ISA T 2000 - Page 69

DOC. MIE11110 Rev. 5
Page
69
of
110
Prior to explain input parameters, let us discuss their definitions. In
a PT, the ratio is defined as shown below.
However, we have three cases of primary and secondary
connections: 1. Yy (or Dd); 2. Yd; 3. Dy.
Case 1: Types Yy or Dd
The ratio is: t = VAB / Vab = VA / Va
This is the case foreseen by the test set. Test parameters are:
. The primary voltage, in kV, either Line to Line or Line to neutral;
. The secondary voltage, in V, either Line to Line or Line to
neutral.
. The selected input measurement range. To this purpose,
consider that the maximum test voltage VT is 3000 V, and can be
much lower that the nominal primary voltage, VPN. Prior to select
the input measurement range, compute the nominal measurement
voltage VM as follows:
VM = VT * VSN / VPN
Case 2: Type Yd