed could be cabled
so that when the
Trip Θ
function operates, an acoustic,
optic or digital signal is generated to warn the
supervisor to take appropriate action to intervene the
situation.
↺