DEMA CPM 310 G User Manual page 45

5. Thermal protection of the power transformer, and phase and earth protections are to be done.
Below calculations and settings are done for this purpose.
Making of Iθ> Thermal Overload Protection Settings
It is assumed that the thermal constant for the power transformer is Te = 20 minutes
according to the information supplied by the manufacturer. Take trip threshold translation
constant k as 1.10, thermal overload trip heating as %ΘTrip = %100 and thermal
overload alarm heating as %ΘAlarm = %80.
Power transformer nominal current is:
Power transformer nominal current / Protection CT primary nominal current ratio:
Make the setting below so as to activate thermal overload protection at 1.00 I
Making of I> Phase Overcurrent Protection Settings
a. Around 1.00 I
suitable according to the PT ratings. Threshold set current in terms of I
b. According to the calculation above, do the following settings: ↺
Notes:

If there are loads of high inrush pick-up current, fine adjustment of the TMS parameter
might be needed.
 If the Thermal Overload Protection is not applied / made passive, set the I> (Phase
Overcurrent Protection Threshold) as 1.0 I
��
������
�� =
������
√ 3 × ��
41.84 ��
�� =
rTR
60 ��
Main Screen » Set » I
, the PT is protected from overloads. Setting I> threshold at 1.3 I
rTR
�� > = 1.3 × ��
Main Screen » Set » I>
2500 ���� ∙ ��
= ≅ 41.84 ��
√ 3 × 34.5 ����
��
≅ 0.70 ��
��
>
Θ
≅ 0.91 ��
������ ��
(0.70 I ) instead of 1.3 I
rTR n
- 45 -
:
rTR
is
rTR
of CT:
n
(0.91 I ).
rTR n