Monitored Data; Operation Principle - ABB REG650 Technical Manual

Section 6
Differential protection
6.1.2.5
6.1.3
82

Monitored data

Table 26: T3WPDIF (87T) Monitored data
Name Type
IDMAG_A REAL
IDMAG_B REAL
IDMAG_C REAL
IBIAS REAL
IDMAG_NS REAL

Operation principle

The task of the power transformer differential protection is to determine whether a
fault is within the protected zone, or outside the protected zone. The protected zone is
limited by the position of current transformers (see figure 31), and in principle can
include more objects than just transformer. If the fault is found to be internal, the faulty
power transformer must be quickly disconnected.
The main CTs are normally supposed to be Wye connected and can be grounded in any
direction (that is, either "ToObject" or "FromObject"). Internally the IED will always
measure the currents on all sides of the power transformer with the same reference
direction towards the power transformer windings as shown in figure 31.
I
W1
Z1
S1
E1
S1
I
W1
ANSI05000186 V1 EN
Figure 31: Typical CT location and definition of positive current direction
Values (Range) Unit
- A
- A
- A
- A
- A
I
W2
Z1
S2
I
W2
IED
en05000186_ansi.vsd
1MRK 502 043-UUS B
Description
Magnitude of fundamental
frequency differential current,
phase A
Magnitude of fundamental
frequency differential current,
phase B
Magnitude of fundamental
frequency differential current,
phase C
Magnitude of the bias current,
which is common to all phases
Magnitude of the negative
sequence differential current
E1
S2
Technical Manual